JP6181426B2 - Masterbatch, production method, rubber composition and pneumatic tire - Google Patents

Description

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

For the purpose of reducing the fuel consumption of rubber compositions, natural rubber, which is widely used as a rubber component, has been studied to reduce fuel consumption by modification. Patent Document 1 discloses that a surfactant is added to natural rubber latex. However, the reduction of protein and gel content is not sufficient, and further reduction of tan δ is desired.

Natural rubber, on the other hand, has a high Mooney viscosity compared to other synthetic rubbers and poor processability, and is usually used after mastication with a masticant added to reduce Mooney viscosity. The nature is bad. Furthermore, the molecular chain of natural rubber is cleaved by mastication, which causes a problem that characteristics (such as good fuel efficiency) of the high molecular weight polymer inherent to natural rubber are lost.

In addition, normal natural rubber does not deteriorate under aging conditions at 80 ° C. for about 18 hours, whereas in modified natural rubber from which proteins and the like have been highly removed, deterioration of the rubber is observed under the same conditions. There is also a problem that it is inferior in heat aging resistance.

For the purpose of reinforcing the rubber composition and improving the modulus (complex elastic modulus), there is a method of blending the rubber composition with microfibrillated plant fibers such as cellulose fibers as a filler. However, since the microfibrillated plant fiber has a strong self-aggregating power and poor compatibility with the rubber component, the dispersibility during rubber kneading is low. Therefore, even if it mix | blends, performances, such as low fuel consumption, may deteriorate, and the method of improving the dispersibility of microfibrillated plant fiber is also calculated | required.

As described above, it is generally difficult to improve fuel economy and heat aging in a well-balanced manner while obtaining excellent processability in a masterbatch blended with natural rubber and cellulose fiber, and improvements are required. .

Japanese Patent No. 3294901

The present invention solves the above-mentioned problems and obtains excellent processability while improving fuel economy and heat aging in a well-balanced manner, a masterbatch production method, a rubber composition containing the masterbatch, and An object of the present invention is to provide a pneumatic tire produced using the rubber composition.

The present invention relates to a masterbatch produced by mixing isoprene-based rubber and microfibrillated plant fiber, adjusting the pH of the resulting mixture to 2-6 and solidifying.

The isoprene-based rubber is preferably an isoprene-based rubber latex.

It is preferable that the isoprene-based rubber is obtained by removing non-rubber components.

The content of the microfibrillated plant fiber with respect to 100 parts by mass of the isoprene-based rubber is preferably 0.1 to 30 parts by mass.

The phosphorus content of the isoprene-based rubber is preferably 200 ppm or less.

The present invention also relates to a method for producing the masterbatch comprising the step (I) of mixing isoprene-based rubber latex and microfibrillated plant fibers, and adjusting the pH of the resulting mixture to 2 to 6 for coagulation.

The present invention also relates to a tire rubber composition comprising the masterbatch, wherein the content of the microfibrillated plant fiber relative to 100 parts by mass of the rubber component is 0.1 to 30 parts by mass.

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

According to the present invention, since it is a masterbatch prepared by mixing isoprene-based rubber and microfibrillated plant fibers and adjusting the pH of the resulting mixture to 2 to 6 and solidifying, excellent processability The performance balance of low fuel consumption and heat aging resistance is significantly improved.

〔Master Badge〕
The master batch of the present invention is produced by mixing isoprene-based rubber and microfibrillated plant fiber, and adjusting the pH of the resulting mixture to 2 to 6 to solidify.

Conventionally, microfibrillated plant fibers can be dispersed in a masterbatch, but when the masterbatch is blended in a rubber composition, it is difficult to uniformly disperse in the rubber composition. However, there were problems in terms of processability and rubber properties. The master batch of the present invention solves these problems by adopting a method of adjusting the pH of the isoprene-based rubber and the microfibrillated plant fiber mixture to 2 to 6 and solidifying the mixture. That is, by adopting this method, when natural rubber is used, proteins and phospholipids in the rubber are removed, and microfibrillated plant fibers are uniformly dispersed in the rubber composition. It is possible to obtain high processability, low fuel consumption and heat aging resistance.

