JP5686588B2 - Rubber composition for tire and pneumatic tire - Google Patents

Description

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

Conventionally, the fuel consumption of a vehicle has been reduced by reducing tire rolling resistance and suppressing heat generation. In recent years, demands for reducing fuel consumption of vehicles using tires are increasing, and demands for reducing fuel consumption for tire members such as treads are increasing. As a method for satisfying the low heat build-up of the rubber composition used in the tire, a method for reducing the amount of reinforcing filler is known.

However, in such a method, the handling performance (steering stability), wet grip performance, and wear resistance (destructive properties) are deteriorated due to a decrease in the hardness, calorific value, and reinforcement of the rubber composition. In addition, when carbon black is used as a reinforcing filler, if the blending amount is reduced, sufficient conductivity cannot be ensured. Therefore, another rubber member is embedded in the tread rubber so as to be exposed on the tire surface. It is necessary to ensure the performance, and the increase in man-hours leads to an increase in cost.

On the other hand, in the composition using silica and carbon black as the reinforcing filler, increasing the carbon black content in the filler improves the reinforcement and wear resistance, and can secure conductivity, but increases the heat generation amount. And rolling resistance deteriorates. Thus, it has been conventionally desired to improve performance such as fuel efficiency, wet grip performance, wear resistance, and handling stability in a balanced manner while ensuring conductivity.

Patent Document 1 describes the use of deproteinized natural rubber and cobalt stearate, but there is still room for improvement in terms of improving fuel economy, wet grip performance, and wear resistance in a well-balanced manner.

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 tire that can improve fuel economy, wet grip performance, and wear resistance in a well-balanced manner, and a pneumatic 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、水素原子又はアルキル基を表す。ｎは整数を表す。） The present invention relates to a tire rubber composition including a modified natural rubber having a phosphorus content of 200 ppm or less and a modified diene rubber modified with a compound represented by the following formula (1).

(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 or an alkyl group, and n represents an integer.)

Here, it is preferable that content of a silica is 10-150 mass parts with respect to 100 mass parts of rubber components. The modified natural rubber is preferably obtained by saponifying natural rubber latex. The content of the modified natural rubber in 100% by mass of the rubber component is preferably 10% by mass or more. The modified diene rubber is preferably a modified styrene butadiene rubber.

The present invention also relates to a pneumatic tire having a tread produced using the rubber composition.

Since the present invention is a tire rubber composition containing a modified natural rubber having a phosphorus content of 200 ppm or less and a modified diene rubber modified with a specific compound, it has low fuel consumption, wet grip performance, and wear resistance. Can improve in a well-balanced manner. Therefore, a pneumatic tire excellent in these performances can be provided.

The rubber composition for tires of the present invention includes a modified natural rubber having a phosphorus content of 200 ppm or less and a modified diene rubber modified with a compound represented by the following formula (1).

（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、水素原子又はアルキル基を表す。ｎは整数を表す。）

(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 or an alkyl group, and n represents an integer.)

By using the modified natural rubber and the modified diene rubber together as the rubber component, the low heat build-up can be remarkably improved without reducing the amount of reinforcing filler such as carbon black. Such an effect is presumed that the exothermicity is synergistically reduced by reducing the amount of phosphorus and nitrogen in natural rubber and suppressing the movement of the polymer end by modification. Therefore, in the present invention, while obtaining good wet grip performance, wear resistance, and steering stability, fuel efficiency can be improved, and the performance balance can be remarkably improved. Moreover, the electrical conductivity of the tire can be ensured.

The modified natural rubber has a phosphorus content of 200 ppm or less. If it exceeds 200 ppm, the tan δ of the vulcanized rubber will increase, and there is a risk that sufficient fuel efficiency will not be 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).

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 it exceeds 0.3% by mass, processability and fuel efficiency may be deteriorated. 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, and more preferably 7% by mass or less. When it exceeds 20 mass%, there exists a tendency for workability and low fuel consumption to deteriorate. The gel content means a value measured as an insoluble content in toluene, and may be simply referred to as “gel content” or “gel content” below. The measuring method of the content rate of a gel part is as follows. First, a natural rubber sample is soaked in dehydrated toluene, light-shielded in the dark and left for 1 week, and then the toluene solution is centrifuged at 1.3 × 10 ⁵ rpm for 30 minutes to obtain an insoluble gel content and a toluene soluble content. Isolate. Methanol is added to the insoluble gel and solidified, and then dried, and the gel content is determined from the ratio between the mass of the gel and the original mass of the sample.

The modified natural rubber is preferably substantially free of phospholipids. “Substantially free of phospholipid” represents a state in which a natural rubber sample is extracted with chloroform and a peak due to phospholipid does not exist at −3 ppm to 1 ppm in ³¹ P-NMR measurement of the extract. The peak of phosphorus present at -3 ppm to 1 ppm is a peak derived from the phosphate structure of phosphorus in the phospholipid.

