JP6381415B2 - Method for producing vulcanized rubber composition, vulcanized rubber composition and studless tire using the same - Google Patents

Description

  The present invention relates to a method for producing a vulcanized rubber composition, a vulcanized rubber composition, and a studless tire using the same.

  Conventionally, spike tires have been used for running on icy and snowy road surfaces, and chains have been attached to tires. Studless tires have been developed as countermeasures to environmental problems such as dust problems. Studless tires have been devised in terms of materials and design in order to improve low-temperature characteristics. For example, rubber compositions containing a large amount of mineral oil in diene rubber with excellent low-temperature characteristics are used. However, generally, when the amount of mineral oil is increased, the wear resistance decreases.

  On snowy and snowy road surfaces, the coefficient of friction of the tire is significantly lower than on ordinary roads, making it more slippery. For studless tires, not only low-temperature characteristics but also snow / snow performance (grip performance on snow and snow) and wear resistance are balanced. It is required to prepare well. However, the performance on ice and snow often contradicts the wear resistance performance, and it is generally difficult to improve both performances at the same time.

  In order to improve performance on snow and snow and wear resistance in a well-balanced manner, a technique for blending a large amount of silica and a softening agent has been found (Patent Document 1). There is room for.

  In addition, as a method for improving various tire performances such as low temperature performance, performance on snow and snow, and wear resistance performance in a well-balanced manner, a method (polymer blend) in which a plurality of polymer (rubber) components are blended has been performed for a long time. Specifically, as a rubber component in a tire, blending several polymer components represented by styrene butadiene rubber (SBR), butadiene rubber (BR), and natural rubber (NR) has become mainstream. . This is a means for drawing out the physical properties of a rubber composition that cannot be achieved by a single polymer component by utilizing the characteristics of each polymer component.

  In this polymer blend, the phase structure (morphology) of each rubber component after vulcanization and the distribution of the filler to each rubber phase (uneven distribution) are important factors that determine physical properties. Factors that determine the control of morphology and uneven distribution of fillers are very complex, and many studies have been made so far to develop tire properties in a well-balanced manner, but there is room for improvement.

  For example, Patent Document 2 discloses a technique that defines the island phase particle size and silica distribution of a sea-island matrix of a tire tread rubber composition containing styrene-butadiene rubber. However, the specific method that can realize the morphology is only described that the silica masterbatch is used to adjust the kneading time and the rotational torque of the rotor. In such a method, the kneading and vulcanizing conditions are described. Therefore, stable morphology control was difficult. Further, the rubber components disclosed in the examples are also of styrene butadiene rubbers having relatively close polarities, and the rubber components having different polarities, i.e., affinity with silica, such as butadiene rubber and natural rubber are greatly different. It is clear that this technique cannot be applied in blends.

  In particular, when interphase dispersion control of silica dispersion is performed using a silica masterbatch, even if the desired morphology and silica dispersion are temporarily achieved, they often change over time, and over time over several months. It was difficult to form a stable morphology.

  Patent Document 3 discloses a technique for controlling the morphology of a compounding system including natural rubber and butadiene rubber and the uneven distribution of silica. However, the application to the butadiene rubber side in the case where butadiene rubber having a disadvantageous distribution of silica becomes a continuous phase is disclosed. There is no description for silica uneven distribution control.

  Natural rubber is an important rubber component in tires, especially sidewall rubber compositions, such as excellent mechanical strength, but when compounded with butadiene rubber, it tends to cause uneven distribution of silica and controls the silica distribution status. However, in the past, sufficient morphology and silica distribution status have not been confirmed, and there have been cases where the physical properties are not sufficiently developed.

  Furthermore, in recent years, there is a tendency to modify natural rubber so as to improve the affinity with silica in order to improve fuel efficiency, and the possibility of uneven distribution of silica in natural rubber is becoming more and more remarkable.

  In recent years, high-cis butadiene rubbers with high wear resistance and low-temperature grip properties and high cis content have been often compounded. Among diene rubbers, high-cis butadiene rubbers are particularly useful with silica. Affinity is low, and when blended with natural rubber, silica tends to be hardly taken into the high-cis butadiene rubber phase. Therefore, in the conventional high cis butadiene rubber compounding system, there are cases where the compound does not exhibit sufficient physical properties without confirming the state of morphology and silica distribution.

  In particular, in the rubber composition for the sidewall, it is important to configure the rubber composition using a butadiene rubber having a performance required for the sidewall such as resistance to flex crack growth as a continuous phase. A technique for controlling the uneven distribution of silica in a continuous phase rubber component that greatly contributes is essential.

  Furthermore, natural rubber tends to be less likely to form a continuous phase than butadiene rubber, and the tendency becomes even more pronounced when the natural rubber has a blending system of 50 parts or less with respect to 100 parts of the rubber component. Will come to form. In general, the rubber component present in the island phase is hardened because the periphery is solidified with the rubber component of the continuous phase, and the rubber elasticity tends to decrease. As a result, the hardness difference from the continuous phase rubber component is increased, so that the rubber strength and the wear resistance are easily lowered. Natural rubber alone tends to be harder than butadiene rubber, and it is inherently undesirable that a difference in hardness can occur due to the uneven distribution of silica. Therefore, it is important to develop a technology that does not allow silica to be unevenly distributed on the natural rubber side.

  Morphology formation in a plurality of polymer components in a rubber composition for tires is a compatible system (single phase) or, in the case of incompatibility, a phase (island) of particulate other components in a continuous phase (sea phase). Only the islands with a sea-island structure in which the phase is present have been studied.

  For this reason, it is useful for the development of tire physical properties, but it is necessary to develop morphological control and silica distribution technology to develop good rubber physical properties in a system using a blend of butadiene rubber and natural rubber with different polarities. Has been.

JP 2011-038057 A JP 2006-089636 A JP 2006-348222 A

  The present invention relates to a method for producing a vulcanized rubber composition capable of improving the performance on ice and wear resistance in a well-balanced manner, a vulcanized rubber composition excellent in performance on ice and wear resistance, and a studless tire using the vulcanized rubber composition as a tread structure. The purpose is to provide.

The present invention
[1] (a) producing a masterbatch containing butadiene rubber and silica;
(B) producing a masterbatch containing modified natural rubber and silica;
(C) a step of kneading the master batch obtained in (a) and the master batch obtained in (b), and (d) a step of vulcanizing the kneaded product obtained in (c). A method for producing a vulcanized rubber composition comprising:
The modified natural rubber is obtained by removing a non-rubber component of natural rubber and then treating with an acidic compound, and the pH is adjusted to 2-7, preferably 3-6, more preferably 4-6 And
The vulcanized rubber composition is
A phase containing butadiene rubber and silica (BR phase) and a phase containing modified natural rubber and silica (modified NR phase);
The BR phase and the modified NR phase are incompatible with each other,
The abundance α of silica in the BR phase 100 hours to 500 hours after the completion of the vulcanization process satisfies the following formula 1.
Method for producing vulcanized rubber composition in which butadiene rubber ratio β satisfies the following formula 2 0.3 ≦ α ≦ 0.7 (preferably 0.5 ≦ α ≦ 0.6) (Formula 1)
0.45 ≦ β ≦ 0.8 (preferably 0.5 ≦ β ≦ 0.7) (Formula 2)
(Where α = silica amount in BR phase / (silica amount in BR phase + silica amount in modified NR phase)), and β = mass of butadiene rubber in vulcanized rubber composition / (vulcanized Mass of butadiene rubber in the rubber composition + mass of modified natural rubber in the vulcanized rubber composition)).
[2] The master batch containing the butadiene rubber and silica is 40 parts by mass or more, preferably 50 parts by mass or more, preferably 100 parts by mass or less, more preferably 80 parts by mass with respect to 100 parts by mass of butadiene rubber. The manufacturing method according to [1] above, which contains:
[3] The masterbatch containing the modified natural rubber and silica is 15 parts by mass or more, preferably 30 parts by mass or more, preferably 100 parts by mass or less, more preferably 100 parts by mass or more with respect to 100 parts by mass of the modified natural rubber. Is a production method according to the above [1] or [2], which contains 80 parts by mass or less
[4] The production method according to any one of [1] to [3], wherein the butadiene rubber is a butadiene rubber having a cis 1,4 bond content of 90% or more, preferably 95% or more.
[5] The vulcanized rubber composition contains 25 to 120 parts by mass of filler, preferably 30 to 70 parts by mass, and 15 softeners for 100 parts by mass of a rubber component containing modified natural rubber and butadiene rubber. -80 parts by mass, preferably 20-70 parts by mass, and the filler contains 50% by mass or more, preferably 70% by mass or more of silica, based on the total amount of filler. The production method according to any one of
[6] The production method according to any one of [1] to [5], wherein a phosphorus content in the rubber of the modified natural rubber is 200 ppm or less, preferably 150 ppm or less.
[7] The production method according to any one of [1] to [6], wherein the nitrogen content of the modified natural rubber is 0.15% by mass or less, preferably 0.1% by mass or less.
[8] The pH of the modified natural rubber is cut to a size of 2 mm square on each side and immersed in distilled water, extracted at 90 ° C. for 15 minutes while being irradiated with microwaves, and immersed The production method according to any one of [1] to [7], wherein water is a value measured using a pH meter,
[9] The heat-resistant aging index (formula 3) after heat treatment at 80 ° C. for 18 hours of the modified natural rubber is 75 to 120%, preferably 40 to 75%, more preferably 50 to 70%, and still more preferably. The production method according to any one of [1] to [8], which is 55 to 65%,
Heat aging index = Mooney viscosity after heat treatment / Mooney viscosity before heat treatment × 100 (Formula 3)
[10] A vulcanized rubber composition having a phase containing butadiene rubber and silica (BR phase) and a phase containing modified natural rubber and silica (modified NR phase),
The modified natural rubber is obtained by removing a non-rubber component of natural rubber and then treating with an acidic compound, and the pH is adjusted to 2-7, preferably 3-6, more preferably 4-6 And
The BR phase and the modified NR phase are incompatible with each other,
The abundance α of silica in the BR phase 100 hours to 500 hours after the completion of the vulcanization process satisfies the following formula 1.
Vulcanized rubber composition in which the ratio β of butadiene rubber satisfies the following formula 2 0.3 ≦ α ≦ 0.7 (preferably 0.5 ≦ α ≦ 0.6)
0.45 ≦ β ≦ 0.8 (preferably 0.5 ≦ β ≦ 0.7) (Formula 2)
(Where α = silica amount in BR phase / (silica amount in BR phase + silica amount in modified NR phase)), and β = mass of butadiene rubber in vulcanized rubber composition / (vulcanized Mass of butadiene rubber in the rubber composition + mass of modified natural rubber in the vulcanized rubber composition)).
[11] The vulcanized rubber composition according to [10], wherein the butadiene rubber is a butadiene rubber having a cis 1,4 bond content of 90% or more, preferably 95% or more.
[12] 25 to 120 parts by mass of filler, preferably 30 to 70 parts by mass, and 15 to 80 parts by mass of softener, preferably 20 to 100 parts by mass of the rubber component containing modified natural rubber and butadiene rubber. The vulcanized rubber composition according to the above [10] or [11], which contains ˜70 parts by mass, and the filler contains 50% by mass or more, preferably 70% by mass or more of silica with respect to the total amount of filler,
[13] The vulcanized rubber composition according to any one of the above [10] to [12], wherein a phosphorus content in the rubber of the modified natural rubber is 200 ppm or less, preferably 150 ppm or less,
[14] The vulcanized rubber according to any one of [10] to [13], wherein the nitrogen content of the modified natural rubber is 0.15% by mass or less, preferably 0.1% by mass or less. Composition,
[15] The modified natural rubber has a pH of less than 2 mm square on each side, soaked in distilled water, extracted at 90 ° C. for 15 minutes while being irradiated with microwaves, and soaked. The vulcanized rubber composition according to any one of the above [10] to [14], wherein water is a value measured using a pH meter,
[16] The heat-resistant aging index (formula 3) after heat treatment at 80 ° C. for 18 hours of the modified natural rubber is 75 to 120%, preferably 40 to 75%, more preferably 50 to 70%, still more preferably. The vulcanized rubber composition according to any one of [10] to [15], which is 55 to 65%,
Heat aging index = Mooney viscosity after heat treatment / Mooney viscosity before heat treatment × 100 (Formula 3)
And [17] A studless tire having a tread composed of the vulcanized rubber composition according to any one of [10] to [16].

