JP2011231251A - Rubber composition for strip layer between breaker and ply, and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for a strip layer between a breaker and a ply, which can improve fuel economy, rupture strength, elongation at rupture and durability (anti-separation performance) in good balance, while keeping good processability; and a pneumatic tire using the composition in the strip layer between the breaker and the ply.SOLUTION: This rubber composition for the strip layer between the breaker and the ply includes: a rubber component containing modified natural rubber with ≤200 ppm phosphorus content, and zinc oxide having ≤200 nm average primary particle diameter.

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 that the use of deproteinized natural rubber for the rubber composition for the breaker / ply strip layer improves the workability, breaking strength, and elongation at break. 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 solves the above-described problems and has a breaker / ply strip layer rubber capable of improving the fuel economy, breaking strength, elongation at break, and durability (separation resistance) in a well-balanced manner while having good processability. It is an object of the present invention to provide a composition and a pneumatic tire using the composition for a breaker / ply strip layer of a tire.

The present invention relates to a rubber composition for a breaker / ply strip layer comprising a rubber component containing 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.

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

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

The modified natural rubber preferably has a nitrogen content of 0.3% by mass or less.

The content of the modified natural rubber in 100% by mass of the rubber component is preferably 5 to 95% by mass.

The content of the zinc oxide is preferably 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 the rubber composition for a breaker / ply strip layer includes a rubber component containing the modified natural rubber and zinc oxide having a specific average primary particle size, the rubber composition has good processability. However, it can improve fuel economy, breaking strength, elongation at break and durability (separation resistance) in a well-balanced manner, and it has excellent fuel economy, breaking strength, elongation at break, and durability (separation resistance). Tires can be provided.

The rubber composition for a breaker / ply strip layer of the present invention includes a rubber component containing the modified natural rubber and zinc oxide having a specific average primary particle size.

Compared to the case of using natural rubber (NR) in the past, when deproteinized natural rubber (DPNR) (natural rubber from which protein contained in NR is reduced and removed) is used, processability, breaking strength, elongation at break Is known to improve. In the present invention, since the rubber component includes modified natural rubber (HPNR) in which not only the protein contained in NR but also the gel content and phospholipid are reduced and removed, the rubber component is low in comparison with the case where DPNR is used. The fuel economy, breaking strength, elongation at break, and durability (separation resistance) can be significantly improved. That is, by using HPNR, mechanical properties before thermal deterioration such as breaking strength and elongation at break can be further enhanced as compared with the case of using DPNR. 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.

Further, in the present invention, zinc oxide having a specific average primary particle diameter (fine particle zinc oxide) is used. Fine particle zinc oxide has a large specific surface area and further improves the dispersibility of zinc oxide, so that it effectively functions as a vulcanization accelerating aid and vulcanizes rubber more uniformly. Therefore, fuel economy, breaking strength, elongation at break, and durability (separation resistance) can be improved in a balanced manner. Furthermore, when the mechanical properties of rubber deteriorate due to thermal deterioration, the aggregated nuclei of zinc oxide can become fracture nuclei and cause damage, but the use of fine zinc oxide improves the dispersibility of zinc oxide and improves oxidation. Aggregation of zinc can be suppressed. Therefore, it is presumed that durability such as separation resistance can be further improved by using fine particle zinc oxide.

The modified natural rubber (HPNR) 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, 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 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 (separation resistance) 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 no phospholipid is present” 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, 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 (separation resistance) tend not to be obtained. Nitrogen is derived from proteins. The nitrogen content can be measured by a conventional method such as Kjeldahl method.

In the rubber composition of the present invention, the content of the modified natural rubber in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 60% by mass or more, particularly Preferably it is 80 mass% or more. If it is less than 5% by mass, sufficient fuel economy, breaking strength, elongation at break and durability (separation resistance) 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 method for producing the modified natural rubber include a method of producing natural rubber latex by saponification with alkali, washing the saponified and agglomerated rubber, and then drying. The saponification treatment is performed by adding an alkali and, if necessary, a surfactant to natural rubber latex and allowing to stand at a predetermined temperature for a predetermined time. In addition, you may perform stirring etc. as needed. 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 present invention, alkali can be added to natural rubber latex for saponification, but by adding it to natural rubber latex, there is an effect that saponification can be efficiently performed.

