JP2012149175A - Rubber composition for tire and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for tire, capable of improving fuel efficiency, wear resistance, workability and rubber strength, and a pneumatic tire.SOLUTION: The rubber composition for tire includes: modified natural rubber having a phosphor content of 200 ppm or less; high-molecular-weight polybutadiene having a weight-average molecular weight of 250,000 or more; and low-molecular-weight polybutadiene having a weight-average molecular weight of 0.5 to 200,000.

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 the rolling resistance of a tire to suppress heat generation. In recent years, there has been a great demand for low fuel consumption of vehicles by using tires, and not only for passenger car tires but also for heavy duty tires for trucks and buses, and particularly for heavy duty tires, wear resistance is also required.

As a method for improving fuel efficiency, a method of replacing carbon black with silica is known. However, since silica has a lower reinforcement than carbon black, the rubber strength tends to decrease and the wear resistance tends to deteriorate. In addition, the conventional silane coupling agent used in combination with silica may adversely affect workability such as an increase in viscosity during kneading and a tendency to shorten the scorch time.

In addition, oil is often blended for the purpose of improving the wet grip performance of the tire, but since the oil does not participate in polymer crosslinking, blending an excess amount may reduce rubber strength and wear resistance.

Patent Documents 1 to 5 describe that rolling resistance is reduced by using modified synthetic rubber such as modified butadiene rubber and modified styrene butadiene rubber or deproteinized natural rubber. However, further improvements are desired in terms of simultaneously improving fuel economy, wear resistance, processability, and rubber strength.

JP 2001-114939 A JP 2005-126604 A JP 2005-325206 A JP-A-8-12814 Japanese Patent Laid-Open No. 11-12306

An object of the present invention is to solve the above-mentioned problems and to provide a rubber composition for a tire and a pneumatic tire that can improve fuel economy, wear resistance, processability, and rubber strength.

The present invention relates to a tire rubber composition comprising a modified natural rubber having a phosphorus content of 200 ppm or less, a high molecular weight polybutadiene having a weight average molecular weight of 250,000 or more, and a low molecular weight polybutadiene having a weight average molecular weight of 0.5 to 200,000. About.

Here, the content of the modified natural rubber in 100% by mass of the rubber component is preferably 60 to 95% by mass, and the content of the high molecular weight polybutadiene is preferably 5 to 40% by mass. The content of low molecular weight polybutadiene is preferably 5 to 29 parts by mass with respect to 100 parts by mass of high molecular weight polybutadiene.

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

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

According to the present invention, since it is a rubber composition for tires containing a modified natural rubber having a phosphorus content of 200 ppm or less, a high molecular weight polybutadiene, and a low molecular weight polybutadiene, low fuel consumption, wear resistance, processability, rubber strength These performances can be obtained at a high level.

The rubber composition for tires of the present invention includes a modified natural rubber (HPNR) having a phosphorus content of 200 ppm or less, a high molecular weight polybutadiene having a weight average molecular weight of 250,000 or more, and a low weight average molecular weight of 0.5 to 200,000. Contains molecular weight polybutadiene.

In the present invention, by using a modified natural rubber, a high molecular weight polybutadiene and a low molecular weight polybutadiene in combination, fuel economy and abrasion resistance can be improved at the same time, and excellent processability and rubber strength can be obtained. It is possible to increase. Therefore, even when carbon black is replaced with silica, excellent rubber strength and wear resistance can be obtained. Further, by substituting the oil with low molecular weight polybutadiene and blended, it is possible to suppress a decrease in rubber strength and wear resistance, and to obtain further excellent rubber strength and wear resistance. Furthermore, when modified natural rubber is used, there is a concern that the wear resistance is lowered, but in the present invention, the above components can be used together to eliminate the concern.

The modified natural rubber has a phosphorus content of 200 ppm or less. If it exceeds 200 ppm, the Mooney viscosity will increase during storage and the processability will deteriorate, and there will be a tendency that excellent 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, the Mooney viscosity will increase during storage, resulting in poor processability, and excellent fuel efficiency may not be obtained. 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 10% by mass or less. If it exceeds 20% by mass, the Mooney viscosity tends to increase and the processability tends 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 the modified natural rubber in 100% by mass of the rubber component is preferably 60% by mass or more, more preferably 70% by mass or more. If it is less than 60% by mass, sufficient low heat build-up and processability may not be obtained. The content is preferably 95% by mass or less, more preferably 80% by mass or less. If it exceeds 95% by mass, sufficient wear resistance may not be obtained.

