JP5670768B2 - Composite, production method thereof, rubber composition and pneumatic tire - Google Patents

Description

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

Conventionally, vehicle fuel efficiency has been reduced by reducing tire rolling resistance and suppressing heat generation. In recent years, there has been a growing demand for lower fuel consumption, as well as tread with a high tire occupancy ratio, as well as lower fuel consumption for sidewalls and the like. In addition, since fuel efficiency is required not only for passenger car tires but also for truck and bus tires, it is also important to improve wear resistance.

Although it is possible to improve the low heat build-up by using a low reinforcing filler in the rubber composition or reducing the amount of filler, the wear resistance and fracture performance are reduced. It is difficult. In addition, although the rolling resistance is reduced by using silica, silica is strong in self-aggregation, and it is not easy to uniformly disperse by a general kneading method, and in particular, fine particle silica has a strong tendency to agglomerate. .

On the other hand, natural rubber has poor processability compared to other synthetic rubbers and is usually inferior in productivity because it is usually used after mastication. In addition, the molecular chain of natural rubber is cleaved by mastication, and the inherent high molecular weight polymer characteristics (low fuel consumption, wear resistance, fracture performance, etc.) are lost.

Patent Document 1 discloses a composite prepared by mixing natural rubber latex with fine-particle silica produced from water glass as a master batch with improved rubber mechanical strength. However, there is still room for improvement in terms of achieving both low fuel consumption, wear resistance and fracture performance, and further improving weather resistance.

JP 2009-51955 A

An object of the present invention is to solve the above-mentioned problems and to provide a composite in which fine particle silica and carbon black are uniformly dispersed in a rubber component and a method for producing the same. Another object of the present invention is to provide a rubber composition containing the composite and a pneumatic tire that can achieve both low fuel consumption, wear resistance, and fracture performance while having excellent processability and weather resistance.

The present invention is to wash a coagulated product of a compounded latex obtained by mixing a modified natural rubber latex and a fine particle silica dispersion having an average particle size of 100 nm or less and a carbon black dispersion, which are produced from water glass, and the phosphorus content in the rubber Relates to a composite obtained by adjusting the content to 200 ppm or less.

It is preferable that the nitrogen content in the rubber is 0.3% by mass or less, and the gel content measured as a toluene insoluble content in the rubber is 20% by mass or less. The modified natural rubber latex is preferably obtained by saponifying natural rubber latex.

The carbon black average particle size of the carbon black dispersion is preferably 100 nm or less. Furthermore, it is preferable that the average particle diameter of carbon black in the carbon black dispersion liquid is 60 nm or less, and the average particle diameter of silica in the fine particle silica dispersion liquid is 20 nm or less.

The fine particle silica dispersion is prepared by adjusting the pH of a water glass aqueous solution to 9 to 11 using an ion exchange resin, and the average particle diameter of silica in the dispersion is 20 nm or less. Is preferred.

The present invention also includes the step (I) of preparing the compounded latex by mixing the modified natural rubber latex, the fine particle silica dispersion, and the carbon black dispersion, and the compounded latex obtained in the step (I). The present invention relates to a method for producing the composite comprising the step (II) of solidification and the step (III) of washing the solidified product obtained in the step (II) and adjusting the phosphorus content in the rubber to 200 ppm or less.

The present invention also relates to a rubber composition containing the composite. The present invention also relates to a pneumatic tire produced using the rubber composition.

According to the present invention, a coagulated product of a compounded latex obtained by mixing a modified natural rubber latex and a fine particle silica dispersion having an average particle size of 100 nm or less and a carbon black dispersion, which is produced from water glass, is washed to obtain phosphorus in the rubber. Since the composite is obtained by adjusting the content to 200 ppm or less, fine-particle silica and carbon black can be uniformly dispersed in the composite, and the effects of both fillers are sufficiently exhibited. For this reason, the composite_body | complex excellent in low exothermic property, mechanical strength, and a weather resistance is obtained. Therefore, by using the composite for a tire member such as a tread, it is possible to achieve both low fuel consumption, wear resistance, and fracture performance, and at the same time, excellent weather resistance.

In addition, a composite in which silica and carbon black are uniformly dispersed has excellent storage curability because silica re-aggregation is suppressed and a change in Mooney viscosity before and after deterioration is suppressed.

Furthermore, since the composite is excellent in processability, good processability can be obtained without performing a mastication step in advance in the production of a rubber composition using the composite. In addition, when the mastication step is not performed, the natural rubber molecular chain is not cleaved in the step, and the characteristics of the high molecular weight polymer inherently can be maintained, so performance such as low heat buildup, wear resistance, and fracture performance is more effective. Is demonstrated.

