JP6073574B2 - Chafer rubber composition and pneumatic tire - Google Patents

Description

The present invention relates to a rubber composition for a chafer and a pneumatic tire having a chafer 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, there has been a growing demand for lower fuel consumption of vehicles using tires, and there has been a demand for lower fuel consumption of rubber compositions used for chafers as well as treads, sidewalls, and internal members.

As a method for reducing the heat generation of the rubber composition, a method using a low reinforcing filler, a method for reducing the amount of the filler, a method using silica as a filler, and the like are known. However, in these methods, since the reinforcing property of the rubber composition is lowered, the breaking strength is lowered. Thus, it has been difficult to improve the fuel efficiency and the breaking strength at the same time.

Further, the chafer is a member for protecting a portion (chaefing portion) that contacts the rim in the bead portion of the pneumatic tire, and natural rubber that exhibits excellent tear strength is widely used. Natural rubber has a Mooney viscosity higher than that of other synthetic rubbers and has poor processability. Therefore, natural rubber is usually used after mastication by adding a chelating agent and lowering the Mooney viscosity. Therefore, productivity is reduced when natural rubber is used. Further, since the molecular chain of natural rubber is cleaved by mastication, there is a problem that the characteristics (low fuel consumption, bending crack growth resistance, etc.) of the high molecular weight polymer inherent to natural rubber are lost.

Patent Document 1 contains natural rubber deproteinized so that the total nitrogen content, which is an index of protein mass, is 0.1% by mass or less, and has good strength, low fuel consumption, and good processability. Although the composition has been disclosed, there is still room for improvement in terms of improving fuel economy and flex crack growth resistance while having good processability.

JP-A-6-329838

The present invention provides a rubber composition for a chafer that solves the above-mentioned problems and can improve workability, fuel efficiency and bending crack growth resistance in a well-balanced manner, and a pneumatic tire having a chafer using the same. Objective.

The present invention includes a modified natural 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 5% by mass or more. It is related with the rubber composition for chafers which is.

The natural rubber preferably has a nitrogen content of 0.3% by mass or less and a gel content measured as a toluene insoluble content of 20% by mass or less.

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

The modified natural rubber is a step of saponifying natural rubber latex to prepare a saponified natural rubber latex (A), and a step of alkali-treating the agglomerated rubber obtained by agglomerating the saponified natural rubber latex ( B) and the step (C) of washing until the phosphorus content contained in the rubber is 200 ppm or less are preferred.

The white filler is preferably silica.

The present invention also relates to a pneumatic tire having a chafer manufactured using the rubber composition.

According to the present invention, since it is a rubber composition for chafers containing a modified natural rubber having a phosphorus content of 200 ppm or less and carbon black and / or white filler, processability, low fuel consumption, and flex crack resistance Can improve growth in a well-balanced manner.

The rubber composition for a chafer according to the present invention includes carbon black and / or white filler added to a rubber component containing a modified natural rubber (HPNR) having a phosphorus content of 200 ppm or less. Yes. By using HPNR (preferably HPNR from which protein and gel content have also been removed) in which phospholipids contained in natural rubber (NR) have been reduced and removed, fuel consumption can be further reduced compared to the use of NR. .

In addition, unvulcanized rubber composition containing HPNR has low Mooney viscosity and excellent processability, and can be sufficiently kneaded without any special mastication process, resulting in decreased physical properties of rubber (such as rubber strength) due to mastication. Can be prevented. For this reason, the rubber properties inherent to natural rubber can be maintained, so that good rubber strength (destructive properties) can be obtained. Furthermore, HPNR does not contain dust components (pebbles, wood chips, etc.) contained in TSR and the like, and does not require a removal process of the components, so that it is excellent in productivity and there is no worry of rubber breakage due to dust components. Therefore, it is possible to improve the fuel efficiency and the flex crack growth resistance in a balanced manner while obtaining excellent workability (productivity).

