Rubber composition and pneumatic tire

Abstract

The present invention aims to provide a rubber composition and a pneumatic tire in which the change in tan delta peak temperature over time is reduced. The present invention relates to a rubber composition comprising at least one copolymer obtained by copolymerizing an aromatic vinyl compound and a conjugated diene compound, the heat aging resistance index defined according to formula (1) of which is 0.45 or less.

Description

Technical Field

[0001] This invention relates to rubber compositions and pneumatic tires. Background Technology

[0002] An exemplary rubber composition for use in motor vehicle tires comprises a diene-based rubber (e.g., polybutadiene or butadiene-styrene copolymer) and a softener (e.g., oil).

[0003] In addition, Patent Document 1 proposes a technique for using hydrogenated styrene-butadiene rubber to improve properties such as abrasion resistance.

[0004] List of cited references

[0005] Patent documents

[0006] Patent Document 1: JP H10-218920 A Summary of the Invention

[0007] Technical issues

[0008] Through extensive research, the inventors have discovered that conventional techniques increase the peak tanδ temperature of rubber during tire use, leading to reduced fuel economy. In other words, it has been found that conventional techniques have room for improvement in reducing the change in peak tanδ temperature over time.

[0009] The present invention aims to solve this problem and provide a rubber composition and a pneumatic tire with a reduced tanδ peak temperature over time.

[0010] Technical solution

[0011] This invention relates to rubber compositions comprising at least one copolymer obtained by copolymerizing an aromatic vinyl compound and a conjugated diene compound.

[0012] The heat aging resistance index of the rubber composition, as defined by formula (1), is 0.45 or less.

[0013] Heat aging resistance index = |(tanδ peak temperature of rubber composition after heat treatment) - (tanδ peak temperature of rubber composition before heat treatment)| / |tanδ peak temperature of rubber composition before heat treatment| × 100 (1)

[0014] In the formula, each tanδ peak temperature represents the tanδ peak temperature of the corresponding rubber composition measured at an initial strain of 10%, a dynamic strain of 1%, a frequency of 10 Hz, and a heating rate of 2 K / min in the temperature range of 193.15 K to 353.15 K, and the heat treatment involves standing the rubber composition at a temperature of 90 °C and an oxygen concentration of 20% for 336 hours.

[0015] The heat aging resistance index is preferably 0.35 or less, more preferably 0.30 or less, even more preferably 0.25 or less, and particularly preferably 0.20 or less.

[0016] Preferably, the rubber composition further comprises at least one softener.

[0017] The copolymer is at least one hydrogenated styrene-butadiene rubber with a weight average molecular weight of 200,000 to 2,000,000 and a degree of hydrogenation of 60 mol% or more.

[0018] The rubber composition, based on the Hansen solubility parameter (HSP) of the hydrogenated styrene-butadiene rubber and the softener, has an A value less than 4.5 calculated using the following formula (2):

[0019] A=√(α 2 +β 2 +γ 2 (2)

[0020] In the formula, α = the absolute value of the difference between δd of the hydrogenated styrene-butadiene rubber and δd of the softener.

[0021] β = The absolute value of the difference between δp of hydrogenated styrene-butadiene rubber and δp of the plasticizer.

[0022] γ = The absolute value of the difference between δh of hydrogenated styrene-butadiene rubber and δh of the plasticizer.

[0023] Where δd: energy from intermolecular dispersion forces,

[0024] δp: Energy from the dipole intermolecular forces between molecules.

[0025] δh: Energy from intermolecular hydrogen bonds.

[0026] The amount of at least one styrene-butadiene rubber is preferably 60% or more, based on 100% by mass of at least one rubber component in the rubber composition.

[0027] The rubber composition preferably includes at least 50 parts by mass of at least one silica, relative to 100 parts by mass of at least one rubber component in the rubber composition.

[0028] The rubber composition preferably includes at least 70 parts by mass of at least one silica, relative to 100 parts by mass of at least one rubber component in the rubber composition.

[0029] The rubber composition preferably includes at least 30 parts by mass of at least one softener, relative to 100 parts by mass of at least one rubber component in the rubber composition.

[0030] The amount of at least one carbon black is preferably 3 parts by mass or less, relative to 100 parts by mass of at least one rubber component in the rubber composition.

[0031] The rubber composition is preferably a tread rubber composition.

[0032] The present invention also relates to pneumatic tires, including tire components comprising at least a portion of any of the above-described rubber compositions.

[0033] The tire component is preferably the tread.

[0034] Beneficial effects of the present invention

[0035] The rubber composition of the present invention comprises at least one copolymer obtained by copolymerizing an aromatic vinyl compound and a conjugated diene compound. Further, the heat aging resistance index of the rubber composition as defined above is below 0.45. The tanδ peak temperature of this rubber composition decreases over time. Detailed Implementation

[0036] The rubber composition of the present invention is characterized in that it comprises at least one copolymer obtained by copolymerizing an aromatic vinyl compound and a conjugated diene compound, and further, the heat aging resistance index of the rubber composition as defined by formula (1) is 0.45 or less. Therefore, the change in tanδ peak temperature over time can be reduced, thereby maintaining good tire performance (fuel economy, etc.) for a longer period of time.

[0037] Heat aging resistance index = |(tanδ peak temperature of rubber composition after heat treatment) - (tanδ peak temperature of rubber composition before heat treatment)| / |tanδ peak temperature of rubber composition before heat treatment| × 100 (1)

[0038] In the formula, each tanδ peak temperature represents the tanδ peak temperature of the corresponding rubber composition measured at an initial strain of 10%, a dynamic strain of 1%, a frequency of 10 Hz, and a heating rate of 2 K / min in the temperature range of 193.15 K to 353.15 K, and the heat treatment involves standing the rubber composition at a temperature of 90 °C and an oxygen concentration of 20% for 336 hours.

[0039] The rubber composition has the above-mentioned effects. The reason for this beneficial effect is not fully understood, but it can be explained as follows.

[0040] To determine whether at least a predetermined level of grip performance can be maintained, the rubber composition is conventionally heat-treated at 80°C for two weeks, followed by analysis of changes in hardness. However, after extensive research, the inventors found that tests under the aforementioned heat treatment conditions cannot simulate tires in actual use. Further extensive research into this problem revealed that heat treatment under the conditions defined herein appropriately simulates the state of tires in actual use, thereby allowing for a highly correlated assessment of changes in the tanδ peak temperature over time.

[0041] Further extensive research by the inventors revealed that when the rubber composition exhibits only a slight change in tanδ peak temperature before and after heat treatment under the conditions defined herein, the change in tanδ peak temperature of the rubber composition over time still decreases even after the tire has actually traveled 50,000 km. More specifically, it has been found that when the tanδ peak temperature of the rubber composition before and after heat treatment under the conditions defined herein, and the heat aging resistance index calculated using equation (1) are below 0.45, the change in tanδ peak temperature of the rubber composition over time also decreases even after the tire has actually traveled 50,000 km.

[0042] As described above, when the tanδ peak temperature of the rubber composition before and after heat treatment under the conditions specified herein, and the heat aging resistance index calculated using formula (1) are 0.45 or less, the change of the tanδ peak temperature of the rubber composition with time decreases.

[0043] Therefore, the present invention addresses the problem (objective) of reducing the change in tanδ peak temperature over time by formulating a rubber composition that satisfies the parameters in formula (1). Specifically, these parameters are not the defining problem (objective); the problem to be solved herein is to reduce the change in tanδ peak temperature over time. To provide a solution to this problem, the rubber composition is formulated to satisfy the parameters in formula (1). In other words, the essential feature is satisfying the parameters in formula (1).

[0044] In this article, the tanδ peak temperature of the rubber composition refers to the tanδ peak temperature of the vulcanized rubber composition.

[0045] The heat treatment is as follows.

[0046] In this article, heat treatment involves setting the (vulcanized) rubber composition at a temperature of 90°C and an oxygen concentration of 20% for 336 hours.

[0047] For example, heat treatment can be performed using a constant-temperature bath with controllable temperature and oxygen concentration. Specifically, the vulcanized rubber composition can be placed in a constant-temperature bath with the aforementioned temperature and oxygen concentration for the aforementioned period of time.

[0048] The method for measuring the peak temperature of tanδ is described below.

[0049] In this paper, the tanδ peak temperature of the (vulcanized) rubber composition refers to the temperature at which tanδ (loss tangent) reaches its peak (maximum) as determined by viscoelasticity measurement. The viscoelasticity measurement was performed under the conditions of initial strain of 10%, dynamic strain of 1%, frequency of 10 Hz, and a heating rate of 2 K / min in the temperature range of 193.15 K to 353.15 K.

[0050] The heat aging resistance index defined by formula (1) is 0.45 or less, preferably 0.434 or less, more preferably 0.427 or less, even more preferably 0.40 or less, particularly preferably 0.394 or less, most preferably 0.387 or less, further preferably 0.35 or less, further preferably 0.348 or less, further preferably 0.310 or less, further preferably 0.308 or less, further preferably 0.30 or less, further preferably 0.271 or less, further preferably 0.25 or less, further preferably 0.20 or less, further preferably 0.194 or less, further preferably 0.193 or less, further preferably 0.15 or less, further preferably 0.115 or less, further preferably 0.10 or less, further preferably 0.077 or less, further preferably 0.05 or less, further preferably 0.019 or less.

[0051] No special restrictions are placed on the lower limit of the heat aging resistance index defined by equation (1). The heat aging resistance index can be as close to 0 as possible, and can be 0.