<Composite>
The composite of the present invention cleans a coagulated product of a compounded latex obtained by mixing a modified natural rubber latex and a fine particle silica dispersion having an average particle size of 100 nm or less and a carbon black dispersion, which are produced from water glass. It is obtained by adjusting the phosphorus content to 200 ppm or less.

That is, first, a natural rubber latex subjected to a modification treatment such as a saponification treatment, a fine particle silica dispersion having an average particle diameter of 100 nm or less derived from water glass, and a carbon black dispersion are prepared, and then the latex and both dispersions are prepared. After the liquid is mixed in a liquid state to produce a compounded latex (mixed liquid) and coagulated, the resulting coagulated product is washed to reduce the phosphorus content in the natural rubber, thereby improving the phosphorus content of 200 ppm or less. A composite containing high quality natural rubber (HPNR) is produced. In addition, since such a technique is used, a composite in which fine particle silica and carbon black are finely dispersed in a modified natural rubber can be prepared.

The composite of the present invention is obtained by, for example, the step (I) of preparing the compounded latex by mixing the modified natural rubber latex, the fine particle silica dispersion, and the carbon black dispersion, and the step (I). More preferably by a production method comprising the step (II) of coagulating the blended latex and the step (III) of washing the coagulated product obtained in the step (II) and adjusting the phosphorus content in the rubber to 200 ppm or less. can get.

(Process (I))
In step 1, the modified natural rubber latex, the fine particle silica dispersion, and the carbon black dispersion are mixed to prepare a compounded latex.

The modified natural rubber latex used in step (I) can be prepared, for example, by saponifying natural rubber latex with an alkali. When the saponification treatment is performed, the phosphorus compound separated by saponification in the step (III) described later is washed and removed, so that the phosphorus content in the natural rubber contained in the prepared composite can be suppressed. Moreover, since the protein in the natural rubber is decomposed by the saponification treatment, the nitrogen content of the natural rubber can be suppressed.

Natural rubber latex is collected as sap of natural rubber trees such as Hevea, and contains rubber, water, proteins, lipids, inorganic salts, etc., and the gel content in rubber is based on the complex presence of various impurities. It is considered a thing. In the present invention, as a natural rubber latex, raw latex (field latex) produced by tapping Hevea tree, concentrated latex (purified latex, high ammonia latex to which ammonia is added by a conventional method) concentrated by centrifugation or creaming method , Zinc oxide, TMTD and ammonia stabilized LATZ latex, etc.) can be used.

As a method for the saponification treatment, for example, the methods described in JP2010-138359A and JP2010-174169A can be suitably performed. Specifically, the saponification treatment can be carried out by adding an alkali and, if necessary, a surfactant to natural rubber latex and allowing to stand at a predetermined temperature for a certain period of time. You can go.

As the alkali used for the saponification treatment, sodium hydroxide, potassium hydroxide and the like are preferable. The surfactant is not particularly limited, and examples thereof include known nonionic surfactants such as polyoxyethylene alkyl ether sulfates, anionic surfactants, and amphoteric surfactants. A polyoxyethylene alkyl ether sulfate ester salt is preferable because it can be saponified. In the saponification treatment, the addition amount of alkali and surfactant, the temperature and time of the saponification treatment may be appropriately set.

In step (I), a fine particle silica dispersion having an average particle diameter of 100 nm or less produced from water glass is used. That is, silica is used by growing it as spherical fine particles, instead of using the raw water glass as it is. In this growth, it is more preferable to take a long ripening time and to make it spherical. When the spherical shape is obtained, the contact between the silica particles is minimized, the cohesive force is reduced, and the silica is easily dispersed.

The fine particle silica dispersion is preferably prepared by adjusting the pH of the aqueous water glass solution to 9-11.
The water glass is usually represented by a composition represented by the following formula.
Na ₂ O · nSiO ₂ · mH ₂ O
The coefficient n is a value represented by a molecular ratio of SiO ₂ / Na ₂ O, and is a range defined in JIS K 1408-1966 generally called a molar ratio. Although this coefficient n is not specifically limited, Preferably it is 2.1-3.3, More preferably, it is 3.1-3.3. When the coefficient n is 3.1 to 3.3, the silica component (in terms of SiO ₂ ) in the water glass increases, so that the efficiency of the composite treatment with rubber is improved.

In general, the water glass having the coefficient n of 3.1 to 3.3 is commercially available as Water Glass No. 3. The water glass which can be used for this invention is not limited to this, For example, No. 1-3 water glass prescribed | regulated to JISK1408, and other various grade products can be used.

