Rubber composition and method for producing the same

Abstract

To provide a silica-containing rubber composition that has improved low heat build-up property and wear resistance over conventional levels, and to provide a method for producing the same.SOLUTION: A rubber composition is provided, including at least one rubber component selected from natural rubber, conjugated diene homopolymer, conjugated diene copolymer and conjugated diene-aromatic vinyl copolymer, and silica, wherein when the storage elastic modulus for 0.4% strain, that for 3% strain and that for 100% strain each at 100°C are denoted as E'(0.4%) [MPa], E'(3%) [MPa] and E'(100%) [MPa] respectively, the difference between storage modulus E'(0.4%) and storage modulus E'(100%) A=E'(0.4%) - E'(100%) is 1.6 MPa or less, and the difference between storage modulus E'(0.4%) and storage modulus E'(3%) B=E'(0.4%) - E'(3%) satisfies the relation 0.252×A-0.007≥B≥0.252×A-0.130.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber composition having low heat buildup and excellent abrasion resistance, and a method for producing the same. [Background technology]

[0002] Environmental regulations for large vehicle tires fitted to trucks and buses are becoming stricter every year. For example, R117-02 was introduced in Europe in November 2016, and will come into effect in Japan in 2023. Furthermore, greenhouse gas (GHG) regulations are becoming stricter in North America, and each vehicle manufacturer is independently seeking fuel-efficiency standards that exceed these. Under these circumstances, tires for large vehicles must meet the fuel-efficiency requirements of both legal regulations and vehicle manufacturers while maintaining a high level of wear resistance, an important characteristic of tires for large vehicles.

[0003] Rubber compositions forming the treads of tires for large vehicles often contain natural rubber to ensure wear resistance. On the other hand, rubber compositions that improve fuel economy are required to have low heat buildup, and so a portion of the carbon black is replaced with silica. To further reduce heat buildup, increased amounts of silica and high dispersion are required. However, it is difficult to disperse a large amount of silica well in rubber compositions containing natural rubber or butadiene rubber. For this reason, the desired silica dispersion state cannot be achieved, making it extremely difficult to obtain a rubber composition that combines low heat buildup and high levels of wear resistance.

[0004] For example, Patent Documents 1 to 3 propose methods for kneading rubber compositions containing silica, but there is a problem that these methods are not necessarily sufficient to achieve the stricter standards for wear resistance and fuel economy performance of tires for large vehicles mentioned above. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4346351 [Patent Document 2] Patent No. 4243979 [Patent Document 3] Patent No. 4887673 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a silica-containing rubber composition having improved low heat buildup and abrasion resistance beyond conventional levels, and a method for producing the same. [Means for solving the problem]

[0007] The rubber composition of the present invention, which achieves the above object, is a rubber composition comprising at least one rubber component selected from natural rubber, a conjugated diene homopolymer, a conjugated diene copolymer, and a conjugated diene-aromatic vinyl copolymer, silica, and a silane coupling agent, and wherein the storage modulus of the rubber composition at 100°C and 0.4% strain is E' (0.4%) [MPa], 100°C, 3% strain, storage modulus E' (3%) [MPa], 100℃, 100% strain, storage modulus E' (100%) [MPa], and the storage elastic modulus E' (0.4%) and storage modulus E' (100%) The difference A is A=E' (0.4%) -E′ (100%) [MPa], the storage modulus E' (0.4%) and storage modulus E' (3%) The difference B is B=E' (0.4%) -E′ (3%) When expressed in [MPa], the difference A and the difference B in storage modulus satisfy the following relational expressions (1) and (2). A ≦ 1.6 (1) 0.252×A-0.007 ≧ B ≧ 0.252×A-0.130 (2)

[0008] The rubber composition of the present invention is a method for producing a rubber composition comprising at least one rubber component selected from natural rubber, a conjugated diene homopolymer, a conjugated diene copolymer, and a conjugated diene-aromatic vinyl copolymer, silica, and a silane coupling agent, and is characterized in that the method includes at least one silica introduction and kneading step of introducing silica into a kneader, kneading the silica, and discharging the silica, and after the silica introduction and kneading step, includes a total kneading step of kneading the rubber composition and discharging the silica, the silica introduction and kneading step is carried out at a mixing temperature of less than 140°C, and at least one total kneading step is carried out at a mixing temperature of 140°C or higher and 160°C or lower. [Effects of the Invention]

[0009] According to the rubber composition of the present invention, silica is well dispersed, so that low heat buildup and abrasion resistance can be improved beyond conventional levels.

[0010] According to the method for producing a rubber composition of the present invention, silica is well distributed macroscopically in the rubber composition in the silica addition and kneading step, and then in the total kneading step in which the components are mixed at 140°C or higher and 160°C or lower, the silica and the silane coupling agent are reacted to disperse the silica more microscopically, thereby enabling the silica to be well dispersed at a high level, making it possible to produce a rubber composition with improved low heat buildup and wear resistance beyond conventional levels. DETAILED DESCRIPTION OF THE INVENTION

[0011] The rubber composition of the present invention contains, as a rubber component, at least one selected from natural rubber, conjugated diene homopolymer, conjugated diene copolymer, and conjugated diene-aromatic vinyl copolymer. The natural rubber may be any natural rubber commonly used in rubber compositions. The conjugated diene homopolymer may also be any natural rubber commonly used in rubber compositions, such as isoprene rubber, butadiene rubber, butyl rubber, chloroprene rubber, and acrylic rubber. Of these, isoprene rubber, butadiene rubber, and butyl rubber are preferred. The conjugated diene copolymer may also be any natural rubber commonly used in rubber compositions, such as butadiene-isoprene rubber, acrylonitrile-butadiene rubber, ethylene-acrylic rubber, and ethylene-propylene-diene rubber. The conjugated diene-aromatic vinyl copolymer may be one that is commonly used in rubber compositions, such as emulsion-polymerized styrene-butadiene rubber, solution-polymerized styrene-butadiene rubber, styrene-isoprene rubber, emulsion-polymerized styrene-butadiene-isoprene rubber, solution-polymerized styrene-butadiene-isoprene rubber, and emulsion-polymerized styrene-acrylonitrile-butadiene rubber.