The modified natural rubber has a phosphorus content of 200 ppm or less. If it exceeds 200 ppm, it is assumed that phosphorus forms a network in natural rubber, leading to an increase in gel amount and an increase in Mooney viscosity. Further, tan δ of the vulcanized rubber tends to increase, and there is a possibility that low fuel consumption and bending crack growth resistance cannot be improved in a well-balanced manner. 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 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.

In the modified natural rubber, the nitrogen content is preferably 0.3% by mass or less, more preferably 0.15% by mass or less. If the nitrogen content exceeds 0.3% by mass, it is presumed that the protein forms a network in natural rubber, leading to an increase in gel amount and an increase in Mooney viscosity. Further, tan δ of the vulcanized rubber tends to increase, and there is a possibility that low fuel consumption and bending crack growth resistance cannot be improved in a well-balanced manner. The nitrogen content can be measured by a conventional method such as Kjeldahl method. Nitrogen is derived from protein.

The gel content in the modified natural rubber is preferably 20% by mass or less, more preferably 10% by mass or less, and still more preferably 7% by mass or less. When it exceeds 20% by mass, the dispersibility of the filler deteriorates, the Mooney viscosity increases, and the workability tends to be lowered, and the balance may not be improved. The gel content means a value measured as an insoluble content with respect to toluene which is a nonpolar solvent, and may be simply referred to as “gel content” or “gel content” below. The measuring method of the content rate of a gel part is as follows. First, a natural rubber sample is soaked in dehydrated toluene, light-shielded in the dark and left for 1 week, and then the toluene solution is centrifuged at 1.3 × 10 ⁵ rpm for 30 minutes to obtain an insoluble gel content and a toluene soluble content. Isolate. Methanol is added to the insoluble gel and solidified, and then dried, and the gel content is determined from the ratio between the mass of the gel and the original mass of the sample.

The modified natural rubber can be obtained, for example, by the production method described in JP 2010-138359 A. Among them, the process (A) of preparing a saponified natural rubber latex by saponifying the natural rubber latex, A production method comprising a step (B) of subjecting the agglomerated rubber obtained by agglomerating the saponified natural rubber latex to an alkali treatment and a step (C) of washing until the phosphorus content contained in the rubber is 200 ppm or less. What is prepared is preferred. By this manufacturing method, phosphorus content, nitrogen content, etc. can be reduced effectively. Moreover, by using the modified natural rubber obtained by the production method, processability, fuel efficiency and bending crack growth resistance can be remarkably improved, and these performances can be obtained at a high level. Further, when the acid is agglomerated with the acid, the remaining acid is neutralized with an alkali treatment to not only prevent the rubber from being deteriorated by the acid but also to further reduce the nitrogen content in the rubber.

In the production method described above, the saponification treatment can be performed by adding an alkali and, if necessary, a surfactant to natural rubber latex and allowing to stand at a predetermined temperature for a certain time. In addition, you may perform stirring etc. as needed. According to the above production method, the phosphorus content and nitrogen content of natural rubber can be suppressed.

As the natural rubber latex, conventionally known latexes such as raw latex, purified latex, and high ammonia latex can be used. Examples of the alkali used for the saponification treatment include sodium hydroxide, potassium hydroxide, calcium hydroxide, and amine compounds. From the viewpoint of good saponification and the stability of natural rubber latex, sodium hydroxide, Potassium hydroxide is preferred. As the surfactant, known anionic surfactants, nonionic surfactants, and amphoteric surfactants can be used. Of these, anionic surfactants are preferred, and sulfonic acid anions are preferred. A surfactant is more preferable.

