JP5848095B2 - Rubber composition for breaker / ply strip layer and pneumatic tire - Google Patents

Description

The present invention relates to a rubber composition for a breaker / ply strip layer, and a pneumatic tire using the same.

In recent years, from the viewpoint of environmental problems such as resource conservation and tightening regulations on carbon dioxide emission suppression, improvement in tire fuel efficiency and durability has been regarded as important. In addition to the tread rubber that occupies most of the tire, tire components other than the tread rubber (for example, a breaker / ply strip layer disposed between the carcass (ply) and the breaker for the purpose of increasing the adhesion between them) ) Is also demanded to improve fuel efficiency and durability (separation resistance (adhesion with adjacent rubber), etc.).

On the other hand, many tire components other than tread rubber contain a lot of natural rubber. Natural rubber (isoprene-based rubber) hardens due to thermal degradation, and therefore causes a decrease in the mechanical properties of the rubber. Therefore, a rubber composition containing a large amount of natural rubber has a problem that sufficient durability cannot be obtained. As one method for solving the above problem, an attempt has been made to suppress the curing phenomenon due to thermal deterioration by increasing the amount of the anti-aging agent. However, when the anti-aging agent is deposited on the rubber surface, there is a problem that the adhesion with the adjacent rubber is lowered, the separation performance is lowered, and the durability improving effect cannot be sufficiently obtained.

Natural rubber contains about 5 to 10% by mass of non-rubber components such as proteins and lipids. These non-rubber components, especially proteins, are said to cause entanglement of molecular chains and cause gelation. When gelation occurs, there is a drawback that the viscosity of the rubber increases and the processability deteriorates. In general, in order to improve the processability of natural rubber, a method of kneading with a kneading roll machine or a closed mixer and lowering the molecular weight is used. Since it cuts at random, it causes deterioration of fuel efficiency.

Therefore, a method for removing a protein, which is one of the causes of gelation, is known, and it has been proposed to use the obtained deproteinized natural rubber as a rubber for a tire component. For example, Patent Document 1 describes the use of a deproteinized natural rubber in a rubber composition for a breaker / ply strip layer. However, there is still room for improvement in terms of improving workability, fuel efficiency, breaking strength, elongation at break, and durability (separation resistance) in a well-balanced manner.

JP 2008-303293 A

The present invention provides a breaker / ply strip layer rubber that solves the above-described problems and has a good workability and can improve fuel economy, breaking strength, elongation at break, and durability (separation resistance) in a well-balanced manner. It aims at providing a composition and a pneumatic tire using the same.

The present invention relates to a rubber composition for a breaker / ply strip layer comprising a modified natural rubber having a phosphorus content of 200 ppm or less and zinc oxide having an average primary particle size of 200 nm or less.

In the rubber composition for the breaker / ply strip layer, the content of the modified natural rubber in 100% by mass of the rubber component is preferably 5 to 95% by mass.

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

The modified natural rubber is preferably obtained by saponifying natural rubber latex. In particular, the modified natural rubber includes a step (A) of preparing a saponified natural rubber latex by saponifying the natural rubber latex, and subjecting the agglomerated rubber obtained by agglomerating the saponified natural rubber latex to an alkali treatment. It is preferable to be obtained by performing the step (B) and the step (C) of washing until the phosphorus content contained in the rubber is 200 ppm or less.

It is preferable that the content of the zinc oxide is 0.5 to 20 parts by mass with respect to 100 parts by mass of the rubber component.

The present invention also relates to a pneumatic tire having a breaker / ply strip layer produced using the rubber composition.

According to the present invention, since it is a rubber composition for a breaker / ply strip layer containing a modified natural rubber having a phosphorus content of 200 ppm or less and zinc oxide having an average primary particle diameter of 200 nm or less, good processability In addition, fuel efficiency, breaking strength, elongation at break, durability (separation resistance) can be improved in a well-balanced manner, and a pneumatic tire excellent in these performances can be provided.

The rubber composition for a breaker / ply strip layer of the present invention contains a modified natural rubber having a phosphorus content of 200 ppm or less and zinc oxide having an average primary particle size of 200 nm or less.

In the present invention, since zinc oxide having a specific average primary particle size (fine zinc oxide) is used together with modified natural rubber (HPNR) from which phospholipids have been reduced and removed, thermal deterioration such as breaking strength and elongation at break The previous mechanical properties can be enhanced. Therefore, even when natural rubber is gradually cured due to thermal degradation, the mechanical properties before thermal degradation are high, so the time required to maintain the minimum required mechanical properties for the breaker / ply strip layer is extended. It is presumed that the durability such as separation resistance can be improved. In addition, processability and fuel efficiency can be improved satisfactorily.

