JP4603615B2 - Rubber composition and tire for covering tread or carcass cord - Google Patents

Description

The present invention relates to a rubber composition for covering a tread or a carcass cord, and a pneumatic tire using the same.

Conventionally, the fuel consumption of a vehicle has been reduced by reducing the rolling resistance of a tire to suppress heat generation. In recent years, there has been an increasing demand for reducing fuel consumption of vehicles by using tires, and there is a particularly large demand for reducing fuel consumption by improving treads that have a high occupation ratio among tire members. Known methods for satisfying the low heat build-up of the rubber composition include a method using a low reinforcing filler, a method for reducing the content of the reinforcing filler, and the like. In addition, by using silica as a filler, rolling resistance is reduced to reduce fuel consumption.

However, the reduction in fuel consumption by such fillers has the problem that the tire softens and wear resistance decreases because the hardness of the rubber composition decreases, and high fuel efficiency (low rolling resistance) It was difficult to achieve both high wear resistance.

On the other hand, since a large load is applied to an automobile tire, a carcass cord such as a steel cord is generally used as a reinforcing material. In particular, if the tires generate heat during running and the rubber and carcass cords are peeled off, this may cause a fatal tire failure. For this reason, the rubber composition covering the carcass cord is required to have high rubber strength and strong adhesion to the carcass cord.

Conventionally, as a rubber composition for covering a carcass cord, natural rubber (NR) and / or isoprene rubber (IR) and emulsion-polymerized styrene butadiene rubber (E-SBR) are used as rubber components, and carbon black is used as a reinforcing filler. Because it is used, there is a problem that it is inferior in fuel efficiency. In general, in order to improve fuel efficiency, it is known to use silica instead of carbon black as a reinforcing filler. In this case, the carcass necessary as a rubber composition for covering a carcass cord is used. Adhesiveness with a cord deteriorated, and it was difficult to achieve both adhesiveness and high fuel efficiency (low rolling resistance).
Therefore, Patent Document 1 discloses a method for achieving both low fuel consumption performance and adhesion performance by using a solution-polymerized styrene butadiene rubber having a modifying group that interacts with silica. Of the components, only the styrene butadiene rubber component has been studied, and the natural rubber component has not been studied.

Natural rubber has a higher Mooney viscosity than other synthetic rubbers and has poor processability. Therefore, it is usually used after mastication by adding a chelating agent to lower the Mooney viscosity. Therefore, when natural rubber is used, such a process is required, so that productivity is lowered. Further, since the molecular chain of natural rubber is cut by mastication, there is a problem that the characteristics (for example, high wear performance, low fuel consumption performance, and rubber strength) of the high molecular weight polymer inherent to natural rubber are lost. It was.

Natural rubber latex is collected as sap of heavy trees and contains water, proteins, lipids, inorganic salts and the like in addition to rubber components. There is a report that processability is improved by removing proteins contained in natural rubber. As a method for reducing proteins contained in natural rubber, for example, Patent Documents 2 and 3 describe a method of adding a proteolytic enzyme and a surfactant to natural rubber latex and ripening, while Patent Document 4 uses a solvent. A method of immersing a swollen solid natural rubber in alkali hydroxide is disclosed in Patent Document 5, in which a phosphate is added to natural rubber latex to remove magnesium phosphate. A method of adding an agent and performing a cleaning treatment is disclosed.

However, the methods disclosed in Patent Documents 2 to 6 can remove proteins and the like to some extent, but are not at a sufficient level. In addition, there is a problem that phospholipids and the like can hardly be removed. Further, it has not been studied to apply the natural rubber obtained by these methods to a tire tread or a rubber for covering a carcass cord.

JP 2007-145898 A Japanese Patent Laid-Open No. 08-12814 JP 2005-82622 A Japanese Patent Laid-Open No. 11-12306 JP 2004-250546 A Japanese Patent No. 3294901

The present invention solves the above-mentioned problems, and has a good processability that does not require a mastication process, and can achieve both high fuel efficiency (low rolling resistance) and high wear resistance. It is an object to provide a rubber composition for use. It is another object of the present invention to provide a pneumatic tire having a tread produced using the rubber composition.
In addition, while having excellent processability that does not require a mastication process, it improves the adhesion performance with the carcass cord and can achieve both high fuel efficiency (low rolling resistance) and high rubber strength. An object of the present invention is to provide a rubber composition for covering a cord. Moreover, it aims at providing the pneumatic tire which has a carcass produced using this rubber composition.

