JP5646971B2 - Rubber composition for tire, method for producing the same, and pneumatic tire - Google Patents

Description

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

Conventionally, it has been attempted to reduce the fuel consumption of a vehicle by reducing the rolling resistance of the tire and suppressing heat generation, but in recent years, there has been an increasing demand for a reduction in fuel consumption.

Known methods for reducing the heat generation of rubber compositions used in tires include a method using a low-reinforcing filler and a method for reducing the amount of filler. In these methods, a rubber composition is used. The reinforcing property of the object is lowered, and the breaking performance (rubber strength) is lowered. Thus, it has been difficult to achieve both low fuel consumption and rubber strength.

On the other hand, natural rubber is widely used for tires, but natural rubber has higher Mooney viscosity and poor processability compared to other synthetic rubbers, so usually adding a chelating agent and masticating, Used after decreasing Mooney viscosity. Therefore, productivity is reduced when natural rubber is used. Moreover, since the molecular chain of natural rubber is cleaved by mastication, there is a problem that the characteristics (low fuel consumption, rubber strength, etc.) of the high molecular weight polymer originally possessed are lost.

As methods for improving the processability of natural rubber, Patent Documents 1 and 2 describe a method in which natural rubber latex is added with a proteolytic enzyme and a surfactant, and in Patent Document 3, solid natural rubber swollen with a solvent is added to water. In the method of immersing in alkali oxide, in Patent Document 4, the method of adding phosphate to natural rubber latex and removing magnesium phosphate is disclosed in Patent Document 5, and in Patent Document 5, the surfactant is added to natural rubber latex and washed. Each method is disclosed.

However, these methods still have room for improvement in terms of achieving both low fuel consumption and rubber strength.

Japanese Patent Laid-Open No. 08-12814 JP 2005-82622 A Japanese Patent Laid-Open No. 11-12306 JP 2004-250546 A Japanese Patent No. 3294901

An object of the present invention is to solve the above-mentioned problems and provide a rubber composition for a tire that can achieve both low fuel consumption and rubber strength, a method for producing the same, and a pneumatic tire using the rubber composition.

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

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.
It is preferable that the white filler is silica.

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.

The present invention includes a rubber component containing a modified natural rubber and isoprene rubber having a phosphorus content of 200 ppm or less, and carbon black and / or a white filler, each having a modified natural rubber content and an isoprene rubber content. Since the tire rubber composition is a predetermined amount and the manufacturing method thereof, both low fuel consumption and rubber strength can be achieved. Moreover, the pneumatic tire excellent in these performances can be provided.

The rubber composition for tires of the present invention includes a rubber component including a modified natural rubber (HPNR) and an isoprene rubber (IR) having a phosphorus content of 200 ppm or less. By combining HPNR and IR, which reduces and removes phospholipids contained in natural rubber (NR), the effect of improving low heat build-up is synergistically reduced. Fuel economy can be improved sufficiently. At the same time, the rubber strength can be increased synergistically, so that both performances can be remarkably improved.

Furthermore, since the unvulcanized rubber composition containing HPNR is excellent in processability, it can be sufficiently kneaded without performing a special kneading step. For this reason, it is possible to suppress the deterioration of the properties of the natural rubber due to mastication, and the above performance can be effectively enhanced. Moreover, the performance can be further improved by reducing not only phospholipids but also proteins and gels.

The modified natural rubber has a phosphorus content of 200 ppm or less. If it exceeds 200 ppm, tan δ will increase and fuel efficiency will deteriorate, or the Mooney viscosity of unvulcanized rubber will increase and processability will tend to deteriorate. 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. When the nitrogen content exceeds 0.3% by mass, the Mooney viscosity increases during storage and the processability tends to deteriorate, or the fuel efficiency tends to deteriorate. 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. When it exceeds 20 mass%, workability tends to deteriorate. The gel content means a value measured as an insoluble content with respect to toluene which is a nonpolar solvent, and may be simply referred to as “gel content” or “gel content” below. The measuring method of the content rate of a gel part is as follows. First, a natural rubber sample is soaked in dehydrated toluene, light-shielded in the dark and left for 1 week, and then the toluene solution is centrifuged at 1.3 × 10 ⁵ rpm for 30 minutes to obtain an insoluble gel content and a toluene soluble content. Isolate. Methanol is added to the insoluble gel and solidified, and then dried, and the gel content is determined from the ratio between the mass of the gel and the original mass of the sample.

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. A modified natural rubber (saponified natural rubber) can be produced by a method of repeatedly washing with water until the rate 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.

In the rubber composition of the present invention, the content of the modified natural rubber in 100% by mass of the rubber component is 5% by mass or more, preferably 15% by mass or more. If it is less than 5% by mass, the fuel economy may not be sufficiently improved. The content is preferably 95% by mass or less, more preferably 85% by mass or less. If it exceeds 95% by mass, the amount of isoprene rubber is relatively reduced, and the effects of the present invention may not be sufficiently obtained.