By preparing an aqueous solution of water glass and adjusting the pH of the aqueous solution in the range of 9 to 11, a fine particle silica dispersion in which fine particle silica having an average particle diameter of 100 nm or less is dispersed can be prepared. When the pH is less than 9, gelation tends to occur, and when the pH exceeds 11, the fine particle silica tends to dissolve. More preferably, the pH is adjusted to a range of 9.5 to 10.5. The method for adjusting the pH to a range of 9 to 11 is not particularly limited, and can be carried out by a conventionally known method such as addition of an acid or alkali, use of an ion exchange resin, etc. Among them, a dispersion in which fine particle silica is more dispersed. From the point that can be obtained, it is preferable to use an ion exchange resin.

Examples of the pH adjustment method using an ion exchange resin include a method of bringing an aqueous solution of water glass into contact with a cation exchange resin. Specifically, an aqueous solution of water glass diluted to a predetermined concentration is brought into contact with a cation exchange resin to be dealkalized, and if necessary, brought into contact with an OH type strongly basic anion exchange resin to deanion. Can be done by. Examples of the contacting method include a batch method in which a cation exchange resin is directly put into an aqueous solution of water glass and stirred and contacted, and a method in which an aqueous solution of water glass is passed through a column filled with a cation exchange resin. . As the cation exchange resin, an H-type strong acid cation exchange resin, a weak acid cation exchange resin, or the like can be used. It is done. By the above method, sodium ions and the like in the water glass can be removed, so that silica particles in a more atomized state can be generated.

When adjusting the pH, the temperature of the aqueous solution of water glass is preferably adjusted to 10 to 90 ° C. When the temperature is less than 10 ° C., the generation rate of the fine particle silica is slow. What is necessary is just to adjust the temperature of the said aqueous solution suitably, and 15-40 degreeC and 60-80 degreeC are mentioned as a preferable range, for example.

The reaction time is preferably in the range of 1 to 72 hours. If it is less than 1 hour, the production of fine-particle silica is not sufficient, and even if it exceeds 72 hours, the reaction has already ended and there is a tendency that there is no further change. When making it react at room temperature, it is suitable to carry out for 6 to 24 hours on stirring conditions. Further, in order to be as close to a true sphere as possible, aging at a high temperature and a long time is good, and a temperature of 60 to 80 ° C. for 24 hours or more is preferable.

The concentration of the silica component (SiO ₂ ) contained in the aqueous water glass solution is preferably in the range of 1 to 30% by mass. When the concentration is less than 1% by mass, a large amount of water glass aqueous solution is required for complexing with the rubber latex, and when it exceeds 30% by mass, silica aggregation tends to occur. The concentration of the silica component is more preferably in the range of 1.5 to 20% by mass, still more preferably 2 to 8% by mass. However, when water glass that has been subjected to desalting treatment is used, the upper limit is not particularly limited because silica aggregation is unlikely to occur.

The average particle diameter of silica contained in the fine particle silica dispersion is 100 nm or less, preferably 30 nm or less, more preferably 20 nm or less, still more preferably 15 nm or less, and particularly preferably 10 nm or less. Here, the size of the average particle diameter can be arbitrarily adjusted by adjusting the pH of the aqueous solution, the concentration of the silica component, the reaction temperature, the reaction time, and the like.

In the present specification, transmission electron microscope (TEM) observation is used as a method for measuring the average particle diameter. Specifically, the microparticles are photographed with a transmission electron microscope. If the shape of the microparticles is spherical, the diameter of the sphere is the particle diameter, and if it is needle-shaped or rod-shaped, the minor diameter is the particle diameter. In this case, the average particle diameter from the center is defined as the particle diameter, and the average value of the particle diameters of 100 fine particles is defined as the average particle diameter.

The nitrogen adsorption specific surface area of silica contained in the fine particle silica dispersion _(N 2 SA) of not particularly limited, preferably ^{30 m} 2 / g or more, more preferably ^{50 m} 2 / g or more, more preferably 100 m ² / g or more. If it is less than 30 m ² / g, the reinforcing effect tends to be small. The N ₂ SA is preferably 500 m ² / g or less, more preferably 400 m ² / g or less, and still more preferably 250 m ² / g or less. If it exceeds 500 m ² / g, the dispersibility is poor and the heat build-up tends to increase.
The _N 2 SA of silica is a value measured by the BET method in accordance with ASTM D3037-81.

In step (I), a carbon black dispersion is used. That is, not a dry carbon black powder but a dispersion (slurry) in which carbon black is dispersed in water is used.