[0012] The rubber component may be unmodified, or may be modified natural rubber, modified conjugated diene homopolymer, modified conjugated diene copolymer, or modified conjugated diene-aromatic vinyl copolymer, each of which has various functional groups at the molecular chain terminals and / or side chains. It is particularly preferable to use at least one selected from the group consisting of conjugated diene homopolymers having a modifying group, conjugated diene copolymers having a modifying group, and conjugated diene-aromatic vinyl copolymers having a modifying group. Examples of functional groups include halogens such as chlorine, bromine, and iodine, hydroxy groups, hydroxysilyl groups, amino groups, alkoxy groups, silyl groups, carboxyl groups, epoxy groups, carbonyl groups, amide groups, oxysilyl groups, silanol groups, isocyanate groups, isothiocyanate groups, and aldehyde groups.

[0013] Among the rubber components, natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, modified natural rubber, modified butadiene rubber, and modified styrene-butadiene rubber are preferred. The natural rubber and modified natural rubber are preferably contained in an amount of 30% by mass or more, more preferably 40 to 70% by mass, based on 100% by mass of the rubber component. By containing 30% by mass or more of natural rubber and modified natural rubber, the breaking properties are improved, which is preferred.

[0014] The butadiene rubber and modified butadiene rubber are preferably contained in an amount of 10 to 40 mass%, more preferably 15 to 35 mass%, based on 100 mass% of the rubber component. A butadiene rubber and modified butadiene rubber content of 10 mass% or more is preferred because it enhances abrasion resistance. Furthermore, a butadiene rubber and modified butadiene rubber content of 40 mass% or less is preferred because it also achieves high breaking strength.

[0015] The styrene-butadiene rubber and modified styrene-butadiene rubber are preferably contained in an amount of 10% by mass or more, more preferably 15 to 90% by mass, based on 100% by mass of the rubber component. By containing 10% by mass or more of the styrene-butadiene rubber and modified styrene-butadiene rubber, tear resistance and crack resistance are improved, which is preferable.

[0016] The silica is not particularly limited, and may be any silica commonly used in rubber compositions. For example, wet-process silica (hydrated silicic acid), dry-process silica (anhydrous silicic acid), calcium silicate, aluminum silicate, carbon-silica (dual-phase filler) in which silica is supported on the surface of carbon black, or surface-treated silica treated with a compound reactive or compatible with both silica and rubber, such as a silane coupling agent or polysiloxane, may be used. These silicas may be used alone or in combination of two or more.

[0017] The CTAB adsorption specific surface area of ​​silica is not particularly limited, but is preferably 100 to 250 m 2 / g, more preferably 120 to 210 m2 / g. The CTAB adsorption specific surface area of ​​silica is 100m 2 By increasing the CTAB adsorption specific surface area of ​​silica to 250 m / g or more, the abrasion resistance and mechanical properties of the rubber composition can be ensured. 2 / g or less, wet performance and low heat buildup can be improved. In this specification, the CTAB specific surface area of ​​silica is a value measured in accordance with ISO 5794.

[0018] The silica is preferably blended in an amount of 20 to 200 parts by mass, more preferably 25 to 160 parts by mass, and even more preferably 30 to 100 parts by mass per 100 parts by mass of the rubber component. By blending 20 or more parts by mass of silica, wet performance and low heat buildup can be improved. Furthermore, by blending 200 or less parts by mass of silica, wear resistance can be ensured.

[0019] The rubber composition preferably contains a silane coupling agent together with silica, which improves the dispersibility of the silica. The silane coupling agent may be a type that is normally contained in a compound with silica. The silane coupling agent is preferably contained in an amount of 2 to 20 mass %, more preferably 4 to 15 mass %, of the silica amount. By containing the silane coupling agent in an amount of 2 mass % or more of the silica amount, the effect of improving the dispersibility of the silica is obtained, which is preferable. Furthermore, by containing the silane coupling agent in an amount of 20 mass % or less, condensation between the silane coupling agents is suppressed, which is preferable, and the desired effect can be obtained.

[0020] The silane coupling agent is not particularly limited as long as it can be used in a rubber composition containing silica, and examples thereof include sulfur-containing silane coupling agents and amino group-containing silane coupling agents. Examples of silane coupling agents include sulfur-containing silane coupling agents such as bis-(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)disulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, γ-mercaptopropyltriethoxysilane, and 3-octanoylthio-1-propyltriethoxysilane; and amino group-containing silane coupling agents such as 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, and N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride. Preferably, a silane coupling agent having a blocked mercapto group, such as 3-octanoylthio-1-propyltriethoxysilane, can be used.

[0021] The rubber composition preferably contains an alkylsilane having an alkyl group with 7 to 20 carbon atoms and / or a liquid polymer in addition to the silica and silane coupling agent, which can improve the dispersibility of the silica.

[0022] Examples of alkylsilanes include alkyltriethoxysilanes and alkyltrimethoxysilanes having an alkyl group of 7 to 20 carbon atoms. Examples of alkyl groups include heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, and icosyl groups. Among these, from the viewpoint of compatibility with rubber components, alkyl groups having 8 to 10 carbon atoms are more preferred, and octyl and nonyl groups are even more preferred. Preferred alkylsilanes include octyltriethoxysilane, octyltrimethoxysilane, nonyltriethoxysilane, and nonyltrimethoxysilane.

[0023] The amount of alkylsilane to be added is preferably 1 to 20% by mass, more preferably 2 to 15% by mass, based on the amount of silica. By adding alkylsilane in an amount of 1% by mass or more of the amount of silica, the dispersibility of silica can be improved. Furthermore, by adding alkylsilane in an amount of 20% by mass or less of the amount of silica, deterioration of the breaking properties can be suppressed, which is preferable.

[0024] The liquid polymer is not particularly limited as long as it can be used in a rubber composition, and examples thereof include liquid butyl rubber, liquid isoprene rubber, liquid butadiene rubber, and liquid styrene-butadiene rubber.