The IR is not particularly limited, and conventionally known ones can be used as appropriate. For example, those having a cis-1,4-bond content of 90% or more and a Mooney viscosity ML _{1 + 4} (100 ° C.) of 65 to 82 can be used.

In the rubber composition of the present invention, the IR content in 100% by mass of the rubber component is 5% by mass or more, preferably 15% by mass or more. If it is less than 5% by mass, the fuel economy may not be sufficiently improved. The content is preferably 95% by mass or less, more preferably 85% by mass or less. If it exceeds 95% by mass, the amount of the modified natural rubber is relatively reduced, and the effects of the present invention may not be sufficiently obtained, and the rubber strength may be reduced.

The total content of the modified natural rubber and IR in 100% by mass of the rubber component is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably from the viewpoint of sufficiently improving fuel economy and rubber strength. Is 100% by mass.

In addition to the modified natural rubber and IR, examples of rubber components that can be used in the present invention include natural rubber (NR), butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), and ethylene propylene. Examples include diene rubbers such as diene rubber (EPDM), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR).

Examples of carbon black include GPF, FEF, HAF, ISAF, and SAF, but are not particularly limited. By blending carbon black, a reinforcing effect can be obtained and good rubber strength can be obtained.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 10 m ² / g or more, and more preferably 30 m ² / g or more. If it is less than 10 m < ² > / g, there is a possibility that sufficient reinforcing effect cannot be obtained and sufficient rubber strength cannot be obtained. Further, the nitrogen adsorption specific surface area of the carbon black is preferably 300 meters ² / g or less, more preferably 150m ² / g. When it exceeds 300 m ² / g, it becomes difficult to disperse well, and there is a tendency that sufficient low fuel consumption cannot be obtained.
In the present specification, the nitrogen adsorption specific surface area of carbon black is determined by the A method of JIS K6217.

As white filler, those commonly used in the rubber industry, for example, mica such as silica, calcium carbonate, sericite, aluminum hydroxide, magnesium oxide, magnesium hydroxide, clay, talc, alumina, titanium oxide Etc. can be used. Among these, silica is preferable from the viewpoint that excellent fuel economy and rubber strength can be obtained.

Examples of the silica include, but are not limited to, dry process silica (anhydrous silicic acid), wet process silica (hydrous silicic acid), and wet process silica is preferable because of its large number of silanol groups.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 50 m ² / g or more, and more preferably 70 m ² / g or more. If it is less than 50 m ² / g, the reinforcing effect is small, and there is a possibility that sufficient rubber strength cannot be obtained. The _N 2 SA of the silica is preferably 300 meters ² / g or less, more preferably 280m ² / g. If it exceeds 300 m ² / g, the dispersibility tends to decrease and the exothermicity tends to increase.
The nitrogen adsorption specific surface area of silica is a value measured by the BET method according to ASTM D3037-81.

In the present invention, it is preferable to use a silane coupling agent together with silica.
The silane coupling agent is not particularly limited, and those conventionally used in the tire field can be used. For example, sulfide-based, mercapto-based, vinyl-based, amino-based, glycidoxy-based, nitro-based, chloro-based silane coupling Agents and the like. Among them, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, etc. A sulfide system can be preferably used.

The content of the silane coupling agent is preferably 2 parts by mass or more and more preferably 4 parts by mass or more with respect to 100 parts by mass of silica. If it is less than 2 parts by mass, there is a possibility that the effect of improving the fuel economy by silica blending cannot be obtained sufficiently. The content is preferably 16 parts by mass or less, and more preferably 12 parts by mass or less. When the amount exceeds 16 parts by mass, there is a tendency that the effect of improving the fuel economy and rubber strength due to the silica compound cannot be sufficiently obtained.

The total content of carbon black and white filler is preferably 10 parts by mass or more, more 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, sufficient rubber strength may not be obtained. The total content is preferably 150 parts by mass or less, more preferably 100 parts by mass or less. If it exceeds 150 parts by mass, processability may be deteriorated or sufficient fuel efficiency may not be obtained.

The content of carbon black is preferably 10 parts by mass or more, more 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, sufficient rubber strength may not be obtained. The content is preferably 150 parts by mass or less, more preferably 100 parts by mass or less. If it exceeds 150 parts by mass, sufficient fuel economy may not be obtained.

The content of silica 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 the amount is less than 5 parts by mass, the effect of improving the fuel efficiency by silica blending may not be sufficiently obtained. The content is preferably 100 parts by mass or less, more preferably 90 parts by mass or less. If it exceeds 100 parts by mass, the workability tends to decrease.

When the rubber composition of the present invention is applied to a truck / bus tire, the oil content is preferably 3 parts by mass or less, more preferably 1 part by mass or less, with respect to 100 parts by mass of the rubber component. It does not have to be included. Thereby, sufficient rubber strength is obtained and the effects of the present invention can be obtained satisfactorily.