The present invention relates to a rubber composition for a tire tread in which carbon black and / or a white filler is blended with a rubber component containing 5% by mass or more of a natural rubber having a phosphorus content of 200 ppm or less.

The nitrogen content of the natural rubber is preferably 0.3% by mass or less.

The nitrogen content of the natural rubber is preferably 0.15% by mass or less.

It is preferable that the gel content measured as a toluene insoluble content of the natural rubber is 20% by mass or less.

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

The white filler is preferably silica.

The present invention also relates to a method for producing the rubber composition for a tire tread that does not include a step of masticating natural rubber.

The present invention also relates to a pneumatic tire having a tread produced using the rubber composition for a tire tread.

The present invention also relates to a rubber composition for covering a carcass cord, in which carbon black and / or a white filler is blended with a rubber component containing 5% by mass or more of a natural rubber having a phosphorus content of 200 ppm or less.

The nitrogen content of the natural rubber is preferably 0.3% by mass or less.

The nitrogen content of the natural rubber is preferably 0.15% by mass or less.

It is preferable that the gel content measured as a toluene insoluble content of the natural rubber is 20% by mass or less.

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

The white filler is preferably silica.

The content of the natural rubber in 100% by mass of the rubber component is preferably 60 to 100% by mass.

It is preferable to contain 4 to 15 parts by mass of zinc oxide with respect to 100 parts by mass of the rubber component.

The present invention also relates to a method for producing the above-described rubber composition for covering a carcass cord that does not include a step of masticating natural rubber.

The present invention also relates to a pneumatic tire having a carcass manufactured using the rubber composition for covering a carcass cord.

According to the present invention, natural rubber having a phosphorus content of 200 ppm or less is used, so that it has excellent processability and does not require a mastication step.
Since the rubber composition of the present invention contains natural rubber having a phosphorus content of 200 ppm or less and carbon black and / or a white filler, by using the rubber composition as a tire tread, high fuel efficiency can be achieved. Properties (low rolling resistance) and high wear resistance can be achieved at the same time. Further, by using the rubber composition as a rubber for covering a carcass cord, it is possible to improve the adhesion performance with the carcass cord and achieve both high fuel efficiency (low rolling resistance) and high rubber strength.

The rubber composition for tire tread and the rubber composition for covering a carcass cord of the present invention contains carbon black and / or a white filler in a rubber component containing 5% by mass or more of natural rubber having a phosphorus content of 200 ppm or less. ing.

The phosphorus content in the natural rubber of the present invention (hereinafter also referred to as saponified natural rubber) is 200 ppm or less, but preferably 150 ppm or less. If it exceeds 200 ppm, the Mooney viscosity will increase during storage, resulting in poor processability, and excellent fuel efficiency tends to be not obtained. Here, the phosphorus content can be measured by a conventional method such as ICP emission analysis. Phosphorus is derived from phospholipids.

The natural rubber of the present invention 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 natural rubber of the present invention, the nitrogen content is preferably 0.3% by mass or less, and more preferably 0.15% by mass or less. If the nitrogen content exceeds 0.3% by mass, the Mooney viscosity may increase during storage and the processability may deteriorate, and excellent fuel efficiency may not be obtained. The nitrogen content can be measured by a conventional method such as Kjeldahl method. Nitrogen is derived from protein.

The gel content in the natural rubber of the present invention is preferably 20% by mass or less, and more preferably 10% by mass or less. When it exceeds 20% by mass, the Mooney viscosity increases and the processability tends to deteriorate. The gel content means a value measured as an insoluble content with respect to toluene which is a nonpolar solvent, and may be simply referred to as “gel content” or “gel content” below. The measuring method of the content rate of a gel part is as follows. First, a natural rubber sample is immersed in dehydrated toluene, light-shielded in a cool dark place 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. To separate. 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 natural rubber of the present invention can be produced, for example, by saponifying natural rubber latex 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 this method, since the phosphorus compound separated by saponification is washed away, the phosphorus content of 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, saponification is performed by adding alkali to natural rubber latex, but there is an effect that saponification treatment can be efficiently performed by adding it to natural rubber latex.

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 is 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 10 parts by mass or less with respect to 100 parts by mass of the solid content of the natural rubber latex. Is preferable, and 7 mass parts or less are more preferable. 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 10 parts by mass, the natural rubber latex may become unstable.

As the surfactant, at least one of an anionic surfactant, a nonionic surfactant and an amphoteric surfactant can be used. Among these, examples of the anionic surfactant include carboxylic acid-based, sulfonic acid-based, sulfate ester-based and phosphate ester-based anionic surfactants. Examples of the nonionic surfactant include nonionic surfactants such as polyoxyalkylene ester, polyoxyalkylene ester, polyhydric alcohol fatty acid ester, glycolipid ester, and alkylpolyglycoside. Examples of the amphoteric surfactant include amphoteric surfactants such as amino acid type, betaine type, and amine oxide type.