[0052] The peak tanδ temperature of the rubber composition (vulcanized rubber composition) before heat treatment can vary appropriately within the range that satisfies formula (1), and is preferably 220K or more, more preferably 230K or more, even more preferably 240K or more, particularly preferably 250K or more, but preferably 268K or less, more preferably 263K or less, even more preferably 258K or less.

[0053] When the tanδ peak temperature is within the range described above, it tends to be more suitable to obtain beneficial effects and more suitable to obtain the properties required by the tire rubber, such as durability.

[0054] The stress (M300) at 300% elongation of the rubber composition before heat treatment (the vulcanized rubber composition) is preferably 6 MPa or more, more preferably 7 MPa or more, and even more preferably 8 MPa or more, but preferably 30 MPa or less, more preferably 25 MPa or less, and even more preferably 20 MPa or less, according to JIS K6251 (2010) by tensile testing of a No. 3 dumbbell-shaped sample at 23°C.

[0055] When M300 is within the above range, it tends to more appropriately obtain beneficial effects and more appropriately obtain the properties required by tire rubber, such as durability.

[0056] The tensile strength (TB) at break, as measured by a tensile test on a dumbbell-shaped sample at 23°C according to JIS K6251 (2010), of the rubber composition before heat treatment (vulcanized rubber composition) is preferably 15 MPa or more, more preferably 18 MPa or more, even more preferably 20 MPa or more, but preferably 60 MPa or less, more preferably 50 MPa or less, even more preferably 45 MPa or less, and particularly preferably 40 MPa or less.

[0057] When TB is within the above range, it tends to more appropriately obtain beneficial effects and more appropriately obtain the properties required by tire rubber, such as durability.

[0058] The elongation at break (EB) of the rubber composition before heat treatment (the vulcanized rubber composition) is preferably 250% or more, more preferably 280% or more, and even more preferably 320% or more, but preferably 700% or less, more preferably 650% or less, and even more preferably 600% or less, according to JIS K6251 (2010) by tensile testing of a No. 3 dumbbell-shaped sample at 23°C.

[0059] When the EB is within the above range, it tends to more appropriately obtain beneficial effects and more appropriately obtain the properties required by the tire rubber, such as durability.

[0060] The heat aging resistance index (tanδ peak temperature change) of a rubber composition, as defined by formula (1), can be controlled by the type and content of chemicals added to the rubber composition (especially rubber components, fillers, softeners, and silane coupling agents). For example, the tanδ peak temperature change tends to decrease by using rubber components with a small number of unsaturated bonds, or by using softeners that are highly compatible with the rubber components, or by using silica as a filler, or by reducing the content of the softener, or by using silane coupling agents that are highly reactive with diene rubbers.

[0061] Conventional diene rubbers containing a large number of unsaturated bonds undergo a change in tanδ peak temperature over time (hardening) due to re-crosslinking. Conversely, rubber components with fewer unsaturated bonds are less likely to undergo re-crosslinking due to their smaller number of unsaturated bonds; therefore, their crosslinking density is less affected by the heat generated during tire use. Consequently, the change in tanδ peak temperature over time can be reduced.

[0062] Softeners that are highly compatible with rubber components are less prone to blooming. This prevents the rubber from hardening over time.

[0063] Compared to carbon black, silica results in less heat generation. This reduces the development of re-crosslinking and thus minimizes the change in the tanδ peak temperature over time.

[0064] Furthermore, the change in the tanδ peak temperature can also be controlled by altering the content of sulfur and sulfidation accelerator.

[0065] More specifically, a heat aging resistance index of less than 0.45, as defined by formula (1), can be imparted to a vulcanized rubber composition, for example, by selecting suitable rubber components, softeners, and / or silica as described below, or by appropriately adjusting their contents. In particular, this property can be imparted, for example, by using a hydrogenated copolymer (hereinafter also referred to as a hydrogenated copolymer) as a rubber component, or by using a hydrogenated copolymer and a softener that is highly compatible with it.

[0066] Because hydrogenated copolymers contain a small number of unsaturated bonds, their crosslinking density is not easily altered by the heat generated during tire use. Therefore, the change in tanδ peak temperature over time can be reduced.

[0067] In this article, "hydrogenation" has the same meaning as "hydrogenation".

[0068] The method using hydrogenated copolymers and highly compatible softeners is described below.

[0069] For example, when a softener compatible with conventional SBR is mixed with hydrogenated styrene-butadiene rubber (also referred to herein as hydrogenated SBR) containing a small number of double bonds, the softener may become incompatible with the hydrogenated SBR and thus bloom. This can easily lead to hardening of the rubber over time.

[0070] In contrast, when using hydrogenated copolymers and softeners highly compatible with them, the softener is less prone to blooming. This prevents the rubber from hardening over time. Furthermore, softeners highly compatible with hydrogenated copolymers can be selected based on their Hansen solubility parameter (HSP). Specifically, it is sufficient to select a softener with an HSP close to that of the hydrogenated copolymer (e.g., hydrogenated SBR). The selected softener is more compatible with the hydrogenated copolymer and therefore less prone to blooming. This prevents the rubber from hardening over time.

[0071] More specifically, in order to give the vulcanized rubber composition a heat aging resistance index of less than 0.45 as defined by formula (1), preferably, the rubber composition comprises a softener and a copolymer obtained by copolymerization of an aromatic vinyl compound and a conjugated diene compound; the copolymer is hydrogenated styrene-butadiene rubber; and the rubber composition has an A value calculated using formula (2) based on the Hansen solubility parameter (HSP) of the hydrogenated styrene-butadiene rubber and the softener [(J / cm²)]. 3 )1 / 2 The value is less than 4.5. The copolymer is preferably a hydrogenated styrene-butadiene rubber with a weight average molecular weight of 200,000 to 2,000,000 and a hydrogenation degree of 60 mol% or more.

[0072] The value of A is more preferably 4.0 or less, even more preferably 3.5 or less, particularly preferably 3.1 or less, most preferably 2.6 or less, further most preferably 2.1 or less, and even more preferably 1.9 or less. There is no particular limitation on the lower limit of the value of A. The value of A is preferably as close to 0 as possible, and can be 0.

[0073] Based on the above A value, the heat aging resistance index defined by equation (1) can be appropriately adjusted to below 0.45.

[0074] When multiple rubber components or softeners are present, the component with the highest content is used to calculate the A value.

[0075] A=√(α 2 +β 2 +γ 2 (2)

[0076] In the formula, α = the absolute value of the difference between δd of hydrogenated styrene-butadiene rubber and δd of the softener [(J / cm²]]. 3 ) 1 / 2 ],

[0077] β = the absolute value of the difference between δp of hydrogenated styrene-butadiene rubber and δp of the softener [(J / cm]]. 3 ) 1 / 2 ],

[0078] γ = the absolute value of the difference between δh of hydrogenated styrene-butadiene rubber and δh of the softener [(J / cm]]. 3 ) 1 / 2 ],

[0079] Where δd: energy from intermolecular dispersion forces [(J / cm²)] 3 ) 1 / 2 ],

[0080] δp: Energy of the dipole intermolecular forces [(J / cm²)] 3 ) 1 / 2 ],

[0081] δh: Energy from intermolecular hydrogen bonds [(J / cm²)] 3 ) 1 / 2 ].

[0082] In this paper, the Hansen solubility parameters δd, δp, and δh refer to the values ​​at 298.15 K and 101.3 kPa determined by the Hansen solubility sphere method.

[0083] As mentioned above, in methods using hydrogenated copolymers and highly compatible softeners, it is important to use a softener that is highly compatible with the hydrogenated copolymer. Examples of softeners include oils, liquid polymers (liquid diene polymers), and resins, as described below. The amount of softener depends on the type of softener used.

[0084] In the case of a softener having unsaturated bonds that can crosslink with rubber components, specifically in the case of liquid diene polymers, the amount of such softener is not limited.

[0085] Conversely, in the absence of a softener having unsaturated bonds that can crosslink with the rubber component, specifically in the case of a resin, the amount is preferably 20 parts by mass or less relative to 100 parts by mass of the rubber component.

[0086] Other techniques for adjusting the heat aging resistance index defined by formula (1) to below 0.45 include: reducing the amount of softener, or using a silane coupling agent that is highly reactive with diene rubbers.

[0087] The peak tanδ temperature, M300, TB, and EB of a rubber composition can be controlled by the weight and content of chemicals (especially rubber components and fillers) added to the rubber composition. For example, increasing the amount of filler or decreasing the amount of plasticizer tends to increase M300, TB, and EB, while decreasing the amount of filler or increasing the amount of plasticizer tends to decrease M300, TB, and EB. Similarly, increasing the amount of filler or decreasing the amount of plasticizer tends to increase the peak tanδ temperature, while decreasing the amount of filler or increasing the amount of plasticizer tends to decrease the peak tanδ temperature.

[0088] Examples of techniques for imparting the above-mentioned tanδ peak temperature, M300, TB, and EB values ​​include: techniques for adjusting the heat aging resistance index defined by equation (1) to below 0.45, and methods for changing the type and content of the fillers used.

[0089] The chemicals that can be used are listed below.

[0090] The rubber composition comprises at least one rubber component (hereinafter referred to as the rubber component), which comprises at least one copolymer obtained by copolymerizing an aromatic vinyl compound and a conjugated diene compound (hereinafter also referred to as a copolymer of an aromatic vinyl compound and a conjugated diene compound). The at least one copolymer may be a single copolymer or a combination of two or more copolymers.