In the saponification treatment, the amount of alkali added may be appropriately set, but is preferably 0.1 to 10 parts by mass, more preferably 0.3 to 5 parts by mass with respect to 100 parts by mass of the solid content of the natural rubber latex. It is. Moreover, the addition amount of the surfactant is preferably 0.01 to 6.0 parts by mass, more preferably 0.1 to 3.5 parts by mass with respect to 100 parts by mass of the solid content of the natural rubber latex. The temperature and time of the saponification treatment may be appropriately set, and is usually about 20 to 70 ° C. (preferably 30 to 70 ° C.) and about 1 to 72 hours (preferably 3 to 48 hours).

After completion of the saponification reaction, the agglomerated rubber obtained by agglomerating the saponified natural rubber latex obtained by the reaction is crushed as necessary, and then the obtained agglomerated rubber or crushed rubber is contacted with an alkali. Perform alkali treatment. By the alkali treatment, the nitrogen content in the rubber can be efficiently reduced, and the effects of the present invention are further exhibited. Examples of the aggregation method include a method of adding an acid such as formic acid. The alkali treatment method is not particularly limited as long as it is a method in which rubber and alkali are brought into contact with each other, and examples thereof include a method in which agglomerated rubber and crushed rubber are immersed in alkali. Examples of the alkali that can be used for the alkali treatment include alkali metal carbonates such as potassium carbonate, sodium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, lithium carbonate, lithium hydrogen carbonate, and ammonia in addition to the alkali in the saponification treatment described above. Water etc. are mentioned. Of these, alkali metal carbonates are preferred, sodium carbonate and potassium carbonate are more preferred, and sodium carbonate is even more preferred from the viewpoint of excellent effects of the present invention.

When the alkali treatment is performed by the above immersion, the treatment can be performed by immersing rubber (crushed rubber) in an alkaline aqueous solution having a concentration of preferably 0.1 to 5 mass%, more preferably 0.2 to 3 mass%. Thereby, the amount of nitrogen in the rubber can be further reduced.

When the alkali treatment is performed by the immersion, the temperature of the alkali treatment can be set as appropriate, but is usually preferably 20 to 70 ° C. The alkali treatment time depends on the treatment temperature, but is preferably 1 to 20 hours, more preferably 2 to 12 hours, considering sufficient treatment and productivity.

Phosphorus content can be reduced by performing a washing treatment after the alkali treatment. Examples of the washing treatment include a method of diluting a rubber component with water and washing, followed by a centrifugal separation treatment, and a method of leaving the rubber to stand and discharging the aqueous phase and taking out the rubber component. When centrifuging, it is first diluted with water so that the rubber content of the natural rubber latex is 5 to 40% by mass, preferably 10 to 30% by mass. Then, it may be centrifuged at 5000 to 10000 rpm for 1 to 60 minutes, and washing may be repeated until a desired phosphorus content is obtained. In addition, when the rubber is allowed to stand still, the addition of water and stirring may be repeated until the desired phosphorus content is obtained. The modified natural rubber according to the present invention is obtained by drying after completion of the washing treatment.

In the rubber composition of the present invention, the content of the modified natural rubber in 100% by mass of the rubber component is 5% by mass or more, preferably 10% by mass or more, more preferably 30% by mass or more, and further preferably 35% by mass. That's it. If it is less than 5% by mass, the processability, fuel efficiency and resistance to flex crack growth may not be sufficiently improved. The content is preferably 90% by mass or less, more preferably 75% by mass or less, and still more preferably 65% by mass or less. When it exceeds 90 mass%, there exists a possibility that the durability of a tire may deteriorate.

In the rubber composition of this invention, you may mix | blend another rubber component in the range which does not inhibit an effect. Examples of other rubber components include diene rubbers such as natural rubber (NR) (unmodified), isoprene rubber (IR), butadiene rubber (BR), and styrene butadiene rubber (SBR). Among these, BR is preferable because it provides good processability, low fuel consumption, and resistance to flex crack growth.

The BR is not particularly limited, and for example, BR having a high cis content, BR containing a syndiotactic polybutadiene crystal, and the like can be used. Among these, BR having a cis content of 95% by mass or more is preferable.