  According to the present invention, the modified natural rubber and butadiene rubber are each masterbatch containing silica and then kneaded, whereby the on-ice performance and the wear resistance performance of the resulting vulcanized rubber composition can be improved in a balanced manner. it can. Further, by using this vulcanized rubber composition for a tire member such as a tread, a studless tire excellent in these performances can be provided.

It is a figure which shows the SEM photograph of the cross section of the vulcanized rubber composition (a) with favorable dispersion | distribution of a silica, and the vulcanized rubber composition (b) in which the silica is unevenly distributed.

  In the present invention, the non-rubber component in the rubber is removed to achieve high purity, and by using the modified natural rubber whose pH is adjusted to 2 to 7, the physical properties of the studless tire are expressed as compared with the conventional natural rubber. A rubber composition that uses a blend with BR, which is useful for rubber, and has improved morphology control and silica distribution technology to develop good rubber properties, resulting in a marked improvement in the balance between on-ice performance and anti-wear performance. It was found that a product was obtained.

  The method for producing a vulcanized rubber composition according to one embodiment of the present invention includes: (a) a step of producing a master batch (BR master batch) containing butadiene rubber (BR) and silica; and (b) a predetermined modified natural product. A step of producing a masterbatch (modified NR masterbatch) containing rubber (modified NR) and silica, (c) BR masterbatch obtained in (a) and modified NR masterbatch obtained in (b) And the step of vulcanizing the kneaded product obtained in (d) and (c), and the resulting vulcanized rubber composition has predetermined properties. Thus, by using a modified NR and preparing and kneading a master batch in which each rubber component and silica are separately kneaded, silica that is likely to be unevenly distributed in natural rubber can be unevenly distributed in butadiene rubber. In addition, a vulcanized rubber composition having the abundance ratio α of silica in the BR phase and the ratio β of butadiene rubber within a predetermined range can be easily produced. Thereby, the performance on ice can be improved by silica without impairing the excellent wear resistance performance of the modified NR, and these performances can be obtained in a well-balanced manner.

  The dispersion state of silica in the rubber component in the vulcanized rubber composition can be observed with a scanning electron microscope (SEM). For example, in an example in which the dispersion of silica is good, as shown in FIG. 1A, a phase containing butadiene rubber (BR phase) 1 forms a sea phase and a phase containing isoprene-based rubber (natural rubber). (IR phase) 2 forms an island phase, and silica 3 is dispersed in both BR phase 1 and IR phase 2. On the other hand, in the example where the silica is unevenly distributed in one phase, as seen in FIG. 1B, the BR phase 1 forms the sea phase and the IR phase 2 becomes the same as in FIG. Although an island phase is formed, silica 3 is unevenly distributed in IR phase 2 and is not dispersed in both phases.

(A) Process for producing a BR master batch (X1 kneading process)
The production method of the BR master batch is not particularly limited, but can be produced by kneading BR and silica. The kneading method is not particularly limited, and a kneader used in a general rubber industry such as a Banbury mixer and an open roll can be used. For example, it can also be produced as a wet masterbatch obtained by mixing BR latex and silica water dispersion.

  The kneading temperature in the X1 kneading step is preferably 80 ° C. or higher, more preferably 100 ° C. or higher, and further preferably 140 ° C. or higher. By setting the kneading temperature to 80 ° C. or higher, the reaction between the silane coupling agent and silica can be sufficiently promoted to disperse the silica well, and the performance on snow and ice and the wear resistance can be easily improved in a balanced manner. The kneading temperature in the X1 kneading step is preferably 200 ° C. or lower, more preferably 190 ° C. or lower, and further preferably 180 ° C. or lower. By setting the kneading temperature to 200 ° C. or less, there is a tendency that an increase in Mooney viscosity can be suppressed and processability can be improved. Moreover, 130-160 degreeC is employable as discharge temperature.

  The kneading time in the X1 kneading step is not particularly limited, but is usually 30 seconds or longer, preferably 1 to 30 minutes, more preferably 3 to 6 minutes.

  The BR is not particularly limited. For example, BR having a cis 1,4 bond content of less than 50% (low cis BR), BR having a cis 1,4 bond content of 90% or more, and a rare earth element-based catalyst. Rare earth-based butadiene rubber (rare earth-based BR), BR containing a syndiotactic polybutadiene crystal (SPB-containing BR), modified BR (high cis-modified BR, low cis-modified BR) and the like can be used. Among these, it is preferable to use at least one selected from the group consisting of high cis BR, low cis BR, and low cis modified BR, and it is more preferable to use high cis BR.

  Examples of the high-sis BR include BR730 and BR51 manufactured by JSR Corporation, BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B manufactured by Ube Industries, Ltd., BR150B, and BR710. Among the high cis BRs, those having a cis 1,4-bond content of 95% or more are more preferable. These may be used alone or in combination of two or more. By containing the high cis BR, low temperature characteristics and wear resistance can be improved. Examples of ROSIS BR include BR1250 manufactured by Nippon Zeon Co., Ltd. These may be used alone or in combination of two or more.

  40 mass parts or more are preferable with respect to 100 mass parts of BR, and, as for the compounding quantity of the silica in a X1 kneading process, 50 mass parts or more are more preferable. There exists a tendency for the effect which disperse | distributed the silica to fully be acquired by the compounding quantity of a silica being 40 mass parts or more. Moreover, the compounding quantity of the silica in the X1 kneading process is preferably 100 parts by mass or less, and more preferably 80 parts by mass or less with respect to 100 parts by mass of BR. By making the compounding quantity of silica 100 mass parts or less, the dispersion of silica becomes easy and the processability can be improved.

  Silica is not particularly limited and, for example, silica (anhydrous silicic acid) prepared by a dry method or silica (hydrous silicic acid) prepared by a wet method is used in the tire industry. can do.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 70 m ² / g or more, and more preferably 140 m ² / g or more. By making the N ₂ SA of silica 70 m ² / g or more, sufficient reinforcement can be obtained, and the fracture strength and wear resistance can be improved. Further, N ₂ SA of silica is preferably 220 m ² / g or less, and more preferably 200 m ² / g or less. By making the N ₂ SA of the silica 220 m ² / g or less, the silica can be easily dispersed and the processability can be improved. Here, N ₂ SA of silica in the present specification is a value measured by the BET method according to ASTM D3037-81.