[0025] The blending amount of the liquid polymer is preferably 1 to 20% by mass, more preferably 2 to 15% by mass, based on the amount of silica. Blending the liquid polymer in an amount of 1% by mass or more of the amount of silica can improve the dispersibility of the silica. Blending the liquid polymer in an amount of 20% by mass or less of the amount of silica is also preferred because it prevents deterioration of the breaking properties.

[0026] The rubber composition may contain fillers other than silica. Examples of such fillers include carbon black, calcium carbonate, magnesium carbonate, talc, clay, alumina, aluminum hydroxide, titanium oxide, and calcium sulfate. These may be used alone or in combination of two or more.

[0027] Examples of carbon black include furnace carbon blacks such as SAF, ISAF, HAF, FEF, GPF, HMF, and SRF, which may be used alone or in combination of two or more. The nitrogen adsorption specific surface area of ​​the carbon black is not particularly limited, but is preferably 70 to 240 m 2 / g, more preferably 90 to 200m 2 / g. The nitrogen adsorption specific surface area of ​​carbon black is preferably 70m 2 By increasing the specific surface area of ​​the carbon black by nitrogen adsorption to 240 m / g or more, the mechanical properties and abrasion resistance of the rubber composition can be ensured. 2 / g or less, the low heat buildup property can be improved. In this specification, the nitrogen adsorption specific surface area of ​​carbon black is measured in accordance with JIS K6217-2.

[0028] The amount of carbon black to be blended is preferably 5 to 100 parts by mass, more preferably 10 to 80 parts by mass, per 100 parts by mass of the rubber component. By blending the amount of carbon black at 5 parts by mass or more, the mechanical properties and abrasion resistance of the rubber composition can be ensured. Furthermore, by blending the amount of carbon black at 100 parts by mass or less, low heat buildup can be ensured.

[0029] The rubber composition may contain various commonly used additives, such as vulcanizing or crosslinking agents, vulcanization accelerators, antioxidants, plasticizers, processing aids, terpene resins, and thermosetting resins, within the range that does not impair the object of the present invention. Furthermore, such additives can be mixed and kneaded with the rubber component to form a rubber composition, which can then be used for vulcanization or crosslinking. The amounts of these additives may be conventional amounts, as long as they do not interfere with the object of the present invention.

[0030] The rubber composition of the present invention has a storage modulus of E' at 100°C and 0.4% strain. (0.4%) [MPa], 100°C, 3% strain, storage modulus E' (3%) [MPa], 100℃, 100% strain, storage modulus E' (100%) [MPa] and storage modulus E' (0.4%) and storage modulus E' (100%) The difference A is A=E' (0.4%) -E′ (100%) [MPa], storage modulus E′ (0.4%) and storage modulus E' (3%) The difference B is B=E' (0.4%) -E′ (3%) When expressed in [MPa], the difference A and the difference B in storage modulus satisfy the following relational expressions (1) and (2). A ≦ 1.6 (1) 0.252×A-0.007 ≧ B ≧ 0.252×A-0.130 (2) In this specification, the storage modulus is defined as E' (0.4%) , E′ (3%) , and E′ (100%) is the dynamic storage modulus E' [unit: MPa] at dynamic strains of 0.4%, 3%, and 100%, measured using a viscoelasticity spectrometer under conditions of a temperature of 100°C, a frequency of 10 Hz, and an initial strain of 0.5%, while changing the dynamic strain from 0.2% to 100% in accordance with JIS-K6394.

[0031] The difference in storage modulus A [MPa] is A = E' (0.4%) -E′ (100%)and is 1.6 MPa or less, preferably 0.75 MPa or more and 1.6 MPa or less, as shown in relational expression (1). By making the storage modulus difference A 1.6 MPa or less, the dispersibility of silica improves and rolling resistance decreases. By setting the lower limit of the storage modulus difference A to 0.75 MPa, it is possible to achieve the desired filler compounding amount and rubber crosslink density, and thus it is preferable to increase abrasion resistance.

[0032] The difference in storage modulus B [MPa] is A = E' (0.4%) -E′ (3%) and satisfies the relational expression (2) with the difference A in storage modulus. 0.252×A-0.007 ≧ B ≧ 0.252×A-0.130 (2) By making the storage modulus difference B equal to or greater than (0.252 × A - 0.130), the filler content can be adjusted to the desired amount, improving abrasion resistance. Furthermore, by making the storage modulus difference B equal to or less than (0.252 × A - 0.007), the number of large, poorly dispersed silica agglomerates is reduced, resulting in low rolling resistance. It is more preferable that the storage modulus difference B and the storage modulus difference A satisfy the relationship (3). 0.252×A-0.027 ≧ B ≧ 0.252×A-0.110 (3)

[0033] When a cross section of the rubber composition of the present invention is measured using a disper grader in accordance with ISO 11345, the frequency of white areas originating from particles or particle agglomerates of 10 μm or less is preferably 80% or more of the frequency of white areas originating from particles or particle agglomerates of 65 μm or less. In this specification, the frequency of white areas refers to the number of particles and particle agglomerates of the corresponding size.

[0034] By setting the frequency of white areas originating from particles or particle agglomerates of 10 μm or less at 80% or more of the frequency of white areas originating from particles or particle agglomerates of 65 μm or less, the number of large, poorly dispersed agglomerates in silica dispersion is reduced, which is preferable because rolling resistance is reduced. The frequency of white areas originating from particles or particle agglomerates of 10 μm or less is more preferably 85% or more, and even more preferably 88% or more.

[0035] In this specification, the frequency value of white areas originating from particles or particle agglomerates having various diameters is measured in accordance with ISO 11345 using a Disper Grader (Disper Tester 3000 manufactured by MonTech) at a magnification of 100x after cutting a flat, scratch-free edge of a vulcanized rubber composition with a sample preparation cutter.

[0036] Generally, the manufacturing method of a rubber composition consists of at least two steps: a kneading step in which raw materials excluding vulcanization compounding agents such as rubber components, silica, and silane coupling agents are mixed and kneaded, and a final mixing step in which the mixture obtained in this kneading step is cooled and mixed with vulcanization compounding agents.