The content of BR in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 25% by mass or more. If the amount is less than 10% by mass, sufficient flex crack growth resistance may not be obtained. The content is preferably 95% by mass or less, more preferably 90% by mass or less, still more preferably 70% by mass or less, and particularly preferably 65% by mass or less. If it exceeds 95% by mass, the content of the modified natural rubber is decreased, and there is a possibility that the processability, fuel efficiency and flex crack growth resistance cannot be improved in a well-balanced manner.

The total content of the modified natural rubber and BR in 100% by mass of the rubber component is preferably 80% by mass or more, more preferably 100% by mass. When the total content is within the above range, excellent processability, low fuel consumption and bending crack growth resistance can be obtained.

As carbon black, GPF, FEF, HAF, ISAF, SAF and the like can be used, but are not particularly limited. By blending carbon black, a reinforcing effect can be obtained, and the effect of the present invention can be favorably obtained by using it together with HPNR.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 50 m ² / g or more, more preferably 100 m ² / g or more, and further preferably 110 m ² / g or more. If it is less than 50 m < ² > / g, there exists a possibility that sufficient reinforcement property and bending crack growth resistance may not be obtained. The _N 2 SA is preferably 220 m ² / g or less, more preferably 200 meters ² / g or less, still more preferably not more than 180 m ² / g. If it exceeds 220 m ² / g, it will be difficult to disperse the carbon black, and the fuel efficiency tends to deteriorate.
Incidentally, _N 2 SA of carbon black, JIS K 6217-2: determined by 2001.

Carbon black has a dibutyl phthalate oil absorption (DBP) of preferably 50 ml / 100 g or more, more preferably 70 ml / 100 g or more, still more preferably 90 ml / 100 g or more. The oil absorption is preferably 150 ml / 100 g or less, more preferably 140 ml / 100 g or less, and still more preferably 120 ml / 100 g or less. Within the above range, excellent rubber strength as a chafer can be obtained.
The DBP of carbon black is measured according to JIS K6217-4: 2001.

The content of carbon black is preferably 20 parts by mass or more, more preferably 40 parts by mass or more, and still more preferably 50 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 20 parts by mass, there is a possibility that sufficient bending crack growth resistance and reinforcement cannot be obtained. The content is preferably 90 parts by mass or less, more preferably 85 parts by mass or less, and still more preferably 80 parts by mass or less. If it exceeds 90 parts by mass, appropriate rubber properties cannot be obtained, and the fuel efficiency tends to deteriorate.

As white fillers, those generally 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 also be used. The white filler may be used alone or in combination with carbon black. Among these, silica is preferable from the viewpoint of obtaining a good balance between low fuel consumption, the reinforcing effect of the rubber composition and dispersibility. The silica is not particularly limited, and examples thereof include dry process silica (anhydrous silica), wet process silica (hydrous silica), and the like, but wet process silica (hydrous silica) is preferable because it has many silanol groups.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 90 m ² / g or more, more preferably 100 m ² / g or more. If it is less than 90 m ² / g, sufficient reinforcement may not be obtained. Further, N ₂ SA of silica is preferably 250 m ² / g or less, more preferably 220 m ² / g or less, and further preferably 130 m ² / g or less. When it exceeds 250 m < ² > / g, the dispersibility of a silica will fall and there exists a tendency for workability to deteriorate.
The nitrogen adsorption specific surface area of silica is a value measured by the BET method according to ASTM D3037-81.

The content of the white filler (preferably silica) is preferably 5 parts by mass or more, more preferably 7 parts by mass or more with respect to 100 parts by mass of the rubber component. The content is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, and still more preferably 30 parts by mass or less. When the content is within the above range, good processability, low fuel consumption and resistance to flex crack growth can be obtained.