As a method for producing the modified natural rubber, for example, the production method described in JP 2010-138359 A, that is, the step (A) of obtaining a saponified natural rubber latex by saponifying the natural rubber latex, and the obtained Examples of the method include a step (B) of washing the saponified natural rubber latex until the phosphorus content in the rubber is 200 ppm or less. Specifically, first, a natural rubber latex is saponified with an alkali to prepare a saponified natural rubber latex, and then the agglomerated rubber obtained by agglomerating the saponified natural rubber latex contains phosphorus to the rubber content. Modified natural rubber (saponified natural rubber) can be produced by a method of repeatedly washing with water until the amount becomes 200 ppm or less and drying.

According to the above production method, the phosphorus compound separated by saponification is washed away, so that the phosphorus content of the natural rubber can be suppressed. Moreover, since the protein in natural rubber is decomposed by the saponification treatment, the nitrogen content of the natural rubber can be suppressed.

The content of HPNR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, and further preferably 20% by mass or more. If it is less than 5% by mass, the effect of improving the fuel efficiency tends not to be sufficiently exhibited. The content is preferably 50% by mass or less, more preferably 40% by mass or less. When it exceeds 50 mass%, there is a possibility that sufficient grip performance cannot be obtained.

The modified diene rubber is one in which one or more (terminals, etc.) of the diene rubber is modified with the compound represented by the above formula (1).
The diene rubber modified with the compound represented by the formula (1) is not particularly limited, and isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR). And diene-based synthetic rubbers such as chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), and butyl rubber (IIR). Of these, SBR is preferred because it provides a good balance between low fuel consumption, wet grip performance, and wear resistance. Modified diene rubbers such as modified SBR may be used alone or in combination of two or more.

Examples of the modified SBR modified with the compound represented by the formula (1) include those described in JP2010-111753A, JP2010-117544A, etc. As R ¹ , R ² and R ³ , an alkoxy group is suitable (preferably an alkoxy group having 1 to 8 carbon atoms, more preferably 1 to 6 carbon atoms, and still more preferably 1 to 4 carbon atoms). R ⁴ and R ⁵ are preferably an alkyl group (preferably an alkyl group having 1 to 4 carbon atoms). n is preferably 1 to 5, more preferably 2 to 4, and still more preferably 3. By modifying with a preferred compound, fuel economy, wet grip performance, and wear resistance can be improved in a well-balanced manner, and the effects of the present invention can be obtained well.

Specific examples of the compound represented by the above formula (1) include 2-dimethylaminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 2-dimethylaminoethyltriethoxysilane, and 3-dimethylaminopropyltriethoxy. Examples include silane, 2-diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 2-diethylaminoethyltriethoxysilane, and 3-diethylaminopropyltriethoxysilane. These may be used alone or in combination of two or more.

The vinyl content of the modified SBR is preferably 90% by mass or less, more preferably 80% by mass or less. When the vinyl content exceeds 90% by mass, the wear resistance tends to deteriorate. The vinyl content is preferably 20% by mass or more, more preferably 30% by mass or more. If the vinyl content is less than 20% by mass, sufficient wet grip performance may not be obtained.
In the present specification, the vinyl content (1,2-bond butadiene unit amount) can be measured by infrared absorption spectrum analysis.

The styrene content of the modified SBR is preferably 50% by mass or less, more preferably 45% by mass or less. If the styrene content exceeds 50% by mass, the fuel efficiency may be deteriorated. The styrene content is preferably 5% by mass or more, more preferably 15% by mass or more. When the styrene content is less than 5% by mass, the wear resistance tends to deteriorate.
The styrene content is calculated by H ¹ -NMR measurement.

The content of the modified diene rubber in 100% by mass of the rubber component is preferably 15% by mass or more, more preferably 40% by mass or more. If it is less than 15% by mass, wet grip performance may be deteriorated. The content is preferably 90% by mass or less, more preferably 80% by mass or less. If it exceeds 90% by mass, fuel economy may be reduced.

In the rubber composition of the present invention, examples of the rubber component that can be used in addition to the modified natural rubber and the modified diene rubber include the aforementioned diene synthetic rubber and natural rubber (NR (unmodified)). Among these, BR is preferable from the viewpoint that low fuel consumption, wet grip performance, and wear resistance can be obtained in a balanced manner.

The content of BR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more. If it is less than 5% by mass, the effect of improving fuel economy may not be sufficient. The content is preferably 80% by mass or less, more preferably 50% by mass or less. When it exceeds 80% by mass, the content of HPNR and modified diene rubber is relatively lowered, and the wet grip performance tends to be lowered.