[0037] The production method of the present invention can use a mixer (kneader) that is normally used in the production of rubber compositions for tires. The rotors constituting the mixer may be either intermeshing or non-intermeshing. The rotation speed of the rotors can be set to the same rotation speed as normally used in the production of rubber compositions for tires.

[0038] The method for producing the rubber composition of the present invention includes the above-mentioned kneading step multiple times, i.e., at least one silica-introducing and kneading step of introducing silica into a kneader, kneading the silica, and discharging the silica, and at least one total-mixing step of kneading the rubber composition and discharging the silica after the silica-introducing and kneading step. That is, the silica-introducing and kneading step and the total-mixing step can each be carried out once or more, and may also be carried out twice or more.

[0039] The silica addition and kneading step is a step in which silica is added to a kneader, kneaded at a mixing temperature of less than 140°C, and then discharged. The silica addition and kneading step may be performed as the first step in producing a rubber composition. Alternatively, a step in which at least a portion of the raw materials other than silica are added to, kneaded with, and discharged from the kneader may be performed prior to the silica addition and kneading step. In either silica addition and kneading step, some or all of the other raw materials can be added and mixed before, simultaneously with, or after the silica is added to the kneader. A preferred silica addition and kneading step is to first add and mix silica and a silane coupling agent to an empty kneader, and then add, knead, and discharge at least a portion of the rubber component into the kneader. By first mixing the silica and the silane coupling agent, the mixer temperature can be lowered, which in turn lowers the temperature when the rubber component is subsequently kneaded, thereby increasing the mixing intensity within the mixer and improving the silica distribution. The entire amount of silica designed may be charged into the kneader at once, or a portion thereof may be divided and charged and mixed into the kneader in the same silica charging and kneading step or in different silica charging and kneading steps. That is, the silica charging and kneading step may be carried out once or more, or may be carried out twice, as described above.

[0040] In the silica introduction and kneading step, silica is introduced into a kneader and kneaded at a mixing temperature of less than 140°C, preferably 125°C to 135°C, and then discharged. Mixing and kneading silica at temperatures less than 140°C allows the silica to be well physically distributed throughout the rubber component. Furthermore, by keeping the mixing temperature below 140°C, reaction between the silica and the silane coupling agent is suppressed during mixing, allowing both to be simultaneously and well distributed throughout the rubber component. This prevents the silica and silane coupling agent from reacting while remaining in large chunks.

[0041] When the silica addition and kneading step is carried out two or more times, the silane coupling agent may be added in its entirety in one silica addition and kneading step, or may be added in multiple divided portions.Furthermore, in the silica addition and kneading step and the total amount kneading step, the silane coupling agent may be added in multiple divided portions.Adding the silane coupling agent in multiple divided portions is preferable because it inhibits the reaction between the silane coupling agent and silica before the physical dispersion of the silica is sufficiently advanced.

[0042] The total mixing step is a mixing step carried out after the silica introduction and mixing step and before the final mixing step of mixing the vulcanization compounding ingredients, and is carried out at a mixing temperature of 140°C to 160°C. By mixing at a temperature of 140°C to 160°C, the silica and silane coupling agent that have been well distributed in the silica introduction and mixing step can react with each other, thereby improving the dispersibility of the silica in the rubber component. The mixing temperature in the total mixing step is preferably 145°C to 155°C.

[0043] In the full-mixing step, a rubber composition containing all raw materials except for the vulcanization-related compounding agents can be added and mixed. However, this does not apply to compounding materials that are preferably added and mixed in the final mixing step, such as thermally expandable microcapsules and hollow fillers. Furthermore, compounding agents other than the vulcanization-related compounding agents may be added and mixed simultaneously with the rubber components, or added and mixed after the rubber components have been mixed. Examples of compounding agents other than the vulcanization-related compounding agents include various additives commonly used in rubber compositions for tires, such as antioxidants, plasticizers, processing aids, liquid polymers, terpene resins, rosin resins, petroleum resins, and thermosetting resins. These compounding agents may be added in conventional amounts as long as they do not deviate from the objectives of the present invention. For example, fillers other than silica, such as carbon black, may be added and mixed simultaneously with the rubber components, or so-called rubber chemicals, such as zinc oxide, stearic acid, and antioxidants, may be added and mixed simultaneously with the rubber components, or aromatic oils may be added and mixed after the rubber components have been mixed.

[0044] After the silica addition and kneading step, a total mixing step performed at a mixing temperature of 140°C or higher and 160°C or lower can be performed once or more, and at least one kneading step performed at a mixing temperature lower than 140°C can be performed. The components kneaded in this kneading step may be the same as those in the silica addition and kneading step, or may be the same as those in the total mixing step. The kneading step lower than 140°C is preferably performed before the total mixing step performed at a mixing temperature of 140°C or higher and 160°C or lower. By performing the kneading step lower than 140°C before the total mixing step, the silica can be physically dispersed well in the rubber component before the reaction between the silica and the silane coupling agent, which is preferable.

[0045] The present invention will be further explained below with reference to examples, but the scope of the present invention is not limited to these examples. [Example]

[0046] Examples 1 to 3, 9 to 11, Standard Examples 1 and 2, and Comparative Examples 1 to 3 Eleven rubber compositions (Examples 1-3, 9-11, Reference Examples 1-2, and Comparative Examples 1-3) listed in Tables 1 and 3, each having the common formulation shown in Table 5, were produced by carrying out the silica-adding and kneading step A and the total-mixing step A shown in Tables 1 and 3. Because SBR2 is an oil-extended product containing 37.5 parts by mass of oil, the amount of SBR2 is listed in the upper column, and the net amount of SBR is listed in parentheses in the lower column. The same applies to Table 4, which will be described later. The common formulations of the rubber compositions in Table 5 are listed in parts by mass per 100 parts by mass of the rubber components in Tables 1 and 3. In the silica-adding and kneading step A, raw materials except for sulfur and vulcanization accelerator were added to a mixer (a 1.7-liter internal Banbury mixer, manufactured by Kobe Steel, Ltd.) and kneaded at the mixing temperature for the silica-adding and kneading step A shown in Tables 1 and 3. Mixture 1 was obtained and discharged from the mixer. Next, in the total mixing step A, the kneaded material 1 was again charged into the mixer and kneaded at the mixing temperature of the total mixing step A shown in Tables 1 and 3 to obtain the kneaded material 2, which was then discharged from the mixer. Thereafter, the kneaded material 2, sulfur, and a vulcanization accelerator were charged into a roll and mixed to prepare a rubber composition.