The carbon black dispersion can be produced by a known method, and is not particularly limited. For example, the carbon black dispersion can be prepared using a known stirrer such as a high-pressure homogenizer, an ultrasonic homogenizer, or a colloid mill. Specifically, the dispersion liquid can be prepared by adding carbon black to an aqueous medium such as water and stirring using the stirrer. The amount of carbon black added to the dispersion is not particularly limited, but is preferably 0.5 to 10% by mass, more preferably 2 to 2%, from the viewpoint of uniform dispersibility in the dispersion (100% by mass). 5% by mass.

Examples of carbon black include those produced by the furnace method, channel method, acetylene method, and lamp method. From the viewpoint of high dispersion efficiency, it is preferable to use carbon black granulated by wet granulation, dry granulation or the like.

The average particle size of carbon black is preferably 100 nm or less, more preferably 80 nm or less, and still more preferably 60 nm or less. If it exceeds 100 nm, sufficient rubber strength may not be obtained. The average particle diameter is preferably 10 nm or more, more preferably 15 nm or more. If the thickness is less than 10 nm, sufficient processability and low fuel consumption cannot be obtained.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 20 m ² / g or more, more preferably 35 m ² / g or more, and still more preferably 40 m ² / g or more. There exists a tendency for a reinforcement effect to be small in it being less than 20 m < ² > / g. The N ₂ SA is preferably 500 m ² / g or less, more preferably 400 m ² / g or less, and still more preferably 300 m ² / g or less. If it exceeds 500 m ² / g, the dispersibility tends to decrease and the exothermicity tends to increase.
The N ₂ SA of carbon black is measured according to JIS K 6217-2: 2001.

Carbon black has a dibutyl phthalate oil absorption (DBP) of preferably 50 ml / 100 g or more, more preferably 80 ml / 100 g or more. The DBP is preferably 200 ml / 100 g or less, more preferably 130 ml / 100 g or less. When the DBP is within the above range, low fuel consumption, wear resistance, and fracture performance can be obtained in a well-balanced manner.
The DBP of carbon black is measured according to JIS K 6217-4: 2008.

In step (I), the modified natural rubber latex, the fine particle silica dispersion, and the carbon black dispersion are mixed by a known method, and then sufficiently stirred until a uniform solution is obtained. ) Is prepared. The modified natural rubber latex preferably has a rubber solid content of 10 to 70% by mass.

In the mixing step, it is preferable to mix the fine particle silica dispersion so that silica is 5 to 150 parts by mass (in terms of SiO ₂ ) with respect to 100 parts by mass (solid content) of the modified natural rubber. If the amount is less than 5 parts by mass, the amount of silica may be reduced when used as a master batch. When it exceeds 150 parts by mass, it is difficult to obtain uniform dispersion of silica in the rubber latex, and the uniform dispersion of silica in the rubber composition after coagulating the compounded latex tends to decrease. More preferably, it is 5-120 mass parts, More preferably, it is 10-100 mass parts.

In the mixing step, it is preferable to mix the carbon black dispersion so that the carbon black is 3 to 100 parts by mass with respect to 100 parts by mass (solid content) of the modified natural rubber. If the amount is less than 3 parts by mass, the effect of improving weather resistance may not be sufficiently obtained. When it exceeds 100 parts by mass, it is difficult to obtain uniform dispersion of carbon black in the rubber latex, and the uniform dispersion of carbon black in the rubber composition after coagulating the compounded latex tends to be lowered. More preferably, it is 3-85 mass parts, More preferably, it is 5-75 mass parts.

In the mixing step, it is preferable to mix both dispersions so that the total amount of silica and carbon black is 10 to 200 parts by mass with respect to 100 parts by mass (solid content) of the modified natural rubber. If it is less than 10 parts by mass, silica and carbon black may not be uniformly finely dispersed. If it exceeds 200 parts by mass, silica and carbon black may not be sufficiently dispersed.

(Process (II))
In step (II), the compounded latex obtained in step (I) is coagulated (aggregated) to produce a composite in which fine-particle silica and carbon black are uniformly dispersed in rubber. Solidification of the blended latex includes acid coagulation, salt coagulation, methanol coagulation, coagulation with a polymer flocculant, etc., but acid coagulation is preferable from the viewpoint that silica and carbon black are coagulated by uniform dispersion. Examples of the acid for coagulation include sulfuric acid, hydrochloric acid, formic acid, acetic acid and the like.

Acid coagulation of the compounded latex is carried out by adjusting the pH of the compounded latex to 5-9 (preferably 6-8, more preferably 6.5-7.5) by adding acid to coagulate the solid content. It is preferable. Thereby, a composite in which silica and carbon black are finely dispersed can be suitably produced.