The modified natural rubber has a phosphorus content of 200 ppm or less. When it exceeds 200 ppm, there is a tendency that sufficient fuel economy, breaking strength, elongation at break, and durability (separation resistance) cannot be obtained. The phosphorus content is preferably 150 ppm or less, more preferably 100 ppm or less, and even more preferably 75 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 tends to increase during storage. Further, sufficient fuel economy, breaking strength, elongation at break, and durability tend not to 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, more preferably 10% by mass or less, and still more preferably 7% by mass or less. If it exceeds 20% by mass, the processability tends to decrease, for example, the Mooney viscosity increases. Further, sufficient fuel economy, breaking strength, elongation at break, and durability tend not to be obtained. The gel content means a value measured as an insoluble content with respect to toluene which is a nonpolar solvent, and may be simply referred to as “gel content” or “gel content” below. The measuring method of the content rate of a gel part is as follows. First, a natural rubber sample is soaked in dehydrated toluene, light-shielded in the dark and left for 1 week, and then the toluene solution is centrifuged at 1.3 × 10 ⁵ rpm for 30 minutes to obtain an insoluble gel content and a toluene soluble content. Isolate. Methanol is added to the insoluble gel and solidified, and then dried, and the gel content is determined from the ratio between the mass of the gel and the original mass of the sample.

The modified natural rubber is preferably substantially free of phospholipids. “Substantially 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.

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, breaking strength, elongation at break and durability can be improved satisfactorily, and these performances can be obtained at a high level. Further, when the agglomeration with acid is performed, the remaining acid is neutralized with an alkali treatment, whereby deterioration of the rubber by the acid can be prevented.

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, and sodium hydroxide and potassium hydroxide are particularly preferable. 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 addition amount of the alkali may be set as appropriate, but is preferably 0.1 to 30 parts by mass, more preferably 10 to 25 parts by mass with respect to 100 parts by mass of the solid content of the natural rubber latex. . The addition amount of the surfactant is preferably 0.01 to 6.0 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 set as appropriate, and is usually about 20 to 70 ° C. and about 1 to 72 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 brought into contact 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 preferable and sodium carbonate and potassium carbonate are preferable 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 in the present invention is obtained by drying after completion of the washing treatment.

The content of the modified natural rubber in 100% by mass of the rubber component contained in the rubber composition of the present invention is preferably 5% by mass or more, more preferably 60% by mass or more, and further preferably 80% by mass or more. If the amount is less than 5% by mass, sufficient fuel economy, breaking strength, elongation at break, and durability tend not to be obtained. The content of the modified natural rubber is preferably 95% by mass or less, more preferably 90% by mass or less. If it exceeds 95% by mass, the cost tends to increase and the workability tends to decrease.

Examples of the rubber component that can be used in the present invention other than the modified natural rubber include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), and styrene isoprene butadiene rubber (SIBR). And diene rubbers such as ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), and butyl rubber (IIR). Among them, NR is preferable because it is excellent in compatibility with the modified natural rubber and good processability can be obtained.

The NR is not particularly limited, and for example, those commonly used in the tire industry such as SIR20, RSS # 3, TSR20, and the like can be used.

The content of NR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more. If it is less than 5% by mass, the workability tends to decrease. The NR content is preferably 95% by mass or less, more preferably 40% by mass or less, and particularly preferably 20% by mass or less. If it exceeds 95% by mass, sufficient fuel economy, breaking strength, elongation at break, and durability tend not to be obtained.

In the present invention, zinc oxide (fine zinc oxide) having a specific average primary particle size is used. By using finely divided zinc oxide, the dispersibility of zinc oxide can be improved, the aggregation of zinc oxide (generation of aggregated nuclei) can be suppressed, and the fuel economy, breaking strength, elongation at break, and durability can be improved satisfactorily. .
The average primary particle diameter of zinc oxide is 200 nm or less, preferably 150 nm or less, more preferably 120 nm or less, still more preferably 90 nm or less, and particularly preferably 75 nm or less. When it exceeds 200 nm, there is a possibility that a sufficient improvement effect cannot be obtained in the dispersibility and rubber physical properties (low fuel consumption, breaking strength, elongation at break, durability) of zinc oxide as compared with normal zinc oxide. The average primary particle diameter of zinc oxide is preferably 20 nm or more, more preferably 50 nm or more. If it is less than 20 nm, the average primary particle size of zinc oxide becomes smaller than the primary particle size of silica or carbon black, and the dispersibility of zinc oxide cannot be sufficiently improved, and rubber properties (low fuel consumption, breaking strength, breaking strength). On the other hand, there is a possibility that the time elongation and durability will deteriorate.
In addition, the average primary particle diameter of zinc oxide represents the average particle diameter (average primary particle diameter) converted from the specific surface area measured by the BET method by nitrogen adsorption.