  In the X1 kneading step, it is preferable to knead a silane coupling agent together with silica. Although it does not specifically limit as a silane coupling agent, In rubber industry, the arbitrary silane coupling agents conventionally used together with a silica can be used together, for example, bis (3-triethoxysilylpropyl). ) Tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide Sulfide, bis (3-trimethoxysilylpropyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, bis (3-trimethoxysilylpropyl) disulfide, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyl Tetrasul 3-triethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 2-trimethoxysilylethyl-N, N-dimethylthio Sulfides such as carbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltrie Mercapto type such as xyloxysilane; vinyl type such as vinyltriethoxysilane and vinyltrimethoxysilane; 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3- (2-aminoethyl) aminopropyltriethoxysilane, Amino compounds such as 3- (2-aminoethyl) aminopropyltrimethoxysilane; γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ -Glycidoxy type such as glycidoxypropylmethyldimethoxysilane; Nitro type such as 3-nitropropyltrimethoxysilane, 3-nitropropyltriethoxysilane; 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysila , 2-chloroethyl trimethoxysilane, chloro system such as 2-chloroethyl triethoxy silane; and the like. These silane coupling agents may be used alone or in combination of two or more. Among these, from the viewpoint of good reactivity with silica, a sulfide system is preferable, and bis (3-triethoxysilylpropyl) disulfide is particularly preferable.

  In the case of containing a silane coupling agent, the content with respect to 100 parts by mass of silica is preferably 3 parts by mass or more, and more preferably 6 parts by mass or more. By setting the content of the silane coupling agent to 3 parts by mass or more, the fracture strength can be improved. Moreover, 12 mass parts or less are preferable and, as for content with respect to 100 mass parts of silica of a silane coupling agent, 10 mass parts or less are more preferable. By setting the content of the silane coupling agent to 12 parts by mass or less, an effect commensurate with the increase in cost can be obtained.

(B) Step of producing a modified NR master batch (X2 kneading step)
The modified NR master batch can be produced by kneading the modified NR and silica. The kneading method and kneading conditions are the same as in the X1 kneading step. Moreover, it can also produce as a wet masterbatch obtained by mixing modified NR latex and a silica water dispersion similarly to a X1 kneading | mixing process.

  The modified NR used in the present invention is obtained by removing a non-rubber component of natural rubber and then treating with an acidic compound, and the pH is adjusted to 2-7. Non-rubber components such as protein phospholipids in natural rubber are removed to make it highly purified, and because it is a modified natural rubber that controls the pH of the rubber to an appropriate value, fuel efficiency and processability are improved. On the other hand, the affinity with silica decreases. Therefore, uneven distribution of the filler such as silica on the modified NR side is improved, and the partitioning property of the filler such as silica on the butadiene rubber side is improved. As a result, the dispersibility of fillers such as silica is improved, and the balance between wear resistance and performance on ice required for studless tires is improved. Further, the modified NR tends to cause deterioration of the rubber by removing non-rubber components in the process of high purity and making the rubber basic or strongly acidic, but adjusts the pH of the rubber to a predetermined range. As a result, a decrease in molecular weight during storage is suppressed, so that good heat aging resistance can be obtained. As a result, the physical properties of rubber during the kneading process can be prevented from being lowered, and the dispersion of fillers such as silica can be improved throughout the rubber component, and the balance between low fuel consumption and performance on ice required for studless tires can be improved.

  The modified NR is not particularly limited as long as it is obtained by removing a non-rubber component of natural rubber and then treating with an acidic compound and the pH is adjusted to 2 to 7. Specifically, (1) A saponified natural rubber latex is washed and further treated with an acidic compound to obtain a modified natural rubber having a pH of 2 to 7, and (2) a deproteinized natural rubber latex is washed with an acidic compound. Examples thereof include modified natural rubber obtained by treatment and having a pH of 2-7.

  As described above, the modified natural rubber can be prepared by a method of washing a saponified natural rubber latex or a deproteinized natural rubber latex with distilled water or the like, and further treating with an acidic compound. Compared to the pH of distilled water, it is important to shift to the acidic side by treatment with an acidic compound to lower the pH value. Usually, the pH of distilled water is not 7.00 and is about 5 to 6, but in this case, it is important to lower the pH value to the acidic side from 5 to 6 by treatment with an acidic compound. It becomes. Specifically, it is preferable to lower the pH by about 0.2 to 2 by treatment with an acidic compound than the pH value of water used for washing.

  The pH of the modified natural rubber is 2 or more, preferably 3 or more, and more preferably 4 or more. The modified natural rubber has a pH of 7 or less, more preferably 6 or less. By adjusting the pH of the modified natural rubber to 2 to 7, deterioration in heat aging resistance is prevented, and the performance balance of low fuel consumption, heat aging resistance and processability can be remarkably improved. The pH of the modified natural rubber is cut into a size of 2 mm square or less on each side, soaked in distilled water, extracted at 90 ° C. for 15 minutes while irradiating with microwaves, and the soaked water was measured using a pH meter. Specifically, it can be measured by the method described in Examples described later. Here, regarding extraction, even if it is extracted for 1 hour with an ultrasonic cleaner or the like, the water-soluble component cannot be completely extracted from the inside of the rubber, so the internal pH cannot be accurately determined. By extracting, it becomes possible to know the substance of the rubber.

  The modified natural rubber is purified by various methods such as (1) or (2). For example, the phosphorus content in the modified natural rubber is preferably 200 ppm or less, more preferably 150 ppm or less. . If the phosphorus content in the modified natural rubber is 200 ppm or less, there is no risk that the Mooney viscosity will increase during storage and the processability will deteriorate, and there is a tendency that the increase in tan δ can be suppressed and fuel efficiency can be improved. The phosphorus content can be measured by a conventional method such as ICP emission analysis. Phosphorus is considered to be derived from phospholipids contained in natural rubber.

  When the modified natural rubber contains an artificial anti-aging agent, the nitrogen content after being immersed in acetone at room temperature (25 ° C.) for 48 hours is preferably 0.15% by mass or less. More preferably, it is 1% by mass or less. If the nitrogen content is 0.15% by mass or less, there is no possibility that the Mooney viscosity will increase during storage and the processability will be deteriorated, and the effect of improving fuel economy tends to be sufficiently obtained. The highly purified natural rubber has a risk of deterioration due to long-term storage because the natural anti-aging component, which is said to be inherent to the natural rubber, has been removed. Therefore, an artificial anti-aging agent may be added. For this reason, the nitrogen content in that case is a measurement value after removing the artificial anti-aging agent in rubber | gum by acetone extraction as above-mentioned. The nitrogen content can be measured by a conventional method such as Kjeldahl method or trace nitrogen meter. Nitrogen is derived from proteins and amino acids.

The modified natural rubber preferably has a Mooney viscosity ML _{1 + 4} (130 ° C.) measured in accordance with JIS K 6300: 2001-1 of 75 or less, more preferably 40 to 75, and even more preferably 50 to 70. Preferably, 55 to 65 is most preferable. When the Mooney viscosity is 75 or less, the kneading which is usually necessary before kneading the rubber becomes unnecessary. Therefore, the modified natural rubber produced without going through the mastication step can be suitably used as a compounding material for the rubber composition. On the other hand, if the Mooney viscosity exceeds 75, mastication is required before use, and there is a tendency for exclusive use of equipment, loss of electric energy, thermal energy, and the like.

The modified natural rubber is preferably a rubber having a Mooney viscosity ML _{1 + 4} (130 ° C.) having a heat aging resistance index represented by the following formula of 75 to 120%.
Heat aging index (%) = Mooney viscosity after heat treatment at 80 ° C. for 18 hours / Mooney viscosity before heat treatment × 100 (Formula 3)

The heat aging index represented by the above formula 3 is more preferably 80 to 115%, further preferably 85 to 110%. Various methods have been reported for evaluating the heat aging resistance of rubber. By using the method of evaluating the Mooney viscosity ML _{1 + 4} (130 ° C.) by the rate of change before and after heat treatment at 80 ° C. for 18 hours, It is possible to accurately evaluate the heat aging resistance at the time of tire manufacture or tire use. Here, if the heat aging index is in the range of 75 to 120%, excellent heat aging resistance can be obtained, and the performance balance of low fuel consumption and heat aging resistance can be remarkably improved.

  The modified natural rubber having a high purity such as (1) or (2) and having a pH adjusted to 2 to 7 comprises: (Production method 1) Step 1-1 of saponifying natural rubber latex; A production method comprising a step 1-2 for washing the natural rubber latex and a step 1-3 for treating with the acidic compound, (Production method 2) a step 2-1 for deproteinizing the natural rubber latex, and a deproteinized natural rubber It can be prepared by a production method including the step 2-2 for washing the latex and the step 2-3 for treating with the acidic compound.

[Production method 1]
(Step 1-1)
In step 1-1, natural rubber latex is saponified. Thereby, saponified natural rubber latex in which phospholipids and proteins in the rubber are decomposed and non-rubber components are reduced is prepared.

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

  As a method for the saponification treatment, for example, known methods described in JP 2010-138359 A and JP 2010-17469 A can be suitably used, and specifically, the following method is used. can do.

  The saponification treatment can be carried out by adding an alkali and, if necessary, a surfactant to natural rubber latex and allowing it to stand at a predetermined temperature for a certain period of time. Stirring may be performed as necessary.

  The alkali used for the saponification treatment is preferably sodium hydroxide, potassium hydroxide or the like, but is not limited thereto. The surfactant is not particularly limited, and examples include known anionic surfactants such as polyoxyethylene alkyl ether sulfate salts, nonionic surfactants, and amphoteric surfactants. Anionic surfactants such as polyoxyethylene alkyl ether sulfates are preferred because they 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.

(Step 1-2)
In step 1-2, the saponified natural rubber latex obtained in step 1-1 is washed. This washing removes non-rubber components such as proteins.