The masterbatch of the present invention is prepared by mixing isoprene-based rubber and microfibrillated plant fiber and adjusting the pH of the resulting mixture to 2-6 to solidify, that is, isoprene-based rubber and microfibrillated plant fiber. It is produced by a production method including the step (I) of mixing and adjusting the pH of the obtained mixture to 2 to 6 to solidify.

Examples of the isoprene-based rubber include natural rubber (NR), epoxidized natural rubber (ENR), isoprene rubber (IR), and highly purified natural rubber (HPNR).

In the present invention, modified isoprene-based rubber having a phosphorus content of 200 ppm or less can be suitably used as the isoprene-based rubber. The modified isoprene-based rubber is obtained by removing non-rubber components. When it is 200 ppm or less, the amount of gel during storage is difficult to increase, tan δ of the vulcanized rubber is lowered and fuel economy is improved, and the Mooney viscosity of the unvulcanized rubber is improved and the processability is improved. . The phosphorus content is preferably 200 ppm or less, 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).

In the isoprene-based rubber, the nitrogen content is preferably 0.3% by mass or less, and more preferably 0.15% by mass or less. When the nitrogen content exceeds 0.3% by mass, the Mooney viscosity increases during storage and the processability tends to deteriorate, and the fuel efficiency may also deteriorate. The nitrogen content can be measured by a conventional method such as Kjeldahl method. Nitrogen is derived from protein.

It is preferable that the isoprene-based rubber is substantially free of phospholipid. “Substantially no phospholipid is present” represents a state in which a natural rubber sample is extracted with chloroform and a peak due to phospholipid does not exist at −3 ppm to 1 ppm in ³¹ P NMR measurement of the extract. The peak of phosphorus present at -3 ppm to 1 ppm is a peak derived from the phosphate structure of phosphorus in the phospholipid.

In the present invention, as the isoprene-based rubber, modified natural rubber latex such as natural rubber latex and saponified natural rubber latex, isoprene-based rubber latex such as epoxidized natural rubber latex and isoprene rubber latex can be suitably used.

That is, the masterbatch of the present invention is prepared by mixing the isoprene-based rubber latex and the microfibrillated plant fiber, adjusting the pH of the resulting mixture to 2 to 6 and coagulating (I). It can manufacture suitably. Specifically, a blended latex (mixed solution) is prepared by adding microfibrillated plant fibers to isoprene-based rubber latex and stirring, and then adjusting the pH to 2 to 6 using an acid or the like. It can be produced by coagulating the compounded latex. Thereby, the composite_body | complex in which the microfibrillated plant fiber was disperse | distributed uniformly in isoprene-type rubber | gum can be manufactured. In addition, it is preferable to move to the next operation, that is, stirring and coagulation in a short time after adding the microfibrillated plant fiber.

Among the isoprene-based rubber latexes, modified natural rubber latexes such as natural rubber latex and saponified natural rubber latex can be preferably used. In the present invention, even when natural rubber latex containing non-rubber components such as phosphorus and nitrogen is used, this is combined with the microfibrillated plant fiber, and is coagulated by adjusting to a predetermined pH. Even without using a rubber latex from which non-rubber components such as natural rubber latex have been removed, the non-rubber components are sufficiently removed. Therefore, even when a normal natural rubber latex is used as the isoprene-based rubber, the effects of the present invention can be sufficiently obtained.

Natural rubber latex is collected as the sap of natural rubber trees such as Hevea trees, 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.

The natural rubber latex may be mixed with the microfibrillated plant fiber as it is, but a saponified one may be used in advance. The saponification treatment can be performed by adding an alkali such as NaOH and a surfactant as necessary to natural rubber latex and allowing to stand at a predetermined temperature for a certain time. In addition, you may perform stirring etc. as needed. By performing the saponification treatment in the latex state, each particle of the natural rubber is uniformly treated, and the saponification treatment can be performed efficiently. When the saponification treatment is performed, the phosphorus compound separated by the saponification is removed, so that the phosphorus content in the natural rubber contained in the prepared master batch 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.

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.

