Rubber composition for tire treads and tires

Abstract

The present invention provides a rubber composition for tire treads that exhibits excellent mixability and extrusion processability, and also provides excellent handling stability, rolling performance, and wet performance when used as a tire tread, and a tire manufactured using this composition as a tire tread. [Solution] A rubber composition for tire treads containing 100 parts by mass of diene rubber containing 30 parts by mass or more of modified styrene-butadiene rubber, 70 to 140 parts by mass of silica, and a specific silane coupling agent, wherein the modified styrene-butadiene rubber has a monomodal molecular weight distribution curve of GPC and a PDI of less than 1.7, the silane coupling agent content is 8 to 20% by mass relative to the silica content, and the Tg is -50°C or higher. A rubber composition for tire treads obtained by mixing diene rubber and silica, and then mixing in a silane coupling agent after the temperature of the mixture system has risen to 80°C or higher and 120°C or lower.

Description

[Technical Field]

[0001] This invention relates to a rubber composition for tire treads and a tire. [Background technology]

[0002] Amidst the growing demand for improved safety performance in tires, Patent Document 1, for example, proposes a tire rubber composition containing a specific styrene-butadiene rubber (SBR) and silica. Patent Document 1 states that using the above composition in tire treads improves the wet performance and wear resistance of the tire. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 7339580 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In recent years, there has been a growing demand for further improvements in the safety performance of tires, particularly in handling stability and wet performance. Furthermore, from an environmental perspective, improvements in tire rolling performance are also required. Additionally, improvements in processability (specifically, mixability and extrusion processability) of the compositions are also desired.

[0005] In this context, when the inventors prepared a rubber composition with reference to Patent Document 1, it became clear that, considering the increasingly demanding requirements in the future, further improvements in processability and rolling performance when made into tires are desirable.

[0006] Therefore, in view of the above circumstances, the present invention aims to provide a rubber composition for tire treads that is excellent in terms of mixability and extrusion processability, and also excellent in handling stability, rolling performance and wet performance when made into a tire, and a tire manufactured using this composition as a tire tread. [Means for solving the problem]

[0007] As a result of diligent research into the above-mentioned problems, the inventors of the present invention discovered that the above-mentioned problems can be solved by mixing diene rubber and silica, and then mixing a silane coupling agent after the temperature of the mixed system reaches a specific temperature, leading to the present invention. In other words, the inventors have found that the above problem can be solved by the following configuration.

[0008] (1) A diene rubber containing 30 parts by mass or more of modified styrene-butadiene rubber, 100 parts by mass of silica, and a silane coupling agent represented by the following formula (1), The above-mentioned modified styrene-butadiene rubber has a unimodal molecular weight distribution curve obtained by gel permeation chromatography (GPC), and its molecular weight distribution (PDI) is less than 1.7. The content of the silane coupling agent is 8 to 20% by mass relative to the silica content. A rubber composition for tire treads having a glass transition temperature of -50°C or higher, A rubber composition for tire treads obtained by mixing the above-mentioned diene rubber and the above-mentioned silica, and then mixing the above-mentioned silane coupling agent after the temperature of the mixed system has risen to 80°C or higher and 120°C or lower. (C n H 2n+1 O)3Si-C m H 2m -S-CO-C k H 2k+1 (1) In equation (1), n ​​is 2, m is 3, and k is 7. (2) The above silica has a CTAB of 140m 2 / g or more 180m 250 to 80 parts by mass of silica 1 with less than / g, and CTAB of 180 m 2 / g or more and less than 220 m 2 The rubber composition for a tire tread according to (1) above, comprising 20 to 60 parts by mass of silica 2 with less than / g. (3) Further containing an alkyltriethoxysilane represented by formula (I) described later, The rubber composition for a tire tread according to (1) or (2) above, wherein the content of the alkyltriethoxysilane is 0.1 to 20% by mass with respect to the content of the silica. (4) The rubber composition for a tire tread according to any one of (1) to (3) above, wherein the diene rubber contains 10 to 20 parts by mass of natural rubber. (5) The rubber composition for a tire tread according to any one of (1) to (4) above, wherein the diene rubber contains 10 to 20 parts by mass of a modified butadiene rubber. (6) The rubber composition for a tire tread according to any one of (1) to (5) above, wherein the diene rubber contains 10 to 20 parts by mass of a modified styrene-butadiene rubber different from the above-mentioned modified styrene-butadiene rubber. (7) A tire manufactured by using the rubber composition for a tire tread according to any one of (1) to (6) above for a tire tread. [Effect of the Invention]