  In Step 1-2, for example, the saponified natural rubber latex obtained in Step 1-1 described above is agglomerated to produce an agglomerated rubber, and then the obtained agglomerated rubber is treated with a basic compound and further washed. Can be implemented. Specifically, after production of the agglomerated rubber, it is possible to remove the non-rubber component by diluting with water and transferring the water-soluble component to the aqueous layer and removing the water, and further treating with a basic compound after agglomeration. Non-rubber components confined in the rubber during agglomeration can be redissolved. Thereby, non-rubber components such as proteins strongly adhered to the agglomerated rubber can be removed.

  Examples of the aggregating method include a method of adjusting the pH by adding an acid such as formic acid, acetic acid and sulfuric acid, and further adding a polymer flocculant as necessary. Thereby, not a large aggregate but a granular rubber having a diameter of several mm to 1 mm or less to about 20 mm is formed, and proteins and the like are sufficiently removed by the basic compound treatment. The pH is preferably adjusted in the range of 3.0 to 5.0, and more preferably in the range of 3.5 to 4.5.

  Examples of polymer flocculants include cationic polymer flocculants such as dimethyl quaternary salt polymer of dimethylaminoethyl (meth) acrylate, anionic polymer flocculants such as acrylate polymer, and acrylamide polymer. Nonionic polymer flocculants such as, and amphoteric polymer flocculants such as dimethylaminoethyl (meth) acrylate methyl chloride quaternary salt-acrylate copolymer. The addition amount of the polymer flocculant can be appropriately selected.

  Subsequently, the obtained agglomerated rubber is treated with a basic compound. Here, although it does not specifically limit as a basic compound, A basic inorganic compound is suitable from the point of removal performance, such as protein.

  Examples of basic inorganic compounds include metal hydroxides such as alkali metal hydroxides and alkaline earth metal hydroxides; metal carbonates such as alkali metal carbonates and alkaline earth metal carbonates; alkali metal hydrogen carbonates and the like Metal phosphates such as alkali metal phosphates; metal acetates such as alkali metal acetates; metal hydrides such as alkali metal hydrides; ammonia and the like.

  Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide and the like. Examples of the alkaline earth metal hydroxide include magnesium hydroxide, calcium hydroxide, and barium hydroxide. Examples of the alkali metal carbonate include lithium carbonate, sodium carbonate, and potassium carbonate. Examples of the alkaline earth metal carbonate include magnesium carbonate, calcium carbonate, barium carbonate and the like. Examples of the alkali metal hydrogen carbonate include lithium hydrogen carbonate, sodium hydrogen carbonate, and potassium hydrogen carbonate. Examples of the alkali metal phosphate include sodium phosphate and sodium hydrogen phosphate. Examples of the alkali metal acetate include sodium acetate and potassium acetate. Examples of the alkali metal hydride include sodium hydride and potassium hydride. Among these, metal hydroxide, metal carbonate, metal bicarbonate, metal phosphate, and ammonia are preferable, alkali metal carbonate, alkali metal bicarbonate, and ammonia are more preferable, sodium carbonate, sodium bicarbonate. Is more preferable. These basic compounds may be used alone or in combination of two or more.

  The method of treating the agglomerated rubber with the basic compound is not particularly limited as long as the agglomerated rubber is brought into contact with the basic compound. For example, the method of immersing the agglomerated rubber in an aqueous solution of the basic compound, The method of spraying the aqueous solution of a compound is mentioned. An aqueous solution of a basic compound can be prepared by diluting and dissolving each basic compound with water.

  The content of the basic compound in 100% by mass of the aqueous solution of the basic compound is preferably 0.1% by mass or more, and more preferably 0.3% by mass or more. If the content of the basic compound is 0.1% by mass or more, the protein tends to be sufficiently removed. 10 mass% or less is preferable and, as for content of the basic compound in 100 mass% of aqueous solution of a basic compound, 5 mass% or less is more preferable. If the content of the basic compound is 10% by mass or less, an increase in the amount of proteolysis with respect to an increase in the amount of the basic compound used can be expected, and the efficiency tends to be good. 9-13 are preferable and, as for pH of the aqueous solution of this basic compound, 10-12 are more preferable from the point of processing efficiency.

  The treatment temperature for treating the agglomerated rubber with a basic compound may be appropriately selected, but is preferably 10 to 50 ° C, more preferably 15 to 35 ° C. Moreover, processing time is 1 minute or more normally, 10 minutes or more are preferable and 30 minutes or more are more preferable. If it is 1 minute or more, there exists a tendency for the effect of this invention to be acquired favorably. Although there is no restriction | limiting in the upper limit of processing time, from the point of productivity, 48 hours or less are preferable, 24 hours or less are more preferable, and 16 hours or less are further more preferable.

  After the treatment with the basic compound, a washing treatment is performed. By this washing treatment, non-rubber components such as proteins can be removed. Examples of the washing method include a method of diluting a rubber component with water and washing and then centrifuging, and a method of allowing the rubber component to float by standing and discharging only the aqueous phase and taking out the rubber component. The number of washings can be any number of times that can reduce non-rubber components such as proteins to a desired amount, but a washing cycle in which 1000 mL of water is added to 300 g of dry rubber and stirred and then dehydrated. In the method of repeating the above, 3 times (3 cycles) or more is preferable, 5 times (5 cycles) or more is more preferable, and 7 times (7 cycles) or more is more preferable.

  The washing treatment is preferably carried out until the phosphorus content in the rubber is 200 ppm or less and / or the nitrogen content is 0.15 mass% or less. By sufficiently removing phospholipids and proteins by the washing treatment, fuel economy and processability are improved, and the affinity with a filler such as silica is lowered.

(Step 1-3)
In Step 1-3, the washed rubber obtained in Step 1-2 is treated with an acidic compound. Although heat aging resistance tends to decrease due to the treatment of a basic compound or the like, further treatment with an acidic compound can prevent such a problem and obtain good heat aging resistance.

  The acidic compound is not particularly limited, and inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, polyphosphoric acid, metaphosphoric acid, boric acid, boronic acid, sulfanilic acid, sulfamic acid; formic acid, acetic acid, glycolic acid, oxalic acid, propion Acid, malonic acid, succinic acid, adipic acid, maleic acid, malic acid, tartaric acid, citric acid, benzoic acid, phthalic acid, isophthalic acid, glutaric acid, gluconic acid, lactic acid, aspartic acid, glutamic acid, salicylic acid, methanesulfonic acid, Itaconic acid, benzenesulfonic acid, toluenesulfonic acid, naphthalenedisulfonic acid, trifluoromethanesulfonic acid, styrenesulfonic acid, trifluoroacetic acid, barbituric acid, acrylic acid, methacrylic acid, cinnamic acid, 4-hydroxybenzoic acid, aminobenzoic acid , Naphthalene disulfonic acid, hydroxybenze Examples include organic acids such as sulfonic acid, toluenesulfinic acid, benzenesulfinic acid, α-resorcinic acid, β-resorcinic acid, γ-resorcinic acid, gallic acid, phloroglicin, sulfosalicylic acid, ascorbic acid, erythorbic acid, and bisphenolic acid. It is done. Of these, acetic acid, sulfuric acid, formic acid and the like are preferable. These acidic compounds may be used alone or in combination of two or more.

  The method of treating the agglomerated rubber with the acidic compound is not particularly limited as long as the agglomerated rubber is brought into contact with the acidic compound. For example, the method of immersing the agglomerated rubber in the aqueous solution of the acidic compound, the aqueous solution of the acidic compound in the agglomerated rubber The method of spraying etc. are mentioned. An aqueous solution of an acidic compound can be prepared by diluting and dissolving each acidic compound with water.

  The content of the acidic compound in 100% by mass of the acidic compound aqueous solution is not particularly limited, but is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and preferably 15% by mass or less. 10 mass% or less is more preferable, and 5 mass% or less is further more preferable. When the content of the acidic compound is in the range of 0.1 to 15% by mass, good heat aging resistance tends to be obtained.

  The treatment temperature for treating the agglomerated rubber with an acidic compound may be appropriately selected, but is preferably 10 to 50 ° C, more preferably 15 to 35 ° C. Further, the treatment time is usually preferably 3 seconds or more, more preferably 10 seconds or more, and further preferably 30 seconds or more. If the treatment time is 3 seconds or more, it can be sufficiently neutralized and the effects of the present invention tend to be obtained satisfactorily. Although there is no restriction | limiting in an upper limit, from the point of productivity, 24 hours or less are preferable, 10 hours or less are more preferable, and 5 hours or less are more preferable.

  In the treatment such as immersion of the acidic compound in an aqueous solution, the pH is preferably adjusted to 6 or less. By such neutralization, excellent heat aging resistance can be obtained. The upper limit of this pH is more preferably 5 or less, and further preferably 4.5 or less. The lower limit is not particularly limited and depends on the immersion time, but if the acid is too strong, the rubber deteriorates or the wastewater treatment becomes troublesome, and is preferably 1 or more, and more preferably 2 or more. The immersion treatment can be performed by leaving the agglomerated rubber in an aqueous solution of an acidic compound.

  After the treatment with the acidic compound, the used acidic compound may be removed, and then the aggregated rubber after the treatment may be appropriately washed. Examples of the washing treatment include the same method as in Step 1-2. For example, by repeating washing, the non-rubber component can be further reduced and adjusted to a desired content. Further, the agglomerated rubber after the treatment with the acidic compound may be squeezed with a roll type squeezer or the like to form a sheet. By adding a step of squeezing the agglomerated rubber, the pH of the agglomerated rubber surface and inside can be made uniform, and a rubber having a desired performance can be obtained. The modified natural rubber can be obtained by carrying out a washing or squeezing step as necessary, then cutting through a creper and drying. In addition, drying is not specifically limited, For example, it can implement using normal dryers, such as a trolley-type dryer used in order to dry TSR, a vacuum dryer, an air dryer, and a drum dryer.