The addition amount of the surfactant is preferably 0.01 to 5 parts by mass with respect to 100 parts by mass of the solid content of the natural rubber latex, the lower limit is 0.1 parts by mass, and the upper limit is 3.5 parts by mass. More preferred. If the addition amount 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 added exceeds 5 parts by mass, the natural rubber latex may become too stable and coagulation may become difficult.

The temperature of the saponification treatment can be appropriately set within the range where the saponification reaction with alkali can proceed at a sufficient reaction rate and the natural rubber latex does not cause alteration such as coagulation, but is usually 20 to 70 ° C. Preferably there is. 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 preferred.

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. Moreover, as a washing | cleaning method, after diluting a rubber part with water and washing | cleaning, the method of performing a centrifugation process and taking out a rubber part is mentioned, for example. 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 10,000 rpm for 1 to 60 minutes. After washing, the rubber is dried.

In the rubber composition for a tire tread of the present invention, the content of the natural rubber in 100% by mass of the rubber component is 5% by mass or more, preferably 10% by mass or more, more preferably 20% by mass or more. If it is less than 5% by mass, excellent fuel efficiency may not be obtained. The content of the natural rubber is preferably 50% by mass or less, more preferably 40% by mass or less. If it exceeds 50% by mass, sufficient grip performance may not be obtained.

In the rubber composition for covering a carcass cord of the present invention, the content of the natural rubber in 100% by mass of the rubber component is 5% by mass or more, preferably 60% by mass or more, more preferably 65% by mass or more, Preferably it is 70 mass% or more. If it is less than 5% by mass, excellent fuel efficiency may not be obtained. The content of the natural rubber may be 100% by mass, but is preferably 80% by mass or less, more preferably 70% by mass or less.

Examples of the rubber component used in the present invention include diene rubbers generally used in tire rubber compositions in addition to the natural rubber. Specific examples of the diene rubber include natural rubber (NR) other than the above natural rubber (saponified natural rubber), styrene butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), ethylene propylene diene rubber. (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), butyl rubber (IIR), styrene isoprene butadiene rubber (SIBR), epoxidized natural rubber, and the like, but are not limited thereto. These may be used alone or in combination of two or more. Especially, in the case of the rubber composition for tire treads, SBR is preferable from the viewpoints of ensuring sufficient tire strength and exhibiting excellent wear resistance. In the case of a rubber composition for covering a carcass cord, SBR is preferable from the viewpoint of ensuring sufficient adhesion to the carcass cord and exhibiting excellent heat resistance. Examples of SBR include those obtained by a solution polymerization method and those obtained by an emulsion polymerization method, but are not particularly limited.

In the rubber composition for a tire tread and the rubber composition for covering a carcass cord of the present invention, when SBR is used, the amount of styrene in SBR is preferably 5% by mass or more, more preferably 10% by mass or more. If it is less than 5% by mass, sufficient grip performance and rubber strength may not be obtained. The styrene content of SBR is preferably 50% by mass or less, more preferably 45% by mass or less. When it exceeds 50 mass%, there is a possibility that an excellent low fuel consumption performance cannot be obtained.
In the present specification, the styrene content of SBR is calculated by H ¹ -NMR measurement.

In the rubber composition for a tire tread and the rubber composition for covering a carcass cord of the present invention, when SBR is used, the vinyl content of SBR is preferably 10% by mass or more, more preferably 15% by mass or more. If it is less than 10% by mass, sufficient grip performance and rubber strength may not be obtained. The vinyl content of SBR is preferably 65% by mass or less, more preferably 60% by mass or less. When it exceeds 65 mass%, there is a possibility that excellent fuel efficiency performance cannot be obtained.
In the present specification, the vinyl content of SBR indicates the vinyl content of the butadiene part, and is calculated by H ¹ -NMR measurement.

In the rubber composition for a tire tread of the present invention, when SBR is used, the content of SBR in 100% by mass of the rubber component is preferably 40% by mass or more, more preferably 50% by mass or more. If it is less than 40% by mass, sufficient grip performance may not be obtained. The content of the SBR is preferably 90% by mass or less, more preferably 80% by mass or less. When it exceeds 90 mass%, there is a possibility that the excellent fuel efficiency performance by the natural rubber cannot be obtained.