In the rubber composition of the present invention, the total content of carbon black and white filler is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, and still more preferably 60 parts by mass with respect to 100 parts by mass of the rubber component. That's it. The total content is preferably 190 parts by mass or less, more preferably 90 parts by mass or less, still more preferably 80 parts by mass or less, and particularly preferably 70 parts by mass or less. When the total content is within the above range, good processability, low fuel consumption and resistance to flex crack growth can be obtained.

In the present invention, when silica is used as the white filler, it is preferable to use a silane coupling agent. Examples of the silane coupling agent include silane coupling agents widely used in the rubber field such as sulfide, mercapto, vinyl, amino, glycidoxy, nitro, and chloro. Among them, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, etc. Sulfide systems are preferred, with bis (3-triethoxysilylpropyl) disulfide being particularly preferred.

When the silane coupling agent is contained, the content of the silane coupling agent is preferably 2 parts by mass or more, more preferably 4 parts by mass or more, and further preferably 6 parts by mass or more with respect to 100 parts by mass of silica. The content is preferably 25 parts by mass or less, more preferably 20 parts by mass or less. When the content is within the above range, good processability, low fuel consumption and resistance to flex crack growth can be obtained.

In the present invention, it is preferable to use sulfur as a vulcanizing agent. The sulfur content is preferably 1.0 parts by mass or more, more preferably 1.5 parts by mass or more, with respect to 100 parts by mass of the rubber component. The content is preferably 3.0 parts by mass or less, more preferably 2.5 parts by mass or less, and still more preferably 2.0 parts by mass or less. When the content is within the above range, a good crosslinking density can be obtained, and excellent processability, low fuel consumption, and flex crack growth resistance can be obtained.

In the present invention, it is preferable to use an antioxidant. As an anti-aging agent, p-phenylenediamine type such as N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine, Quinoline-based anti-aging agents such as 4-trimethyl-1,2-dihydroquinoline polymer are preferred, and their combined use is more preferred.

The content of the antioxidant is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and further preferably 3 parts by mass or more with respect to 100 parts by mass of the rubber component. The content is preferably 6 parts by mass or less, more preferably 5 parts by mass or less. When the content is within the above range, the effect of the present invention can be obtained satisfactorily. In addition, when manufacturing HPNR, there is a tendency for the anti-degradation component to be removed during the saponification treatment of NR. it can.

The rubber composition of the present invention preferably contains a wax. Examples of the wax include petroleum waxes such as paraffin waxes and vegetable waxes such as carnauba waxes. Among these, petroleum-based waxes are preferable and paraffin-based waxes are more preferable because the effects of the present invention can be obtained satisfactorily.

The content of the wax is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 0.5 parts by mass, the effect of improvement by wax may not be sufficiently obtained. The wax content is preferably 4 parts by mass or less, more preferably 3 parts by mass or less. When the amount exceeds 4 parts by mass, the wax may excessively bloom on the rubber surface and the resulting rubber composition may be discolored.

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 oil, stearic acid, zinc oxide, vulcanization accelerators, vulcanization accelerators, and the like. It can mix | blend suitably.

The rubber composition of the present invention can be 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 used for a chafer of a pneumatic tire. Specifically, the rubber composition is used for a member shown in FIG. 2 of JP-A-2009-137437. The chafer may be a canvas chafer made of a woven fabric and a topping rubber covering the woven fabric, or may be a chafer made of only a rubber composition without including the woven fabric.

The pneumatic tire of the present invention can be produced by a usual method using the chafer rubber composition. That is, if necessary, the rubber composition containing various additives is extruded in accordance with the shape of the chafer at an unvulcanized stage, molded by a normal method on a tire molding machine, etc. The tire members are bonded together to form an unvulcanized tire. This unvulcanized tire can be heated and pressurized in a vulcanizer to produce a tire.

The pneumatic tire of the present invention is suitably used as a tire for passenger cars, a tire for commercial vehicles (light trucks), a tire for trucks and buses, a tire for industrial vehicles, etc., and particularly suitable as a tire for passenger cars and tires for commercial vehicles. Used.