[Production method 2]
(Step 2-1)
In step 2-1, the natural rubber latex is deproteinized. Thereby, a deproteinized natural rubber latex from which non-rubber components such as proteins are removed can be prepared. Examples of the natural rubber latex used in Step 2-1 include the same rubber latex as described in Production Method 1.

  As a method for deproteinization, a known method capable of removing a protein can be used without particular limitation, and examples thereof include a method of degrading a protein by adding a proteolytic enzyme to natural rubber latex.

  The proteolytic enzyme used for the deproteinization treatment is not particularly limited, and any of those derived from bacteria, those derived from filamentous fungi, and those derived from yeast can be used. Specifically, protease, peptidase, cellulase, pectinase, lipase, esterase, amylase and the like can be used alone or in combination.

  The amount of the proteolytic enzyme added is preferably 0.005 parts by mass or more, more preferably 0.01 parts by mass or more, and even more preferably 0.05 parts by mass or more with respect to 100 parts by mass of the solid content in the natural rubber latex. . If the amount of the proteolytic enzyme added is 0.005 parts by mass or more, the protein degradation reaction tends to be sufficiently performed.

  In the deproteinization treatment, a surfactant may be added together with the proteolytic enzyme. Examples of the surfactant include anionic, cationic, nonionic, and amphoteric surfactants.

(Process 2-2)
In step 2-2, the deproteinized natural rubber latex obtained in step 2-1 is washed. This washing removes non-rubber components such as proteins.

  Step 2-2 can be performed, for example, by aggregating the deproteinized natural rubber latex obtained in Step 2-1 to produce an agglomerated rubber, and then washing the obtained agglomerated rubber. Thereby, non-rubber components such as proteins strongly adhered to the agglomerated rubber can be removed.

  The aggregation method can be carried out in the same manner as in step 1-2 of production method 1. Furthermore, you may process with a basic compound as demonstrated in the manufacturing method 1 as needed. After the production of the agglomerated rubber, a cleaning process is performed. This washing treatment can be carried out in the same manner as in step 1-2 of production method 1, whereby non-rubber components such as proteins can be removed. The washing treatment is preferably carried out for the same reason as in Production Method 1 until the phosphorus content in the rubber is 200 ppm or less and / or the nitrogen content is 0.15 mass% or less.

(Step 2-3)
In step 2-3, the washed rubber obtained in step 2-2 is treated with an acidic compound. When the acid amount is small in acid aggregation as well as in the treatment with a basic compound, the heat aging resistance is reduced due to the fact that the finally obtained rubber becomes alkaline to neutral when extracted with water. Tend. In general, an enzyme having an optimum pH in the alkaline region is used as a proteolytic enzyme because it can be suitably deproteinized, and the enzyme reaction is performed under alkaline conditions in accordance with the optimum pH. There are many cases. Thereafter, it is coagulated under acidity at the time of agglomeration, but if the rubber is washed only with water, the pH will be higher than that of the extract by the extraction described later, and in this case, the deterioration of heat aging resistance will be particularly large. On the other hand, after coagulation, after treatment with a basic compound as necessary, treatment with an acidic compound can prevent such a problem and obtain good heat aging resistance.

  As an acidic compound, the thing similar to what was demonstrated in process 1-3 of the manufacturing method 1 is mentioned. The method of treating the agglomerated rubber with the acidic compound is not particularly limited as long as the agglomerated rubber is brought into contact with the acidic compound. For example, the method of immersing the agglomerated rubber in an aqueous solution of the acidic compound, Examples include a method of spraying an aqueous solution. An aqueous solution of an acidic compound can be prepared by diluting and dissolving each acidic compound with water.

  The content of the acidic compound in 100% by mass of the acidic compound aqueous solution is not particularly limited, but is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and preferably 15% by mass or less. 10 mass% or less is more preferable, and 5 mass% or less is further more preferable. When the content of the acidic compound is in the range of 0.01 to 15% by mass, good heat aging resistance tends to be obtained.

  What is necessary is just to select the processing temperature and processing time at the time of processing agglomerated rubber with an acidic compound suitably, and the temperature similar to the process 1-3 of the manufacturing method 1 should just be employ | adopted. In the treatment such as immersion of the acidic compound in an aqueous solution, the pH is preferably adjusted to the same value as in Step 1-3 of Production Method 1.

  After the treatment with the acidic compound, the used acidic compound may be removed, and thereafter, the treated agglomerated rubber may be washed appropriately. Examples of the washing treatment include the same method as in Step 1-3 of Production Method 1. For example, the non-rubber component can be further reduced and adjusted to a desired content by repeating washing. After the washing treatment is completed, the modified natural rubber used in the present invention is obtained by drying. In addition, drying is not specifically limited, The method described in the process 1-3 of the manufacturing method 1 including a drawing process etc. can be employ | adopted.

  The compounding amount of silica in the X2 kneading step is preferably 15 parts by mass or more and more preferably 30 parts by mass or more with respect to 100 parts by mass of the modified NR. By making the compounding amount of silica 15 parts by mass or more, the effect of dispersing silica can be sufficiently obtained. Moreover, the compounding amount of silica in the X2 kneading step is preferably 100 parts by mass or less, and more preferably 80 parts by mass or less with respect to the modified NR00 part by mass. By making the compounding quantity of silica 100 mass parts or less, the dispersion of silica becomes easy, and the processability can be improved.

  The silica used in the X2 kneading step is not particularly limited, and is as described in the X1 kneading step.

  Also in the X2 kneading step, it is preferable to knead the silane coupling agent together with silica, and the silane coupling agent is as described in the X1 kneading step.

(C) Process of kneading BR master batch and modified NR master batch (Y kneading process)
The BR masterbatch obtained by X1 kneading and the modified NR masterbatch obtained by X2 kneading are kneaded. As the kneading method, for example, as in the above-described X1 and X2 kneading steps, a kneading machine used in a general rubber industry such as a Banbury mixer and an open roll is used, and is performed under conditions used in a general rubber industry. be able to.

  The kneading temperature in the Y kneading step is preferably 80 ° C. or higher, more preferably 100 ° C. or higher, further preferably 145 ° C. or higher. By setting the kneading temperature to 80 ° C. or higher, the reaction between the silane coupling agent and silica can be sufficiently promoted, silica can be dispersed well, and the performance on ice and snow and the wear resistance can be easily improved in a balanced manner. . The kneading temperature in the Y kneading step is preferably 200 ° C. or lower, more preferably 190 ° C. or lower, and further preferably 160 ° C. or lower. By setting the kneading temperature to 200 ° C. or less, there is a tendency that an increase in Mooney viscosity can be suppressed and processability can be improved. Moreover, 130-160 degreeC is employable as discharge temperature.

  The kneading time in the Y kneading step is not particularly limited, but is usually 30 seconds or longer, preferably 1 to 30 minutes, and more preferably 2 to 6 minutes.

  In the method for producing a vulcanized rubber composition of the present invention, an X1 kneading step, an X2 kneading step, a Y kneading step or other steps are provided, and if necessary, other than the modified NR and BR Rubber components, fillers such as carbon black, softeners such as oil, waxes, anti-aging agents, stearic acid, zinc oxide, and other materials commonly used in the tire industry may also be kneaded together. .

  Other rubber components include diene rubbers such as styrene butadiene rubber.

  Examples of carbon black include furnace black, acetylene black, thermal black, channel black, graphite, and the like. These carbon blacks may be used alone or in combination of two or more. Among these, furnace black is preferable because it can improve the low-temperature characteristics and wear resistance in a well-balanced manner. The step of kneading carbon black is not particularly limited, but X2 kneading is preferred for reasons such as preferentially dispersing silica in the BR phase.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 70 m ² / g or more, more preferably 90 m ² / g or more, from the viewpoint of obtaining sufficient reinforcement and wear resistance. Also, N ₂ SA of carbon black is excellent in dispersibility, from the viewpoint that it is difficult to heat generation, preferably 300 meters ² / g or less, more preferably 250m ² / g. N ₂ SA can be measured according to JIS K 6217-2 “Carbon black for rubber—Basic characteristics—Part 2: Determination of specific surface area—Nitrogen adsorption method—Single point method”.

  In the case of containing carbon black, the content with respect to 100 parts by mass of the total rubber component is preferably 1 part by mass or more, and more preferably 5 parts by mass or more. When the carbon black content is 1 part by mass or more, sufficient reinforcing properties tend to be obtained. Moreover, 95 mass parts or less are preferable, as for content of carbon black, 60 mass parts or less are more preferable, and 20 mass parts or less are further more preferable. When the carbon black content is 95 parts by mass or less, processability is improved, heat generation is suppressed, and wear resistance can be improved.

  Although it does not specifically limit as oil, For example, a process oil, vegetable oil, or its mixture can be used. As the process oil, for example, a paraffin process oil, an aroma process oil, a naphthenic process oil, or the like can be used. Vegetable oils include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, palm oil, peanut oil, rosin, pine oil, pineapple, tall oil, corn oil, rice bran oil, safflower oil, sesame oil, olive oil, Sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, tung oil and the like. Among them, it is preferable to use process oil, particularly paraffinic process oil.

  The content with respect to 100 parts by mass of the total rubber component when oil is contained is preferably 15 parts by mass or more, and more preferably 20 parts by mass or more. By setting the oil content to 15 parts by mass or more, the performance on snow and ice necessary for the studless tire tends to be exhibited. The oil content is preferably 80 parts by mass or less, and more preferably 70 parts by mass or less. By setting the oil content to 80 parts by mass or less, there is a tendency to prevent deterioration of workability, wear resistance, and aging physical properties.