[0009] As shown below, according to the present invention, there can be provided a rubber composition for a tire tread that is excellent in mixing processability and extrusion processability, and also excellent in handling stability, rolling performance, and wet performance when formed into a tire, and a tire manufactured by using this for a tire tread. [Brief Description of the Drawings]

[0010] [Figure 1] It is a schematic partial cross-sectional view showing an example of an embodiment of the tire of the present invention. [Modes for Carrying Out the Invention]

[0011] The rubber composition for tire treads and the like of the present invention will be described below. In this specification, numerical ranges represented by "~" mean a range that includes the numbers written before and after "~" as the lower and upper limits, respectively. Furthermore, each component may be used alone or in combination of two or more. When two or more components are used in combination, the content of each component refers to the total content unless otherwise specified. In particular, when a composition contains two or more types of silica, the two or more types of silica are collectively referred to as "total silica," and the amount is also called the "total silica content." Furthermore, with respect to rubber compositions for tire treads, the handling stability, rolling performance, and wet performance when made into tires are also simply referred to as "handling stability," "rolling performance," and "wet performance," respectively.

[0012] [I] Rubber composition for tire treads The rubber composition for tire treads of the present invention (hereinafter also simply referred to as "the composition of the present invention") is It contains 100 parts by mass of a diene rubber containing 30 parts by mass or more of modified styrene-butadiene rubber, 70 to 140 parts by mass of silica, and a silane coupling agent represented by formula (1) described later. The above-mentioned modified styrene-butadiene rubber has a unimodal molecular weight distribution curve obtained by gel permeation chromatography (GPC), and its molecular weight distribution (PDI) is less than 1.7. The content of the above-mentioned silane coupling agent is 8 to 20% by mass relative to the above-mentioned silica content (total silica amount). A rubber composition for tire treads having a glass transition temperature of -50°C or higher, This is a rubber composition for tire treads obtained by mixing the above-mentioned diene rubber and the above-mentioned silica, and then mixing in the above-mentioned silane coupling agent after the temperature of the mixed system has risen to 80°C or higher and 120°C or lower.

[0013] The composition of the present invention is thought to be able to solve the above-mentioned problems by adopting such a configuration. The reason for this is not clear, but it is speculated to be as follows. As described above, the composition of the present invention uses a modified SBR (hereinafter also referred to as "specific SBR") in which the molecular weight distribution curve of the GPC has a unimodal shape and its molecular weight distribution is less than 1.7. Such a specific SBR with monodisperse and a narrow molecular weight distribution is prone to polymer aggregation and does not mix well with silica. Therefore, when these components are mixed with a silane coupling agent at the same time, coupling between the two occurs while the dispersibility of silica is insufficient. On the other hand, in the case of the composition of the present invention, a diene rubber containing a specific SBR is first mixed with silica, and then a silane coupling agent is mixed in after the temperature reaches a specific range, so that coupling occurs in a sufficiently dispersed state. Furthermore, because a specific silane coupling agent is used, the bond between the two is extremely strong. As a result, the composition of the present invention is thought to have extremely high silica dispersibility, and the desired properties can be obtained.

[0014] While it may be theoretically possible to measure the difference in silica dispersibility using an electron microscope, in practice, it would require manufacturing or purchasing statistically significant numbers of compositions from both the present invention and the prior art, measuring the numerical characteristics of electron microscope images, and then statistically processing the results to identify a significant indicator and its value that distinguishes the present invention from the prior art. This would be extremely time-consuming and costly. Moreover, since there are a vast number of possibilities for the prior art, it is impossible to uniquely determine a statistically significant number. Therefore, it is not at all practical to identify the above-mentioned indicators and their values, and to directly specify the features of the present invention by the structure or properties of the object.