In the present invention, high molecular weight polybutadiene and low molecular weight polybutadiene are used together with the modified natural rubber. The high molecular weight polybutadiene can be produced, for example, using a catalyst composed of a cobalt compound such as Co.oct and an organoaluminum compound such as AlEt ₂ Cl and H ₂ O. The low molecular weight polybutadiene, for example, high molecular weight polybutadiene as well as Co · oct nickel compounds such as catalysts and Ni · naph comprising an organic aluminum compound -H ₂ O, such as a cobalt compound -AlEt ₂ Cl such -AlEt ₂ Cl It can be prepared by using a catalyst comprising an organoaluminum compound -H 2 _O, such as.

As the high molecular weight polybutadiene and the low molecular weight polybutadiene, for example, a mixture obtained by previously mixing these two components can be preferably used. The preparation method of the said mixture is not specifically limited, It can manufacture by blending the high molecular weight polybutadiene prepared by the said manufacturing method etc. and low molecular weight polybutadiene.

The lower limit of the molecular weight distribution (Mw / Mn) of the mixture is preferably 15 or more, more preferably 25 or more, and the upper limit is preferably 70 or less, more preferably 50 or less. When the molecular weight distribution is within the above range, low fuel consumption, wear resistance, processability, and rubber strength can be obtained in a well-balanced manner.
In the present specification, the number average molecular weight (Mn) and the weight average molecular weight (Mw) are values converted from standard polystyrene using a gel permeation chromatograph (GPC).

The weight average molecular weight (Mw) of the high molecular weight polybutadiene is 250,000 or more, preferably 350,000 or more, more preferably 500,000 or more. If it is less than 250,000, the wear resistance may not be sufficiently improved. The Mw is preferably 1.5 million or less, more preferably 1 million or less. If it exceeds 1.5 million, the workability may not be sufficiently improved.

The cis content of the high molecular weight polybutadiene is preferably 80% by mass or more, more preferably 90% by mass or more. If it is less than 80% by mass, the wear resistance may not be sufficiently improved.
The cis content of polybutadiene (cis-1,4-bonded butadiene unit amount) can be measured by infrared absorption spectrum analysis.

The weight average molecular weight (Mw) of the low molecular weight polybutadiene is not less than 50,000, preferably not less than 7,000. If it is less than 5,000, industrial production may be difficult. The Mw is 200,000 or less, preferably 70,000 or less, more preferably 20,000 or less. If it exceeds 200,000, the wear resistance may not be sufficiently improved when used in place of oil.

In the present invention, high molecular weight polybutadiene corresponds to the rubber component, and low molecular weight polybutadiene does not correspond to the rubber component.

The content of high molecular weight polybutadiene 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, sufficient wear resistance may not be obtained. The content is preferably 40% by mass or less, more preferably 30% by mass or less. If it exceeds 40% by mass, sufficient rubber strength may not be obtained.

The content of the low molecular weight polybutadiene is preferably 5 parts by mass or more, more preferably 10 parts by mass or more with respect to 100 parts by mass of the high molecular weight polybutadiene. If it is less than 5 parts by mass, grip performance tends to deteriorate. The content is preferably 29 parts by mass or less, more preferably 27 parts by mass or less. If it exceeds 29 parts by mass, the effect of improving wear resistance may not be sufficiently exhibited.

The rubber composition of the present invention may contain rubber components other than modified natural rubber and high molecular weight polybutadiene. Examples of other rubber components include natural rubber (NR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR). And diene rubbers such as butyl rubber (IIR). Of these, NR and SBR are preferable because they exhibit a good balance of wear resistance and fuel efficiency.

The rubber composition of the present invention may contain carbon black. The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 30 m ² / g or more, and more preferably 50 m ² / g or more. If it is less than 30 m ² / g, sufficient reinforcing properties cannot be obtained, and sufficient abrasion resistance tends to be not obtained. Further, the _N 2 SA is preferably 300 meters ² / g or less, more preferably 150m ² / g. When it exceeds 300 m < ² > / g, the viscosity at the time of unvulcanized | curing becomes very high, and there exists a tendency for workability to deteriorate. Moreover, the dispersibility tends to deteriorate and the fuel efficiency tends to deteriorate.
In addition, N ₂ SA of carbon black is obtained by A method of JIS K 6217.