  As the anti-aging agent used in the present invention, it is possible to appropriately select and mix amine-based, phenol-based, imidazole-based compounds, and anti-aging agents such as carbamic acid metal salts, and these anti-aging agents are These may be used alone or in combination of two or more. Among them, an amine-based anti-aging agent is preferable because ozone resistance can be remarkably improved and the effect lasts long, and N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine is more preferable. .

  The content with respect to 100 parts by mass of the total rubber component in the case of containing an antioxidant is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and further preferably 1.2 parts by mass or more. There is a tendency that sufficient ozone resistance can be obtained by setting the content of the antioxidant to 0.5 parts by mass or more. Further, the content of the anti-aging agent is preferably 8 parts by mass or less, more preferably 4 parts by mass or less, and further preferably 2.5 parts by mass or less. When the content of the antioxidant is 8 parts by mass or less, discoloration can be suppressed and bleeding can be suppressed.

  Any of waxes, stearic acid, and zinc oxide that are commonly used in the rubber industry can be suitably used.

(D) Step of vulcanizing (F kneading step and vulcanizing step)
A vulcanizing agent and, if necessary, a vulcanization accelerator are kneaded by F-kneading to the kneaded product obtained by the Y-kneading to obtain a kneaded product (unvulcanized rubber composition). And after shape | molding this unvulcanized rubber composition to a required shape and bonding together as a tire member, the vulcanized rubber composition of this invention can be obtained by vulcanizing | curing by a well-known method.

  The F-kneading step is carried out by starting kneading from about 50 ° C. when the kneader is cold, and from about 80 ° C. when continuously used, and kneading until the discharge temperature reaches 95 to 110 ° C. it can.

  The vulcanization temperature is preferably 120 ° C. or higher, more preferably 140 ° C. or higher, preferably 200 ° C. or lower, and more preferably 180 ° C. or lower from the viewpoint that the effects of the present invention can be obtained satisfactorily. The vulcanization time is preferably 5 to 30 minutes from the viewpoint that the effects of the present invention can be obtained satisfactorily.

  The vulcanizing agent is not particularly limited, and those commonly used in the rubber industry can be used, but those containing sulfur atoms are preferred, and powdered sulfur is particularly preferably used.

  The vulcanization accelerator is not particularly limited, and those generally used in the rubber industry can be used.

  The vulcanized rubber composition obtained by the method for producing a vulcanized rubber composition of the present invention as described above includes a phase containing BR and silica (BR phase), a phase containing modified NR and silica (modified NR phase). The BR phase and the modified NR phase are incompatible with each other. Here, in the present specification, “incompatible” means, for example, that the average equivalent circle radius of the discontinuous phase in the cross section of the vulcanized rubber composition is 100 nm or more. For example, a scanning electron microscope (SEM) ) Can be easily evaluated by the image taken.

In addition, the vulcanized rubber composition obtained by the method for producing a vulcanized rubber composition of the present invention has a wear resistance performance of the vulcanized rubber composition when the abundance α of silica in the BR phase satisfies the following formula 1. When used in a tread, the performance on ice is also improved. In the present specification, “the abundance ratio α of silica in the BR phase” refers to how much of the total silica amount in the rubber composition is present in the BR phase after 100 to 500 hours from the completion of the vulcanization step. It is an index indicating whether or not.
0.3 ≦ α ≦ 0.7 (Formula 1)
(Where α = silica amount in BR phase / (silica amount in BR phase + silica amount in modified NR phase))

  Specifically, for example, a vulcanized rubber composition is surfaced and used as a sample. For a scanning electron microscope (SEM) photograph of one sample, 10 regions of 2 μm × 2 μm that do not overlap each other are selected. In each region, the silica area per unit area and the silica area in the BR phase in the unit area are measured, and the silica abundance γ of the BR phase is calculated. If it can be confirmed that the difference between the maximum value and the minimum value of γ at 10 locations is within 10%, the average of γ at the 10 locations is α.

  The abundance ratio α of silica in the BR phase is 0.3 or more, and preferably 0.5 or more. When the abundance ratio α of silica in the BR phase is less than 0.3, improvement in wear resistance and performance on ice cannot be expected, but rather tends to decrease. Further, the abundance ratio α of silica in the BR phase is 0.7 or less, and preferably 0.6 or less. When the abundance ratio α of silica in the BR phase exceeds 0.7, particularly improvement in wear resistance performance cannot be expected, but there is a tendency to decrease rather.

In the vulcanized rubber composition obtained by the method for producing a vulcanized rubber composition of the present invention, the ratio β of butadiene rubber satisfies the following formula 2.
0.45 ≦ β ≦ 0.8 (Formula 2)
(Where β = mass of butadiene rubber in the vulcanized rubber composition / (mass of butadiene rubber in the vulcanized rubber composition + mass of modified natural rubber in the vulcanized rubber composition) and vulcanization (The mass of the butadiene rubber in the rubber composition and the mass of the modified natural rubber in the vulcanized rubber composition correspond to the contents of the respective rubbers contained in the production of the vulcanized rubber composition.)

  The ratio β of butadiene rubber is 0.45 or more, preferably 0.5 or more. When the ratio β of butadiene rubber is less than 0.45, the improvement on the obtained performance on ice cannot be expected. Moreover, the ratio β of butadiene rubber is 0.8 or less, and preferably 0.7 or less. When the upper limit of the ratio β of butadiene rubber exceeds 0.8, the content of the modified natural rubber decreases, and there is a tendency that sufficient fracture strength and wear resistance cannot be obtained.

  In the vulcanized rubber composition obtained by the method for producing a vulcanized rubber composition of the present invention, the total content of butadiene rubber and modified natural rubber in all rubber components is preferably 70% by mass or more, 80 mass% or more is more preferable, 90 mass% or more is further more preferable, and it is especially preferable that it is 100 mass%. The higher the total content of butadiene rubber and modified natural rubber, the better the low-temperature properties and the necessary performance on snow and ice. The rubber component consists only of butadiene rubber and modified natural rubber. It is preferable to use a rubber component.

  By the above-described method for producing a vulcanized rubber composition of the present invention, silica that is likely to be unevenly distributed in the modified NR is also unevenly distributed in BR, and silica can be dispersed throughout the vulcanized rubber composition. Thereby, the performance on ice can be improved by silica without impairing the excellent wear resistance of the modified NR, and these performances can be obtained in a well-balanced manner.

A vulcanized rubber composition which is still another embodiment of the present invention is a vulcanized rubber composition having a phase containing butadiene rubber and silica (BR phase) and a phase containing modified natural rubber and silica (modified NR phase). A rubber composition, in which the BR phase and the modified NR phase are incompatible with each other, and the abundance α of silica in the BR phase 100 hours to 500 hours after the completion of the vulcanization step is expressed by the following formula 1. A vulcanized rubber composition satisfying the following formula 2 in which the ratio of butadiene rubber is satisfied, and can be produced, for example, by the method for producing a vulcanized rubber composition of the present invention.
0.3 ≦ α ≦ 0.7 (Formula 1)
0.45 ≦ β ≦ 0.8 (Formula 2)
(Where α = silica amount in BR phase / (silica amount in BR phase + silica amount in modified NR phase)), and β = mass of butadiene rubber in vulcanized rubber composition / (vulcanized The mass of butadiene rubber in the rubber composition + the mass of modified natural rubber in the vulcanized rubber composition))

  The explanation regarding the vulcanized rubber composition in the present specification is based on the method for producing the vulcanized rubber composition which is one embodiment of the present invention as well as the vulcanized rubber composition which is one embodiment of the present invention. It should be applied to the obtained vulcanized rubber composition, and various materials and compounding ratios obtained in the description of the method for producing a vulcanized rubber composition which is one embodiment of the present invention in this specification, and the obtained vulcanized rubber composition. The description relating to the properties of the vulcanized rubber composition is also applied to the vulcanized rubber composition which is one embodiment of the present invention.

  In the vulcanized rubber composition of the present invention, the butadiene rubber forms a sea phase, the modified natural rubber forms an island phase, and the silica content on the butadiene rubber side is 30% or more. Is not observed, that is, when the silica abundance ratio α in the butadiene rubber phase is less than 0.3, the modified natural rubber tends to have a hardness higher than that of the butadiene rubber alone. The wear resistance performance tends to be reduced.

  The vulcanized rubber composition of the present invention may contain 25 to 120 parts by mass of a filler and 15 to 80 parts by mass of a softening agent with respect to 100 parts by mass of a rubber component containing modified natural rubber and butadiene rubber. preferable.

  The filler content is preferably 25 parts by mass or more and more preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. By setting the filler content to 25 parts by mass or more, wear resistance and fracture characteristics tend to be improved. Moreover, 120 mass parts or less are preferable, and, as for content of a filler, 70 mass parts or less are more preferable. By setting the filler content to 120 parts by mass or less, workability and workability are improved, and there is a tendency to prevent a decrease in low temperature characteristics due to an increase in filler content. The filler includes silica, carbon black, aluminum hydroxide, and the like, and preferably 50% by mass or more, more preferably 70% by mass or more of silica is blended with respect to the total amount of filler.

  The total content of silica is preferably 25 parts by mass or more and more preferably 38 parts by mass or more with respect to 100 parts by mass of the rubber component. When the total content of silica is 25 parts by mass or more, there is a tendency that the wear resistance and fracture characteristics are improved. Moreover, 100 mass parts or less are preferable with respect to 100 mass parts of rubber components, and, as for the total content of a silica, 80 mass parts or less are more preferable. By making the total content of silica 100 parts by mass or less, workability and workability are improved, and there is a tendency to prevent a decrease in low temperature characteristics due to an increase in silica.