In addition to the above components, the rubber composition of the present invention contains compounding agents generally used in the production of rubber compositions, such as zinc oxide, stearic acid, various anti-aging agents, vulcanizing agents such as sulfur, and vulcanization. An accelerator or the like can be appropriately blended.

The rubber composition of the present invention is produced by a general method. That is, it can be produced by a method of kneading the above components with a Banbury mixer, 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, trucks and buses, and is particularly suitable for trucks and buses.

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 and TSR used by evaluation of the rubber composition 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 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 (%) 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 the ³¹ P NMR measurement of an extract obtained by extracting from the saponified natural rubber, it did not detect the peak due to phospholipids -3Ppm～1ppm.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
Saponified natural rubber: Production example TSR: Natural rubber TSR
IR: Nippon IR2200 made by Nippon Zeon Co., Ltd.
Carbon black: Dia Black (N ₂ SA: 50 m ² / g) manufactured by Mitsubishi Chemical Corporation
Silica: ULTRASIL VN3 (N ₂ SA: 175 m ² / g) manufactured by EVONIK-DEGUSSA
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by EVONIK-DEGUSSA
Zinc oxide: Zinc Hana No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Stearic acid “Kashiwa” manufactured by NOF Corporation
Anti-aging agent: Nocrack 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Sulfur: Sulfur powder vulcanization accelerator (NS) manufactured by Tsurumi Chemical Industry Co., Ltd .: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Vulcanization accelerator (DPG): Noxeller D manufactured by Ouchi Shinsei Chemical Co., Ltd.

Examples and Comparative Examples According to the composition shown in Table 2, chemicals other than sulfur and a vulcanization accelerator were kneaded using 1.7 L Banbury. Next, using a roll, sulfur and a vulcanization accelerator were added to the obtained kneaded product and kneaded to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press vulcanized at 150 ° C. for 30 minutes to obtain a vulcanized product. In Comparative Example 3 using TSR, mastication was performed in advance.

The following evaluation was performed about the obtained unvulcanized rubber composition and vulcanizate. The results are shown in Table 2.

(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.) The loss tangent tan δ of Comparative Examples 1 and 4 was taken as 100, and the result was expressed as an index (rolling resistance index) by the following formula. The larger the index, the better the rolling resistance characteristics.
(Rolling resistance index) = (tan δ of Comparative Examples 1 and 4) / (tan δ of each formulation) × 100

(Rubber strength)
Using the resulting vulcanized rubber sheet, 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”. TB) and elongation at break (EB) were measured, and the product (TB × EB) was calculated. The rubber strength (TB × EB) of each compound (vulcanized product) was indicated by an index according to the following formula. In addition, it shows that it is excellent in rubber strength, so that a rubber strength index is large.
(Rubber strength index) = (TB × EB of each formulation) / (TB × EB of Comparative Examples 1 and 4) × 100

(Mooney viscosity)
About the obtained unvulcanized rubber composition, it measured at 130 degreeC according to the measuring method of the Mooney viscosity based on JISK6300. The Mooney viscosity (ML _{1 + 4} ) of Comparative Examples 1 and ₄ was set to 100, and the index was expressed by the following formula (Mooney viscosity index). The larger the index, the lower the Mooney viscosity and the better the processability.
(Muvis viscosity index) = (ML _{1 + 4} of Comparative Examples 1 and ₄ ) / (ML _{1 + 4 of} each formulation) × 100

Although the examples using saponified natural rubber were not masticated, the processability was superior to the comparative examples using masticated TSR (for example, Examples 1 and 3). . In addition, the combined use of saponified natural rubber and IR has synergistically improved fuel economy and rubber strength.

Claims (8)

A rubber component including a modified natural rubber and isoprene rubber having a phosphorus content of 200 ppm or less and carbon black and / or a white filler;
And the content of the modified natural rubber 100% by mass of the rubber component is 5 wt% or more state, and are the content of the isoprene rubber is 5 mass% or more, the total content of the modified natural rubber and the isoprene rubber The rubber composition for a tire Ru der 80 mass% or more. The tire rubber composition according to claim 1, wherein the nitrogen content of the modified natural rubber is 0.3 mass% or less. The rubber composition for a tire according to claim 1 or 2, 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 a tire according to any one of claims 1 to 3, wherein the modified natural rubber is obtained by saponifying natural rubber latex. The tire rubber composition according to any one of claims 1 to 4, wherein the white filler is silica. A process of saponifying natural rubber latex to prepare a saponified natural rubber latex, a process of agglomerating the saponified natural rubber latex, and washing until the phosphorus content contained in the rubber is 200 ppm or less. A method for producing a rubber composition for a tire according to any one of claims 1 to 5, comprising a step of obtaining a natural rubber and a step of kneading the obtained modified natural rubber and isoprene rubber. The pneumatic tire produced using the rubber composition in any one of Claims 1-5. A pneumatic tire for trucks and buses having a tread and / or a sidewall produced using the rubber composition according to any one of claims 1 to 5.