The content of carbon black is preferably 1 part by mass or more, more preferably 3 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 rubber strength may not be obtained. The content is preferably 50 parts by mass or less, more preferably 20 parts by mass or less. If it exceeds 50 parts by mass, heat generation will increase and the fuel efficiency tends to deteriorate.

The rubber composition of the present invention usually contains silica. 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 it has many silanol groups.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 30 m ² / g or more, and more preferably 50 m ² / g or more. If it is less than 30 m ² / g, the reinforcing effect is small and the rubber strength may not be sufficiently improved. Further, the _N 2 SA is preferably at most 500 meters ² / g, more preferably at most 250m ² / g. When it exceeds 500 m < ² > / g, the dispersibility of a silica will fall, and there exists a tendency for low exothermic property and workability to fall.
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 10 parts by mass or more, more preferably 50 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 100 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.

The total content of carbon black and silica is preferably 15 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 180 parts by mass or less, more preferably 120 parts by mass or less. When the content is within the above range, low fuel consumption, wear resistance, processability, and rubber strength can be obtained in a well-balanced manner.

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. Here, the lower limit of the content of the silane coupling agent is preferably 2 parts by mass or more, more preferably 4 parts by mass or more, and the upper limit is preferably 15 parts by mass or less, more preferably 100 parts by mass of silica. It is 10 parts by mass or less.

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.

As the oil, for example, process oil, vegetable oil, or a mixture thereof can be used. As the process oil, for example, a paraffin process oil, an aroma process oil, a naphthenic process oil, or the like can be used. As vegetable oils and fats, castor oil, cottonseed oil, sesame oil, rapeseed oil, soybean oil, palm oil, palm oil, peanut water, rosin, pine oil, pineapple, tall oil, corn oil, rice bran oil, beet flower oil, sesame oil, Examples include olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil. Of these, an aroma-based process oil is preferably used.

The oil content is preferably 2 parts by mass or more, more preferably 8 parts by mass or more, with respect to 100 parts by mass of the rubber component. If it is less than 2 parts by mass, the effect of improving workability may not be sufficiently obtained. The content is preferably 30 parts by mass or less, more preferably 15 parts by mass or less. When it exceeds 30 mass parts, there exists a possibility that abrasion resistance may deteriorate.

When the rubber composition contains oil, the total content of oil and low molecular weight polybutadiene is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, with respect to 100 parts by mass of the rubber component. If it is less than 5 parts by mass, sufficient processability may not be obtained. The content is preferably 40 parts by mass or less, more preferably 25 parts by mass or less. If it exceeds 40 parts by mass, sufficient wear resistance may not be obtained.

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

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

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

The pneumatic tire of the present invention can be suitably used for passenger cars, high-load tires and the like.

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 Production Examples 1 and 2 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 1 (HPNR1))
After adjusting the solid rubber latex solids concentration (DRC) to 30% (w / v), 1000 g of natural rubber latex was added with 10 g of Emal-E and 20 g of NaOH, followed by saponification at room temperature for 48 hours. Natural rubber latex was obtained. Water was added to the latex to dilute to DRC 15% (w / v), and then formic acid was added with slow stirring to adjust the pH to 4.0 to 4.5 to cause aggregation. The agglomerated rubber was pulverized, washed repeatedly with 1000 ml of water, and then dried at 110 ° C. for 2 hours to obtain a solid rubber (saponified natural rubber 1 (HPNR1)).

(Production Example 2: Preparation of saponified natural rubber 2 (HPNR2))
Solid rubber (saponified natural rubber 2 (HPNR2)) was obtained under the same conditions as in Production Example 1 except that NaOH 20 g was changed to 15 g.

About HPNR1 and 2 obtained by the said manufacture example, and TSR mentioned later, nitrogen content, phosphorus content, and gel content rate were measured with 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 Co., Ltd.). 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, HPNR1 and 2 had reduced nitrogen content, phosphorus content, and gel content as compared with TSR. Further, in ³¹ P-NMR measurement, HPNR1 and 2 did not have a peak due to phospholipid at −3 ppm to 1 ppm.