[0015] The following describes each component contained in the composition of the present invention.

[0016] [1] Diene rubber The composition of the present invention contains 100 parts by mass of diene rubber containing 30 parts by mass or more of a specific SBR.

[0017] [Specific SBR] A specific SBR is a modified SBR whose gel permeation chromatography (GPC) molecular weight distribution curve has a unimodal shape and whose molecular weight distribution (PDI) is less than 1.7.

[0018] [Body structure] The skeleton of a specific SBR is a copolymer of styrene and butadiene.

[0019] [Modified group] The modifying groups that a particular SBR possesses are not particularly limited, but specific examples include alkoxysilyl groups, amino groups (for example, groups represented by -NR2, where R represents a hydrogen atom or substituent), hydroxyl groups, carboxyl groups, etc. Among these, alkoxysilyl groups are preferred because they provide superior effects for which the present invention is most effective.

[0020] Examples of the above alkoxysilyl group include -Si(OR1) n (R2) 3-n Examples of groups are those represented by (where R1 is an alkyl group, R2 is a hydrogen atom or an alkyl group, and n is an integer from 1 to 3).

[0021] A specific SBR may have modifying groups at the terminal, main chain, or side chain, but for reasons that the effects of the present invention are superior, it is preferable to have modifying groups at the terminal, and more preferably at both terminals.

[0022] [Molecular weight distribution curve and molecular weight distribution] A specific SBR is characterized by a unimodal molecular weight distribution curve when measured by gel permeation chromatography (GPC), and a molecular weight distribution (PDI) of less than 1.7. When the molecular weight distribution curve is unimodal, the uniformity of the molecules increases, and they are homogeneously distributed within the diene rubber. The molecular weight distribution (PDI) is the ratio (Mw / Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) measured by gel permeation chromatography. When the molecular weight distribution (PDI) is less than 1.7, the molecular weight distribution curve is unimodal, indicating high molecular uniformity and homogeneous distribution within the diene rubber. For superior effects of the present invention, the molecular weight distribution (PDI) is preferably 1.0 or more and less than 1.7, and more preferably 1.1 to 1.6. Such modified styrene-butadiene rubber can preferably be obtained by continuous polymerization.

[0023] When measuring the molecular weight distribution curve, weight-average molecular weight (Mw), and number-average molecular weight (Mn) of a specific SBR by gel permeation chromatography (GPC), the following conditions can be used as examples. Equipment: Gel permeation chromatography [GPC: HLC-8020 manufactured by Tosoh Corporation] Column: Tosoh Corporation GMH-HR-H (2 connected in series) Measurement temperature: 40℃ Carrier gas: Helium Flow rate: 5mmol / L Sample: Dissolve 10 mg in 10 mL of THF (tetrahydrofuran). Injection volume: 10μL Detector: Differential refractometer (RI-8020)

[0024] [Molecular weight] The weight-average molecular weight (Mw) of a specific SBR is not particularly limited, but for reasons that the effects of the present invention are superior, it is preferably 100,000 or more and 10,000,000 or less, more preferably 200,000 to 4,000,000, and even more preferably 300,000 to 2,000,000.

[0025] The number-average molecular weight (Mn) of a specific SBR is not particularly limited, but for reasons that the effects of the present invention are superior, it is preferably 100,000 or more and 10,000,000 or less, more preferably 200,000 to 4,000,000, and even more preferably 300,000 to 2,000,000.

[0026] [Tg] The glass transition temperature (Tg) of a particular SBR is not particularly limited, but it is preferably -60 to -10°C, and more preferably -40 to -20°C, for better effects of the present invention. The above Tg can be adjusted, for example, by the amount of styrene or vinyl. In this specification, the glass transition temperature (Tg) is calculated using the midpoint method after measuring it with a differential scanning calorimeter (DSC) at a heating rate of 10°C / min.