  The content of the softening agent is preferably 15 parts by mass or more and more preferably 20 parts by mass or more with respect to 100 parts by mass of the rubber component. By making the content of the softening agent 15 parts by mass or more, there is a tendency to exhibit the performance on snow and ice necessary for the studless tire. Moreover, 80 mass parts or less are preferable and, as for content of a softening agent, 70 mass parts or less are more preferable. By setting the softener content to 80 parts by mass or less, there is a tendency to prevent deterioration in workability, wear resistance, and aging physical properties. Softening agents include aroma oils, naphthenic oils, paraffin oils, terpene resins, and the like.

  The vulcanized rubber composition which is one embodiment of the present invention and the vulcanized rubber composition obtained by the method for producing the vulcanized rubber composition which is one embodiment of the present invention are tire members such as treads, carcass, In addition to tire applications such as sidewalls and beads, it can also be used in anti-vibration rubber, belts, hoses, and other industrial products. Among them, it is suitable for treads because of its excellent performance on ice and wear resistance, and is suitable for cap treads when the tread is a tread with a two-layer structure consisting of a cap tread and a base tread. It is what is used.

  The studless tire of this invention can be manufactured by a normal method using the vulcanized rubber composition which is one embodiment of this invention. That is, at the unvulcanized stage of the vulcanized rubber composition of the present invention, the unvulcanized rubber composition is extruded to match the shape of the tread, and pasted together with other tire members on a tire molding machine, and the ordinary method is applied. The studless tire of the present invention can be manufactured by forming an unvulcanized tire by molding and heating and pressurizing the unvulcanized tire in a vulcanizer.

  EXAMPLES Hereinafter, although this invention is demonstrated based on an Example, this invention is not limited only to an Example.

<Manufacture of modified natural rubber>
Hereinafter, various materials used in the production examples are shown.
Field latex: Field latex anionic surfactant obtained from Muhiba Latex, Malaysia: Emar E-27C (Polyoxyethylene lauryl ether sodium sulfate, active ingredient 27% by mass) manufactured by Kao Corporation
NaOH: NaOH manufactured by Wako Pure Chemical Industries, Ltd.
Anti-aging agent: Wingstay L manufactured by ELIOKEM (a compound in which a condensate of ρ-cresol and dicyclopentadiene is butylated)
Surfactant: Emalvin W (aromatic polyglycol ether) manufactured by LANXESS
Surfactant: Tamol NN9104 manufactured by BASF (Naphthalenesulfonic acid / formaldehyde sodium salt)
Surfactant: Van gel B (magnesium aluminum silicate hydrate) manufactured by Vanderbilt

(Preparation of anti-aging agent dispersion)
A total of 1000 g of water (462.5 g), Emulvin W (12.5 g), Tamol NN9104 (12.5 g), Van gel B (12.5 g) and Wingstay L (500 g) are mixed for 16 hours with a ball mill to prevent aging. An agent dispersion was prepared and used in the following production examples.

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 this latex and saponified at room temperature for 24 hours. Reaction was performed to obtain a saponified natural rubber latex. 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). Thereafter, formic acid was added with slow stirring to adjust the pH to 4.0, and then a cationic polymer flocculant was added and stirred for 2 minutes for aggregation. The diameter of the aggregate (aggregated rubber) thus obtained was about 0.5 to 5 mm. The obtained agglomerates were taken out and immersed in 1000 ml of a 2% by weight aqueous sodium carbonate solution at room temperature for 4 hours, and then the rubber was taken out. To this, 2000 ml of water was added and stirred for 2 minutes to remove water as much as possible 7 times. Thereafter, 500 ml of water was added, 2% by mass formic acid was added until pH 4 was reached, and the mixture was allowed to stand for 15 minutes. Further, the operation of removing water as much as possible, adding water again and stirring for 2 minutes was repeated three times, and then the water was squeezed with a water squeezing roll to form a sheet. Then, it dried at 90 degreeC for 4 hours and obtained solid rubber.

Comparative 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 this latex and saponified at room temperature for 24 hours. Reaction was performed to obtain a saponified natural rubber latex. 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). Thereafter, formic acid was added with slow stirring to adjust the pH to 4.0, and then a cationic polymer flocculant was added and stirred for 2 minutes for aggregation. The diameter of the aggregate (aggregated rubber) thus obtained was about 3 to 15 mm. The obtained agglomerates were taken out and immersed in 1000 ml of a 2% by weight aqueous sodium carbonate solution at room temperature for 4 hours, and then the rubber was taken out. To this, 1000 ml of water was added and stirred for 2 minutes to remove water as much as possible. Thereafter, 500 ml of water was added, 2% by mass formic acid was added until pH 4 was reached, and the mixture was stirred for 15 minutes. Further, the operation of removing water as much as possible, adding water again and stirring for 2 minutes was repeated three times, and then dried at 90 ° C. for 4 hours to obtain a solid rubber.

Comparative production example 2
The same procedure was followed, except that it was treated with an aqueous sodium carbonate solution in Production Example 1 and washed with water seven times, and then the sheet was formed by squeezing water with a water squeezing roll without acid treatment with 2% by mass formic acid. A solid rubber was obtained.

  The solid rubbers obtained in Production Example 1 and Comparative Production Examples 1 and 2 were subjected to the following test, and the results are shown in Table 1.

<Measurement of pH of rubber>
5 g of the obtained rubber was cut to 5 mm or less (about 1-2 × about 1-2 × about 1-2 (mm)) and placed in a 100 ml beaker, and 50 ml of distilled water at room temperature was added to 90 ° C. for 2 minutes. The temperature was raised, and then irradiation with microwaves (300 W) was performed for 13 minutes (15 minutes in total) while adjusting the temperature to be maintained at 90 ° C. Next, the immersion water was cooled with an ice bath to 25 ° C., and then the pH of the immersion water was measured using a pH meter.

<Measurement of nitrogen content>
(Acetone extraction (test piece preparation))
About 0.5 g of a sample obtained by chopping each solid rubber into 1 mm square was prepared. The sample was immersed in 50 g of acetone, and after 48 hours at room temperature (25 ° C.), the rubber was taken out and dried to obtain each test piece (extracted with anti-aging agent).

(Measurement)
The nitrogen content of the obtained test piece was measured by the following method. The nitrogen content was determined by decomposing and gasifying each of the acetone-extracted test pieces obtained above using a trace nitrogen carbon measuring device “SUMIGRAPH NC95A (manufactured by Sumika Chemical Analysis Center)”. The nitrogen content was quantified by analyzing with a gas chromatograph “GC-8A (manufactured by Shimadzu Corporation)”.

<Measurement of phosphorus content>
The phosphorus content was determined using an ICP emission spectrometer (P-4010, manufactured by Hitachi, Ltd.).

<Measurement of gel content>
About 70 mg of a raw rubber sample cut to 1 mm × 1 mm was accurately 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

<Heat aging resistance>
The Mooney viscosity ML _{1 + 4} (130 ° C.) of the solid rubber before and after being heat-treated at 80 ° C. for 18 hours was measured according to JIS K6300: 2001-1, and the heat aging index was calculated by the following formula. If the Mooney viscosity before heat treatment is in the range of 50 to 70, particularly in the range of 50 to 65, the physical properties are good and there is no need for mastication, which is excellent. If it is too low, the rubber properties are poor. Moreover, the greater the heat aging index, the better the heat aging resistance.
Heat aging index (%) = Mooney viscosity after heat treatment / Mooney viscosity before heat treatment × 100

Hereinafter, various materials used in Examples and Comparative Examples are shown together.
Modified natural rubber (modified NR): manufactured in Production Example 1 Natural rubber (NR): TSR20
Butadiene rubber (BR): BR730 manufactured by JSR Corporation (cis 1,4-content 95%)
Carbon black: Diablack I (ISAF carbon, N ₂ SA: 114 m ² / g, average particle size: 23 nm) manufactured by Mitsubishi Chemical Corporation
Silica: ULTRASIL® VN3 (N ₂ SA: 175 m ² / g) manufactured by Evonik Degussa
Silane coupling agent: Si266 manufactured by Evonik Degussa
Mineral oil: PS-32 (paraffinic process oil) manufactured by Idemitsu Kosan Co., Ltd.
Stearic acid: “paulownia” made by NOF Corporation
Zinc oxide: 2 types of anti-aging of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd .: NOCRACK 6C (N- (1,3-dimethylbutyl) -N-phenyl-p-phenylene manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.) Diamine)
Wax: Ozoace wax manufactured by Nippon Seiki Co., Ltd. Sulfur: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd. NS: Noxeller NS (N-tert-butyl- manufactured by Ouchi Shinsei Chemical Co., Ltd.) 2-benzothiazolylsulfenamide)
Vulcanization accelerator DPG: Noxeller D (1,3-diphenylguanidine) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

Examples 1-5 and Comparative Examples 1-4
In accordance with the formulation shown in step (I) of Table 2, the rubber component, silica and other materials are added and kneaded for 3 minutes at a discharge temperature of 150 ° C. using a 1.7 L Banbury mixer, A kneaded product containing silica (BR master batch) and a kneaded product containing modified natural rubber and silica (modified NR master batch) were obtained. Next, according to the blended product obtained and the formulation shown in step (II) of Table 2, other materials were added and kneaded at a discharge temperature of 150 ° C. for 5 minutes to obtain a kneaded product. To the obtained kneaded product, sulfur and a vulcanization accelerator were added according to the formulation shown in step (III) of Table 2, and kneaded at 150 ° C. for 5 minutes using an open roll to obtain an unvulcanized rubber composition. Obtained. In addition, only the process (II) was performed if there is no description of the blending amount in the process (I) of Table 2.