[0091] As mentioned earlier, the change in tanδ peak temperature over time can be easily reduced by using hydrogenated copolymers; therefore, the following description focuses on embodiments where the copolymer is a hydrogenated copolymer. However, it should be noted that the use of non-hydrogenated copolymers as copolymers is not excluded.

[0092] The term "rubber component" refers to rubber with a preferred weight-average molecular weight (Mw) of 150,000 or more, more preferably 350,000 or more. There is no upper limit on the Mw, but it is preferably 4,000,000 or less, more preferably 3,000,000 or less.

[0093] The rubber component preferably comprises at least one hydrogenated copolymer obtained by means of the conjugated diene portion of a copolymer of a hydrogenated aromatic vinyl compound and a conjugated diene compound.

[0094] Hydrogenated copolymers (in which the number of double bonds has been reduced through hydrogenation) contain a small number of reaction sites for re-crosslinking. Therefore, the change in tanδ peak temperature over time can be reduced.

[0095] Examples of aromatic vinyl compounds include styrene, α-methylstyrene, 1-vinylnaphthalene, 3-vinyltoluene, ethylvinylbenzene, divinylbenzene, 4-cyclohexylstyrene, and 2,4,6-trimethylstyrene. These can be used alone or in combination of two or more. Styrene is particularly preferred from a practical standpoint (e.g., the availability of monomers) and for reasons of achieving more suitable beneficial effects.

[0096] Examples of conjugated diene compounds include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethylbutadiene, 2-phenyl-1,3-butadiene, and 1,3-hexadiene. These can be used alone or in combination of two or more. From a practical standpoint (e.g., monomer availability) and for reasons of achieving more suitable beneficial effects, 1,3-butadiene or isoprene is preferred, with 1,3-butadiene being more preferred.

[0097] The copolymer of the aromatic vinyl compound and the conjugated diene compound is preferably a copolymer of styrene and 1,3-butadiene (styrene-butadiene copolymer (SBR)). Therefore, the copolymer is preferably a styrene-butadiene copolymer, and more preferably a hydrogenated styrene-butadiene copolymer.

[0098] Styrene-butadiene copolymers can be produced by copolymerizing styrene and 1,3-butadiene in any order. The copolymerization can be random or block copolymerization, with random copolymerization being preferred. Besides styrene-butadiene copolymers, this also applies to copolymers of aromatic vinyl compounds / conjugated dienes.

[0099] The degree of hydrogenation of the copolymer (the degree of hydrogenation of the conjugated diene portion in the copolymer of the aromatic vinyl compound and the conjugated diene compound) is preferably 60 mol% or more, more preferably 75 mol% or more, even more preferably 80 mol% or more, particularly preferably 90 mol% or more, and most preferably 93 mol% or more. The degree of hydrogenation of the copolymer is also preferably 99 mol% or less, more preferably 98 mol% or less. When the degree of hydrogenation is within the above range, beneficial effects are more readily obtained.

[0100] Degree of hydrogenation can be based on 1 The reduction rate of the unsaturated bond signal in the H-NMR spectrum was calculated.

[0101] The weight-average molecular weight (Mw) of the copolymer is preferably 200,000 or more, more preferably 400,000 or more. The Mw of the copolymer is also preferably 2,000,000 or less, more preferably 1,000,000 or less, even more preferably 800,000 or less, and particularly preferably 600,000 or less. When Mw is within the above ranges, it tends to more appropriately obtain beneficial effects.

[0102] In this paper, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) were determined by gel permeation chromatography (GPC) calibrated with polystyrene standards (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M manufactured by Tosoh Corporation).

[0103] The glass transition temperature (Tg) of the copolymer is preferably -45°C or higher, more preferably -35°C or higher, even more preferably -30°C or higher, further more preferably -25°C or higher, particularly preferably -24.5°C or higher, and most preferably -24°C or higher. The Tg of the copolymer is also preferably less than -10°C, more preferably less than -12.5°C, even more preferably less than -13°C, further more preferably less than -15°C, particularly preferably less than -17.5°C, and most preferably less than -20°C. When the Tg is within the above range, it tends to more appropriately obtain beneficial effects.

[0104] The glass transition temperature (Tg) of the copolymer was determined as described in the subsequent Examples section.

[0105] When the copolymer is a styrene-butadiene copolymer, the styrene content of the styrene-butadiene copolymer is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, particularly preferably 20% by mass or more, and most preferably 25% by mass or more. The styrene content of the styrene-butadiene copolymer is also preferably 40% by mass or less, more preferably 35% by mass or less. When the styrene content is within the above range, it tends to more appropriately obtain beneficial effects.

[0106] The styrene content was determined as described in the subsequent Examples section.

[0107] The copolymer can be an unmodified copolymer or a modified copolymer.

[0108] The modified copolymer can be any copolymer having functional groups that can interact with fillers (e.g., silica). For example, it can be a chain-end modified copolymer (a chain-end modified copolymer capped with the aforementioned functional groups) obtained by modifying at least one chain end of the copolymer with a compound (modifier) ​​having the aforementioned functional groups; a main-chain modified copolymer having the aforementioned functional groups on the main chain; a main-chain and chain-end modified copolymer having the aforementioned functional groups on both the main chain and the chain ends (e.g., a main-chain and chain-end modified copolymer having the aforementioned functional groups on the main chain and at least one chain end modified with the aforementioned modifier); or a chain-end modified copolymer modified (coupled) by using a polyfunctional compound having two or more epoxy groups in the molecule to introduce hydroxyl or epoxy groups.

[0109] Examples of the aforementioned functional groups include amino, amide, silyl, alkoxysilyl, isocyanate, imino, imidazo, urea, ether, carbonyl, oxycarbonyl, mercapto, sulfide group, disulfide group, sulfonyl, sulfinyl, thiocarbonyl, ammonium, imide, hydrazogroup, azo, diazo, carboxyl, nitrile group, pyridyl, alkoxy, hydroxy, oxygen, and epoxy. These functional groups can be substituted. Among them, amino (preferably amino whose hydrogen atoms are substituted by C1-C6 alkyl), alkoxy (preferably C1-C6 alkoxy), and alkoxysilyl (preferably C1-C6 alkoxysilyl) are preferred.

[0110] The copolymer can be synthesized, for example, by polymerizing an aromatic vinyl compound and a conjugated diene compound, as described below.

[0111] Furthermore, hydrogenated copolymers can be synthesized, for example, by polymerizing aromatic vinyl compounds and conjugated diene compounds to obtain polymers, and then hydrogenating the polymers, as described below.

[0112] <Methods for producing copolymers>

[0113] (Aggregation Method)

[0114] Copolymers of aromatic vinyl compounds and conjugated dienes can be produced by any polymerization method (including solution polymerization, gas-phase polymerization, and bulk polymerization), with solution polymerization being particularly preferred. Furthermore, polymerization can be carried out in batch mode or continuously.

[0115] For solution polymerization, the monomer concentration in the solvent (in the case of styrene-butadiene copolymers, the total amount of styrene and 1,3-butadiene) is preferably 5% by mass or more, more preferably 10% by mass or more. The monomer concentration in the solvent is also preferably 50% by mass or less, more preferably 30% by mass or less.

[0116] (Polymerization initiators used in anionic polymerization)

[0117] For anionic polymerization, any polymerization initiator can be used, but organolithium compounds are preferred. Examples of organolithium compounds include those having C2-C20 alkyl groups, such as ethyllithium, n-propyllithium, isopropyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium, tert-octyllithium, n-decyllithium, phenyllithium, 2-naphthyllithium, 2-butylphenyllithium, 4-phenylbutyllithium, cyclohexyllithium, cyclopentyllithium, and the reaction product of diisopropenylbenzene with butyllithium. From the perspectives of usability, safety, and other aspects, n-butyllithium or sec-butyllithium is preferred.

[0118] Furthermore, the polymerization reaction can be carried out in the presence of compound (R), which is prepared by mixing at least one of the aforementioned organolithium compounds with compound (B1) having a functional group capable of interacting with silica. By polymerizing in the presence of compound (R), a functional group capable of interacting with silica can be introduced into the polymerization initiation end of the copolymer. The resulting copolymer thus has a modified initiation end. The term "interaction" as used herein refers to intermolecular forces (e.g., intermolecular electromagnetic forces such as ion-dipole interactions, dipole-dipole interactions, hydrogen bonds, or van der Waals forces) that can form covalent bonds between molecules. The term "functional group capable of interacting with silica" refers to a group having at least one atom capable of interacting with silica (e.g., nitrogen, sulfur, phosphorus, or oxygen atom).

[0119] Specifically, compound (R) is preferably the reaction product of an organolithium compound and a nitrogen-containing compound (e.g., a secondary amine compound). Specific examples of nitrogen-containing compounds include dimethylamine, diethylamine, dipropylamine, dibutylamine, dodecylmethyleneimine, N,N′-dimethyl-N′-trimethylsilyl-1,6-diaminohexane, piperidine, pyrrolidine, hexamethyleneimine, heptamethylimine, dicyclohexylamine, N-methylbenzylamine, di-(2-ethylhexyl)amine, diallylamine, morpholine, N-(trimethylsilyl)piperazine, N-(tert-butyldimethylsilyl)piperazine, and 1,3-di(trimethylsilyl)-1,3,5-triazine. Polymerization in the presence of compound (R) can be carried out by pre-mixing the organolithium compound with compound (B1) to prepare compound (R), adding compound (R) to the polymerization system, and then carrying out polymerization. Alternatively, it can be carried out by adding an organolithium compound and compound (B1) to a polymerization system, mixing them in the polymerization system to prepare compound (R), and then polymerizing.