(Step (III))
In step (III), the coagulated product (agglomerated rubber, aggregate containing silica and carbon black) obtained in step (II) is washed, and the phosphorus content in the rubber (natural rubber) is adjusted (reduced) to 200 ppm or less. ) By performing the washing treatment after the saponification treatment, the amount of phosphorus in the natural rubber in the coagulated product can be reduced to 200 ppm or less.

As the washing method in step (III), the rubber content is diluted with water and then centrifuged, or the mixture is allowed to stand to float the rubber and discharge only the aqueous phase until the phosphorus content is 200 ppm or less. And a method of performing cleaning.

After washing, it is usually dried by a known method (such as an oven). When the rubber is kneaded with a biaxial roll or Banbury after drying, a composite containing modified natural rubber (HPNR) having a phosphorus content of 200 ppm or less, silica and carbon black is obtained. In addition, the said composite_body | complex may contain another component in the range which does not inhibit the effect of this invention.

The modified natural rubber contained in the composite has a phosphorus content of 200 ppm or less. If it exceeds 200 ppm, the Mooney viscosity will increase during storage, resulting in poor processability and insufficient fuel economy. The phosphorus content is preferably 150 ppm or less, and more preferably 120 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 nitrogen content of the modified natural rubber contained in the composite is preferably 0.3% by mass or less, more preferably 0.15% by mass or less. If it exceeds 0.3% by mass, the Mooney viscosity will increase during storage, resulting in poor processability and insufficient fuel economy. Nitrogen is derived from proteins. The nitrogen content can be measured by a conventional method such as Kjeldahl method.

The modified natural rubber contained in the composite preferably has a gel content measured as a toluene insoluble content of 20% by mass or less, and more preferably 10% by mass or less. If it exceeds 20% by mass, the Mooney viscosity tends to increase 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 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.

<Rubber composition>
The rubber composition of the present invention contains the above composite. As a result, excellent fuel economy, wear resistance, fracture performance, weather resistance, workability, and storage curability can be obtained. The composite can be used as a master batch. In the composite, since silica and carbon black are uniformly dispersed in the rubber, silica and carbon black are also uniformly distributed in the rubber composition of the present invention obtained when mixed with other rubber components and a rubber compounding agent. Can be dispersed. Therefore, the aforementioned performance can be obtained at a high level.

The rubber composition of the present invention may contain a rubber component other than the modified natural rubber. Examples of other rubber components include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), Examples include chloroprene rubber (CR) and acrylonitrile butadiene rubber (NBR).

About the rubber component (modified natural rubber and other rubber components in the composite) contained in the rubber composition, the content of the modified natural rubber (solid content) contained in the composite in 100% by mass of the rubber component The amount is preferably 60% by mass or more, more preferably 80% by mass or more, and may be 100% by mass. If it is less than 60% by mass, sufficient fuel efficiency may not be obtained.

The rubber composition of the present invention may further contain silica in addition to the silica in the composite. Furthermore, it does not specifically limit as a silica to mix | blend, A dry method silica (anhydrous silicic acid), a wet method silica (hydrous silicic acid), etc. are mentioned.

In the rubber composition, the content of silica (total content of silica contained in the composite and further compounded silica) is preferably 5 parts by mass or more, more preferably 100 parts by mass of the rubber component. It is 10 parts by mass or more. If it is less than 5 parts by mass, sufficient reinforcement may not be obtained. The content is preferably 150 parts by mass or less, more preferably 100 parts by mass or less. If it exceeds 150 parts by mass, sufficient fuel economy may not be obtained.

The rubber composition of the present invention usually contains a silane coupling agent. Examples of the silane coupling agent include sulfide, mercapto, vinyl, amino, glycidoxy, nitro, and chloro silane coupling agents. Among them, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, etc. Sulfide type is preferable, and bis (3-triethoxysilylpropyl) disulfide and bis (3-triethoxysilylpropyl) tetrasulfide are more preferable.

The content of the silane coupling agent is preferably 4 parts by mass or more, more preferably 6 parts by mass or more with respect to 100 parts by mass of silica (total content of silica contained in the composite and further compounded silica). is there. If the amount is less than 4 parts by mass, sufficient reinforcing properties tend not to be obtained. The content is preferably 20 parts by mass or less, more preferably 15 parts by mass or less. If it exceeds 20 parts by mass, the effect of improving the rubber strength and wear resistance by adding the silane coupling agent tends to be insufficient. Also, the cost tends to increase.

The rubber composition of the present invention may further contain carbon black in addition to the carbon black in the composite. Furthermore, as carbon black to mix | blend, the thing similar to the said carbon black is suitable.