Natural rubber latex is collected as sap of heavy trees and contains rubber, water, proteins, lipids, inorganic salts, etc., and the gel content in rubber is thought to be based on the complex presence of various impurities. . In the present invention, raw latex produced by tapping a heavy tree or purified latex concentrated by centrifugation can be used. Furthermore, high ammonia latex to which ammonia is added by a conventional method may be used in order to prevent the progress of decay due to bacteria present in the raw rubber latex and to avoid coagulation of the latex.

Examples of the alkali used for the saponification treatment include sodium hydroxide, potassium hydroxide, calcium hydroxide, and an amine compound. From the viewpoint of the effect of the saponification treatment and the influence on the stability of the natural rubber latex, it is particularly hydroxylated. Sodium or potassium hydroxide is preferably used.

The amount of alkali added is not particularly limited, but the lower limit is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and the upper limit is 12 parts by mass or less with respect to 100 parts by mass of the solid content of natural rubber latex. Is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and particularly preferably 5 parts by mass or less. If the amount of alkali added is less than 0.1 parts by mass, saponification may take time. Conversely, if the amount of alkali added exceeds 12 parts by mass, the natural rubber latex may be destabilized.

As the surfactant, an anionic surfactant, a nonionic surfactant, and an amphoteric surfactant can be used. Examples of the anionic surfactant include carboxylic acid-based, sulfonic acid-based, sulfate ester-based and phosphate ester-based anionic surfactants. Examples of nonionic surfactants include nonionic surfactants such as polyoxyalkylene ethers, polyoxyalkylene esters, polyhydric alcohol fatty acid esters, sugar fatty acid esters, and alkyl polyglycosides. Examples of the amphoteric surfactant include amphoteric surfactants such as amino acid type, betaine type, and amine oxide type. Among these, an anionic surfactant is preferable, and a sulfonic acid anionic surfactant is more preferable.

The addition amount of the surfactant is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 1.1 parts by mass or more with respect to 100 parts by mass of the solid content of the natural rubber latex. The upper limit is preferably 6.0 parts by mass or less, more preferably 5.0 parts by mass or less, and further preferably 3.5 parts by mass or less. If the addition amount of the surfactant is less than 0.01 parts by mass, the natural rubber latex may become unstable during the saponification treatment. On the other hand, if the amount of the surfactant added exceeds 6.0 parts by mass, the natural rubber latex may be overstabilized and coagulation may be difficult. Moreover, when it is 1.1 mass parts or more, the phosphorus content, the nitrogen content, and the gel content in the natural rubber can be further reduced.

The temperature of the saponification treatment can be appropriately set within a range where the saponification reaction with alkali can proceed at a sufficient reaction rate and within a range where the natural rubber latex does not undergo alteration such as coagulation, but is usually 20 to 70 ° C. Preferably, 30-70 degreeC is more preferable. Further, the treatment time is 3 to 48 hours in consideration of both sufficient treatment and productivity improvement, depending on the treatment temperature when the treatment is performed with natural rubber latex standing. Is preferable, and 3 to 24 hours is more preferable.

After completion of the saponification reaction, the agglomerated rubber is crushed and washed. Examples of the aggregation method include a method of adjusting pH by adding an acid such as formic acid. Examples of the washing treatment include a method of diluting the rubber with water and washing it, and then performing a centrifugal separation treatment to take out the rubber. 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. After completion of the washing treatment, a saponified natural rubber latex is obtained. The modified natural rubber according to the present invention is obtained by drying the saponified natural rubber latex.

In the above production method, the saponification, washing and drying steps are preferably completed within 15 days after collecting the natural rubber latex. More preferably, it is within 10 days, and more preferably within 5 days. This is because the gel content increases if the sample is left for more than 15 days without solidification after collection.

In addition to HPNR, examples of rubber components used in the present invention include natural rubber (NR), deproteinized natural rubber (DPNR) (natural rubber from which protein contained in NR is removed), isoprene rubber (IR), butadiene Diene rubbers such as rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), butyl rubber (IIR), etc. Is mentioned. Among these, NR is preferable because it has excellent compatibility with HPNR.

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. Here, NR means a nitrogen content of about 2 to 20% by mass. Processability can be improved by blending NR with the modified natural rubber (HPNR).

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 90% by mass or less, still 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 (separation resistance) tend not to be obtained.