[0120] (Methods of anionic polymerization)

[0121] The copolymer can be manufactured by anionic polymerization using the above-mentioned polymerization initiator, which can be carried out by any conventional method.

[0122] Specifically, monomers (e.g., styrene and 1,3-butadiene) can be anionicly polymerized in an inert organic solvent (e.g., hydrocarbon solvents such as aliphatic, alicyclic, or aromatic hydrocarbon compounds) using a polymerization initiator (e.g., butyllithium), optionally in the presence of a randomizer, to produce target copolymers such as styrene-butadiene copolymers.

[0123] (Hydrocarbon fluxes used in anionic polymerization)

[0124] Hydrocarbon solvents are preferably C3-C8 hydrocarbon solvents, examples of which include propane, n-butane, isobutane, n-pentane, isopentane, n-hexane, cyclohexane, propylene, 1-butene, isobutene, trans-2-butene, cis-2-butene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, benzene, toluene, xylene, and ethylbenzene. These can be used alone or in mixtures of two or more.

[0125] (Randomizing agent used in anionic polymerization)

[0126] A atactic agent is a compound that functions to control the microstructure of the conjugated diene moiety of a copolymer (e.g., by adding 1,2-butadiene or 3,4-isoprene units) or to control the distribution of monomer unit composition in a copolymer (e.g., the atacticization of styrene and butadiene units in a styrene-butadiene copolymer). There are no limitations on the atactic agent; any known compound commonly and conventionally used as an atactic agent can be used. Examples include ethers and tertiary amines, such as dimethoxybenzene, tetrahydrofuran, dimethoxyethane, diethylene glycol dibutyl ether, diethylene glycol dimethyl ether, bis(tetrahydrofuran)propane, triethylamine, pyridine, N-methylmorpholine, N,N,N′,N′-tetramethylethylenediamine, and 1,2-dipiperidinylethane. Other examples include potassium salts, such as potassium tert-amyloxide and potassium tert-butoxide, and sodium salts, such as sodium tert-amyloxide. These atactic agents can be used alone or in mixtures of two or more. The amount of the randomizing agent used per mole of organolithium compound is preferably 0.01 molar equivalents or more, more preferably 0.05 molar equivalents or more. The amount of the randomizing agent used per mole of organolithium compound is also preferably 1000 molar equivalents or less, more preferably 500 molar equivalents or less.

[0127] The Tg of a copolymer can be controlled by changing the type and amount of the randomizing agent used. For example, the Tg of the copolymer can be reduced by decreasing the amount of tetrahydrofuran.

[0128] (Reaction temperature)

[0129] Anionic polymerization can be carried out at any reaction temperature suitable for the reaction. Typically, the reaction temperature is preferably from -10°C to 100°C, more preferably from 25°C to 70°C.

[0130] (Reaction terminated)

[0131] Anionic polymerization can be terminated by adding reaction terminators commonly used in the art. Examples of such reaction terminators include polar solvents containing active protons, such as acetic acid and alcohols (e.g., methanol, ethanol, isopropanol), and mixtures thereof. Other examples include mixtures of the aforementioned polar solvents and nonpolar solvents (such as hexane or cyclohexane). Typically, the amount of reaction terminator added is approximately equal to or twice the molar amount of the initiator used for anionic polymerization.

[0132] In addition, modifications can be made using known techniques.

[0133] (Double connection)

[0134] In the copolymer production method, the coupling agent can be added to the hydrocarbon solution of the copolymer at any time from the start of monomer polymerization until the polymer is recovered as described later. The coupling agent can be a compound represented by the following formula (3-1):

[0135] R1 a ML 4-a (3-1)

[0136] In the formula, R 1 It represents alkyl, alkenyl, cycloalkenyl, or aryl; M represents a silicon or tin atom; L represents a halogen or alkyl group; a represents an integer from 0 to 2.

[0137] Examples of coupling agents of formula (3-1) include silicon tetrachloride, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, tin tetrachloride, methyltin trichloride, dimethyltin dichloride, trimethyltin chloride, tetramethoxysilane, methyltrimethoxysilane, dimethoxydimethylsilane, methyltriethoxysilane, ethyltrimethoxysilane, dimethoxydiethylsilane, diethoxydimethylsilane, tetraethoxysilane, ethyltriethoxysilane, and diethoxydiethylsilane.

[0138] To enhance the processability of the polymer, the amount of coupling agent added is preferably 0.03 mol or more, more preferably 0.05 mol or more, relative to each mole of alkali metal derived from the alkali metal catalyst. Furthermore, to improve fuel economy, this amount is preferably 0.4 mol or less, more preferably 0.3 mol or less.

[0139] <Hydrogenation Method>

[0140] In the production of hydrogenated copolymers, the above copolymers can be hydrogenated to obtain hydrogenated copolymers.

[0141] Hydrogenation can be carried out under any reaction conditions and by any method, including known methods and conditions. Typically, hydrogenation is carried out in the presence of a hydrogenation catalyst, at temperatures ranging from 20 to 150°C, and at hydrogen pressures ranging from 0.1 to 10 MPa. The degree of hydrogenation can be arbitrarily set by changing, for example, the amount of hydrogenation catalyst, the hydrogen pressure during the hydrogenation reaction, or the duration of the reaction. The hydrogenation catalysts used are typically compounds containing any metal from Groups 4 to 11 of the periodic table. For example, compounds containing any of the following atoms can be used as hydrogenation catalysts: Ti, V, Co, Ni, Zr, Ru, Rh, Pd, Hf, Re, and Pt. More specific examples of hydrogenation catalysts include: metallocene compounds containing Ti, Zr, Hf, Co, Ni, Pd, Pt, Ru, Rh, Re, or other metals; supported heterogeneous catalysts in which metals such as Pd, Ni, Pt, Rh, or Ru are supported on a support such as carbon, silica, alumina, or diatomaceous earth; homogeneous Ziegler catalysts in which an organometallic salt or acetylacetone salt of a metal element (e.g., Ni or Co) is combined with a reducing agent such as an organoaluminum; organometallic compounds or complexes containing Ru, Rh, or other metals; and fullerenes and carbon nanotubes in which hydrogen is stored.

[0142] Metallocene compounds containing Ti, Zr, Hf, Co, or Ni are preferred because they allow the hydrogenation reaction to be carried out in a homogeneous system in an inert organic solvent. More preferably, metallocene compounds containing Ti, Zr, or Hf are preferred. In particular, hydrogenation catalysts obtained by reacting titanocene compounds with alkyllithium are preferred because such catalysts are inexpensive and industrially useful. Specific examples include, for instance, the hydrogenation catalysts described in JP H1-275605 A, JP H5-271326 A, JP H5-271325 A, JP H5-222115 A, JP H11-292924 A, JP 2000-37632 A, JP S59-133203 A, JP S63-5401 A, JPS62-218403 A, JP H7-90017 A, JP S43-19960 B, and JP S47-40473B. These hydrogenation catalysts can be used alone or in combination of two or more.

[0143] Based on 100% by mass of the rubber component, the amount of copolymer (preferably hydrogenated copolymer) is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, particularly preferably 90% by mass or more, and most preferably 100% by mass. When this amount is within the above range, it tends to obtain beneficial effects more appropriately.

[0144] Based on 100% by mass of the rubber component, the amount of styrene-butadiene rubber (preferably hydrogenated styrene-butadiene rubber) is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, particularly preferably 90% by mass or more, and most preferably 100% by mass. When this amount is within the above range, it tends to obtain beneficial effects more appropriately.

[0145] Preferably, the rubber composition comprises at least one styrene-butadiene rubber (preferably hydrogenated styrene-butadiene rubber) in a content of 60% or more based on 100% by weight of the rubber component, and further comprises at least one silica in a content of 50 parts by weight or more (but preferably 70 parts by weight or less) relative to 100 parts by weight of the rubber component. Furthermore, the rubber composition preferably comprises at least 30 parts by weight of at least one softener relative to 100 parts by weight of the rubber component. Additionally, the amount of at least one carbon black is preferably 3 parts by weight or less relative to 100 parts by weight of the rubber component.

[0146] In addition to the copolymers described above, examples of other rubber components that can be used include diene rubbers such as polybutadiene rubber (BR), isoprene rubber, acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), and butyl rubber (IIR). These rubber components can be used alone or in combination of two or more.

[0147] Any BR commonly used in the tire industry can be used. They can be used alone or in combination of two or more.

[0148] BR can be purchased from companies such as Ube Industries, Ltd., JSR Corporation, Asahi Kasei Corporation, and Zeon Corporation.

[0149] Examples of isoprene-based rubbers include natural rubber (NR), polyisoprene rubber (IR), modified NR, altered NR, and modified IR. NR can be any NR commonly used in the tire industry, such as SIR20, RSS#3, or TSR20. Non-limiting examples of IR include those commonly used in the tire industry, such as IR2200. Examples of modified NR include deproteinized natural rubber (DPNR) and high-purity natural rubber (UPNR). Examples of modified NR include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Examples of modified IR include epoxidized polyisoprene rubber, hydrogenated polyisoprene rubber, and grafted polyisoprene rubber. They can be used alone or in combination of two or more.