The content of the zinc oxide is preferably 0.5 parts by mass or more, more preferably 2.0 parts by mass or more, still more preferably 4.0 parts by mass or more, and particularly preferably 6 parts by mass with respect to 100 parts by mass of the rubber component. 0.0 part by mass or more. If it is less than 0.5 parts by mass, sufficient rubber properties (low fuel consumption, breaking strength, elongation at break, durability) tend not to be obtained. The zinc oxide content is preferably 20 parts by mass or less, more preferably 12 parts by mass or less, and still more preferably 10 parts by mass or less. If it exceeds 20 parts by mass, the workability, fuel efficiency, breaking strength, elongation at break, and durability tend to be reduced.

In addition to the above components, the rubber composition of the present invention includes compounding agents conventionally used in the rubber industry, such as inorganic and organic fillers such as carbon black, stearic acid, various anti-aging agents, waxes, oils and the like. A softener, a vulcanizing agent such as sulfur or a sulfur compound, a vulcanization accelerator, and the like can be appropriately blended as necessary.

Examples of carbon black include GPF, FEF, HAF, ISAF, and SAF, but are not particularly limited. By blending carbon black, the reinforcing property can be enhanced, and the breaking strength and breaking elongation can be further improved.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 30 m ² / g or more, and more preferably 120 m ² / g or more. If it is less than 30 m < ² > / g, reinforcement will fall and it exists in the tendency for break strength and elongation at break to fall. Also, _N 2 SA of carbon black is preferably 200 meters ² / g or less, more preferably 160 m ² / g. If it exceeds 200 m ² / g, the fuel efficiency may be significantly deteriorated.
Incidentally, _N 2 SA of carbon black, JIS K 6217-2: determined by 2001.

When carbon black is blended, the content of carbon black is preferably 20 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 20 parts by mass, the reinforcing property is lowered, and the breaking strength and elongation at break tend to be lowered. Moreover, this content becomes like this. Preferably it is 100 mass parts or less, More preferably, it is 70 mass parts or less. If it exceeds 100 parts by mass, the dispersibility of the filler may be deteriorated. Moreover, there exists a possibility that low-fuel-consumption property may deteriorate.

The sulfur is not particularly limited, and sulfur produced by Tsurumi Chemical Co., Ltd., which has been used in the rubber industry, can be used. 3-10 mass parts is preferable with respect to 100 mass parts of rubber components, and, as for the compounding quantity of sulfur, the effect of this invention is fully acquired, and 4-8 mass parts is more preferable.

The vulcanization accelerator is not particularly limited, and N-tert-butyl-2-benzothiazolylsulfenamide, N, N′-dicyclohexyl-2-benzothiazolylsulfenamide, N, N′-diphenylguanidine Etc. can be used. Among these, N, N′-dicyclohexyl-2-benzothiazolylsulfenamide is preferable because the effects of the present invention can be sufficiently obtained.
0.5-5 mass parts is preferable with respect to 100 mass parts of rubber components, and, as for the compounding quantity of a vulcanization accelerator, 0.8-4 mass parts is more preferable.

The antiaging agent is not particularly limited, and amine type antiaging agents such as diphenylamine type and p-phenylenediamine type can be used. Among these, a p-phenylenediamine-based antiaging agent is preferable from the viewpoint that the effects of the present invention can be sufficiently obtained. Examples of p-phenylenediamine-based antioxidants include N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine (6PPD), N-phenyl-N′-isopropyl-p-phenylene. Examples include diamine (IPPD) and N, N′-di-2-naphthyl-p-phenylenediamine.

The content of the anti-aging agent is preferably 0.2 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 0.2 parts by mass, there is a possibility that sufficient deterioration resistance performance of rubber cannot be obtained. Moreover, this content becomes like this. Preferably it is 3.0 mass parts or less, More preferably, it is 2.2 mass parts or less. When the amount exceeds 3.0 parts by mass, the anti-aging agent is precipitated on the rubber surface, whereby the adhesiveness with the adjacent rubber is lowered and the separation resistance tends to be lowered.
In the present invention, the blending amount of the anti-aging agent can be set to the above-mentioned amount, so that precipitation of the anti-aging agent on the rubber surface can be prevented, a decrease in adhesiveness with the adjacent rubber can be suppressed, and sufficient durability can be achieved. (Separation resistance) can be obtained.