In the rubber composition, the content of carbon black (the total content of carbon black contained in the composite and further blended carbon black) is preferably 3 parts by mass or more with respect to 100 parts by mass of the rubber component. More preferably, it is 5 parts by mass or more. If it is less than 3 parts by mass, sufficient reinforcement may not be obtained. The content is preferably 100 parts by mass or less, more preferably 75 parts by mass or less. When it exceeds 100 parts by mass, there is a possibility that sufficient low fuel consumption and wear resistance may not be obtained.

The total content of silica and carbon black is preferably 10 parts by mass or more, and more preferably 50 parts by mass or more with respect to 100 parts by mass of the rubber component. The total content is preferably 200 parts by mass or less, more preferably 100 parts by mass or less. Thereby, the effect of this invention is acquired favorably.

In addition to the above materials, various materials such as zinc oxide, stearic acid, anti-aging agent, sulfur, and vulcanization accelerator, which are generally used in the tire industry, are appropriately blended in the rubber composition of the present invention. It may be.

As a method for producing the rubber composition of the present invention, known methods can be used. For example, the above components are kneaded using a rubber kneader such as an open roll, a Banbury mixer, a closed kneader, and then added. It can be manufactured by a method of sulfurating. When producing a rubber composition containing natural rubber, a natural rubber mastication step is usually performed before the kneading step of each component such as a rubber component and a filler. In the present invention, since a composite using a modified natural rubber is used, the kneading step can be carried out satisfactorily without performing the kneading step, and a desired rubber composition can be produced.

The rubber composition can be applied to each member of a tire, and among them, it can be suitably used for a tread and a sidewall.

<Pneumatic tire>
The pneumatic tire of the present invention is produced by a usual method using the rubber composition. That is, a rubber composition containing various additives as necessary is extruded in accordance with the shape of each member of the tire at an unvulcanized stage and molded by a normal method on a tire molding machine. After forming an unvulcanized tire by heating, the tire can be manufactured by heating and pressing in a vulcanizer.

The pneumatic tire of the present invention can be suitably used for passenger cars, trucks and buses, and low-pollution vehicles (eco-cars) compatible with global environmental conservation.

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

The various chemicals used in the examples are described below.
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.
Water glass: Water glass No. 3 manufactured by Fuji Chemical Co., Ltd. (Na ₂ O.nSiO ₂ .mH ₂ O, n = 3.2, silica component (SiO ₂ equivalent) content: 28% by mass)
Natural rubber: TSR
Silica (1): Ultrasil VN3 (N ₂ SA: 175 m ² / g) manufactured by EVONIK-DEGUSSA
Silica (2): Premium 200MP (N ₂ SA: 200 m ² / g) manufactured by Rhodia
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by EVONIK-DEGUSSA
Carbon black (1): Seast V manufactured by Tokai Carbon Co., Ltd. (average particle size: 62 nm, N ₂ SA: 27 m ² / g, DBP: 87 ml / 100 g)
Carbon black (2): Seast 9 (average particle size: 19 nm, N ₂ SA: 142 m ² / g, DBP: 115 ml / 100 g) manufactured by Tokai Carbon Co., Ltd.
Zinc oxide: Zinc Hua No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Anti-aging agent manufactured by NOF Corporation: NOCRACK 6C (N- (1,3-3-) manufactured by Ouchi Shinsei Chemical Co., Ltd. Dimethylbutyl) -N′-phenyl-p-phenylenediamine)
Sulfur: powder sulfur vulcanization accelerator NS manufactured by Tsurumi Chemical Co., Ltd. NS: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Vulcanization accelerator DPG: Noxeller D (N, N'-diphenylguanidine) manufactured by Ouchi Shinsei Chemical Co., Ltd.

(Preparation of saponified natural rubber latex with alkali)
After adjusting the solid rubber latex solids concentration (DRC) to 30% (w / v), 1000 g of natural rubber latex was added with 10 g of Emal-E and 20 g of NaOH, followed by saponification at room temperature for 48 hours. Natural rubber latex was obtained.

(Production of saponified natural rubber (solid rubber))
After adding water to the saponified natural rubber latex obtained above to adjust the solid content concentration (DRC) to 15% (w / v), formic acid is added while slowly stirring to adjust the pH to 4.0-4. .5 and agglomerated. The agglomerated rubber was pulverized, washed repeatedly with 1000 ml of water, and then dried at 110 ° C. for 2 hours to obtain a saponified natural rubber (solid rubber).

(Preparation of fine particle silica dispersions (1) and (2))
Using water glass, a water glass aqueous solution having a silica component content (concentration) of 2% by mass is prepared, adjusted to pH 10, stirred at 25 ° C. for 10 to 24 hours, and the fine particle silica dispersion (1) and (2) was obtained. The pH was adjusted with sulfuric acid.
Observation of the TEM photograph confirmed that silica having an average particle size of about 20 nm (fine particle silica dispersion (1)) and silica having an average particle size of about 15 nm (fine particle silica dispersion (2)) were obtained.