[0150] The rubber composition may include at least one silica.

[0151] Examples of silica include dry silica (silicic anhydride) and wet silica (hydrated silicic acid). Wet silica is preferred because it contains a large number of silanol groups. These can be used alone or in combination of two or more.

[0152] The nitrogen adsorption specific surface area (N2SA) of silica is 40 m². 2 / g or more, preferably 60m 2 / g or more, preferably 80m 2 / g or more, and more preferably 160m 2 / g or more. N2SA is also preferably 600m 2 / g or less, more preferably 300m 2 Below / g, and more preferably 250m 2 / g or less, especially preferably 200m 2 / g or less. When N2SA is within the above range, it tends to be more suitable to obtain beneficial effects.

[0153] The N2SA of silica is determined by the BET method according to ASTM D3037-81.

[0154] Silica can be purchased from companies such as Degussa, Rhodia, Tosoh Silica Corporation, Solvay Japan, and Tokuyama Corporation.

[0155] Relative to 100 parts by weight of the rubber component, the amount of silica is preferably 30 parts by weight or more, more preferably 40 parts by weight or more, even more preferably 50 parts by weight or more, particularly preferably 55 parts by weight or more, but preferably 150 parts by weight or less, more preferably 100 parts by weight or less, even more preferably 80 parts by weight or less, and particularly preferably 70 parts by weight or less. When the amount of silica is within the above range, it tends to obtain better beneficial effects.

[0156] In the rubber composition, based on 100% by mass of filler (reinforcing filler), the amount of silica is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, particularly preferably 90% by mass or more, and most preferably 100% by mass. When the amount of silica is within the above range, it tends to obtain advantageous effects more appropriately.

[0157] The rubber composition containing silica preferably further contains at least one silane coupling agent.

[0158] Any silane coupling agent can be used, examples of which include sulfide-based silane coupling agents, such as bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(2-triethoxysilylethyl)trisulfide, etc. (4-Trimethoxysilylbutyl) trisulfide, bis(3-triethoxysilylpropyl) disulfide, bis(2-triethoxysilylethyl) disulfide, bis(4-triethoxysilylbutyl) disulfide, bis(3-trimethoxysilylpropyl) disulfide, bis(2-triethoxysilylethyl) disulfide, bis(4-triethoxysilylbutyl) disulfide, bis(3-trimethoxysilylpropyl) disulfide, bis(2-trimethoxysilylethyl) disulfide, bis(4-trimethoxysilylbutyl) disulfide, 3-trimethoxysilylpropyl 2-Triethoxysilyl ethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilyl ethyl-N,N-dimethylthiocarbamoyl tetrasulfide, and 3-triethoxysilyl propyl methacrylate monosulfide; mercapto-based silane coupling agents, such as 3-mercaptopropyltrimethoxysilane and 2-mercaptoethyltriethoxysilane; vinyl-based silane coupling agents, such as vinyltriethoxysilane and vinyltrimethoxysilane; amino-based... Silane coupling agents, such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; epoxypropoxy-based silane coupling agents, such as γ-epoxypropoxypropyltriethoxysilane and γ-epoxypropoxypropyltrimethoxysilane; nitro-based silane coupling agents, such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chlorinated silane coupling agents, such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Commercially available products from Degussa, Momentive, Shin-Etsu Silicones, Tokyo Chemical Industries, AZmax, Dow Corning Toray Industries, Ltd., etc., can be used. They can be used alone or in combination of two or more. Sulfide-based and mercapto-based silane coupling agents are preferred because they tend to provide better results. More preferably, disulfide-based silane coupling agents having disulfide bonds, such as bis(3-triethoxysilylpropyl) disulfide.

[0159] The amount of silane coupling agent relative to 100 parts by weight of silica is preferably 3 parts by weight or more, more preferably 5 parts by weight or more, but preferably 20 parts by weight or less, more preferably 15 parts by weight or less. When the amount of silane coupling agent is within the above range, it tends to obtain better beneficial effects.

[0160] The rubber composition may contain at least one type of carbon black.

[0161] Non-limiting examples of carbon black include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550 and N762. They can be used alone or in combination of two or more.

[0162] The nitrogen adsorption specific surface area (N2SA) of carbon black is preferably 80 m². 2 / g or more, preferably 100m 2 / g or more, but preferably 150m 2 / g or less, more preferably 130m 2 / g or less. When the N2SA of carbon black is within the above range, it tends to achieve better results.

[0163] In this article, the N2SA of carbon black was determined according to JIS K6217-2:2001.

[0164] Carbon black can be purchased from companies such as Asahi Carbon Co., Ltd., Cabot Corporation, Tokai Carbon Co., Ltd., Mitsubishi Chemical Co., Ltd., Lion Corporation, NSCC Carbon Co., Ltd., and Columbia Carbon.

[0165] The incorporation of carbon black can enhance heat accumulation and potentially accelerate the progress of re-crosslinking. Therefore, the amount of carbon black relative to 100 parts by weight of the rubber component is preferably 10 parts by weight or less, more preferably 3 parts by weight or less, even more preferably 1 part by weight or less, and particularly preferably 0 parts by weight. When the amount of carbon black is within the above range, it tends to obtain better beneficial effects.

[0166] The rubber composition preferably contains at least one plasticizer. Any plasticizer can be used. Examples include oils, liquid polymers (liquid diene polymers), and resins. These plasticizers can be used alone or in combination of two or more.

[0167] The softener is preferably selected from at least one of oils, liquid polymers, and resins. More preferably, it is a liquid polymer and / or resin, and even more preferably, it is a combination of liquid polymers and resins.

[0168] Any oil can be used. Examples of oils include conventional oils, including processing oils such as alkane-based, aromatic, and naphthenic processing oils, low-PCA (polycyclic aromatic) processing oils such as TDAE and MES, vegetable oils, and mixtures thereof. These can be used alone or in combination of two or more. Aromatic processing oils are preferred. Specific examples of aromatic processing oils include the Diana AH series of processing oils available from Idemitsu Kosan Co., Ltd.

[0169] These oils can be obtained from companies such as Idemitsu Kosan Co., Ltd., Sankyo Oil & Chemical Co., Ltd., Nippon Energy Co., Ltd., Olisoy Co., Ltd., H&R Co., Ltd., Toyokuni Oil Co., Ltd., Showa Shell Oil Co., Ltd., and Fuji Kosan Co., Ltd.

[0170] Liquid polymers (liquid diene polymers) refer to diene polymers that are liquid at room temperature (25°C).

[0171] The weight-average molecular weight (Mw) of the liquid diene polymer, determined by gel permeation chromatography (GPC) based on polystyrene, is preferably 1.0 × 10⁻⁶. 3 The above, more preferably 3.0×10 3 The above is further preferred to be 5.0×10 3 The above is particularly preferred, with 1.0 × 10⁻⁶ being the optimal value. 4 The optimal value is 2.0 × 10⁻⁶. 4 The above, but preferably 2.0 × 10 5 Hereinafter, 1.0 × 10 is more preferred. 5 Below, 5.0×10 is even more preferred. 4 The following is particularly preferred: 3.5 × 10⁻⁶ 4 The following applies. When Mw is within the above range, it tends to achieve more favorable results.

[0172] Examples of liquid diene polymers include at least one (co)polymer selected from butadiene, isoprene, styrene, farnesene, and their derivatives. These (co)polymers can be used alone or in combination of two or more. Examples of such liquid diene polymers include liquid styrene-butadiene copolymer (liquid SBR), liquid polybutadiene polymer (liquid BR), liquid polyisoprene polymer (liquid IR), and liquid styrene-isoprene copolymer (liquid SIR). Liquid SBR and liquid IR are preferred, and liquid IR is more preferred.

[0173] In addition, liquid diene polymers can be hydrogenated.

[0174] Liquid polymers are available from Cray Valley Corporation and Kuraray Corporation.

[0175] Any resin can be used. Examples include coumarone-based resins, styrene-based resins, terpene-based resins, dicyclopentadiene-based resins (DCPD-based resins), C5-based petroleum resins, C9-based petroleum resins, C5C9-based petroleum resins, p-tert-butylphenol acetylene resins, and acrylic (ester)-based resins. These resins can be used alone or in combination of two or more.

[0176] The resin can be hydrogenated.

[0177] In particular, resins that are highly compatible with the hydrogenated copolymers used are preferred, specifically resins with an HSP close to that of hydrogenated SBRs, and more specifically, resins with an A value less than 4.5 calculated according to equation (2), i.e., terpene resins.

[0178] Terpene resins can be any resin having units derived from terpene compounds. Examples include polyterpenes (resins prepared by polymerizing terpene compounds), aromatic terpene resins (resins prepared by copolymerizing terpene compounds and aromatic compounds), and aromatic-modified terpene resins (resins obtained by modifying terpene resins with aromatic compounds). These terpene resins can be used alone or in combination of two or more. Polyterpenes are preferred.