(Production Example 3: Preparation of low molecular weight polybutadiene 1)
The inside of the 1.5 L autoclave was purged with nitrogen, and water (H ₂ O) was added to a solution consisting of 23% by mass of butadiene, 36% by mass of cyclohexane, 15% by mass of benzene and 26% by mass of C4 fraction at room temperature of 0.7L. 2.3 mmol) and vigorously stirred at 700 rpm for 30 minutes. Next, 3 mmol of diethylaluminum chloride (DEAC) (cyclohexane solution) was added and stirred at room temperature for 5 minutes. This was heated to 50 ° C., a toluene solution of 23 mmol of nickel octylate (Ni (Oct) ₂ ) was added, and further polymerized at 65 ° C. for 25 minutes. Polymerization was stopped by adding 5 mL of an ethanol / heptane (1/1) solution containing an antioxidant. After releasing the pressure inside the autoclave, the polymerization solution was put into ethanol to recover polybutadiene. The recovered polybutadiene was then vacuum-dried at 50 ° C. for 6 hours, and 79 g of polybutadiene was obtained. Mw of the obtained low molecular weight polybutadiene 1 was 57,000.

(Production Example 4: Preparation of low molecular weight polybutadiene 2)
Polybutadiene was obtained under the same conditions as in Production Example 3 except that 2.3 mmol of water was changed to 3 mmol, 1 kg / cm ^{2 of} ethylene was added after vigorous stirring, and 3 mmol of DEAC was changed to 4 mmol. 80 g of low molecular weight polybutadiene 2 was obtained, and Mw was 12,000.

In addition, the number average molecular weight (Mn) and the weight average molecular weight (Mw) of the low molecular weight polybutadiene 1-2, the high molecular weight polybutadiene described below, and the polybutadiene mixtures 1-3 described below were evaluated by the following methods.

(Measurement of number average molecular weight (Mn), weight average molecular weight (Mw))
Number average molecular weight (Mn) and weight average molecular weight (Mw) are gel permeation chromatograph (GPC) (GPC-8000 series, manufactured by Tosoh Corp., detector: differential refractometer, column: TSKGEL manufactured by Tosoh Corp.) It calculated | required by standard polystyrene conversion based on the measured value by SUPERMALTPORE HZ-M).

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.

HPNR1: Production Example 1
HPNR2: Production Example 2
TSR: TSR20
High molecular weight polybutadiene: BR150B manufactured by Ube Industries, Ltd. (cis content: 96% by mass, Mw: 440,000, Mw / Mn 3.2)
Low molecular weight polybutadiene 1: Production Example 3 (Mw: 57,000, Mw / Mn: 2.5)
Low molecular weight polybutadiene 2: Production Example 4 (Mw: 12,000)
Polybutadiene mixture 1: 10 parts by weight of low molecular weight polybutadiene 1 mixed with 100 parts by weight of high molecular weight polybutadiene (Mw / Mn: 30)
Polybutadiene mixture 2: 100 parts by mass of high molecular weight polybutadiene mixed with 10 parts by mass of low molecular weight polybutadiene 2 (Mw / Mn: 33)
Polybutadiene mixture 3: 100 parts by weight of low molecular weight polybutadiene 1 mixed with 100 parts by weight of high molecular weight polybutadiene (Mw / Mn: 45)
Carbon black: N351 (N ₂ SA: 69 m ² / g) manufactured by Cabot Japan
Silica: Zeosil 1115MP manufactured by Rhodia (CTAB specific surface area: 110 m ² / g, BET specific surface area: 115 m ² / g)
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa
Wax: Sunnock wax N manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Process oil: Diana process AH-24 (aromatic process oil) manufactured by Idemitsu Kosan Co., Ltd.
Zinc oxide: 2 types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Anti-aging agent manufactured by NOF Corporation: Antigen 6C (N- (1,3-dimethylbutyl) manufactured by Sumitomo Chemical Co., Ltd. -N'-phenyl-p-phenylenediamine)
Sulfur: Powder sulfur vulcanization accelerator DPG manufactured by Karuizawa Sulfur Co., Ltd. DPG: Noxeller D (N, N'-diphenylguanidine) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Vulcanization accelerator CZ: Noxeller CZ (N-cyclohexyl-2-benzothiazolylsulfenamide) 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 170 ° C. for 10 minutes, so that a test tire (tire size: 195) was obtained. / 65R15).