[0047] Example 4 The rubber composition of Example 4 in Table 2, which had the common formulation shown in Table 5, was produced by carrying out the silica introduction kneading step A and the total amount kneading step A. The common formulation of the rubber compositions in Table 5 is shown in parts by mass relative to 100 parts by mass of the rubber component in Table 2. In the silica introduction kneading step A, first, silica and a coupling agent were introduced into a mixer (a 1.7-liter internal Banbury mixer, manufactured by Kobe Steel, Ltd.) and mixed. Raw materials other than silica, coupling agent, sulfur, and vulcanization accelerator were introduced into the mixer and kneaded at the mixing temperature of the silica introduction kneading step A to obtain kneaded product 1, which was then discharged from the mixer. Next, in the total amount kneading step A, kneaded product 1 was introduced into the mixer again and kneaded at the mixing temperature of the total amount kneading step A to obtain kneaded product 2, which was then discharged from the mixer. Subsequently, kneaded product 2, sulfur, and a vulcanization accelerator were introduced into a roll and mixed to prepare the rubber composition of Example 4.

[0048] Example 5 The rubber composition of Example 5 in Table 2, having the common formulation shown in Table 5, was produced by carrying out the silica introduction and kneading step A, the silica introduction and kneading step B, and the total amount kneading step A. The common formulation of the rubber composition in Table 5 is shown in parts by mass relative to 100 parts by mass of the rubber component in Table 2. In the silica introduction and kneading step A, the common compounding ingredients except for sulfur and the vulcanization accelerator, and the raw materials listed in the silica introduction and kneading step A in Table 2 were charged into a mixer (a 1.7-liter internal Banbury mixer, manufactured by Kobe Steel, Ltd.) and kneaded at the mixing temperature for the silica introduction and kneading step A to obtain kneaded product 1, which was then discharged from the mixer. Next, in the silica introduction and kneading step B, kneaded product 1 and the raw materials listed in the silica introduction and kneading step B in Table 2 were again charged into the mixer and kneaded at the mixing temperature for the silica introduction and kneading step B to obtain kneaded product 2, which was then discharged from the mixer. Further, in the total mixing step A, the kneaded material 2 was again charged into the mixer and kneaded at the mixing temperature of the total mixing step A to obtain the kneaded material 3, which was then discharged from the mixer. Thereafter, the kneaded material 3, sulfur, and a vulcanization accelerator were charged into a roll and mixed to prepare the rubber composition of Example 5.

[0049] Example 6 The rubber composition of Example 6 in Table 2, having the common formulation shown in Table 5, was produced by carrying out the silica introduction and kneading step A, the silica introduction and kneading step B, and the total amount kneading step A. The common formulation of the rubber compositions in Table 5 is shown in parts by mass relative to 100 parts by mass of the rubber component in Table 2. In the silica introduction and kneading step A, first, silica and a coupling agent were charged into a mixer (a 1.7-liter internal Banbury mixer manufactured by Kobe Steel, Ltd.) and mixed. The silica, the coupling agent, the common compounding ingredients excluding the sulfur and vulcanization accelerator listed in Table 5, and the raw materials listed in the silica introduction and kneading step A in Table 2 were charged into the mixer and kneaded at the mixing temperature of the silica introduction and kneading step A to obtain kneaded product 1, which was then discharged from the mixer. Next, in the silica introduction and kneading step B, kneaded product 1 and the raw materials listed in the silica introduction and kneading step B in Table 2 were again charged into the mixer and kneaded at the mixing temperature of the silica introduction and kneading step B to obtain kneaded product 2, which was then discharged from the mixer. Further, in the total mixing step A, the kneaded material 2 was again charged into the mixer and kneaded at the mixing temperature of the total mixing step A to obtain the kneaded material 3, which was then discharged from the mixer. Thereafter, the kneaded material 3, sulfur, and a vulcanization accelerator were charged into a roll and mixed to prepare the rubber composition of Example 6.

[0050] Example 7 The rubber composition of Example 7 in Table 2, having the common formulation shown in Table 5, was produced by carrying out the silica introduction kneading step A, the total amount kneading step A, and the total amount kneading step B. The common formulation of the rubber composition in Table 5 is shown in parts by mass relative to 100 parts by mass of the rubber component in Table 2. In the silica introduction kneading step A, the common compounding ingredients except for sulfur and the vulcanization accelerator, and the raw materials listed in the silica introduction kneading step A in Table 2 were introduced into a mixer (a 1.7-liter internal Banbury mixer, manufactured by Kobe Steel, Ltd.) and kneaded at the mixing temperature of the silica introduction kneading step A to obtain kneaded product 1, which was then discharged from the mixer. Next, in the total amount kneading step A, kneaded product 1 was introduced into the mixer again and kneaded at the mixing temperature of the total amount kneading step A to obtain kneaded product 2, which was then discharged from the mixer. Furthermore, in the total amount kneading step B, kneaded product 2 was introduced into the mixer again and kneaded at the mixing temperature of the total amount kneading step B to obtain kneaded product 3, which was then discharged from the mixer. Thereafter, the kneaded material 3, sulfur, and vulcanization accelerator were charged into the roll and mixed, thereby preparing the rubber composition of Example 7.