(Preparation of fine particle silica dispersion (3))
A water glass aqueous solution having a silica component content (concentration) of 2 mass% was prepared using water glass, adjusted to pH 10 and stirred at 80 ° C. for 24 hours to obtain a fine particle silica dispersion (3). . The pH was adjusted using an H-type strongly acidic cation exchange resin (IR120B manufactured by Organo Corporation).
It was confirmed by observation of the TEM photograph that silica having an average particle diameter of about 10 nm was obtained.

(Preparation of carbon black dispersion)
Using the granulated carbon black (1) and (2), an aqueous carbon black solution was prepared so that the carbon black content (concentration) was 5% by mass, and a stirrer (SDRT: Satake Chemical Machinery Co., Ltd.) )), Carbon black dispersion liquids (1) and (2) were obtained by stirring for 30 minutes at a liquid temperature of 25 ° C. and a rotational speed of 10,000 min ⁻¹ .

(Preparation of compounded latex, coagulation, preparation of composite)
Blended saponified natural rubber latex or natural rubber latex, fine particle silica dispersions (1) to (3) and carbon black dispersions (1) to (2) in a blending amount as shown in Table 1, and blended latex Was prepared. After sufficiently stirring until the blended latex became uniform, the blended latex was adjusted to pH 7 with sulfuric acid and coagulated. The obtained solid was filtered to recover the rubber component, washed repeatedly with 1000 ml of water, and then dried at 110 ° C. for 2 hours to obtain composites (A) to (J).

Modified natural rubber contained in composites (A) to (E), natural rubber contained in composites (F) to (H), modified natural rubber contained in composites (I) to (J), Ken With regard to the modified natural rubber (solid rubber) and TSR, the nitrogen content, phosphorus content, and gel content were measured by the methods described below. The results are shown in Table 2.

(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 the average value was obtained from the measurement results of three times to obtain the nitrogen content.

(Measurement of phosphorus content)
The phosphorus content of the sample was determined using an ICP emission spectrometer (ICPS-8100, manufactured by Shimadzu Corporation).

(Measurement of gel content)
A sample of 70.00 mg cut to 1 mm × 1 mm was weighed, 35 mL of toluene was added thereto, and the mixture was allowed to stand in a cool dark place for 1 week. Subsequently, centrifugation was performed to precipitate a gel component insoluble in toluene, the soluble component of the supernatant was removed, and only the gel component was solidified with methanol, and then dried and the mass was measured. The gel content (mass%) was determined by the following formula.
Gel content (mass%) = [mass mg after drying / mg of initial sample] × 100

As shown in Table 2, in the HPNR forming the complexes (A) to (E) and (I) to (J), the phosphorus content, nitrogen, compared to the complexes (F) to (H) and TSR The content and gel content were reduced.

(Production of rubber test piece)
In accordance with the formulation shown in Table 3, 1.7 L Banbury was used to knead chemicals other than sulfur and a vulcanization accelerator. Next, using a roll, sulfur and a vulcanization accelerator were added to the obtained kneaded product and kneaded to obtain an unvulcanized rubber composition.
The obtained unvulcanized rubber composition was press vulcanized at 150 ° C. for 30 minutes to obtain a vulcanized product.
In Comparative Examples 6 to 7 using TSR and Comparative Examples 1 to 3 using natural rubber latex, mastication was performed in advance.
Each unvulcanized rubber composition and vulcanizate obtained were evaluated as follows, and the results are shown in Table 3.

(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 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 7) / (ML _{1 + 4 of} each formulation) × 100

(Rolling resistance)
Loss tangent (tan δ) of each compound (vulcanized product) using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.) under the conditions of a temperature of 50 ° C., an initial strain of 10%, a dynamic strain of 2%, and a frequency of 10 Hz. Was measured, and the loss coefficient tan δ of Comparative Example 7 was taken as 100 and expressed as an index according to the following formula (rolling resistance index). The larger the index, the better the rolling resistance characteristics (low fuel consumption).
(Rolling resistance index) = (tan δ of Comparative Example 7) / (tan δ of each formulation) × 100

(Abrasion test)
Using a Lambourn abrasion tester, the Lambourn abrasion amount was measured under the conditions of a temperature of 20 ° C., a slip ratio of 20% and a test time of 2 minutes. Further, the volume loss amount was calculated from the measured amount of lamborn wear, and the volume loss amount of each compound (vulcanized product) was displayed as an index according to the following formula, with the volume loss amount of Comparative Example 7 being 100. In addition, it shows that it is excellent in abrasion resistance, so that a Lambourn abrasion index is large.
(Lambourn wear index) = (volume loss amount of Comparative Example 7) / (volume loss amount of each formulation) × 100