[0027] [Content] The content of specific SBR is 30 parts by mass or more per 100 parts by mass of diene rubber. In particular, it is preferable that it be 50 parts by mass or more, and more preferably 60 parts by mass or more, for the reason that the effects of the present invention are superior. There is no particular upper limit, but for the reason that the effects of the present invention are superior, it is preferable that it be 90 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 70 parts by mass or less.

[0028] [Other diene-based rubbers] The diene rubber may include diene rubbers other than specific SBR. Examples of such diene rubbers include styrene-butadiene rubber (SBR) other than specific SBR, natural rubber (NR), butadiene rubber (BR), isoprene rubber (IR), acrylonitrile-butadiene rubber (NBR), butyl rubber (IIR), halogenated butyl rubber (Br-IIR, Cl-IIR), and chloroprene rubber (CR).

[0029] [Natural rubber] Diene rubber preferably contains natural rubber (NR) because it provides superior effects in the present invention.

[0030] <Content> The amount of natural rubber is preferably 5 to 30 parts by mass, and more preferably 10 to 20 parts by mass, per 100 parts by mass of diene rubber, for the reasons that the effects of the present invention are superior.

[0031] [Modified butadiene rubber] For the present invention, it is preferable that the diene rubber contains modified butadiene rubber (modified BR) because it provides superior effects.

[0032] <modified group> Specific examples and preferred embodiments of the modifying groups in the modified butadiene rubber are the same as those for the specific SBR described above.

[0033] <Content> The amount of modified butadiene rubber is preferably 5 to 30 parts by mass, and more preferably 10 to 20 parts by mass, per 100 parts by mass of diene rubber, for the reasons that the effects of the present invention are superior.

[0034] [Modified styrene-butadiene rubber different from specific SBR] The diene rubber preferably contains a modified styrene-butadiene rubber different from specific SBR, for the reason that the effects of the present invention are superior.

[0035] <modified group> Specific examples and preferred embodiments of the modifying groups possessed by modified styrene-butadiene rubber, which differs from the specified SBR, are the same as those described above for the specified SBR.

[0036] <Content> The content of modified styrene-butadiene rubber, which is different from specific SBR, is preferably 5 to 30 parts by mass, and more preferably 10 to 20 parts by mass, per 100 parts by mass of diene rubber, for the reason that the effects of the present invention are superior.

[0037] [Molecular weight] The preferred embodiments of Mw and Mn in the diene-based rubber are the same as those for the specific SBR described above.

[0038] [2] Silica The composition of the present invention contains silica. The silica mentioned above is not particularly limited, and any conventionally known silica can be used. Examples of silica include wet silica, dry silica, fumed silica, and diatomaceous earth. Biomass-derived silica, such as rice husks, may also be used. The above silica may be used alone or in combination of two or more types.

[0039] [CTAB] The specific surface area of ​​the above silica for cetyltrimethylammonium bromide (CTAB) adsorption (hereinafter, "CTAB adsorption specific surface area" will also simply be referred to as "CTAB") is not particularly limited, but for reasons that the effects of the present invention are superior, 100 to 300 m is preferred. 2 It is preferable that the amount be / g, and 150-200m 2 It is more preferable that it be / g. Here, the CTAB adsorption specific surface area is the value measured in accordance with JIS K6430:2008 Annex G.

[0040] [Content] In the composition of the present invention, the silica content is 70 to 140 parts by mass per 100 parts by mass of the diene rubber described above.

[0041] [Preferred embodiment] Silica is used because it provides superior effects in this invention, and CTAB is 140m 2 / g or more 180m 2 50-80 parts by mass of silica 1 (hereinafter also simply referred to as "silica 1") which is less than / g, and 180m of CTAB 2 / g or more 220m 2 It is preferable to include 20 to 60 parts by mass of silica-2 (hereinafter also simply referred to as "silica-2") in a quantity of less than / g.