[0051] Example 8 The rubber composition of Example 8 in Table 2, having the common formulation shown in Table 5, was produced by carrying out the silica introduction and kneading step A, the silica introduction and kneading step B, the total amount kneading step A, and the total amount kneading step B. The common formulation of the rubber composition in Table 5 is shown in parts by mass per 100 parts by mass of the rubber component in Table 2. In the silica introduction and kneading step A, the common compounding ingredients except for sulfur and the vulcanization accelerator, and the raw materials listed in the silica introduction and kneading step A in Table 2 were charged into a mixer (a 1.7-liter internal Banbury mixer, manufactured by Kobe Steel, Ltd.) and kneaded at the mixing temperature for the silica introduction and kneading step A to obtain kneaded product 1, which was then discharged from the mixer. Next, in the silica introduction and kneading step B, kneaded product 1 and the raw materials listed in the silica introduction and kneading step B in Table 2 were again charged into the mixer and kneaded at the mixing temperature for the silica introduction and kneading step B to obtain kneaded product 2, which was then discharged from the mixer. Next, in the total mixing step A, the kneaded material 2 was again charged into the mixer and kneaded at the mixing temperature of the total mixing step A to obtain the kneaded material 3, which was then discharged from the mixer. Furthermore, in the total mixing step B, the kneaded material 3 was again charged into the mixer and kneaded at the mixing temperature of the total mixing step B to obtain the kneaded material 4, which was then discharged from the mixer. Thereafter, the kneaded material 4, sulfur, and a vulcanization accelerator were charged into a roll and mixed to prepare the rubber composition of Example 8.

[0052] Example 12 The rubber composition of Example 12 in Table 4, which had the common formulation shown in Table 5, was produced by performing the silica introduction kneading step A and the total amount kneading step A. The common formulation of the rubber compositions in Table 5 is shown in parts by mass relative to 100 parts by mass of the rubber component in Table 4. In the silica introduction kneading step A, first, silica and a coupling agent were introduced into a mixer (a 1.7-liter internal Banbury mixer manufactured by Kobe Steel, Ltd.) and mixed. Raw materials other than silica, coupling agent, sulfur, and vulcanization accelerator were introduced into the mixer and kneaded at the mixing temperature of the silica introduction kneading step A to obtain kneaded product 1, which was then discharged from the mixer. Next, in the total amount kneading step A, kneaded product 1 was introduced into the mixer again and kneaded at the mixing temperature of the total amount kneading step A to obtain kneaded product 2, which was then discharged from the mixer. Subsequently, kneaded product 2, sulfur, and a vulcanization accelerator were introduced into a roll and mixed to prepare the rubber composition of Example 12.

[0053] Example 13 The rubber composition of Example 13 in Table 4, having the common formulation shown in Table 5, was produced by carrying out the silica introduction and kneading step A, the silica introduction and kneading step B, and the total amount kneading step A. The common formulation of the rubber composition in Table 5 is shown in parts by mass relative to 100 parts by mass of the rubber component in Table 4. In the silica introduction and kneading step A, the common compounding ingredients excluding sulfur and the vulcanization accelerator, and the raw materials listed in the silica introduction and kneading step A in Table 4 were charged into a mixer (a 1.7-liter internal Banbury mixer, manufactured by Kobe Steel, Ltd.) and kneaded at the mixing temperature for the silica introduction and kneading step A to obtain kneaded product 1, which was then discharged from the mixer. Next, in the silica introduction and kneading step B, kneaded product 1 and the raw materials listed in the silica introduction and kneading step B in Table 4 were again charged into the mixer and kneaded at the mixing temperature for the silica introduction and kneading step B to obtain kneaded product 2, which was then discharged from the mixer. Further, in the total mixing step A, the kneaded material 2 was again charged into the mixer and kneaded at the mixing temperature of the total mixing step A to obtain the kneaded material 3, which was then discharged from the mixer. Thereafter, the kneaded material 3, sulfur, and a vulcanization accelerator were charged into a roll and mixed to prepare the rubber composition of Example 13.

[0054] Example 14 The rubber composition of Example 14 in Table 4, having the common formulation shown in Table 5, was produced by carrying out the silica introduction and kneading step A, the silica introduction and kneading step B, and the total amount kneading step A. The common formulation of the rubber composition in Table 5 is shown in parts by mass relative to 100 parts by mass of the rubber component in Table 4. In the silica introduction and kneading step A, first, silica and a coupling agent were charged into a mixer (a 1.7-liter internal Banbury mixer manufactured by Kobe Steel, Ltd.) and mixed. The silica, the coupling agent, the common compounding ingredients excluding the sulfur and vulcanization accelerator listed in Table 5, and the raw materials listed in the silica introduction and kneading step A in Table 4 were charged into the mixer and kneaded at the mixing temperature of the silica introduction and kneading step A to obtain kneaded product 1, which was then discharged from the mixer. Next, in the silica introduction and kneading step B, kneaded product 1 and the raw materials listed in the silica introduction and kneading step B in Table 2 were again charged into the mixer and kneaded at the mixing temperature of the silica introduction and kneading step B to obtain kneaded product 2, which was then discharged from the mixer. Further, in the total mixing step A, the kneaded material 2 was again charged into the mixer and kneaded at the mixing temperature of the total mixing step A to obtain the kneaded material 3, which was then discharged from the mixer. Thereafter, the kneaded material 3, sulfur, and a vulcanization accelerator were charged into a roll and mixed to prepare the rubber composition of Example 14.

[0055] Example 15 The rubber composition of Example 15 in Table 4, having the common formulation shown in Table 5, was produced by carrying out the silica introduction kneading step A, the total amount kneading step A, and the total amount kneading step B. The common formulation of the rubber composition in Table 5 is shown in parts by mass relative to 100 parts by mass of the rubber component in Table 4. In the silica introduction kneading step A, the common compounding ingredients excluding sulfur and vulcanization accelerator, and the raw materials listed in the silica introduction kneading step A in Table 4 were introduced into a mixer (a 1.7-liter internal Banbury mixer, manufactured by Kobe Steel, Ltd.) and kneaded at the mixing temperature of the silica introduction kneading step A to obtain kneaded product 1, which was then discharged from the mixer. Next, in the total amount kneading step A, kneaded product 1 was introduced into the mixer again and kneaded at the mixing temperature of the total amount kneading step A to obtain kneaded product 2, which was then discharged from the mixer. Furthermore, in the total amount kneading step B, kneaded product 2 was introduced into the mixer again and kneaded at the mixing temperature of the total amount kneading step B to obtain kneaded product 3, which was then discharged from the mixer. Thereafter, the kneaded material 3, sulfur, and vulcanization accelerator were charged into the roll and mixed, thereby preparing a rubber composition of Example 15.