In the rubber composition for covering a carcass cord of the present invention, when SBR is used, the content of SBR in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 20% by mass or more. If it is less than 10% by mass, sufficient adhesion and rubber strength may not be obtained. The content of SBR is preferably 50% by mass or less, more preferably 40% by mass or less. If it exceeds 50% by mass, excellent low heat generation performance and sufficient adhesion and rubber strength may not be obtained.

As carbon black, for example, FEF, GPF, HAF, ISAF, SAF, S-SAF and the like can be used. By using the natural rubber and carbon black in the tread, the strength of the rubber can be increased and excellent wear resistance can be obtained. Moreover, high adhesiveness and rubber strength can be obtained by using it for carcass cord-coated rubber.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black used for the tire tread rubber composition and the carcass cord covering rubber composition is preferably 20 m ² / g or more, and more preferably 30 m ² / g or more. If it is less than 20 m < ² > / g, there exists a possibility that sufficient abrasion resistance performance, adhesiveness, and rubber | gum strength may not be obtained. Also, _N 2 SA of carbon black is preferably 150 meters ² / g or less, more preferably 120 m ² / g. When it exceeds 150 m ² / g, workability tends to deteriorate or low heat build-up tends to decrease.
In the present specification, the nitrogen adsorption specific surface area of carbon black is determined by the A method of JIS K6217.

The dibutyl phthalate oil absorption (DBP oil absorption) of carbon black used in the tire tread rubber composition and the carcass cord covering rubber composition is preferably 60 ml / 100 g or more, more preferably 80 ml / 100 g or more. When the DBP oil absorption is less than 60 ml / 100 g, there is a tendency that good steering stability cannot be obtained. The DBP oil absorption is preferably 140 ml / 100 g or less, more preferably 120 ml / 100 g or less. If the DBP oil absorption exceeds 140 ml / 100 g, the workability may be deteriorated.
In addition, in this specification, DBP of carbon black is calculated | required by the measuring method of JISK6217-4.

In the rubber composition for tire tread and the rubber composition for covering a carcass cord of the present invention, the content of carbon black is preferably 5 parts by mass or more, more preferably 10 parts by mass or more with respect to 100 parts by mass of the rubber component. is there. If the amount is less than 5 parts by mass, sufficient wear resistance, adhesiveness, and rubber strength may not be obtained. The carbon black content is preferably 80 parts by mass or less, more preferably 60 parts by mass or less, with respect to 100 parts by mass of the rubber component. When it exceeds 80 parts by mass, workability and mechanical strength tend to deteriorate.

As white filler, those commonly used in the rubber industry, for example, mica such as silica, calcium carbonate, sericite, aluminum hydroxide, magnesium oxide, magnesium hydroxide, clay, talc, alumina, titanium oxide Etc. can be used. Among them, silica is preferable because it can achieve both wear resistance and low fuel consumption when used in a tread, and can provide excellent adhesion, low fuel consumption, and rubber strength when used in a carcass cord-coated rubber. . The silica is not particularly limited, and for example, silica (anhydrous silicic acid) obtained by a dry method and / or silica (hydrous silicic acid) obtained by a wet method can be used. Especially, it is preferable to use the silica (hydrous silicic acid) obtained by a wet method from the reason that there are many silanol groups.

The nitrogen adsorption specific surface area by the BET method of silica is preferably 30 m ² / g or more, and more preferably 100 m ² / g or more. If it is less than 30 m ² / g, the fracture strength after vulcanization tends to decrease. Further, BET of silica is 500m or less preferably ² / g, more preferably at most 300m ² / g. If it exceeds 500 m ² / g, the processability tends to deteriorate. In addition, the nitrogen adsorption specific surface area by the BET method of a silica can be measured by the method based on ASTM-D-4820-93.

The content of silica is preferably 5 parts by mass or more, more preferably 10 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 5 parts by mass, sufficient fuel efficiency may not be obtained. The content of silica is preferably 100 parts by mass or less, more preferably 80 parts by mass or less. If it exceeds 100 parts by mass, the workability tends to decrease.

In the present invention, it is preferable to use a silane coupling agent in combination with silica. The silane coupling agent is not particularly limited, and those conventionally used in combination with silica in the tire industry can be used. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) Tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (3-trimethoxysilylpropyl) trisulfide Bis (3-triethoxysilylpropyl) disulfide, bis (3-trimethoxysilylpropyl) disulfide, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N, N Dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 2-trimethoxysilylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazolyl Sulfide systems such as tetrasulfide, 3-triethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyl Mercapto series such as triethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, vinyltriethoxy Lan, vinyl type such as vinyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3- (2-aminoethyl) aminopropyltriethoxysilane, 3- (2-aminoethyl) amino Amino group such as propyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, etc. Glycidoxy series, 3-nitropropyltrimethoxysilane, nitro series such as 3-nitropropyltriethoxysilane, 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, 2-chloroethyltrimethoxysilane, 2- Chloroethylto Chloro-based such as ethoxy silane. In addition, said silane coupling agent may be used independently and may be used in combination of 2 or more type.