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.
Natural rubber latex: Field latex surfactant obtained from Muhibah Lateks, Inc .: Emal-E27C (polyoxyethylene lauryl ether sodium sulfate) manufactured by Kao Corporation
NaOH: NaOH manufactured by Wako Pure Chemical Industries, Ltd.

(Production of saponified natural rubber)
Production Example 1
After adjusting solid content concentration (DRC) of natural rubber latex to 30% (w / v), 25 g of 10% Emal-E27C aqueous solution and 50 g of 40% NaOH aqueous solution are added to 1000 g of natural rubber latex (wet state), A saponification reaction was carried out at room temperature for 48 hours to obtain a saponified natural rubber latex. Water was added to the latex to dilute to DRC 15% (w / v), and then formic acid was added with slow stirring to adjust the pH to 4.0 for aggregation.
The agglomerated rubber is pulverized, dipped in a 1% aqueous sodium carbonate solution at room temperature for 5 hours, pulled up, washed repeatedly with 1000 ml of water, and then dried at 90 ° C. for 4 hours to obtain a solid rubber (saponified natural rubber A). Obtained.

Production Example 2
A solid rubber (saponified natural rubber B) was obtained in the same manner as in Production Example 1 except that the amount of the 40% NaOH aqueous solution was changed to 25 g.

The solid content (saponified natural rubber A, B) and TSR obtained in Production Examples 1 and 2 were measured for nitrogen content, phosphorus content, and gel content 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 sample was weighed, and an 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 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 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

As shown in Table 1, the saponified natural rubbers A and B had a reduced nitrogen content, phosphorus content, and gel content as compared with TSR.
In ³¹ P-NMR measurement, the saponified natural rubbers A and B did not have a peak due to phospholipid at -3 ppm to 1 ppm.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
Saponified natural rubber A: Production Example 1
Saponified natural rubber B: Production Example 2
NR: TSR20
BR: Ubepol BR150B manufactured by Ube Industries, Ltd. (cis content: 97% by mass)
Carbon Black: Show Black N220 (N ₂ SA: 125 m ² / g, DBP: 115 ml / 100 g) manufactured by Cabot Japan
Silica: Zeosil 115Gr (N ₂ SA: 110 m ² / g) manufactured by Rhodia
Silane coupling agent: Si266 (bis (3-triethoxysilylpropyl disulfide)) manufactured by Evonik Degussa
Wax: Ozoace 0355 (paraffinic wax) manufactured by Nippon Seiwa Co., Ltd.
Anti-aging agent A: Vulcanox (N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine, 6PPD) manufactured by Bayer
Anti-aging agent B: Nocrack 224 (2,2,4-trimethyl-1,2-dihydroquinoline polymer) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Stearic acid: Zinc oxide manufactured by NOF Corporation: Zinc oxide No. 3 20% oil treatment manufactured by Mitsui Mining & Smelting Co., Ltd. Insoluble sulfur: Mucron OT-20 manufactured by Shikoku Kasei Kogyo Co., Ltd. (insoluble, oil-containing) Amount: 19-21%)
Vulcanization accelerator: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

(Preparation of unvulcanized rubber composition and vulcanized rubber composition)
According to the formulation shown in Tables 2 to 4, materials other than sulfur and a vulcanization accelerator were kneaded using a 1.7 L Banbury mixer to obtain a kneaded product. Next, using an open roll, sulfur and a vulcanization accelerator were kneaded into the obtained kneaded material to obtain an unvulcanized rubber composition. In Comparative Examples 1 to 3 using TSR, 0.4 part by mass of a peptizer was added to 100 parts by mass of the rubber component of TSR, and kneading was performed in advance using a 1.7 L Banbury mixer. Then, the cooled one was used. On the other hand, in Examples 1 to 6 , no mastication was performed.
Next, the obtained unvulcanized rubber composition was press vulcanized with a 2 mm thick mold at 170 ° C. for 15 minutes to obtain a vulcanized rubber composition (vulcanized rubber sheet).
The obtained unvulcanized rubber composition and vulcanized rubber composition were evaluated as follows. The results are shown in Table 2-4. In the following, the reference comparative example of Table 2 is Comparative Example 1, the reference comparative example of Table 3 is Comparative Example 2, and the reference comparative example of Table 4 is Comparative Example 3.