[0042] [3] Specific silane coupling agents The composition of the present invention contains a silane coupling agent represented by the following formula (1) (hereinafter also referred to as the "specific silane coupling agent"). (C n H 2n+1 O)3Si-C m H 2m -S-CO-C k H 2k+1 (1) In equation (1), n ​​is 2, m is 3, and k is 7.

[0043] [Content] In the composition of the present invention, the content of the specific silane coupling agent is 8 to 20% by mass relative to the silica content described above. In particular, 12 to 18% by mass is preferred because it provides superior effects of the present invention.

[0044] In the composition of the present invention, the content of the specific silane coupling agent is preferably 10 to 40% by mass, and more preferably 15 to 35% by mass, relative to the content of the specific SBR mentioned above, for the reason that the effects of the present invention are superior.

[0045] [4] Optional component The composition of the present invention may optionally contain components other than those described above (optional components). Examples of such components include fillers other than silica (preferably carbon black), silane coupling agents other than specific silane coupling agents, thermally expandable microcapsules, zinc oxide (zinc oxide), stearic acid, antioxidants, waxes, processing aids, liquid polymers, vulcanizing agents (e.g., sulfur), vulcanization accelerators (accelerators), vulcanization activators, and various other additives commonly used in rubber compositions.

[0046] [Specific alkyltriethoxysilanes] The composition of the present invention preferably further contains an alkyltriethoxysilane represented by the following formula (I) (hereinafter also referred to as "specific alkyltriethoxysilane") for reasons that the effects of the present invention are superior.

[0047] [ka] In formula (I), R 1 represents an alkyl group with 7 to 20 carbon atoms, and Et represents an ethyl group.

[0048] [Content] In the composition of the present invention, the content of the specific alkyltriethoxysilane is preferably 0.1 to 20% by mass, more preferably 1 to 10% by mass, and even more preferably 3 to 7% by mass, relative to the silica content, for the reason that the effects of the present invention are superior.

[0049] [5] Glass transition temperature The glass transition temperature (Tg) of the composition of the present invention is -50°C or higher. In particular, it is preferable that it be -45°C or higher because the effects of the present invention are superior. There is no particular upper limit, but it is preferably -10°C or lower, more preferably -20°C or lower, and even more preferably -30°C or lower.

[0050] [6] Condition A The composition of the present invention is obtained by mixing the above-mentioned diene rubber and the above-mentioned silica (hereinafter, this mixture will also be referred to as "mixture 1"), and then, after the temperature of the mixed system has risen to 80°C or higher and 120°C or lower, mixing in the above-mentioned specific silane coupling agent (hereinafter, this mixture will also be referred to as "mixture 2"). Hereinafter, the composition obtained in this manner will also be referred to as "condition A".

[0051] Generally, when preparing a rubber composition, components other than the vulcanizing system (vulcanizing agent, vulcanization accelerator) are placed in a mixer and mixing (kneading) is started at room temperature (around 20°C). At this time, the temperature of the mixed system (mixture) rises due to friction between the components during kneading.

[0052] In the composition of the present invention, first, the diene rubber and silica are mixed (mix 1). Then, as the temperature of the mixed system rises due to kneading, a specific silane coupling agent is added to the mixed system when the temperature of the mixed system reaches 80°C to 120°C (mix 2). If the composition of the present invention contains the above-mentioned optional components, it is preferable to mix the optional components other than the vulcanizing agent in Mix 1. If the composition of the present invention contains a vulcanizing system, it is preferable to release the mixed system (masterbatch) from the mixer after mixing 1 and mixing 2, allow it to cool, and then mix in the vulcanizing system.

[0053] [II] Tires The tire of the present invention is a tire manufactured using the above-described composition of the present invention in the tire tread. The tire of the present invention is preferably a pneumatic tire and can be filled with air, an inert gas such as nitrogen, and other gases. The tire of the present invention is particularly useful as a studless tire because it has excellent performance on ice.

[0054] Figure 1 shows a schematic partial cross-sectional view of a tire representing an example of an embodiment of the tire of the present invention. However, the tire of the present invention is not limited to the embodiment shown in Figure 1.