In the present invention, zinc oxide (fine zinc oxide) having a specific average primary particle size is used.
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. If it exceeds 200 nm, a sufficient improvement effect is obtained in dispersibility of zinc oxide and rubber properties (low fuel consumption, breaking strength, elongation at break, durability (separation resistance)) compared to normal zinc oxide. There is a risk of not. 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 is 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 (separation resistance) may 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 0.6 parts by mass or more, still more preferably 2.0 parts by mass or more, particularly preferably 4 parts per 100 parts by mass of the rubber component. 0.0 parts by mass or more, and most preferably 6.0 parts 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 (separation resistance)) tend not to be obtained. The zinc oxide content is preferably 20 parts by mass or less, more preferably 19 parts by mass or less, still more preferably 12 parts by mass or less, and particularly 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 (separation resistance) 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.
In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required by A method of JISK6217.

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 80 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-cyclohexyl-2-benzothiazolylsulfenamide, N, N′-diphenylguanidine, etc. are used. it can. 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 antioxidant is preferably 0.2 parts by mass or more, and more preferably 0.3 parts 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 2.5 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 is produced by a general method. That is, it can be produced by a method of kneading the above components with a Banbury mixer, a kneader, an open roll or the like and then vulcanizing.

The rubber composition of the present invention can be suitably used for each member of a tire such as a breaker / ply strip layer.

The rubber composition for a breaker / ply strip layer of the present invention is used for a breaker / ply strip layer (BP strip layer) disposed outside a carcass (ply) and inside a breaker. Therefore, the separation resistance can be improved without increasing the thickness of the breaker or ply gauge. 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 is 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 is formed. The unvulcanized tire is heated and pressurized in a vulcanizer to obtain a tire.

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.
NR: TSR
Modified natural rubber: Solid rubber (HPNR) obtained by Production Example 1 below
Carbon Black: Show Black N110 (N ₂ SA: 143 m ² / g, DBP: 113 ml / 100 g) manufactured by Cabot Japan
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 Industry Co., Ltd .: Noxeller DZ (N, N'-dicyclohexyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

(Production of saponified natural rubber with alkali)
Production Example 1
After adjusting the solid content concentration (DRC) of natural rubber latex to 30% (w / v), 10 g of Emal-E (manufactured by Kao Corporation, sodium polyoxyethylene lauryl ether sulfate) and 20 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. 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 (modified natural rubber).

With respect to the solid rubber and TSR obtained in Production Example 1, the nitrogen content, phosphorus content, and gel content were measured 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 modified natural rubber or TSR obtained in Production Example 1 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 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 modified natural rubber had a reduced nitrogen content, phosphorus content, and gel content as compared with TSR. Further, in the ³¹ P NMR measurement of an extract obtained by extracting from the modified natural rubber obtained in Production Example 1 it did not detect the peak due to phospholipids -3Ppm～1ppm.

Examples 1-6 and Comparative Examples 1-4
According to the blending content shown in Table 2, materials other than sulfur and vulcanization accelerator were kneaded for 5 minutes at 150 ° C. using a 1.7 L Banbury mixer manufactured by Kobe Steel Co., Ltd. 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. Then, the TB index and EB index of Comparative Example 1 were set to 100, and TB and EB of each formulation were displayed as 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) = (TB of each formulation) / (TB 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 fuel consumption index) = (tan δ of Comparative Example 1) / (tan δ of each formulation) × 100

According to Table 2, in Examples including a rubber component containing the modified natural rubber and zinc oxide having a specific average primary particle size, while having good processability, fuel efficiency, breaking strength, at break Elongation and durability (separation resistance) were improved in a well-balanced manner.

Claims (7)

A rubber composition for a breaker / ply strip layer comprising a rubber component containing 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. 2. The rubber composition for a breaker / ply strip layer according to claim 1, wherein the modified natural rubber has a gel content measured as a toluene insoluble content of 20% by mass or less. 3. The breaker / ply gap according to claim 1, wherein the modified natural rubber has no phospholipid peak at -3 ppm to 1 ppm and substantially no phospholipid in ³¹ P NMR measurement of a chloroform extract. Rubber composition for strip layer. The rubber composition for a breaker / ply strip layer according to any one of claims 1 to 3, wherein the modified natural rubber has a nitrogen content of 0.3 mass% or less. The rubber composition for a breaker / ply strip layer according to any one of claims 1 to 4, wherein the content of the modified natural rubber in 100% by mass of the rubber component is 5 to 95% by mass. The rubber composition for a breaker / ply strip layer according to any one of claims 1 to 5, 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 pneumatic tire having a breaker / ply strip layer produced using the rubber composition according to claim 1.