(Rubber strength)
A vulcanized product was used to prepare a No. 3 dumbbell-shaped rubber test piece, which was subjected to a tensile test according to JIS K6251 “Vulcanized rubber and thermoplastic rubber-Determination of tensile properties”. The time elongation (EB) was measured, and the product (TB × EB) was calculated. The rubber strength (TB × EB) of each compound (vulcanized product) was indicated by an index according to the following formula. In addition, it shows that it is excellent in rubber strength, so that a rubber strength index is large.
(Rubber Strength Index) = (TB × EB of each formulation) / (TB × EB of Comparative Example 7) × 100

(Weatherability)
In accordance with JIS-K6266, a direct outdoor exposure test was performed, and then the tensile test was performed to measure the rubber strength before and after the exposure. The rubber strength residual ratio of each compound was calculated from the following calculation formula, and the weather resistance was displayed as an index. In addition, it shows that it is excellent in a weather resistance, so that an index | exponent is large.
(Rubber strength residual ratio) = (TB × EB after exposure) / (TB × EB before exposure) × 100
(Weather resistance index) = (Rubber strength residual ratio of each compound) / (Rubber strength residual ratio of Comparative Example 7) × 100

(Storage curability)
After the unvulcanized rubber composition was deteriorated at 70 ° C. for 168 hours in accordance with the accelerated deterioration test A-2 method of JIS-K6257, the Mooney viscosity of the unvulcanized rubber composition before and after deterioration was determined in accordance with JIS K6300. It was measured. The rate of change was defined as storage curability, and the storage curability of each formulation was indicated by an index from the following formula. In addition, it shows that it is excellent in storage curability, so that an index | exponent is large.
(Storage curability) = (Mooney viscosity after exposure) / (Mooney viscosity before exposure) × 100
(Storage curability index) = (Storage curability of Comparative Example 7) / (Storage curability of each formulation) × 100

From the results of Table 3, in Examples using composites obtained from blended latex obtained by mixing saponified natural rubber latex, fine particle silica dispersion produced from water glass and carbon black dispersion, the dispersibility of the filler is greatly increased. Therefore, the wear resistance, fracture performance, weather resistance, and storage curability were greatly improved. In addition, the fuel efficiency was excellent. Furthermore, compared with Comparative Examples 6 to 7 where mastication was performed in advance, the machinability was excellent even though mastication was not performed.

Moreover, since the rubber composition of the Example manufactured with the said manufacturing method has high filler dispersibility, even if it compares with the comparative examples 8-9 produced in the normal kneading | mixing process using saponified natural rubber, silica, and carbon black. All performance was excellent.

Furthermore, Comparative Examples 1 to 3 and carbon black using a composite obtained from a compounded latex obtained by mixing a normal natural rubber latex, a fine particle silica dispersion prepared from water glass, and a carbon black dispersion are used in a normal kneading step. Even when compared with the added Comparative Examples 4 to 5, excellent performance was exhibited.

Claims (8)

A coagulated product of a blended latex obtained by mixing a modified natural rubber latex obtained by saponifying natural rubber latex , a fine particle silica dispersion having an average particle diameter of 100 nm or less produced from water glass , and a carbon black dispersion. A composite obtained by washing and adjusting the phosphorus content in the rubber to 200 ppm or less. The composite according to claim 1, wherein the rubber has a nitrogen content of 0.3% by mass or less and a gel content measured as a toluene insoluble content in the rubber is 20% by mass or less. The composite according to claim 1 or 2, wherein an average particle diameter of carbon black in the carbon black dispersion is 100 nm or less. The average particle diameter of the carbon black in carbon black dispersion is 60nm or less, the complex according to any one of claims 1 to 3 mean particle size of the silica of the fine silica dispersion liquid is 20nm or less. The fine particle silica dispersion is prepared by adjusting the pH of a water glass aqueous solution to 9 to 11 using an ion exchange resin, and the average particle diameter of silica in the dispersion is 20 nm or less. Item 5. The complex according to any one of Items 1 to 4 . Step (I) of preparing the compounded latex by mixing the modified natural rubber latex, the fine particle silica dispersion and the carbon black dispersion, and the step of coagulating the compounded latex obtained in the step (I) (II ), and then washing the obtained coagulated product in the step (II), according to any one of claims 1 to 5 including the step (III) for adjusting the phosphorus content in the rubber 200ppm or less of the complex Production method. The rubber composition containing the composite_body | complex in any one of Claims 1-5 . A pneumatic tire produced using the rubber composition according to claim 7 .