  Each obtained unvulcanized rubber composition was press vulcanized with a 0.5 mm thick mold at 170 ° C. for 12 minutes to obtain a vulcanized rubber composition.

  Further, each unvulcanized rubber composition obtained was molded into a cap tread shape, bonded together with other tire members, and vulcanized at 170 ° C. for 15 minutes, whereby a test studless tire (tire size: 195). / 65R15).

  The obtained vulcanized rubber composition and test studless tire were stored at room temperature, and those with 200 hours after vulcanization completion (about one week later) were evaluated for wear resistance, performance on ice, and uneven distribution of silica by the following tests. Went. Moreover, about the vulcanized rubber composition, the state after 200 hours from the completion of vulcanization and the state after one year from the completion of vulcanization were compared, and the temporal stability of the silica dispersion state was evaluated by the following test. Each test result is shown in Table 2.

<Abrasion resistance>
Using a Lambourne abrasion tester manufactured by Iwamoto Seisakusho, the amount of wear was measured at a surface rotation speed of 50 m / min, an additional load of 3.0 kg, a sandfall of 15 g / min and a slip rate of 20%. The inverse of was taken. And the reciprocal number of the abrasion amount of the comparative example 1 was set to 100, and the reciprocal number of the other abrasion amount was represented by the index | exponent. A larger index indicates better wear resistance. Note that the performance target value is 105 or more.

<Performance on ice>
Using the studless tires of Examples and Comparative Examples, actual vehicle performance was evaluated on ice under the following conditions. The test place was the Hokkaido Nayoro Test Course of Sumitomo Rubber Industries, Ltd., and the temperature on ice was −2 to −6 ° C. A test tire was mounted on a domestic 2000cc FR vehicle, and the stopping distance on ice required to stop the lock brake at 30 km / h was measured. And it computed from the following formula on the basis of the comparative example 1. Note that the performance target value is 110 or more.
(Performance on ice) = (braking stop distance of Comparative Example 1) / (stop distance of each formulation) × 100

<Evaluation of morphology and evaluation of uneven distribution of silica>
The vulcanized rubber composition was surfaced and observed using a scanning electron microscope (SEM). The morphology of each phase could be confirmed by contrast comparison. As a result, in Examples and Comparative Examples, it was confirmed that the phase containing butadiene rubber (BR phase) and the phase containing modified natural rubber (modified NR phase) were incompatible with each other. The BR phase formed a sea phase, the modified NR phase formed an island phase, and silica was dispersed in both the BR phase and the modified NR phase in the examples.

  Silica can be observed as a granular form. For the SEM photograph of one sample, 10 regions of 2 μm × 2 μm that do not overlap each other were selected. In each region, the silica area per unit area of each phase was measured, and the silica abundance γ of the BR phase was calculated. The difference between the maximum value and the minimum value of γ at 10 locations was confirmed to be within 10%, and the average of 10 γ values was listed as α in the table.

<Stability over time in silica dispersion>
In the same manner as described above, the silica abundance ratio α in the BR phase in the state one year after the completion of vulcanization was measured for the same vulcanized rubber composition. Then, the rate of change in the abundance ratio α of silica in the BR phase in the state one year after the completion of vulcanization was examined with reference to the abundance ratio α of silica in the BR phase in the state 200 hours after the completion of vulcanization.
Rate of change (%) = | α (after 1 year) −α (after 200 hours) | / α (after 200 hours) × 100

Examples and comparative examples were evaluated based on the following evaluation criteria. The smaller the rate of change, the better the results.
A: Change rate is within 10% B: Change rate is over 10%, and within 30% C: Change rate is over 30%

  From the results shown in Table 2, by preparing two master batches of BR and modified NR each containing silica, and having a production method in which they are kneaded, the silica has a good silica abundance α of the BR phase. It can be seen that a vulcanized rubber composition can be prepared and the dispersion stability of silica is good. It can also be seen that such a vulcanized rubber composition having a good BR phase silica abundance α can improve the wear resistance and on-ice performance in a well-balanced manner.

1 BR phase 2 IR phase 3 Silica 4 Carbon black

Claims (17)

(A) producing a masterbatch containing butadiene rubber and silica;
(B) producing a masterbatch containing modified natural rubber and silica;
(C) a step of kneading the master batch obtained in (a) and the master batch obtained in (b), and (d) a step of vulcanizing the kneaded product obtained in (c). A method for producing a vulcanized rubber composition comprising:
The modified natural rubber is obtained by removing a non-rubber component of natural rubber and then treating with an acidic compound, and the pH is adjusted to 2 to 7,
The vulcanized rubber composition is
A phase containing butadiene rubber and silica (BR phase) and a phase containing modified natural rubber and silica (modified NR phase);
The BR phase and the modified NR phase are incompatible with each other,
The abundance α of silica in the BR phase 100 hours to 500 hours after the completion of the vulcanization process satisfies the following formula 1.
A method for producing a vulcanized rubber composition, wherein the proportion of butadiene rubber β satisfies the following formula 2.
0.3 ≦ α ≦ 0.7 (Formula 1)
0.45 ≦ β ≦ 0.8 (Formula 2)
(Where α = silica amount in BR phase / (silica amount in BR phase + silica amount in modified NR phase)), and β = mass of butadiene rubber in vulcanized rubber composition / (vulcanized The mass of butadiene rubber in the rubber composition + the mass of modified natural rubber in the vulcanized rubber composition)) The manufacturing method of Claim 1 in which the masterbatch containing the said butadiene rubber and a silica contains 40 mass parts or more of silica with respect to 100 mass parts of butadiene rubbers. The production method according to claim 1 or 2, wherein the masterbatch containing the modified natural rubber and silica contains 15 parts by mass or more of silica with respect to 100 parts by mass of the modified natural rubber. The manufacturing method according to claim 1, wherein the butadiene rubber is a butadiene rubber having a cis 1,4 bond content of 90% or more. The vulcanized rubber composition contains 25 to 120 parts by mass of a filler and 15 to 80 parts by mass of a softening agent with respect to 100 parts by mass of a rubber component containing a modified natural rubber and a butadiene rubber. The manufacturing method of any one of Claims 1-4 which contains 50 mass% or more of silica with respect to the total amount of fillers. The manufacturing method according to any one of claims 1 to 5, wherein a phosphorus content in the rubber of the modified natural rubber is 200 ppm or less. The production method according to any one of claims 1 to 6, wherein a nitrogen content in the rubber of the modified natural rubber is 0.15% by mass or less. The modified natural rubber has a pH value of less than 2 mm square on each side, soaked in distilled water, extracted at 90 ° C. for 15 minutes while irradiating with microwaves, It is the value measured using the pH meter, The manufacturing method of any one of Claims 1-7. The manufacturing method according to claim 1, wherein the modified natural rubber has a heat aging index (Equation 3) after heat treatment at 80 ° C. for 18 hours of 75 to 120%.
Heat aging index = Mooney viscosity after heat treatment / Mooney viscosity before heat treatment × 100 (Formula 3) A vulcanized rubber composition having a phase containing butadiene rubber and silica (BR phase) and a phase containing modified natural rubber and silica (modified NR phase),
The modified natural rubber is obtained by removing a non-rubber component of natural rubber and then treating with an acidic compound, and the pH is adjusted to 2 to 7,
The BR phase and the modified NR phase are incompatible with each other,
The abundance α of silica in the BR phase 100 hours to 500 hours after the completion of the vulcanization process satisfies the following formula 1.
A vulcanized rubber composition in which the proportion β of butadiene rubber satisfies the following formula 2.
0.3 ≦ α ≦ 0.7 (Formula 1)
0.45 ≦ β ≦ 0.8 (Formula 2)
(Where α = silica amount in BR phase / (silica amount in BR phase + silica amount in modified NR phase)), and β = mass of butadiene rubber in vulcanized rubber composition / (vulcanized The mass of butadiene rubber in the rubber composition + the mass of modified natural rubber in the vulcanized rubber composition)) The vulcanized rubber composition according to claim 10 , wherein the butadiene rubber is a butadiene rubber having a cis 1,4 bond content of 90% or more. 25 to 120 parts by mass of filler and 15 to 80 parts by mass of a softening agent are contained with respect to 100 parts by mass of a rubber component containing modified natural rubber and butadiene rubber, and the filler is 50 parts by mass with respect to the total amount of filler. The vulcanized rubber composition according to claim 10 or 11, comprising at least silica. The vulcanized rubber composition according to any one of claims 10 to 12, wherein a phosphorus content in the rubber of the modified natural rubber is 200 ppm or less. The vulcanized rubber composition according to any one of claims 10 to 13, wherein a nitrogen content in the rubber of the modified natural rubber is 0.15% by mass or less. The modified natural rubber has a pH value of less than 2 mm square on each side, soaked in distilled water, extracted at 90 ° C. for 15 minutes while irradiating with microwaves, The vulcanized rubber composition according to any one of claims 10 to 14, which is a value measured using a pH meter. The vulcanized rubber composition according to any one of claims 10 to 15, wherein the modified natural rubber has a heat aging index (Equation 3) after heat treatment at 80 ° C for 18 hours of 75 to 120%.
Heat aging index = Mooney viscosity after heat treatment / Mooney viscosity before heat treatment × 100 (Formula 3) The studless tire which has a tread comprised with the vulcanized rubber composition of any one of Claims 10-16.