When the silane coupling agent is contained, the content of the silane coupling agent is preferably 2 parts by mass or more and more preferably 4 parts by mass or more with respect to 100 parts by mass of silica. If it is less than 2 parts by mass, rubber strength and wear resistance tend to deteriorate. Moreover, 15 mass parts or less are preferable and, as for content of a silane coupling agent, 13 mass parts or less are more preferable. When the amount exceeds 15 parts by mass, the effect of improving the rubber strength and wear resistance due to the blending of the silane coupling agent is not observed, and the cost tends to increase.

In the tire tread rubber composition of the present invention, the total content of carbon black and white filler is preferably 30 parts by mass or more, more preferably 35 parts by mass or more, further with respect to 100 parts by mass of the rubber component. Preferably it is 40 mass parts or more. If it is less than 30 parts by mass, sufficient wear resistance may not be obtained. The total content of carbon black and white filler is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, and still more preferably 100 parts by mass or less with respect to 100 parts by mass of the rubber component. If it exceeds 150 parts by mass, processability may be deteriorated or sufficient low exothermic property may not be obtained.

In the rubber composition for covering a carcass cord of the present invention, the total content of carbon black and white filler is preferably 30 parts by mass or more, more preferably 35 parts by mass or more with respect to 100 parts by mass of the rubber component. is there. If it is less than 30 parts by mass, sufficient rubber strength may not be obtained. The total content of carbon black and white filler is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, with respect to 100 parts by mass of the rubber component. If it exceeds 100 parts by mass, the workability may be deteriorated or sufficient low heat build-up may not be obtained.

In addition to the components described above, the rubber composition of the present invention includes compounding agents generally used in the production of rubber compositions such as zinc oxide, stearic acid, various anti-aging agents, oils such as aroma oil, waxes, additives. A sulfurizing agent, a vulcanization accelerator, and the like can be appropriately blended.

In the case of the rubber composition for covering a carcass cord, it is preferable to contain zinc oxide.
In the rubber composition for covering a carcass cord of the present invention, the content of zinc oxide is preferably 4 parts by mass or more, more preferably 5 parts by mass or more with respect to 100 parts by mass of the rubber component.
If it is less than 4 mass parts, there exists a possibility that adhesive performance may deteriorate. Further, the content of zinc oxide is preferably 15 parts by mass or less, more preferably 10 parts by mass or less with respect to 100 parts by mass of the rubber component. If it exceeds 15 parts by mass, the rubber strength may be reduced.

Examples of the vulcanization accelerator include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N′-dicyclohexyl-2- Examples include benzothiazolylsulfenamide (DZ), mercaptobenzothiazole (MBT), dibenzothiazolyl disulfide (MBTS), and diphenylguanidine (DPG). These vulcanization accelerators may be used alone or in combination of two or more. Among them, sulfenamide-based vulcanization accelerators such as TBBS and CBS are superior because they have excellent vulcanization characteristics, excellent physical properties of rubber after vulcanization, excellent low heat build-up, and great effects of improving mechanical hardness. preferable. In particular, it is preferable to use TBBS and DPG in combination.

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. When natural rubber is used, a mastication step is usually performed before the kneading and vulcanization. In the present invention, the phosphorus content and nitrogen content are reduced by a method of saponification with an alkaline aqueous solution. Since excellent processability can be obtained by using natural rubber with a low gel content, no special mastication step is required. The kneading step can be performed by kneading components such as rubber components such as natural rubber and peptizers (aromatic disulfide compounds, aromatic mercaptan compounds, etc.) using a kneading apparatus such as a Banbury mixer. .