Examples of microfibrillated plant fibers (cellulose nanofibers) include those derived from natural products such as wood, bamboo, hemp, jute, kenaf, crop residue, cloth, recycled pulp, waste paper, bacterial cellulose, and squirt cellulose. Can be mentioned. Although it does not specifically limit as a manufacturing method of microfibrillated plant fiber, For example, after processing the said natural product with chemical | medical agents, such as sodium hydroxide, a refiner, a twin-screw kneading machine (double-screw extruder), a twin-screw mixing Examples of the method include mechanical pulverization or beating using a smelting extruder, a high-pressure homogenizer, a medium stirring mill, a stone mill, a grinder, a vibration mill, a sand grinder, and the like.

The microfibrillated plant fiber may be added to the isoprene-based rubber latex in an aqueous solution (microfibrillated plant fiber aqueous solution) dispersed in water, or after the microfibrillated plant fiber is directly input to the isoprene-based rubber latex. If necessary, it may be diluted with water. From the viewpoint that the microfibrillated plant fiber can be well dispersed, it is preferable to add the microfibrillated plant fiber aqueous solution to the isoprene-based rubber latex. In the microfibrillated plant fiber aqueous solution, the content (solid content) of the microfibrillated plant fiber is preferably 0.2 to 20% by mass, more preferably 0.5 to 10% by mass, and still more preferably 0.5 to 3% by mass.

The loosening state (cutting state) of the microfibrillated plant fiber can be judged by the viscosity of the aqueous solution of the microfibrillated plant fiber. The higher the viscosity, the more the fiber is loosened (the fiber is cut and shortened). Means that. The viscosity of the microfibrillated plant fiber aqueous solution is preferably 50 mPa · s or more, more preferably 80 mPa · s or more. If it is less than 50 mPa · s, the fibers are not sufficiently loosened and sufficient reinforcing properties may not be obtained. In addition, the fiber mass becomes a fracture nucleus, and the elongation at break may be reduced. The viscosity of the microfibrillated plant fiber aqueous solution is preferably 200 mPa · s or less, more preferably 150 mPa · s or less. When it exceeds 200 mPa · s, the aqueous solution becomes difficult to be stirred, and the fibers around the stirring rotor are locally pulverized, which may make it difficult to pulverize uniform fibers. Further, kneading with the saponified natural rubber latex may be difficult.
The viscosity of the aqueous solution of microfibrillated plant fibers is such that the aqueous solution of microfibrillated plant fibers containing 0.5% by mass of microfibrillated plant fibers and 99.5% by mass of water is measured at room temperature (23 (° C.).
Moreover, the degree of loosening of the microfibrillated plant fiber can be adjusted by the stirring speed, stirring time, etc. of the microfibrillated plant fiber aqueous solution. The faster the stirring speed and the longer the stirring time, the more the fibers can be loosened. In addition, it is possible to loosen the fibers efficiently by appropriately selecting the type of homogenizer used for stirring, the shape of the rotating teeth, and the shearing ability.

The step of mixing the isoprene-based rubber latex and the microfibrillated plant fiber to produce these mixtures can be prepared by sequentially dropping them, injecting them, etc., and then mixing them by a known method.

When adjusting the pH of the obtained mixture to 2-6 and solidifying, the said pH becomes like this. Preferably it is 3-6, More preferably, it is 3.5-6. Here, pH adjustment can be performed by adding an acid, a base, or the like. By adjusting the pH during coagulation to 2 to 6, even when natural rubber is used, the rubber component in the coagulated product can be highly purified. Specifically, non-rubber components such as proteins and phospholipids in natural rubber are removed and purified, and fuel efficiency and processability are improved. In addition, the deterioration of the rubber is likely to proceed by removing the non-rubber component, etc., but since the decrease in the molecular weight of the rubber during storage is suppressed by adjusting the pH during solidification to a predetermined range, it is favorable. Heat aging resistance is obtained. Therefore, the performance balance of low fuel consumption, heat aging resistance and processability can be remarkably improved.

Here, the purification of natural rubber means removing impurities such as phospholipids and proteins other than natural polyisoprenoid components. Natural rubber has a structure in which the isoprenoid component is covered with the impurity component. By removing the component, the structure of the isoprenoid component changes, and the interaction with the compounding agent changes, resulting in energy. It is assumed that loss can be reduced, durability can be improved, and a better masterbatch can be obtained.