The rubber composition of the present invention usually contains carbon black. Thereby, the strength of the rubber can be improved, wet grip performance and wear resistance can be improved, and conductivity can be secured. Examples of carbon black that can be used include GPF, FEF, HAF, ISAF, and SAF.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 30 m ² / g or more, and more preferably 70 m ² / g or more. If it is less than 30 m ² / g, there is a tendency that sufficient reinforcing properties cannot be obtained. Further, the _N 2 SA is preferably 250 meters ² / g or less, more preferably 150m ² / g. When it exceeds 250 m ² / g, the viscosity at the time of unvulcanization becomes very high, and the workability and fuel efficiency tend to deteriorate.
In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required by A method of JISK6217.

The content of carbon black is preferably 30 parts by mass or more, more preferably 35 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 30 parts by mass, it tends to be difficult to ensure conductivity. The content is preferably 60 parts by mass or less, more preferably 50 parts by mass or less. If it exceeds 60 parts by mass, heat generation will increase and fuel economy tends to deteriorate.

The rubber composition of the present invention may contain silica. Good low heat build-up can be obtained by blending silica together with the modified diene rubber. Examples of the silica include dry process silica (anhydrous silicic acid), wet process silica (hydrous silicic acid) and the like, but wet process silica is preferred because of the large number of silanol groups.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 40 m ² / g or more, and more preferably 50 m ² / g or more. If it is less than 40 m < ² > / g, there exists a tendency for the fracture strength after vulcanization to fall. The _N 2 SA of the silica is preferably 250 meters ² / g or less, more preferably 200m ² / g. When it exceeds 250 m ² / g, there is a tendency to be inferior in fuel efficiency and rubber processability.
The nitrogen adsorption specific surface area of silica is a value measured by the BET method according to ASTM D3037-81.

The content of silica is preferably 10 parts by mass or more, more preferably 20 parts by mass or more with respect to 100 parts by mass of the rubber component. When the amount is less than 10 parts by mass, there is a tendency that a sufficient effect due to silica blending cannot be obtained. The content is preferably 150 parts by mass or less, more preferably 120 parts by mass or less. When the amount exceeds 150 parts by mass, it is difficult to disperse silica in rubber, and the processability of rubber tends to deteriorate.

Further, the total content of carbon black and silica is preferably 30 parts by mass or more, more preferably 50 parts by mass or more with respect to 100 parts by mass of the rubber component. The total content is preferably 150 parts by mass or less, more preferably 110 parts by mass or less. Thereby, the effect of this invention is acquired favorably.

The rubber composition of the present invention preferably contains 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 type is preferable, and bis (3-triethoxysilylpropyl) disulfide and bis (3-triethoxysilylpropyl) tetrasulfide are more preferable.

The content of the silane coupling agent is preferably 5 parts by mass or more, more preferably 8 parts by mass or more with respect to 100 parts by mass of silica. If it is less than 5 parts by mass, the fracture strength tends to be greatly reduced. The content is preferably 15 parts by mass or less, more preferably 10 parts by mass or less. When the amount exceeds 15 parts by mass, effects such as an increase in fracture strength and a reduction in rolling resistance due to the addition of the silane coupling agent tend not to be obtained.

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 zinc oxide, stearic acid, oil, various anti-aging agents, waxes, sulfur vulcanizations and the like. An agent, a vulcanization accelerator, and the like can be appropriately blended.

In the present invention, it is preferable to use a vulcanization accelerator such as sulfenamide, guanidine and thiuram. As sulfenamide-based vulcanization accelerators, N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N-dicyclohexyl -2-Benzothiazolylsulfenamide (DCBS) and the like, and CBS is particularly preferable. Examples of the guanidine vulcanization accelerator include diphenyl guanidine, diortotriguanidine, triphenyl guanidine, and the like. Among them, diphenyl guanidine is preferable. Examples of the thiuram-based vulcanization accelerator include tetramethylthiuram disulfide (TMTD), tetraethylthiuram disulfide, a compound represented by the following formula (2), and the like, among which a compound represented by the following formula (2) is preferable. .

（式（２）中、ｚは１〜８の整数を表す。）

(In formula (2), z represents an integer of 1 to 8.)

Z in the above formula (2) is preferably 1 to 6, more preferably 1 to 3. As the vulcanization accelerator represented by the above formula (2), tetrabenzylthiuram disulfide can be preferably used.

As a method for producing the rubber composition of the present invention, known methods can be used. For example, the above components are kneaded using a rubber kneader such as an open roll, a Banbury mixer, a closed kneader, and then added. It can be manufactured by a method of sulfurating.
The rubber composition of the present invention can be suitably used for tire treads and the like.

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

The 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 Synthesis of Saponified Natural Rubber>
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).

About the solid rubber obtained by the manufacture example, TSR mentioned later, nitrogen content, phosphorus content, and gel content rate were measured by the method shown below. The results are shown in Table 1.