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.

The rubber composition of the present invention is used for a breaker / ply strip layer (BP strip layer) disposed outside a carcass (ply) and inside a breaker. Separation resistance can be improved without increasing the thickness. Specifically, it is used for the BP strip layer shown in FIG. 1 of Japanese Patent Application Laid-Open No. 2007-168643, FIG. 1 of Japanese Patent Application Laid-Open No. 2008-303293, and the like.

The pneumatic tire of the present invention can be produced by a usual method using the rubber composition. That is, a rubber composition containing the above components is extruded in accordance with the shape of the breaker / ply strip layer at an unvulcanized stage, and molded together with other tire members on a tire molding machine by a normal method. By doing so, an unvulcanized tire can be formed. A tire is obtained by heating and pressurizing the unvulcanized tire in a vulcanizer.

The pneumatic tire of the present invention can be suitably used as a tire for passenger cars, a tire for heavy-duty vehicles (trucks, buses, etc.), 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 Examples and Comparative 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
TSR: NR (TSR20)
Modified natural rubber A: solid rubber (HPNR) obtained in Production Example 1
Modified natural rubber B: solid rubber (HPNR) obtained in Production Example 2
Untreated natural rubber: Solid rubber carbon black obtained by Production Example 3: Show Black N110 (N ₂ SA: 143 m ² / g, DBP: 113 ml / 100 g) manufactured by Cabot Japan Co., Ltd.
Anti-aging agent: NOCRACK 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Stearic acid: Zinc stearate manufactured by NOF Corporation: 2 types of zinc oxide manufactured by Hakusuitec Co., Ltd. (average primary particle size: 250 nm)
Fine zinc oxide (1): Zincock Super F-1 (average primary particle size: 100 nm) manufactured by Hakusuitec Co., Ltd.
Fine zinc oxide (2): Zincock Super F-2 (average primary particle size: 65 nm) manufactured by Hakusuitec Co., Ltd.
Sulfur: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd .: Noxeller DZ (N, N′-dicyclohexyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Co., Ltd.

(Production of modified natural rubber)
Production Example 1
After adjusting the solid rubber latex solid content concentration (DRC) to 30% (w / v), 10 g of Emal-E27C (manufactured by Kao Corporation, sodium polyoxyethylene lauryl ether sulfate) and 50 g of NaOH with respect to 1000 g of natural rubber latex. And 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 to 4.5 to cause aggregation.
Crush the agglomerated rubber, soak it in a 1% aqueous sodium carbonate solution at room temperature for 5 hours, pull it up, repeat washing with 1000 ml of water, and then dry at 90 ° C. for 4 hours to obtain a solid rubber (modified natural rubber A). Obtained.

Production Example 2
A solid rubber (modified natural rubber B) was obtained in the same manner as in Production Example 1 except that the immersion treatment in a 1% sodium carbonate aqueous solution was not performed.

(Production of untreated natural rubber)
Production Example 3
After adjusting the solid rubber concentration (DRC) of natural rubber latex to 15% (w / v), formic acid was added with slow stirring to adjust the pH to 4.0 to 4.5 and agglomerate. The agglomerated rubber was pulverized and dried at 90 ° C. for 4 hours to obtain a solid rubber (untreated natural rubber).

The solid content (modified natural rubbers A and B, untreated natural rubber) and TSR obtained in Production Examples 1 to 3 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 (mass%) was determined by the following formula.
Gel content (mass%) = [mass mg after drying / mg of initial sample] × 100

As shown in Table 1, the modified natural rubbers A and B had a reduced nitrogen content, phosphorus content, and gel content as compared with TSR and untreated natural rubber.
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.

Examples and Comparative Examples According to the composition 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 manufactured by Kobe Steel Co., Ltd. And kneaded material was obtained. Next, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and kneaded for 5 minutes under the condition of 80 ° C. using an open roll to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press vulcanized with a 0.5 mm thick mold at 150 ° C. for 35 minutes to obtain a vulcanized rubber composition.

The resulting unvulcanized rubber composition is molded into the shape of a tire breaker / ply strip layer and bonded to other tire members to form an unvulcanized tire, which is press-cured at 150 ° C. for 35 minutes. The test tire (size: 11R22.5) was manufactured.