Methods for coagulating the mixture include acid coagulation, salt coagulation, methanol coagulation, etc., but in order to coagulate the microfibrillated plant fiber uniformly dispersed in the masterbatch, acid coagulation, salt coagulation, or these Is preferred, and acid coagulation is more preferred. Examples of the acid for coagulation include formic acid, sulfuric acid, hydrochloric acid, acetic acid and the like, and sulfuric acid is preferable from the viewpoint of cost. Examples of the salt include 1 to 3 metal salts (calcium salts such as sodium chloride, magnesium chloride, calcium nitrate, and calcium chloride).

When the mixture is rapidly solidified, the microfibrillated plant fibers are hardened in a hairball shape and taken into isoprene-based rubber latex, and the microfibrillated plant fibers tend to be difficult to disperse. Therefore, the coagulation of the mixture is preferably performed under conditions such that the microfibrillated plant fiber is gently taken into the isoprene-based rubber latex. From such a viewpoint, when the mixture is solidified, the temperature of the mixture is preferably 40 ° C. or less, and more preferably 35 ° C. or less. From the same viewpoint, it is preferable to add the above-mentioned coagulants such as acid, salt, methanol and the like in stages (the whole amount is added in divided portions).

(Process (II))
You may wash | clean the coagulated material (aggregate containing aggregate rubber | gum and microfibrillated plant fiber) obtained by process (I) as needed. That is, the obtained solidified product may be further subjected to a washing treatment to adjust the amount of phosphorus or nitrogen to a desired amount.

Examples of the washing method include a method of centrifuging after diluting the rubber component with water, and a method of allowing the rubber component to stand still after diluting with the water to float or precipitate the rubber and discharge only the aqueous phase. When centrifuging, first, it is diluted with water so that the rubber content of the isoprene-based rubber latex is 5 to 40% by mass, preferably 10 to 30% by mass, and then centrifuged at 5000 to 10000 rpm for 1 to 60 minutes. The washing may be repeated until the desired phosphorus content is obtained. In addition, even when the rubber is allowed to stand and float or precipitate, washing may be repeated until the desired phosphorus content is obtained by repeatedly adding water and stirring.
The washing method is not limited to these, and the solution may be washed by removing the liquid phase after neutralization with weak alkaline water such as sodium carbonate so that the pH is in the range of 6-7.

After washing as necessary, it is usually dried by a known method (oven, reduced pressure, etc.). When the rubber is kneaded with a biaxial roll, a Banbury mixer or the like after drying, a crumb-like masterbatch containing isoprene-based rubber and microfibrillated plant fibers is obtained. The masterbatch is preferably formed into a sheet having a thickness of several centimeters by a rolling roll in order to improve unity and handling properties. In addition, the said masterbatch may contain another component in the range which does not inhibit the effect of this invention.

In the master batch, the content of the microfibrillated plant fiber with respect to 100 parts by mass of the isoprene-based rubber is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, and further preferably 3 parts by mass or more. If the amount is less than 0.1 parts by mass, the amount of the modified natural rubber will be too large and the crosslinking density will be low when trying to secure the necessary microfibrillated plant fiber in the rubber composition containing the masterbatch. Thus, the fuel efficiency may be deteriorated. Moreover, this content becomes like this. Preferably it is 30 mass parts or less, More preferably, it is 20 mass parts or less, More preferably, it is 10 mass parts or less. If it exceeds 30 parts by mass, the dispersibility of the microfibrillated plant fiber may be lowered, and the fuel efficiency may be deteriorated.

[Rubber composition for tire]
The rubber composition for tires of this invention contains the said masterbatch. By using the masterbatch, a rubber composition in which microfibrillated plant fibers are uniformly dispersed in a highly purified isoprene-based rubber can be obtained. As a result, it is possible to prevent the deterioration of physical properties of rubber in the kneading step and improve the dispersion of fillers and the like, and to remarkably improve the performance balance between low fuel consumption and heat aging resistance while obtaining excellent processability.

In the rubber composition of the present invention, the content of isoprene-based rubber in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 50% by mass or more, and further preferably 80% by mass. If it is less than 5% by mass, excellent fuel efficiency may not be obtained.

Examples of rubber components that can be used other than the isoprene-based rubber include butadiene rubber (BR), styrene butadiene rubber (SBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), and the like.