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

(Abrasion resistance)
Using a LAT tester (Laboratory Abbreviation and Skid Tester), the volume loss of each vulcanized rubber composition was measured under the conditions of a load of 50 N, a speed of 20 km / h, and a slip angle of 5 °. The volume loss amount of Comparative Example 3 was taken as 100 and displayed as an index. In addition, it shows that it is excellent in abrasion resistance, so that an index | exponent is large.
(Abrasion resistance index) = (Volume loss amount of Comparative Example 3) / (Volume loss amount of each formulation) × 100

(Rolling resistance)
Loss tangent (tan δ) of each compound (vulcanized product) under the conditions of a temperature of 70 ° C., an initial strain of 10%, a dynamic strain of 2%, and a frequency of 10 Hz using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.) Was measured and indexed by the following formula (rolling resistance index). A larger index indicates better fuel economy.
(Rolling resistance index) = (tan δ of Comparative Example 3) / (tan δ of each formulation) × 100

(Processability)
About the obtained unvulcanized rubber composition, it measured at 130 degreeC according to the measuring method of the Mooney viscosity based on JISK6300, and displayed as an index | exponent by the following formula (workability index). The larger the index, the lower the Mooney viscosity and the better the workability.
(Workability index) = (ML _{1 + 4} of Comparative Example 3) / (ML _{1 + 4 of} each formulation) × 100

(Rubber strength)
Using the resulting vulcanizate, a No. 3 dumbbell-shaped rubber test piece was prepared and subjected to a tensile test according to JIS K6251 “Vulcanized rubber and thermoplastic rubber—How to obtain tensile properties”. ) And elongation at break (EB) were measured, and the product (TB × EB) was calculated. Then, the rubber strength (TB × EB) of each compound (vulcanized product) was displayed as an index (rubber strength index) by the following calculation formula. The larger the index, the better the rubber strength.
(Rubber strength index) = (TB of each formulation × EB) / (TB of comparative example 3 × EB) × 100

(Abrasion resistance: test tire)
Wear test tires on all wheels of a vehicle (domestic FF2000cc) and run on the test track. Measure the decrease in groove depth after running 30000 km, and determine the distance traveled when the groove depth decreases by 1 mm. Calculated. And the running distance of the comparative example 3 was set to 100, and the abrasion resistance of each formulation was displayed as an index according to the following formula. It shows that it is excellent in abrasion resistance, so that an index | exponent is large.
(Abrasion resistance index) = (travel distance of each formulation) / (travel distance of Comparative Example 3) × 100

(Rolling resistance: test tire)
Using a rolling resistance tester, each tire was mounted on a regular rim (22.5 × 8.25 15 ° deep rim), and the rolling resistance was measured at an internal pressure of 700 kPa, an speed of 80 km / h, and a load of 24.52 KN. The rolling resistance of Comparative Example 3 was set to 100, and the rolling resistance of each formulation was indicated by an index. The smaller the index, the smaller the rolling resistance and the better.

From the results shown in Table 2, the combined use of modified natural rubber, high molecular weight polybutadiene and low molecular weight polybutadiene can improve fuel economy, wear resistance, processability, and rubber strength, and these performances can be obtained at a high level. Became clear.

Claims (8)

A tire rubber composition comprising a modified natural rubber having a phosphorus content of 200 ppm or less, a high molecular weight polybutadiene having a weight average molecular weight of 250,000 or more, and a low molecular weight polybutadiene having a weight average molecular weight of 0.5 to 200,000. The tire rubber composition according to claim 1, wherein the content of the modified natural rubber in 100% by mass of the rubber component is 60 to 95% by mass, and the content of the high molecular weight polybutadiene is 5 to 40% by mass. The tire rubber composition according to claim 1 or 2, wherein the content of the low molecular weight polybutadiene is 5 to 29 parts by mass with respect to 100 parts by mass of the high molecular weight polybutadiene. The tire rubber composition according to any one of claims 1 to 3, wherein the nitrogen content of the modified natural rubber is 0.3 mass% or less. The rubber composition for tires according to any one of claims 1 to 4, wherein a gel content measured as a toluene insoluble content of the modified natural rubber is 20% by mass or less. The rubber composition for tires according to any one of claims 1 to 5, wherein the modified natural rubber is obtained by saponifying natural rubber latex. The method for producing a rubber composition according to any one of claims 1 to 6, which does not include a step of kneading the modified natural rubber. The pneumatic tire produced using the rubber composition in any one of Claims 1-6.