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

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

(Measurement of gel content)
A sample of 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 rubber (HPNR) had a reduced nitrogen content, phosphorus content, and gel content as compared to TSR. Further, in ³¹ P-NMR measurement of an extract extracted from saponified natural rubber, no peak due to phospholipid was detected at -3 ppm to 1 ppm.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
NR: TSR20
HPNR: Saponified natural rubber (HPNR) prepared in Production Example
SBR (non-modified): Nipol 1502 (styrene content: 23.5% by mass) manufactured by Nippon Zeon Co., Ltd.
SBR (modified): modified styrene butadiene rubber manufactured by Sumitomo Chemical Co., Ltd. (vinyl content 57% by mass, styrene content 25% by mass, R ¹ , R ² and R ^{3 in} formula (1) = — OCH ₃ , R ⁴ And R ⁵ = —CH ₂ CH ₃ , n = 3)
BR: Nipol BR1220 manufactured by Nippon Zeon Co., Ltd.
Carbon black: Dia Black N220 manufactured by Mitsubishi Chemical Corporation (N ₂ SA: 114 m ² / g)
Silica: Ultrasil VN3 manufactured by Evonik Degussa (average primary particle size: 15 nm, N ₂ SA: 175 m ² / g)
Silane coupling agent: Si266 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Evonik Degussa
Zinc oxide: Zinc Hana No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Sakai aroma oil manufactured by NOF Corporation: Process X-140 manufactured by Japan Energy Co., Ltd.
Anti-aging agent: Antigen 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Wax: Sunnock N manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Sulfur: Powder sulfur vulcanization accelerator manufactured by Karuizawa Sulfur Co., Ltd. (1): Noxeller CZ (N-cyclohexyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Vulcanization accelerator (2): Noxeller D (N, N'-diphenylguanidine) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Vulcanization accelerator (3): Noxeller TBzTD (tetrabenzylthiuram disulfide, z = 2 in the above formula (2)) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

<Examples and Comparative Examples>
In accordance with the formulation shown in Table 2, materials other than sulfur and a vulcanization accelerator were kneaded for 5 minutes at 150 ° C. using a 1.7 L Banbury mixer to obtain a kneaded product. Next, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and kneaded for 3 minutes at 80 ° C. using an open roll to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press vulcanized with a 2 mm thick mold at 150 ° C. for 30 minutes to obtain a vulcanized rubber composition.
Further, the obtained unvulcanized rubber composition was formed into a tread shape, bonded to another tire member, and vulcanized at 150 ° C. for 35 minutes, so that a test tire (tire size: 195) was obtained. / 65R15).

The following evaluation was performed about the obtained vulcanized rubber composition and the tire for a test. The results are shown in Table 2.

(Low heat generation)
Using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), tan δ of each vulcanized rubber composition was measured under the conditions of a temperature of 70 ° C., an initial strain of 10%, and a dynamic strain of 2%. The index was expressed as tan δ = 100. The lower the exothermic index, the lower the heat generation.

(Wet grip performance)
Using the test tire, the braking distance from the initial speed of 100 km / h was measured on the wet asphalt road surface, and the braking distance of Comparative Example 3 was set as 100 and indicated as an index. The larger the wet grip performance index, the better the wet grip performance.

(Abrasion resistance)
An actual vehicle was run using the test tire, and the change in pattern groove depth before and after running 30000 km was measured. The greater the wear resistance index, the better the wear resistance.

(Conductivity)
The volume resistivity of the vulcanized rubber composition was measured according to JIS K6271. From the measurement results, it was judged as ○ if it was 10 ⁸ Ω · cm or less, and x if it exceeded it.

Compared with the comparative example, in the example in which HPNR and modified SBR were used in combination, the fuel economy, wet grip performance, and wear resistance could be improved in a balanced manner. The conductivity of the test tire was also good.

Claims (5)

Including a modified natural rubber having a phosphorus content of 200 ppm or less and a modified styrene butadiene rubber modified with a compound represented by the following formula (1), carbon black, and silica;
The content of carbon black is 30 to 60 parts by mass, the content of silica is 10 to 20 parts by mass , and the total content of carbon black and silica is 50 to 150 parts by mass with respect to 100 parts by mass of the rubber component. Rubber composition for 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 represents an alkyl group having 1 to 4 carbon atoms, and n represents an integer.) The tire rubber composition according to claim 1, wherein the modified natural rubber is obtained by saponifying natural rubber latex. The rubber composition for a tire according to claim 1 or 2, wherein the content of the modified natural rubber in 100% by mass of the rubber component is 10% by mass or more. The rubber composition for tires in any one of Claims 1-3 containing the compound represented by following formula (2).

(In formula (2), z represents an integer of 1 to 8.) The pneumatic tire which has a tread produced using the rubber composition in any one of Claims 1-4 .