In the rubber composition of the present invention, the content of the microfibrillated plant fiber is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, further preferably 3 parts by mass with respect to 100 parts by mass of the rubber component. That's it. Moreover, this content becomes like this. Preferably it is 30 mass parts or less, More preferably, it is 20 mass parts or less, More preferably, it is 10 mass parts or less. There exists a possibility that the effect by mix | blending microfibrillated plant fiber may not be acquired as it is less than 0.1 mass part. If it exceeds 30 parts by mass, the dispersibility of the microfibrillated plant fiber may be lowered, and the fuel efficiency may be deteriorated.

The rubber composition of the present invention preferably contains carbon black and / or a white filler. Thereby, the reinforcement effect is acquired.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 70 m ² / g or more, and more preferably 100 m ² / g or more. There exists a tendency for sufficient reinforcement effect not to be acquired as it is less than 70 m < ² > / g. _N 2 SA is preferably at most 200 meters ² / g of carbon black, 180 m ² / g or less is more preferable. If it exceeds 200 m ² / g, the fuel efficiency tends to decrease. In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required by A method of JISK6217.

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.

The content of carbon black is preferably 10 parts by mass or more, more preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. The content is preferably 150 parts by mass or less, more preferably 100 parts by mass or less. Within the above range, good fuel efficiency can be obtained.

In the rubber composition of the present invention, the total content of carbon black and white filler is preferably 10 parts by mass or more, more preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. The content is preferably 150 parts by mass or less, more preferably 100 parts by mass or less. Within the above range, good fuel efficiency can be obtained.

In addition to the above materials, the rubber composition of the present invention includes zinc oxide, stearic acid, various antioxidants, softeners (oil, wax, etc.), vulcanizing agents (sulfur, organic peroxides, etc.), additives Various materials generally used in the tire industry such as a sulfur accelerator (sulfenamide-based, guanidine-based vulcanization accelerator, etc.) may be appropriately blended.

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 or a Banbury mixer, and then vulcanized. Can be manufactured.

The rubber composition of the present invention includes a cap tread, a base tread, an under tread, a clinch apex, a bead apex, a sidewall, a breaker, an edge band, a full band, a breaker cushion rubber, a rubber for covering a carcass cord, and a run flat reinforcing layer. It can be suitably used for tire members such as insulation, chafer, and inner liner, belts, rolls, and the like.

The tire of the present invention is produced by a usual method using the rubber composition. That is, a rubber composition containing various materials as necessary is extruded in accordance with the shape of each member (tread, etc.) of the tire at an unvulcanized stage, and is processed on a tire molding machine by a normal method. After forming an unvulcanized tire by molding, it can be manufactured by heating and pressing in a vulcanizer.

Examples of the tire of the present invention include a pneumatic tire and an airless (solid) tire. Among them, a pneumatic tire is preferable.

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.
Field Latex: Field Latex Emar E-27C (surfactant) obtained from Muhiba Latex Co., Ltd .: Emar E-27C (Polyoxyethylene lauryl ether sodium sulfate, 27% by mass of active ingredient) manufactured by Kao Corporation
NaOH: NaOH manufactured by Wako Pure Chemical Industries, Ltd.
Wingstay L (anti-aging agent): WINGSTAY L (compound obtained by butylating the condensate of ρ-cresol and dicyclopentadiene) manufactured by ELIOKEM
Emulvin W (surfactant): Emalvin W (aromatic polyglycol ether) manufactured by LANXESS
Tamol NN9104 (surfactant): Tamol NN9104 manufactured by BASF (Naphthalenesulfonic acid / formaldehyde sodium salt)
Van gel B (surfactant): Van gel B (magnesium aluminum silicate hydrate) manufactured by Vanderbilt
Microfibrillated plant fiber: Neofiber coagulant manufactured by Oji Bag Co., Ltd .: 1% sulfuric acid NR: TSR20 manufactured by Wako Pure Chemical Industries, Ltd.
Carbon black: N220 (N ₂ SA: 111 m ² / g) manufactured by Cabot Japan
Zinc oxide: 2 types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Beads stearic acid anti-aging agent manufactured by NOF Corporation: NOCRACK 6C (N-phenyl-) manufactured by Ouchi Shinsei Chemical Co., Ltd. N ′-(1,3-dimethylbutyl) -p-phenylenediamine) (6PPD)
Sulfur: Seimi Sulfur (oil content: 10%) manufactured by Nippon Kiboshi Kogyo Co., Ltd.
Vulcanization accelerator: Noxeller NS manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