[0056] Example 16 The rubber composition of Example 16 in Table 4, having the common formulation shown in Table 5, was produced by carrying out the silica introduction and kneading step A, the silica introduction and kneading step B, the total amount kneading step A, and the total amount kneading step B. The common formulation of the rubber composition in Table 5 is shown in parts by mass per 100 parts by mass of the rubber component in Table 4. In the silica introduction and kneading step A, the common compounding ingredients except for sulfur and the vulcanization accelerator, and the raw materials listed in the silica introduction and kneading step A in Table 2 were charged into a mixer (a 1.7-liter internal Banbury mixer, manufactured by Kobe Steel, Ltd.) and kneaded at the mixing temperature for the silica introduction and kneading step A to obtain kneaded product 1, which was then discharged from the mixer. Next, in the silica introduction and kneading step B, kneaded product 1 and the raw materials listed in the silica introduction and kneading step B in Table 4 were again charged into the mixer and kneaded at the mixing temperature for the silica introduction and kneading step B to obtain kneaded product 2, which was then discharged from the mixer. Next, in the total mixing step A, the kneaded product 2 was again charged into the mixer and kneaded at the mixing temperature of the total mixing step A to obtain the kneaded product 3, which was then discharged from the mixer. Furthermore, in the total mixing step B, the kneaded product 3 was again charged into the mixer and kneaded at the mixing temperature of the total mixing step B to obtain the kneaded product 4, which was then discharged from the mixer. Thereafter, the kneaded product 4, sulfur, and a vulcanization accelerator were charged into a roll and mixed to prepare the rubber composition of Example 16.

[0057] The resulting tire rubber composition was vulcanized at 150°C for 30 minutes using a mold of a predetermined shape (inner dimensions: length 150 mm, width 150 mm, thickness 2 mm) to prepare vulcanized rubber test pieces. The resulting vulcanized rubber test pieces were used to measure dynamic viscoelasticity, silica dispersion (% frequency of white areas of 10 μm or less), abrasion resistance, and low rolling resistance using the test methods described below.

[0058] Dynamic Viscoelasticity Using the obtained vulcanized rubber test piece, a viscoelasticity spectrometer (EPLEXOR 500N manufactured by GABO) was used in accordance with JIS-K6394. The dynamic storage modulus E' [Mpa] was measured at a dynamic strain of 0.4%, 3%, and 100% under the conditions of a temperature of 100°C, a frequency of 10 Hz, and an initial strain of 0.5%, while changing the dynamic strain from 0.2% to 100%. E' (0.4%) , E′ (3%) , and E′ (100%)From the results obtained, A=E′ (0.4%) -E′ (100%) [MPa] B=E′ (0.4%) -E′ (3%) [MPa] were calculated and are shown in Tables 1 to 4. In addition, the values ​​of the left and right sides of the relational expression (2) were calculated and are also shown.

[0059] Silica dispersion (percentage of white area frequency value of 10 μm or less) The silica dispersion of the resulting vulcanized rubber test pieces was measured in accordance with ISO 11345 using a MonTech Disper Tester 3000. The vulcanized rubber test pieces were cut with a specimen cutter to create a flat, scratch-free cut, and then observed at 100x magnification to measure the frequency of white areas originating from particles or particle agglomerates of 10 μm or less and from particles or particle agglomerates of 65 μm or less. From the results obtained, the percentage of the frequency of white areas originating from particles or particle agglomerates of 10 μm or less relative to the frequency of white areas originating from particles or particle agglomerates of 65 μm or less was calculated and is shown in Tables 1 to 4. A higher percentage of the frequency of white areas of 10 μm or less indicates better silica dispersibility.

[0060] Abrasion resistance (Lambourn abrasion) The resulting test pieces were subjected to measurement of wear in accordance with JIS K6264 using a Lambourn abrasion tester (manufactured by Iwamoto Seisakusho Co., Ltd.) under conditions of a temperature of 20°C, a load of 39 N, a slip ratio of 30%, and a time of 4 minutes. The results are shown in the "Wear Resistance" column of Tables 1 to 4 as an index where the reciprocal of Standard Example 1 is set to 100 in Tables 1 and 2, and as an index where the reciprocal of Standard Example 2 is set to 100 in Tables 3 and 4. A higher index indicates better wear resistance.

[0061] Low rolling resistance [tanδ at 60°C] The dynamic viscoelasticity of the obtained vulcanized rubber test pieces was measured using a viscoelasticity spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. under conditions of an initial strain of 10%, an amplitude of ±2%, a frequency of 20 Hz, and a temperature of 60°C, and tan δ(60°C) was calculated. The results are shown in the "Rolling Resistance" column of Tables 1 to 4, with the reciprocal of Reference Example 1 set to 100 in Tables 1 and 2, and the reciprocal of Reference Example 2 set to 100 in Tables 3 and 4. Furthermore, a larger rolling resistance index means a smaller tan δ(60°C) and lower heat buildup, which in turn means lower rolling resistance and better fuel economy when made into a tire.