[0179] Terpenes are compounds that possess the properties of (C5H8) n The terms represent hydrocarbons or their oxygen-containing derivatives, each possessing a terpene skeleton, and are classified, for example, as monoterpenes (C14-C24-C24-C24). 10 H 16 ), sesquiterpenes (C 15 H 24 ) or diterpenes (C 20 H 32 Examples of terpenoid compounds include α-pinene, β-pinene, dipentene, limonene, myrcene, allocirrhene, ocimene, α-phellandrene, α-terpinene, γ-terpinene, isoterpinene, 1,8-cineole, 1,4-cineole, α-terpineol, β-terpineol, and γ-terpineol. Other examples of terpenoid compounds include resin acids (rosin acids), such as abietic acid, neoabietic acid, longleaf abietic acid, L-piperidine, piratic acid, and isopiratic acid. In other words, terpene resins also include rosin resins, which primarily contain rosin acids produced through the processing of rosin. Examples of rosin resins include natural rosin resins (polymerized rosin), such as gum rosin, wood rosin, and tall oil rosin; modified rosin resins, such as maleic acid modified rosin resin and rosin modified phenolic resin; rosin esters, such as rosin glycerol ester; and disproportionated rosin resins obtained by disproportionating rosin resins.

[0180] Aromatic compounds can be any compound containing an aromatic ring. Examples include phenolic compounds such as phenols, alkylphenols, alkoxyphenols, and phenols containing unsaturated hydrocarbon groups; naphthols such as naphthols, alkylnaphthols, alkoxynaphthols, and naphthols containing unsaturated hydrocarbon groups; and styrene and styrene derivatives such as alkylstyrene, alkoxystyrene, and styrene containing unsaturated hydrocarbon groups. Styrene is preferred.

[0181] The softening point of the resin is preferably -30°C or higher, more preferably 30°C or higher, even more preferably 60°C or higher, particularly preferably 80°C or higher, and most preferably 100°C or higher. The softening point is also preferably 200°C or lower, more preferably 160°C or lower. When the softening point is within the above range, it tends to more appropriately obtain advantageous effects.

[0182] The softening point of the resin is determined according to JIS K 6220-1:2001 using a sphere-type softening point measuring device and is defined as the temperature at which the sphere is dropped.

[0183] The resin can be purchased from companies such as Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Co., Ltd., Rutgers Chemicals, BASF, Arizona Chemical Company, Nippon Paint Co., Ltd., Nippon Shokubai Co., Ltd., JXTG Nippon Oil & Energy Corporation, Arakawa Chemical Industry Co., Ltd., and Taoka Chemical Industry Co., Ltd.

[0184] Relative to 100 parts by weight of the rubber component, the amount of softener is preferably 5 parts by weight or more, more preferably 10 parts by weight or more, even more preferably 20 parts by weight or more, and particularly preferably 30 parts by weight or more. The amount of softener is also preferably 60 parts by weight or less, more preferably 50 parts by weight or less, and even more preferably 45 parts by weight or less. When the amount of softener is within the above range, it tends to more appropriately obtain beneficial effects.

[0185] If a plasticizer is used, the amount of plasticizer includes the amount of oil contained in the rubber (oil-extended rubber).

[0186] The amount of liquid polymer (liquid diene polymer) is not limited, but is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 20 parts by mass or more. This amount is also preferably 60 parts by mass or less, more preferably 55 parts by mass or less, even more preferably 50 parts by mass or less, and particularly preferably 45 parts by mass or less. When this amount is within the above range, it tends to more appropriately obtain beneficial effects.

[0187] The amount of resin is preferably 5 parts by mass or more, more preferably 8 parts by mass or more. The amount of resin is also preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less. When the amount of resin is within the above range, it tends to more appropriately obtain beneficial effects.

[0188] Since oil makes rubber more prone to blooming and causes it to harden over time, the amount of oil is preferably 5 parts by weight or less, more preferably 3 parts by weight or less, even more preferably 1 part by weight or less, and particularly preferably 0 parts by weight. When the amount of oil is within the above range, it tends to obtain more suitable and beneficial effects.

[0189] The rubber composition may include at least one wax.

[0190] Non-limiting examples of waxes include petroleum-based waxes such as paraffin and microcrystalline waxes; naturally occurring waxes such as plant waxes and animal waxes; and synthetic waxes such as polymers of ethylene, propylene, or other similar monomers. These can be used alone or in combination of two or more. Petroleum-based waxes are preferred, and paraffin waxes are more preferred.

[0191] Wax can be purchased from companies such as Ouchi Shinshin Chemical Industry Co., Ltd., Nippon Fine Wax Co., Ltd., and Seiko Chemical Co., Ltd.

[0192] The amount of wax relative to 100 parts by weight of rubber component is preferably 0.3 parts by weight or more, more preferably 0.5 parts by weight or more, but preferably 20 parts by weight or less, more preferably 10 parts by weight or less. When the amount of wax is within the above range, it tends to obtain better beneficial effects.

[0193] The rubber composition may include at least one antioxidant.

[0194] Examples of antioxidants include naphthylamine antioxidants, such as phenyl-α-naphthylamine; diphenylamine antioxidants, such as octyl diphenylamine and 4,4′-bis(α,α′-dimethylbenzyl)diphenylamine; p-phenylenediamine antioxidants, such as N-isopropyl-N′-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine and N,N′-di-2-naphthyl-p-phenylenediamine; quinoline antioxidants, such as 2,2,4-trimethyl-1,2-dihydroquinoline polymers; monophenol antioxidants, such as 2,6-di-tert-butyl-4-methylphenol and stylated phenol; and bisphenol, triphenol, or polyphenol antioxidants, such as tetra[methylene-3-(3′,5′-di-tert-butyl-4′-hydroxyphenyl)propionate]methane. They can be used alone or in combination of two or more, with p-phenylenediamine antioxidants and / or quinoline antioxidants being preferred.

[0195] Antioxidants can be purchased from companies such as Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinsei Chemical Co., Ltd., and Flexsys.

[0196] Relative to 100 parts by weight of the rubber component, the amount of antioxidant is preferably 0.5 parts by weight or more, more preferably 1 part by weight or more, but preferably 10 parts by weight or less, more preferably 5 parts by weight or less. When the amount of antioxidant is within the above range, it tends to obtain better beneficial effects.

[0197] The rubber composition may contain at least one type of stearic acid.

[0198] Stearic acid can be conventional stearic acid, for example, it can be purchased from Nippon Oil Co., Ltd., Kao Corporation, Fujifilm and Koh Geny Co., Ltd., or Chiba Fatty Acid Co., Ltd.

[0199] The amount of stearic acid relative to 100 parts by weight of the rubber component is preferably 0.5 parts by weight or more, more preferably 1 part by weight or more, but preferably 10 parts by weight or less, more preferably 5 parts by weight or less. When the amount of stearic acid is within the above range, it tends to obtain better beneficial effects.

[0200] The rubber composition may include at least one zinc oxide.

[0201] Zinc oxide can be conventional zinc oxide, for example, purchased from Mitsui Metal Mining Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., or Sakai Chemical Industry Co., Ltd.

[0202] The amount of zinc oxide relative to 100 parts by weight of the rubber component is preferably 0.5 parts by weight or more, more preferably 1 part by weight or more, but preferably 10 parts by weight or less, more preferably 5 parts by weight or less. When the amount of zinc oxide is within the above range, it tends to obtain better beneficial effects.

[0203] The rubber composition may include at least one sulfur.

[0204] Examples of sulfur include those commonly used in the rubber industry, such as powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersed sulfur, and soluble sulfur. They can be used alone or in combination of two or more.

[0205] Sulfur can be obtained from companies such as Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemical Industry Co., Ltd., Flex Industries, Nippon Inkyu Corporation, and Hosoi Chemical Industry Co., Ltd.

[0206] Relative to 100 parts by mass of the rubber component, the amount of sulfur is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, however, preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less. When the amount of sulfur is within the above range, it tends to obtain better beneficial effects.

[0207] The rubber composition may contain at least one vulcanization accelerator.

[0208] Any vulcanization accelerator can be used. Examples include guanidine vulcanization accelerators, sulfenamide vulcanization accelerators, thiazole vulcanization accelerators, thiuram vulcanization accelerators, dithiocarbamate vulcanization accelerators, thiourea vulcanization accelerators, and xanthate vulcanization accelerators. These can be used alone or in combination of two or more. For better results, guanidine, sulfenamide, thiazole, and thiuram vulcanization accelerators are preferred.

[0209] Examples of guanidine vulcanization accelerators include 1,3-diphenylguanidine, 1,3-di-o-tolylguanidine, 1-o-tolylbiguanidine, di-o-tolylguanidine salts of dicatechin borate, 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, and 1,3-di-o-cumenyl-2-propionylguanidine. They can be used alone or in combination of two or more. 1,3-diphenylguanidine or 1,3-di-o-tolylguanidine are preferred.

[0210] Examples of sulfenamide-based vulcanization accelerators include N-cyclohexyl-2-benzothiazolyl sulfenamide, N,N-dicyclohexyl-2-benzothiazolyl sulfenamide, N-tert-butyl-2-benzothiazolyl sulfenamide, N-oxadiethylene-2-benzothiazolyl sulfenamide, and N-methyl-2-benzothiazolyl sulfenamide. They can be used alone or in combination of two or more. N-cyclohexyl-2-benzothiazolyl sulfenamide is preferred.

[0211] Examples of thiazole-based vulcanization accelerators include 2-mercaptobenzothiazole (MBT), dibenzothiazole disulfide (MBTS), 2-(2,4-dinitrophenyl)mercaptobenzothiazole, and 2-(2,6-diethyl-4-morpholinothio)benzothiazole. They can be used alone or in combination of two or more. 2-mercaptobenzothiazole or dibenzothiazole disulfide is preferred.

[0212] Examples of thiuram-based vulcanization accelerators include tetra(2-ethylhexyl)thiuram disulfide, tetrabenzylthiuram disulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetrabispentamethylenethiuram tetrasulfide. They can be used alone or in combination of two or more. Tetra(2-ethylhexyl)thiuram disulfide or tetrabenzylthiuram disulfide are preferred.