<Examples , reference examples, and comparative examples>
(Preparation of anti-aging agent dispersion)
462.5 g of water was mixed with 12.5 g of Emulvin W, 12.5 g of Tamol NN9104, 12.5 g of Van gel B, and 500 g of Wingstay L (total of 1000 g) for 16 hours by a ball mill to prepare an antioxidant dispersion.

(Preparation of microfibrillated plant fiber aqueous solution)
After diluting the microfibrillated plant fiber with 200 times (mass ratio) of water, the mixture was stirred for 2 hours using a magic LAB (circulation type / MK colloid mill) manufactured by IKA Japan, and the microfibrillated plant fiber was 1 A microfibrillated plant fiber aqueous solution containing 99% by mass of water and 99% by mass of water was obtained. The viscosity of the aqueous solution of microfibrillated plant fibers was measured at room temperature (23 ° C.) using a tuning fork type vibration viscometer (SV-10 manufactured by A & D Co., Ltd.), and is shown in Table 1.

(Production Example 1)
After adjusting the solid content concentration (DRC) of the field latex to 30% (w / v), 25 g of 10% Emar E-27C aqueous solution and 60 g of 25% NaOH aqueous solution were added to 1000 g of the latex and saponified for 24 hours at room temperature. Reaction was performed to obtain a saponified natural rubber latex. The obtained saponified natural rubber latex and the microfibrillated plant fiber aqueous solution were weighed and mixed so as to have a mass ratio shown in Table 1 when dried, and a cylindrical homogenizer (Automixer Model 20 manufactured by Primix Co., Ltd.) ) For 1 hour at 8000 rpm. Next, 6 g of the anti-aging dispersion was added and stirred for 2 hours, and then further diluted with water to a rubber concentration of 15% (w / v). Next, a coagulant is added with slow stirring to adjust the pH to 4.0 to obtain a coagulated product, which is then squeezed with a water squeezing roll to form a sheet, and then dried at 90 ° C. for 4 hours. Master batch 1 (MB1) was obtained.

(Production Example 2)
Masterbatch 2 (MB2) was obtained in the same procedure except that the pH was adjusted to 5.2 in Production Example 1.

(Production Example 3)
Masterbatch 3 (MB3) was obtained in the same procedure except that the pH was adjusted to 5.7 in Production Example 1.

(Production Example 4)
A master batch 4 (MB4) was obtained in the same procedure except that the pH was adjusted to 3.5 in Production Example 1.

(Production Example 5)
A latex in which the solid content concentration (DRC) of the field latex is adjusted to 30% (w / v) and a microfibrillated plant fiber aqueous solution are weighed and mixed so that the mass ratio shown in Table 1 is obtained when dried. It stirred for 1 hour on condition of 8000 rpm using the type | mold homogenizer (Automixer 20 type | mold by PRIMIX Co., Ltd.). Next, 6 g of the anti-aging dispersion was added and stirred for 2 hours, and then further diluted with water to a rubber concentration of 15% (w / v). Next, a coagulant is added with slow stirring to adjust the pH to 5.0 to obtain a coagulated product, which is then squeezed with a water squeezing roll to form a sheet, and then dried at 90 ° C. for 4 hours. Master batch 5 (MB5) was obtained.

(Comparative Production Example 1)
Master batch 6 (MB6) was obtained in the same procedure except that the pH was adjusted to 8.0 in Production Example 1.

(Comparative Production Example 2)
Master batch 7 (MB7) was obtained in the same procedure except that the pH was adjusted to 8.8 in Production Example 1.

(Comparative Production Example 3)
Master batch 8 (MB8) was obtained in the same procedure except that the pH was adjusted to 8.1 in Production Example 5.

(Comparative Production Example 4)
A master batch 9 (MB9) was obtained in the same procedure except that the pH was adjusted to 8.5 in Production Example 5.