The following evaluation was performed about the obtained unvulcanized rubber composition and vulcanized rubber composition. The results are shown in Tables 2-4.

(Mooney viscosity)
About the obtained unvulcanized rubber composition, it measured at 130 degreeC according to the measuring method of Mooney viscosity based on JIS-K-6300, and displayed it as an index with the following formula (Mooney viscosity index). The larger the index, the lower the Mooney viscosity (ML _{1 + 4} ), which indicates superior workability.
(Mooney viscosity index) = (ML _{1 + 4} of reference comparative example) / (ML _{1 + 4 of} each formulation) × 100

(Low heat generation)
Loss tangent (tan δ) of each compound (vulcanized rubber sheet) using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.) under conditions of a temperature of 70 ° C., an initial strain of 10%, a dynamic strain of 2%, and a frequency of 10 Hz. ) And indexed by the following formula (low exothermic index). The larger the index, the smaller the tan δ and the better the fuel efficiency.
(Low exothermic index) = (tan δ of reference comparative example) / (tan δ of each formulation) × 100

(Flexible crack growth resistance)
Using a vulcanized rubber composition, a sample (rubber sheet) was prepared based on JIS-K-6260 "Vulcanized rubber and thermoplastic rubber-Dematcher bending crack test method", subjected to a bending crack growth test, and stretched by 70%. Was bent 1,000,000 times to bend the rubber sheet, and the length of the generated crack was measured. The results were expressed as an index according to the following formula (flexible crack growth resistance). The larger the index is, the more the crack growth is suppressed and the resistance to flex crack growth is excellent.
(Bending crack growth resistance index) = (Measured value of reference comparative example) / (Measured value of each formulation) × 100

As shown in Tables 2 to 4, in the examples using the modified natural rubber (saponified natural rubbers A and B) having a phosphorus content of 200 ppm or less in both the carbon black compounding and the silica compounding, processability and low fuel consumption Properties and flex crack growth resistance were improved in a well-balanced manner.

Claims (5)

Saponifying natural rubber latex to prepare saponified natural rubber latex (A), alkali-treating the agglomerated rubber obtained by agglomerating the saponified natural rubber latex (B), contained in rubber Washing until the phosphorus content is 200 ppm or less, modified natural rubber having a phosphorus content of 200 ppm or less obtained through the steps (A) to (C) , carbon black and / or white Obtained by the step (D) of kneading a filler to obtain a rubber composition for chafers in which the content of the modified natural rubber in 100% by mass of the rubber component is 5% by mass or more , and the step (D) A step (E) of producing a chafer by using the chafer rubber composition obtained,
The alkali treatment is a method for manufacturing a pneumatic tire having a chafer using an alkali metal carbonate . 2. The method for producing a pneumatic tire according to claim 1, wherein the modified natural rubber has a nitrogen content of 0.3 mass% or less and a gel content measured as a toluene insoluble content is 20 mass% or less. The method of manufacturing a pneumatic tire according to claim 1 or 2, wherein the white filler is silica. The rubber composition for the chafer has a nitrogen adsorption specific surface area of 100 to 220 m. ² The manufacturing method of the pneumatic tire in any one of Claims 1-3 containing carbon black of / g. The method for producing a pneumatic tire according to any one of claims 1 to 4, wherein, in the chafer rubber composition, the content of the white filler is 5 to 30 parts by mass with respect to 100 parts by mass of the rubber component.