[0213] Vulcanization accelerators can be purchased from companies such as Kawaguchi Chemical Industry Co., Ltd., Ouchi Shinsei Chemical Industry Co., Ltd., and Sanshin Chemical Industry Co., Ltd.

[0214] Relative to 100 parts by weight of the rubber component, the amount of vulcanization accelerator is preferably 1 part by weight or more, more preferably 2 parts by weight or more, however preferably 10 parts by weight or less, more preferably 7 parts by weight or less, and even more preferably 5 parts by weight or less. When the amount of vulcanization accelerator is within the above range, it tends to obtain better beneficial effects.

[0215] In addition to the components described above, the rubber composition may further include additives commonly used in the tire industry, such as organic peroxides, and fillers such as calcium carbonate, talc, alumina, clay, aluminum hydroxide, and mica. The amount of each of these additives is preferably 0.1 to 200 parts by weight relative to 100 parts by weight of the rubber component.

[0216] Rubber compositions can be prepared, for example, by kneading the components together using rubber kneading equipment such as an open roll mill or a Banbury mixer, and then vulcanizing the kneaded mixture.

[0217] The kneading conditions are as follows: In the basic kneading step, which involves kneading additives other than the vulcanizing agent and vulcanization accelerator, the kneading temperature is typically 100 to 180°C, preferably 120 to 170°C. In the final kneading step, which involves kneading the vulcanizing agent and vulcanization accelerator, the kneading temperature is typically below 120°C, preferably 80 to 110°C. The composition after kneading the vulcanizing agent and vulcanization accelerator is typically vulcanized, for example, by pressure vulcanization. The vulcanization temperature is typically 140 to 190°C, preferably 150 to 185°C. The vulcanization time is typically 5 to 15 minutes.

[0218] Rubber compositions can be used in tire components (i.e., as tire rubber compositions), including, for example, the tread (tread running surface), sidewall, tread base, bottom tread, overlap, bead gusset, cushion rubber, rubber for bonding carcass cords, separator layer, bead wrapping and inner liner, and sidewall reinforcement layers of run-flat tires. Among these, the rubber composition is suitable for the tread.

[0219] The pneumatic tires of the present invention can be produced using the above-described rubber composition by conventional methods. Specifically, an uncured rubber composition containing additives as needed can be extruded into the shape of a tire component (particularly, the tread (driving surface)), and then formed and assembled with other tire components in a tire forming machine in a conventional manner to produce an uncured tire. The uncured tire can then be heated and pressurized in a vulcanizing machine to produce a tire.

[0220] It is sufficient for the tire components (e.g., the tread) of a pneumatic tire to at least partially comprise any of the aforementioned rubber compositions. The entire tire component may contain any of the aforementioned rubber compositions.

[0221] Pneumatic tires are suitable for passenger car tires, large passenger car tires, large SUV tires, truck and bus tires, or two-wheeled vehicle tires, racing tires, studless anti-skid winter tires, run-flat tires, aircraft tires, mining tires, or other tires.

[0222] Example

[0223] The present invention will be described in detail with reference to the following embodiments, but is not limited to the following embodiments.

[0224] The chemicals used in the synthesis and polymerization processes are listed below. The chemicals are purified using conventional techniques as needed.

[0225] n-Hexane: A product of Kanto Chemical Co., Ltd.

[0226] Styrene: A product of Kanto Chemical Co., Ltd.

[0227] Butadiene: 1,3-butadiene purchased from Tokyo Chemical Industry Co., Ltd.

[0228] TMEDA: N,N,N',N'-Tetramethylethylenediamine purchased from Kanto Chemical Co., Ltd.

[0229] n-Butyllithium solution: 1.6M n-Butyllithium in hexane solution purchased from Kanto Chemical Co., Ltd.

[0230] Ethanol: A product of Kanto Chemical Co., Ltd.

[0231] 2,6-Di-tert-butyl-p-cresol: Nocrac 200 purchased from Ouchi Shinshin Chemical Industry Co., Ltd.

[0232] The method for evaluating the prepared copolymer is described in general below.

[0233] (Determination of the degree of hydrogenation of the conjugated diene moiety of the copolymer)

[0234] A 15% by mass solution was prepared using carbon tetrachloride as the solvent, and this solution was used to measure H at 100 MHz. 1 -NMR spectrum. Degree of hydrogenation based on H 1 - Calculation of the reduction rate of unsaturated bond signal in NMR spectrum.

[0235] (Determination of styrene content)

[0236] Measurements were performed using a JEOL JNM-A 400NMR instrument at 25°C. 1 ¹H-NMR spectra. The ratio of phenyl protons in styrene units at 6.5 to 7.2 ppm to vinyl protons in butadiene units at 4.9 to 5.4 ppm was calculated from the spectra, and this ratio was used to determine the styrene content.

[0237] (Determination of weight-average molecular weight (Mw) and number-average molecular weight (Mn))

[0238] The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of each copolymer were determined by gel permeation chromatography (GPC) calibrated according to polystyrene standards (GPC-8000 series from Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M).

[0239] (Measurement of glass transition temperature (Tg))

[0240] The glass transition temperature (Tg) is defined as the temperature at which the glass transition begins, as measured by a differential scanning calorimeter (Q200, TA equipment, Japan) at a heating rate of 10 °C / min, according to JIS K 7121.

[0241] <Example of Copolymer Manufacturing>

[0242] Synthesis Example 1 (Synthesis of SBR 1, degree of hydrogenation (hereinafter referred to as DH): 0 mol%)

[0243] In a heat-resistant reaction vessel thoroughly purged with nitrogen, 2000 mL of n-hexane, 60 g of styrene, 140 g of butadiene, 0.93 g of TMEDA, and 0.45 mmol of n-butyllithium were added, and the mixture was stirred at 50 °C for 5 hours to carry out the polymerization reaction. The reaction was then terminated by adding ethanol. 1 g of 2,6-di-tert-butyl-p-cresol was added to the reaction solution, followed by purification by reprecipitation to obtain SBR1. SBR1 had a weight-average molecular weight (Mw) of 490,000 and a styrene content of 30% by mass.

[0244] Synthesis Example 2 (Synthesis of hydrogenated SBR 1, DH: 95 mol%)

[0245] The preparation method of hydrogenated SBR 1 is the same as that of SBR 1, except that the obtained polymer is hydrogenated. Specifically, after the polymerization conversion reaction of SBR 1, the polymerization reaction is not terminated by the addition of ethanol. Instead, hydrogen is supplied at a gauge pressure of 0.4 MPa while the reaction solution is stirred for 20 minutes to react unreacted polymer terminal lithium with hydrogen to form lithium hydride. Hydrogenation is carried out using a diacene dichloride catalyst at a hydrogen supply pressure of 0.7 MPa gauge pressure and a reaction temperature of 90°C. Once the cumulative amount of absorbed hydrogen reaches the amount corresponding to the target degree of hydrogenation, the reaction temperature is brought to room temperature and the hydrogen pressure is returned to atmospheric pressure. The reaction solution is then extracted from the reaction vessel and introduced into water with stirring. The solvent is removed by steam distillation to obtain hydrogenated SBR 1. The degree of hydrogenation of hydrogenated SBR 1 is 95 mol% and the weight-average molecular weight (Mw) is 450,000.

[0246] Synthesis Example 3 (Synthesis of hydrogenated SBR 2, DH: 80 mol%)

[0247] The preparation method of hydrogenated SBR 2 is the same as that of hydrogenated SBR 1, except that the cumulative amount of absorbed hydrogen is adjusted to correspond to the target degree of hydrogenation. The degree of hydrogenation of hydrogenated SBR 2 is 80 mol% and the weight-average molecular weight (Mw) is 480,000.

[0248] Synthesis Example 4 (Synthesis of hydrogenated SBR 3, DH: 60 mol%)

[0249] The preparation method of hydrogenated SBR 3 is the same as that of hydrogenated SBR 1, except that the cumulative amount of absorbed hydrogen is adjusted to correspond to the target degree of hydrogenation. The degree of hydrogenation of hydrogenated SBR 3 is 60 mol% and the weight-average molecular weight (Mw) is 450,000.

[0250] [Table 1]

[0251]

[0252]

[0253] The chemicals used in the examples and comparative examples are listed below.

[0254] SBR 1: Unhydrogenated SBR, synthesized according to the above method.

[0255] Hydrogenated SBR 1-3: Hydrogenated SBR, synthesized according to the above.

[0256] Silicon dioxide 1: VN3 (N2SA: 175m) 2 / g), acquired by Evonik Degussa.

[0257] Silicon dioxide 2: 115GR (N2SA: 115m) 2 / g), purchased by Solvay Japan.

[0258] Silica 3: 9000GR (N2SA: 235m) 2 / g), acquired by Evonik Degussa.

[0259] Softener 1: Diana process AH-24 (aromatic oil), purchased from Idemitsu Kosan Co., Ltd.

[0260] Softener 2: PS-32 (mineral oil), purchased from Idemitsu Kosan Co., Ltd.

[0261] Softener 3: SYLVARES SA85 (α-methylstyrene resin (copolymer of α-methylstyrene and styrene), softening point: 85℃), purchased from Arizona Chemical Company.

[0262] Softener 4: NOVARES C100 (coumarone-indene resin, softening point: 95 to 105°C), purchased from Rutgers Chemical Company.