The physical properties of rubber contained in MB1 to MB9 were evaluated as follows, and the results are shown in Table 1.

<Measurement of nitrogen content>
The nitrogen content was quantified with a gas chromatograph after pyrolysis.

<Measurement of phosphorus content>
The phosphorus content was determined using an ICP emission spectrometer (P-4010, manufactured by Hitachi, Ltd.).
In addition, ³¹ P-NMR measurement of phosphorus uses an NMR analyzer (400 MHz, AV400M, manufactured by Nippon Bruker Co., Ltd.), and the measurement peak of P atom in 80% phosphoric acid aqueous solution is used as a reference point (0 ppm) for rubber with chloroform. The component extracted from the sample was purified, dissolved in CDCl ₃ and measured.

<Heat aging resistance>
The weight average molecular weight of each rubber before and after aging was measured, and the heat aging resistance was evaluated by calculating the molecular weight retention rate according to the following formula. The aging treatment was carried out by storing each rubber component in an oven at 80 ° C. for 72 hours, and the weight average molecular weight was measured using isoprene as a standard substance using a gel permeation chromatograph. The larger the value, the better the heat aging resistance.
(Heat aging resistance) = Molecular weight after aging / Molecular weight before aging × 100 (%).

According to Table 1, the master batch obtained by the method including the step of adjusting the pH at the time of coagulation to 2 to 6 was excellent in heat aging resistance as compared with the master batch having a pH outside the range. Also, the nitrogen content and phosphorus content were reduced.

<Preparation of vulcanized rubber composition>
In accordance with the formulation shown in Table 2, chemicals other than sulfur and a vulcanization accelerator were kneaded using a 1.7 L Banbury mixer manufactured by Kobe Steel. Next, using an open roll, sulfur and a vulcanization accelerator were added to the kneaded product and kneaded to obtain an unvulcanized rubber composition. Next, the obtained unvulcanized rubber composition was pressed with a 2 mm thick mold at 150 ° C. for 30 minutes to obtain a vulcanized rubber composition. The obtained unvulcanized rubber composition and vulcanized rubber composition were evaluated as follows. The results are shown in Table 2.

<Mooney viscosity (ML (1 + 4))>
The Mooney viscosity of the unvulcanized rubber composition was measured at 130 ° C. according to JIS K6300: 2001-1. At the time of molding, when the Mooney viscosity (130 ° C.) is 30 to 70, workability is good, and when it is 35 to 60, it is better.

<Rolling resistance>
Using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), loss tangent (tan δ) of each compound (vulcanized product) under the conditions of temperature 70 ° C., initial strain 10%, dynamic strain 1%, frequency 10 Hz. ) Was measured, and the rolling resistance index of Comparative Example 1 was set to 100, which was calculated by the following formula. The smaller the rolling resistance index, the lower the rolling resistance, which is preferable.
(Rolling resistance index) = (tan δ of each formulation) / (tan δ of Comparative Example 1) × 100

From Table 2, it was clarified that in Examples using Master Batches 1 to 4 , the performance balance of low fuel consumption and heat aging resistance was remarkably improved while obtaining excellent processability.

Claims (6)

A method for producing a masterbatch comprising a step of mixing isoprene-based rubber having a phosphorus content of 200 ppm or less and microfibrillated plant fibers, and adjusting the pH of the resulting mixture to 2 to 6 for solidification. The method for producing a masterbatch according to claim 1, wherein the isoprene-based rubber is an isoprene-based rubber latex. The method for producing a masterbatch according to claim 1 or 2, wherein the isoprene-based rubber has a non-rubber component removed. The method for producing a masterbatch according to claim 1 or 2, wherein a content of the microfibrillated plant fiber is 0.1 to 30 parts by mass with respect to 100 parts by mass of the isoprene-based rubber. Including a step of kneading the masterbatch obtained by the method for producing a masterbatch according to any one of claims 1 to 4 with other components ,
The manufacturing method of the rubber composition for tires whose content of the said microfibrillated plant fiber with respect to 100 mass parts of rubber components is 0.1-30 mass parts. The pneumatic tire manufacturing method for manufacturing a pneumatic tire using the rubber compositions obtained by the process of claim 5 the rubber composition.