The rubber composition for tire treads of the present invention is used as a tire tread. The pneumatic tire of the present invention is produced by a usual method using the rubber composition for tire tread. That is, a rubber composition containing various additives as necessary is extruded in accordance with the shape of the tread of the tire 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 rubber composition for covering a carcass cord of the present invention is used as a rubber for covering a carcass cord. The pneumatic tire of the present invention is produced by a usual method using the rubber composition for covering a carcass cord. That is, a rubber composition containing various additives as necessary is kneaded at an unvulcanized stage, and then the carcass cord is covered with the obtained kneaded product and is formed into a carcass shape on a tire molding machine. Molded and bonded together with other tire members 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 passenger car tire, bus tire, truck tire and the like.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

First, various chemicals used in Examples and Comparative Examples will be described.
Natural rubber latex: Field latex obtained from Taitex Co., Ltd. Surfactant: Emal-E manufactured by Kao Corporation
NaOH: NaOH manufactured by Wako Pure Chemical Industries, Ltd.
Natural rubber: TSR
SBR (1): NS116 manufactured by JSR Corporation (vinyl content: 60% by mass, styrene content: 20% by mass)
SBR (2): Nipol 1502 manufactured by Nippon Zeon Co., Ltd. (emulsion polymerization styrene butadiene rubber (E-SBR), styrene content: 23.5% by mass)
Carbon black (1): N220 manufactured by Cabot Japan Co., Ltd. (N ₂ SA: 120 m ² / g, DBP: 114 ml / 100 g)
Carbon black (2): Dia Black H (N330, N ₂ SA: 79 m ² / g, DBP: 100 ml / 100 g) manufactured by Mitsubishi Chemical Corporation
Silica: ZEOSIL 115GR manufactured by Rhodia (BET: 115 m ² / g)
Silane coupling agent: Si266 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Degussa
Oil: Process X-140 manufactured by Japan Energy Co., Ltd.
Zinc oxide: Zinc Hua 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Anti-aging agent manufactured by NOF Corporation: Antigen 6C (N- (1,3-dimethylbutyl) manufactured by Sumitomo Chemical Co., Ltd. -N'-phenyl-p-phenylenediamine)
Sulfur: Sulfur powder vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd. (1): Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Vulcanization accelerator (2): Noxeller D (N, N'-diphenylguanidine) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Kneading accelerator: Nouchitizer SD manufactured by Ouchi Shinsei Chemical Co., Ltd.

(Production of saponified natural rubber with alkali)
Production Example 1
After adjusting the solid rubber latex solids concentration (DRC) to 30% (w / v), 1000 g of natural rubber latex was added with 10 g of Emal-E and 20 g of NaOH, followed by saponification reaction for 48 hours at room temperature. Natural rubber latex was obtained. Water was added to the latex to dilute to DRC 15% (w / v), and then formic acid was added with slow stirring to adjust the pH to 4.0 to 4.5 to cause aggregation. The agglomerated rubber was pulverized, washed repeatedly with 1000 ml of water, and then dried at 110 ° C. for 2 hours to obtain a solid rubber (saponified natural rubber A).
Production Example 2
After adjusting the solid rubber latex solids concentration (DRC) to 30% (w / v), 1000 g of natural rubber latex was added with 10 g of Emal-E and 15 g of NaOH, followed by saponification reaction at room temperature for 48 hours. Natural rubber latex was obtained. Water was added to the latex to dilute to DRC 15% (w / v), and then formic acid was added with slow stirring to adjust the pH to 4.0 to 4.5 to cause aggregation. The agglomerated rubber was pulverized, washed repeatedly with 1000 ml of water, and then dried at 110 ° C. for 2 hours to obtain a solid rubber (saponified natural rubber B).
Production Example 3
After adjusting the solid content concentration (DRC) of the natural rubber latex to 30% (w / v), the 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 110 ° C. for 2 hours to obtain a solid rubber (untreated natural rubber).

With respect to the solid rubbers and TSRs obtained in Production Examples 1 to 3, the nitrogen content, phosphorus content, and gel content were measured by the following methods. 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 natural rubber obtained in each production example 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).

(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, saponified natural rubbers A and B have a reduced nitrogen content, phosphorus content, and gel content as compared to untreated natural rubber and TSR.

(Production of rubber test piece and tire 1)
Examples 1-6, Comparative Examples 1-4
In accordance with the formulation shown in Tables 2 and 3, chemicals other than sulfur and a vulcanization accelerator were kneaded using a 1.7 L Banbury mixer. Next, using an open roll, sulfur and a vulcanization accelerator were added to the kneaded product and kneaded to obtain an unvulcanized rubber composition. In Comparative Examples 1 and 3 using TSR, 0.4 parts by mass of a peptizer was added to 100 parts by mass of the rubber component of TSR, and mastication was performed in advance using a 1.7 L Banbury mixer. It was. On the other hand, in Examples 1 to 6 and Comparative Examples 2 and 4, natural rubber was not masticated.
Next, the obtained unvulcanized rubber composition was formed into a tread shape on a tire molding machine, and bonded to another tire member to produce an unvulcanized tire. A test tire was produced by vulcanizing an unvulcanized tire at 150 ° C. for 30 minutes.