[0062] [Table 1]

[0063] [Table 2]

[0064] [Table 3]

[0065] [Table 4]

[0066] [Table 5]

[0067] In Tables 1 to 5, the types of raw materials used are as follows. NR: Natural rubber, TSR20, Glass transition temperature: -65℃ BR: Butadiene rubber, Nipol BR1220 manufactured by Nippon Zeon Co., Ltd., Glass transition temperature: -105°C Modified BR1: Modified butadiene rubber, Nipol BR1261 manufactured by Nippon Zeon Co., Ltd. Modified BR2: Modified butadiene rubber, JSR BR54 SBR: Styrene butadiene rubber, Nipol SBR1502 manufactured by Nippon Zeon Co., Ltd. SBR2: Styrene butadiene rubber, Nipol 1723 manufactured by Nippon Zeon Co., Ltd., oil-extended product containing 100 parts by weight of SBR and 37.5 parts by weight of oil Modified SBR1: Modified styrene butadiene rubber, Nipol NS612 manufactured by ZS Elastomers Modified SBR2: Modified styrene butadiene rubber, manufactured by Asahi Kasei Corporation, TUFDENE E581 Silica: Solvay ZEOSIL 1165MP, CTAB adsorption specific surface area 157m 2 / g Silane coupling agent: Sulfide-based silane coupling agent, Si69 manufactured by Evonik Degussa Carbon black: CB, Niteron #300IH manufactured by Shin-Nichika Carbon Co., Ltd., nitrogen adsorption specific surface area 115m 2 / g Oil: Showa Shell Sekiyu Extract No. 4 S Stearic acid: NOF Corporation stearic acid Zinc oxide: Three types of zinc oxide manufactured by Seido Chemical Industry Co., Ltd. Anti-aging agent 1: Flexis Santoflex 6PPD Sulfur: Kinka brand finely powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator 1: Noccela CZ-G (CZ) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Sumitomo Chemical Co., Ltd. Soksil DG

[0068] As is clear from Tables 1 to 4, it was confirmed that the rubber compositions obtained by the production methods of Examples 1 to 16 had excellent silica dispersibility and improved abrasion resistance and low rolling resistance.

[0069] The rubber composition obtained in Comparative Example 1 does not satisfy the relations (1) and (2) because the kneading temperature in the entire kneading step is less than 140° C., and the silica dispersibility, abrasion resistance, and low rolling resistance are deteriorated. The rubber composition obtained in Comparative Example 2 satisfies the relational expression (1), but does not satisfy the relational expression (2), and therefore the low rolling resistance is deteriorated. The rubber composition obtained in Comparative Example 3, in which the kneading temperature in the entire kneading step was less than 140° C., did not satisfy the relations (1) and (2), and the silica dispersibility, abrasion resistance, and low rolling resistance were deteriorated.

Claims

1. A rubber composition comprising 100 parts by mass of a rubber component containing at least one selected from a conjugated diene homopolymer, a conjugated diene copolymer, and a conjugated diene-aromatic vinyl copolymer and 60% by mass or more of natural rubber, 20 parts by mass or more and 200 parts by mass or less of silica, and a silane coupling agent, wherein the storage modulus of the rubber composition at 100°C and 0.4% strain is E' (0.4%) [MPa], 100 ° C., strain 3% storage modulus E' (3%) [MPa], 100 ° C., 100% strain storage modulus E ′ (100%) [MPa], and the storage elastic modulus E′ (0.4%) and storage modulus E' (100%) The difference A is A = E' (0.4%) -E' (100%) [MPa], the storage elastic modulus E′ (0.4%) and storage modulus E' (3%) The difference B is B = E' (0.4%) -E' (3%) The rubber composition is characterized in that, when expressed as a storage modulus of elasticity (MPa), the difference A and the difference B satisfy the following relational expressions (1) and (2): A ≦ 1.4 (1) 0.252×A-0.007 ≧ B ≧ 0.252×A-0.130 (2)

2. The rubber composition according to claim 1, characterized in that, when a cross section of the rubber composition is measured using a disper grader in accordance with ISO 11345, the frequency of white areas originating from particles or particle agglomerates of 10 μm or less is 80% or more of the frequency of white areas originating from particle agglomerates of 65 μm or less.

3. The rubber composition according to claim 1 or 2, wherein the rubber component contains at least one selected from a conjugated diene homopolymer having a modifying group, a conjugated diene copolymer having a modifying group, and a conjugated diene-aromatic vinyl copolymer having a modifying group.

4. 4. The rubber composition according to claim 1, wherein the silane coupling agent has a blocked mercapto group.

5. 5. The rubber composition according to claim 1, further comprising an alkylsilane having an alkyl group having 7 to 20 carbon atoms and / or a liquid polymer compounded therein.

6. A method for producing a rubber composition comprising at least one selected from a conjugated diene homopolymer, a conjugated diene copolymer, and a conjugated diene-aromatic vinyl copolymer, 100 parts by mass of a rubber component containing 60% by mass or more of natural rubber, 20 to 200 parts by mass of silica, and a silane coupling agent, the method comprising at least one silica-feeding and kneading step in which the silica, the silane coupling agent, and at least a portion of the rubber component are fed into a kneader, kneaded, and then discharged; and after the silica-feeding and kneading step, a total-mixing step in which the rubber composition is kneaded and discharged, the silica-feeding and kneading step is carried out at a mixing temperature of less than 140°C, and at least one total-mixing step is carried out at a mixing temperature of 140°C or higher and 160°C or lower.

7. 6. A method for producing a rubber composition according to claim 1, comprising at least one silica-feeding and kneading step of feeding silica, a silane coupling agent, and at least a part of a rubber component into a kneader, kneading them, and discharging them; and after the silica-feeding and kneading step, comprising a total-mixing step of kneading and discharging the rubber composition, wherein the silica-feeding and kneading step is carried out at a mixing temperature of less than 140°C, and the at least one total-mixing step is carried out at a mixing temperature of 140°C or higher and 160°C or lower.

8. A method for producing a rubber composition as described in claim 6 or 7, characterized in that the silica introduction and kneading process is a process in which the silica and silane coupling agent are introduced into the kneader and mixed, and then at least a portion of the rubber component is introduced into the kneader, kneaded, and released, and the silica introduction and kneading process is carried out first.

9. The method for producing a rubber composition according to any one of claims 6 to 8, characterized in that after the silica introduction kneading step, in addition to the total kneading step, a kneading step performed at a mixing temperature of less than 140°C is carried out at least once.

10. The method for producing a rubber composition according to any one of claims 6 to 9, characterized in that the silane coupling agent is divided into a plurality of portions and added in two or more of the silica adding and kneading steps, or in the silica adding and kneading step and the total amount kneading step.

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