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

(Mooney viscosity)
The obtained unvulcanized rubber composition was heated at 130 ° C. by preheating for 1 minute using a Mooney viscosity tester manufactured by Shimadzu Corporation according to JIS K6300 “Testing method for unvulcanized rubber”. Under this temperature condition, the small rotor was rotated, and the Mooney viscosity of the unvulcanized rubber composition after 4 minutes was measured. Then, the Mooney viscosity index of Comparative Example 1 was set to 100, and the Mooney viscosity of each formulation was displayed as an index according to the following calculation formula. In addition, it shows that it is easy to process and the workability is excellent, so that the value of Mooney viscosity index is large.
(Mooney viscosity index) = (Mooney viscosity of Comparative Example 1) / (Mooney viscosity of each formulation) × 100

(Tensile test)
A No. 3 dumbbell-shaped test piece was prepared from the obtained vulcanized rubber composition, and a tensile test was performed according to JIS K6251 “Vulcanized rubber and thermoplastic rubber-Determination of tensile properties”. The breaking strength (TB) and the elongation at break (EB) were measured. And TB index and EB index of the comparative example 1 were set to 100, and TB and EB of each compounding were indicated by an index by the following calculation formula. Note that the larger the TB index and the EB index, the better the rubber strength.
(TB index) = (TB of each formulation) / (TB of Comparative Example 1) × 100
(EB index) = (EB of each formulation) / (EB of Comparative Example 1) × 100

(Separation resistance reproduction drum test)
Abnormalities such as swelling of the tread occur when the test tire is run on a drum at a speed of 80 km / h under a load overload condition of 140% of the maximum load (maximum air pressure condition) of the JIS standard. The distance traveled until this time was measured, the separation performance index of Comparative Example 1 was taken as 100, and the distance traveled for each formulation was indicated by the following formula. In addition, it shows that it is excellent in the separation-proof performance (durability), so that a separation-proof performance index is large.
(Separation resistance index) = (travel distance of each formulation) / (travel distance of Comparative Example 1) × 100

(Viscoelasticity test)
Using the viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), the vulcanized rubber composition obtained was measured for tan δ of each formulation under conditions of a temperature of 70 ° C., an initial strain of 10%, and a dynamic strain of 2%. Then, tan δ of Comparative Example 1 was set to 100, and the index was displayed by the following calculation formula. The larger the index, the better the fuel efficiency.
(Low exothermic index) = (tan δ of Comparative Example 1) / (tan δ of each formulation) × 100

As shown in Table 2, in the examples using the modified natural rubber and zinc oxide having a specific average primary particle diameter (particulate zinc oxide (1), (2)), workability, fuel efficiency, fracture Strength, elongation at break, and durability (separation resistance) were improved in a well-balanced manner. In particular, when the modified natural rubber A obtained by dipping in a 1% sodium carbonate aqueous solution was used, an excellent improvement effect was obtained.

Claims (10)

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 with an alkali metal carbonate ( B), the step (C) of washing until the phosphorus content contained in the rubber is 200 ppm or less, the modified natural rubber obtained through the steps (A) to (C), and the average primary particle size A method for producing a rubber composition for a breaker / ply strip layer comprising a step (D) of kneading zinc oxide having a thickness of 200 nm or less. The method for producing a rubber composition for a breaker / ply strip layer according to claim 1, wherein the content of the modified natural rubber in 100% by mass of the rubber component is 5 to 95% by mass. The breaker / ply strip layer according to claim 1 or 2, 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. manufacturing method of use rubber composition. The modified natural rubber according to any one of claims 1 to 3, wherein a peak due to phospholipid does not exist at -3 ppm to 1 ppm and substantially no phospholipid exists in ³¹ P NMR measurement of a chloroform extract. A method for producing a rubber composition for a breaker / ply strip layer. The method for producing a rubber composition for a breaker / ply strip layer according to any one of claims 1 to 4 , wherein a content of the zinc oxide is 0.5 to 20 parts by mass with respect to 100 parts by mass of the rubber component. . 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 with an alkali metal carbonate ( B), the step (C) of washing until the phosphorus content contained in the rubber is 200 ppm or less, the modified natural rubber obtained through the steps (A) to (C), and the average primary particle size Manufacturing method of a pneumatic tire including the process (D) which knead | mixes zinc oxide with 200 nm or less. The method for producing a pneumatic tire according to claim 6, wherein the content of the modified natural rubber in 100% by mass of the rubber component is 5 to 95% by mass. The method for producing a pneumatic tire according to claim 6 or 7, 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 modified natural rubber is a chloroform extract. ³¹ The method for producing a pneumatic tire according to any one of claims 6 to 8, wherein a peak due to phospholipid does not exist at -3 ppm to 1 ppm and substantially no phospholipid exists in P NMR measurement. The method for producing a pneumatic tire according to any one of claims 6 to 9, wherein a content of the zinc oxide is 0.5 to 20 parts by mass with respect to 100 parts by mass of the rubber component.