(Production of rubber test piece and tire 2)
Examples 7-12, Comparative Examples 5-8
In accordance with the formulation shown in Tables 4 and 5, chemicals other than sulfur and a vulcanization accelerator were kneaded using a 1.7 L Banbury mixer. Next, using an open roll, sulfur and a vulcanization accelerator were added to the kneaded product and kneaded to obtain an unvulcanized rubber composition. In Comparative Examples 5 and 7 using TSR, 0.4 parts 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. It was. On the other hand, in Examples 7 to 12 and Comparative Examples 6 and 8, natural rubber was not masticated.
The obtained unvulcanized rubber composition was press vulcanized for 15 minutes at 170 ° C. to obtain a vulcanized rubber composition.
Next, a carcass cord was coated with the obtained unvulcanized rubber composition, formed into a carcass shape on a tire molding machine, and bonded to another tire member to produce an unvulcanized tire. A test tire was produced by vulcanizing an unvulcanized tire at 150 ° C. for 30 minutes.

The obtained unvulcanized rubber composition, vulcanized rubber composition and test tire were evaluated as follows. The results are shown in Tables 2-5.

(Measurement of Mooney viscosity)
About the obtained unvulcanized rubber composition, it measured at 130 degreeC according to the measuring method of the Mooney viscosity based on JISK6300. The Mooney viscosity (ML _{1 + 4} ) of Comparative Example 1, Comparative Example 3, Comparative Example 5, or Comparative Example 7 was set to 100, and indexed by the following formula (Mooney viscosity index). The larger the index, the lower the Mooney viscosity and the better the processability.
(Mooney viscosity index) = (ML _{1 + 4 of} Comparative Example 1, Comparative Example 3, Comparative Example 5 or Comparative Example 7) / (ML _{1 + 4 of} each formulation) × 100

(Rolling resistance)
Using a rolling resistance tester, the rolling resistance when the test tire is mounted on a rim (15 × 6JJ) and running under conditions of a tire internal pressure of 230 kPa, a load of 3.43 kN, and a speed of 80 km / h is measured. The rolling resistance index of Comparative Example 1, Comparative Example 3, Comparative Example 5 or Comparative Example 7 was set to 100, and the rolling resistance of each formulation was indicated by an index according to the following formula. In addition, it shows that rolling resistance is reduced and a fuel consumption performance is excellent, so that a rolling resistance index | exponent is large.
(Rolling resistance index) = (Rolling resistance of Comparative Example 1, Comparative Example 3, Comparative Example 5 or Comparative Example 7) / (Rolling resistance of each formulation) × 100

(Abrasion test)
About Examples 1-6 and Comparative Examples 1-4, the tire for a test was mounted | worn with the car, and the reduction | decrease amount of the groove depth after drive | working a city area for 8000 km was measured. Furthermore, the reduction amount of the groove depth of the comparative example 1 or the comparative example 3 was set to 100, and the reduction amount of the groove depth of each composition was indicated by an index by the following calculation formula. In addition, it shows that it is excellent in abrasion resistance, so that an abrasion resistance index | exponent is large.
(Abrasion resistance index) = (reduction amount of groove depth of Comparative Example 1 or Comparative Example 3) / (reduction amount of groove depth of each composition) × 100

(Rubber strength)
For Examples 7-12 and Comparative Examples 5-8, No. 3 dumbbell-type rubber test pieces were prepared using the obtained vulcanized rubber sheets, and JIS K 6251 “vulcanized rubber and thermoplastic rubber—of tensile properties. Perform a tensile test according to “How to obtain”, measure breaking strength (TB) and elongation at break (EB), calculate the product (TB × EB), and calculate TB × EB of Comparative Example 5 or Comparative Example 7 100, the rubber strength (TB × EB) of each compound was indicated by an index according to the following calculation formula. In addition, it shows that it is excellent in rubber strength, so that a rubber strength index is large.
(Rubber Strength Index) = (TB × EB of each formulation) / (TB × EB of Comparative Example 5 or Comparative Example 7) × 100

(Adhesion test)
About Examples 7-12 and Comparative Examples 5-8, the obtained unvulcanized rubber composition and a carcass cord were bonded together, vulcanized for 40 minutes under the condition of 180 ° C., and a tensile tester (manufactured by Instron) ) Was used to visually evaluate the adhesion between the rubber and the carcass cord.
○: Good adhesion between rubber sheet and carcass cord ×: Poor adhesion between rubber sheet and carcass cord

From Table 2, when saponification natural rubber was used for the rubber composition for tire treads (Examples 1 to 3), the processability superior to that of Comparative Example 1 using masticated TSR was shown. On the other hand, the untreated natural rubber of Comparative Example 2 that was not masticated had poor processability. As described above, when saponified natural rubber was used, excellent processability was exhibited even without mastication. In addition, the fuel efficiency performance and the wear performance were better in the example than in the comparative example.