[0263] Softener 5: Kuraprene LIR30 (liquid IR, weight average molecular weight: 29000), purchased from Kuraprene Co., Ltd.

[0264] Softener 6: Sylvatraxx 4150 (polyterpene resin, softening point: 150℃), purchased from KRATON.

[0265] Softener 7: RICON 100 (liquid SBR, styrene content: 20% by mass, vinyl content: 70% by mass, weight average molecular weight: 4500), purchased from Sartomer.

[0266] Softener 8: Dercolyte L120 (polylimonene resin, softening point: 120℃), purchased from DRT Company.

[0267] Silane coupling agent 1: Si266 (bis(3-triethoxysilylpropyl) disulfide), purchased from Evonik Degussa.

[0268] Silane coupling agent 2: Si69 (bis(3-triethoxysilylpropyl)tetrasulfide), purchased from Evonik Degussa.

[0269] Silane coupling agent 3: Si363 (3-[ethoxybis(3,6,9,12,15-pentaoctacosan-1-yloxy)silyl]-1-propanethiol, a compound represented by the following formula, was obtained from Evonik Degussa.

[0270]

[0271] Antioxidant: Nocrac 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine), purchased from Ouchi Shinsei Chemical Co., Ltd.

[0272] Stearic acid: Stearic acid beads "TSUBAKI", purchased from Nippon Oil Co., Ltd.

[0273] Zinc oxide: Zinc oxide No. 3, purchased from Hakusui Technology Co., Ltd.

[0274] Wax: Ozoace 0355, purchased from Nippon Seiwa Co., Ltd.

[0275] Sulfur: Powdered sulfur, purchased from Tsurumi Chemical Industry Co., Ltd.

[0276] Vulcanization accelerator 1: Vulcanization accelerator: NOCCELER CZ (N-cyclohexyl-2-benzothiazolyl sulfenamide), purchased from Ouchi Shinshin Chemical Industry Co., Ltd.

[0277] Vulcanization accelerator 2: SANCELER TBZTD (tetrabenzyliuram disulfide), purchased from Sanshin Chemical Industry Co., Ltd.

[0278] Vulcanization accelerator 3: NOCCELER DT (1,3-di-o-tolylguanidine), purchased from Ouchi Shinsei Chemical Co., Ltd.

[0279] Vulcanization accelerator 4: NOCCELER MP (2-mercaptobenzothiazole), purchased from Ouchi Shinsei Chemical Co., Ltd.

[0280] Vulcanization accelerator 5: NOCCELER TOT-N (tetra(2-ethylhexyl)thiuram disulfide), purchased from Ouchi Shinshin Chemical Industry Co., Ltd.

[0281] Vulcanization accelerator 6: NOCCELER D (1,3-diphenylguanidine), purchased from Ouchi Shinshin Chemical Industry Co., Ltd.

[0282] (Examples and Comparative Examples)

[0283] According to the formulation shown in Table 2, the chemicals, excluding sulfur and vulcanization accelerator, were kneaded for 5 minutes at 150°C using a 1.7L Banbury internal mixer (Kobe Steel Corporation) to obtain a kneaded mixture. Then, sulfur and vulcanization accelerator were added to the kneaded mixture, and the mixture was subsequently kneaded for 5 minutes at 80°C using an open-roll mill to obtain an unvulcanized rubber composition.

[0284] The uncured rubber composition was subjected to pressure vulcanization at 170°C for 10 minutes to obtain a vulcanized rubber composition.

[0285] Individually, the uncured rubber composition prepared above is shaped into the tread pattern and assembled with other tire components to manufacture an uncured tire. The uncured tire is then pressurized at 170°C for 10 minutes to prepare a test tire (size: 195 / 65R15).

[0286] (Heat treatment)

[0287] Furthermore, the vulcanized rubber composition was heat-treated by placing it in an oven at 90°C and 20% oxygen concentration for 336 hours. Thus, a heat-treated vulcanized rubber composition was prepared.

[0288] The vulcanized rubber composition prepared as described above, the heat-treated vulcanized rubber composition, and the test tire were evaluated as follows. Table 2 shows the results.

[0289] (tanδ peak temperature)

[0290] The tanδ of vulcanized rubber compositions (samples) and heat-treated vulcanized rubber compositions (samples) was measured using a spectrometer (Uejima Manufacturing Co., Ltd.) at an initial strain of 10%, a dynamic strain of 1%, a frequency of 10 Hz, and a heating rate of 2 K / min within a temperature range of 193.15 K to 353.15 K. The peak tanδ temperature (peak tanδ(K)) is defined as the temperature at which tanδ reaches its peak value.

[0291] Five test tires with the same formulation were prepared. Four of the five test tires were mounted on each wheel of a motor vehicle (a Japanese-made, 2000cc front-engine, front-wheel-drive vehicle), and the vehicle was driven for 50,000 km. Samples were then cut from the treads of the test tires after 50,000 km of driving and from the unused test tires. The peak tanδ temperature (peak tanδ(K)) of each sample was measured as described above. The change in peak tanδ temperature before and after driving was then calculated using the following formula. A smaller change in peak tanδ temperature before and after driving indicates less change in peak tanδ temperature over time.

[0292] Change in peak tanδ temperature before and after driving = |(peak tanδ temperature of the sample cut from the test tire after 50,000 km) - (peak tanδ temperature of the sample cut from the unused test tire| / |peak tanδ temperature of the sample cut from the unused test tire| × 100

[0293] (Tension test)

[0294] According to JIS K6251 (2010), dumbbell-shaped sample No. 3 was prepared from a vulcanized rubber composition. The sample was subjected to tensile testing at 23°C, and the stress (M300), tensile strength at break (TB), and elongation at break (EB) at 300% elongation were determined.

[0295] [Table 2]

[0296]

[0297]

[0298]

[0299]

[0300]

[0301]

[0302] Table 2 shows that in examples containing copolymers obtained by copolymerizing aromatic vinyl compounds and conjugated diene compounds and having a heat aging resistance index of less than 0.45 as defined above, the tanδ peak temperature decreases over time.

Claims

1. A rubber composition comprising at least one copolymer obtained by copolymerizing an aromatic vinyl compound and a conjugated diene compound, and at least one carbon black. The amount of the at least one carbon black is 3 parts by mass or less, relative to 100 parts by mass of the rubber component in the rubber composition. The rubber composition further comprises at least one softener. The copolymer is at least one hydrogenated styrene-butadiene rubber with a weight average molecular weight of 200,000 to 2,000,000 and a degree of hydrogenation of 60 mol% or more. Relative to 100 parts by weight of the rubber component in the rubber composition, the rubber composition contains 50 parts by weight or more of at least one type of silica. The rubber composition contains 3 to 20 parts by weight of a silane coupling agent relative to 100 parts by weight of silica. The heat aging resistance index of the rubber composition, as defined by formula (1), is below 0.

45. Heat aging resistance index = |(tan δ peak temperature of rubber composition after heat treatment) - (tan δ peak temperature of rubber composition before heat treatment)| / |tan δ peak temperature of rubber composition before heat treatment| × 100 (1) In the formula, each tan δ peak temperature represents the tan δ peak temperature of the corresponding rubber composition measured at an initial strain of 10%, a dynamic strain of 1%, a frequency of 10 Hz, and a heating rate of 2 K / min in the temperature range of 193.15 K to 353.15 K. The heat treatment involves setting the rubber composition at 90 °C and 20% oxygen concentration for 336 hours. The rubber composition uses the following formula (2), and the A value calculated based on the Hansen solubility parameter (HSP) of the hydrogenated styrene-butadiene rubber and the softener is less than 4.5: （2） In the formula, α = the absolute value of the difference between δd of the hydrogenated styrene-butadiene rubber and δd of the softener. β = the absolute value of the difference between δp of hydrogenated styrene-butadiene rubber and δp of the plasticizer. γ = the absolute value of the difference between δh of hydrogenated styrene-butadiene rubber and δh of the plasticizer. in, δd: Energy from intermolecular dispersion forces. δp: Energy from the dipole intermolecular forces between molecules. δh: Energy from intermolecular hydrogen bonds In the formula, δd, δp, and δh refer to the values ​​determined by the Hansen solubility sphere method at 298.15 K and 101.3 kPa.

2. The rubber composition according to claim 1, in, The heat aging resistance index is below 0.

35.

3. The rubber composition according to claim 1, in, The heat aging resistance index is below 0.

30.

4. The rubber composition according to claim 1, in, The heat aging resistance index is below 0.

25.

5. The rubber composition according to claim 1, in, The heat aging resistance index is below 0.

20.

6. The rubber composition according to any one of claims 1 to 5, in, Based on 100% by mass of the rubber component in the rubber composition, the amount of at least one styrene-butadiene rubber is 60% by mass or more.

7. The rubber composition according to any one of claims 1 to 5, in, The rubber composition contains at least 70 parts by mass of at least one silica, relative to 100 parts by mass of the rubber component in the rubber composition.

8. The rubber composition according to any one of claims 1 to 5, in, The rubber composition contains at least 30 parts by mass of at least one softener relative to 100 parts by mass of the rubber component in the rubber composition.

9. The rubber composition according to any one of claims 1 to 5, in, The rubber composition is a tire tread rubber composition.

10. A pneumatic tire comprising a tire component that at least partially comprises the rubber composition of any one of claims 1 to 8.

11. The pneumatic tire according to claim 10, in, The tire component is the tread.

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