Table 3 shows that even in a tread compound containing both silica and carbon, when saponified natural rubber is used (Examples 4 to 6), the processability is superior to Comparative Example 3 using a masticated TSR. It was. On the other hand, the untreated natural rubber of Comparative Example 4 that was not masticated had poor processability. In addition, the fuel efficiency performance and the wear performance were better in the example than in the comparative example.

From Table 4, when saponified natural rubber is used for the rubber composition for covering a carcass cord (Examples 7 to 9), Comparative Example 5 using a masticated TSR, or natural maturation without mastication. The processability and high rubber strength superior to those of Comparative Example 6 using rubber were shown. Moreover, in the Example, the adhesive performance superior to the comparative example 6 was shown, and the fuel consumption performance was also favorable compared with the comparative examples 5 and 6.

From Table 5, even in the case of a carcass cord coating composition containing both silica and carbon, when saponified natural rubber was used (Examples 10 to 12), Comparative Example 7 using masticated TSR and mastication were performed. The processability and high rubber strength were superior to those of Comparative Example 8 using untreated natural rubber. Moreover, although the adhesive performance was poor in the comparative example, the adhesive performance was improved when saponified natural rubber was used. Further, the fuel efficiency performance of the example was better than that of the comparative example.

Claims (18)

A rubber composition for a tire tread in which carbon black and / or a white filler is blended with a rubber component containing 5% by mass or more of a natural rubber having a phosphorus content of 200 ppm or less ,
The natural rubber is obtained by saponifying natural rubber latex with alkali, washing the agglomerated rubber after saponification repeatedly, and washing and removing the phosphorus compound separated by saponification.
Rubber composition for tire tread. The rubber composition for a tire tread according to claim 1, wherein the nitrogen content of the natural rubber is 0.3 mass% or less. The rubber composition for a tire tread according to claim 1, wherein the natural rubber has a nitrogen content of 0.15 mass% or less. The rubber composition for a tire tread according to any one of claims 1 to 3, wherein a gel content measured as a toluene insoluble matter of the natural rubber is 20% by mass or less. The rubber composition for a tire tread according to any one of claims 1 to 4 , wherein the white filler is silica. The rubber composition for a tire tread according to any one of claims 1 to 4, comprising silica. The manufacturing method of the rubber composition for tire treads in any one of Claims 1-6 which does not include the process of masticating natural rubber. The pneumatic tire which has a tread produced using the rubber composition for tire treads in any one of Claims 1-6. A rubber composition for covering a carcass cord in which carbon black and / or a white filler is blended with a rubber component containing 5% by mass or more of a natural rubber having a phosphorus content of 200 ppm or less ,
The natural rubber is obtained by saponifying natural rubber latex with alkali, washing the agglomerated rubber after saponification repeatedly, and washing and removing the phosphorus compound separated by saponification.
Rubber composition for carcass cord coating. The rubber composition for coating a carcass cord according to claim 9, wherein the natural rubber has a nitrogen content of 0.3 mass% or less. The rubber composition for covering a carcass cord according to claim 9, wherein the natural rubber has a nitrogen content of 0.15% by mass or less. The rubber composition for covering a carcass cord according to any one of claims 9 to 11, wherein the natural rubber has a gel content measured as a toluene insoluble content of 20% by mass or less. The rubber composition for covering a carcass cord according to any one of claims 9 to 12 , wherein the white filler is silica. The rubber composition for covering a carcass cord according to any one of claims 9 to 12, comprising silica. The rubber composition for covering a carcass cord according to any one of claims 9 to 14, wherein a content of the natural rubber in 100% by mass of the rubber component is 60 to 100% by mass. The rubber composition for covering a carcass cord according to any one of claims 9 to 15, comprising 4 to 15 parts by mass of zinc oxide with respect to 100 parts by mass of the rubber component. The method for producing a rubber composition for covering a carcass cord according to any one of claims 9 to 16, which does not include a step of kneading natural rubber. A pneumatic tire having a carcass manufactured using the rubber composition for covering a carcass cord according to any one of claims 9 to 16.