[0055] In Figure 1, reference numeral 1 represents the bead portion, reference numeral 2 represents the sidewall portion, and reference numeral 3 represents the tire tread portion (tread portion). Furthermore, a carcass layer 4 with embedded fiber cords is installed between the pair of left and right bead sections 1, and the ends of this carcass layer 4 are folded back and wrapped around the bead core 5 and bead filler 6 from the inside to the outside of the tire. Furthermore, in the tire tread section 3, a belt layer 7 is arranged around the entire circumference of the tire, on the outside of the carcass layer 4. Furthermore, a rim cushion 8 is positioned in the bead portion 1 where it contacts the rim. At least the tire tread portion 3 is formed by the composition of the present invention as described above.

[0056] The tire of the present invention can be manufactured, for example, by conventionally known methods. In addition to ordinary air or air with adjusted oxygen partial pressure, inert gases such as nitrogen, argon, and helium can be used as the gas to fill the tire. [Examples]

[0057] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0058] [Synthesis of Modified SBR2] Two 4L stainless steel pressure vessels, vacuum-dried, were prepared. In the first pressure vessel, 6,922g of cyclohexane, 85g of the compound represented by chemical formula (i) below, and 60g of tetramethylethylenediamine were added to prepare the first reaction solution. Simultaneously, in the second pressure vessel, 180g of liquid 2.0M n-butyllithium and 6,926g of cyclohexane were added to prepare the second reaction solution. In this case, the molar ratio of the compound represented by chemical formula (i), n-butyllithium, and tetramethylethylenediamine was 1:1:1. While maintaining the pressure in each pressure vessel at 7 bar, the first reaction solution was injected into the continuous reactor via the first continuous channel at an injection rate of 1.0 g / min, and the second reaction solution was injected via the second continuous channel at an injection rate of 1.0 g / min, using a mass flow meter. During this process, the temperature of the continuous reactor was maintained at -10°C, the internal pressure was maintained at 3 bar using a back pressure regulator, and the residence time in the reactor was adjusted to be within 10 minutes. The reaction was then terminated to obtain the denaturing initiator.

[0059] [ka]

[0060] In the first reactor of a continuous reactor consisting of three reactors connected in series, a styrene solution prepared by dissolving styrene at 60% by mass in n-hexane was injected at a rate of 6.5 kg / h (hours) (62.4 mol / h in terms of styrene), a 1,3-butadiene solution prepared by dissolving 1,3-butadiene at 60% by mass in n-hexane was injected at a rate of 7.7 kg / h (85.4 mol / h in terms of 1,3-butadiene), 47.0 kg / h of n-hexane, a 1,2-butadiene solution prepared by dissolving 1,2-butadiene at 2.0% by mass in n-hexane was injected at a rate of 400.0 g / h, and as a polar additive, a solution prepared by dissolving N,N,N′,N′-tetramethylethylenediamine (TMEDA) at 10% by mass in n-hexane was injected at a rate of 50.0 g / h. The resulting denaturing initiator was then injected at a rate of 400.0 g / h. During this process, the temperature of the first reactor was maintained at 55°C, and when the polymerization conversion rate reached 41%, the polymer was transferred from the first reactor to the second reactor via a transfer pipe. Next, a 1,3-butadiene solution, in which 1,3-butadiene was dissolved in n-hexane at a rate of 60% by mass, was injected into the second reactor at a rate of 2.3 kg / h (25.5 mol / h in terms of 1,3-butadiene). During this process, the temperature of the second reactor was maintained at 65°C, and when the polymerization conversion rate reached 95% or higher, the polymer was transferred from the second reactor to the third reactor via a transfer pipe. The polymer was transferred from the second reactor to the third reactor, and a solution of N-(3-(1H-1,2,4-triazole-1-yl)propyl)-3-(trimethoxysilyl)-N-(3-(trimethoxysilyl)propyl)propan-1-amine (solvent: n-hexane) was continuously added to the third reactor as a modifying agent [modifying agent: act.Li (polymerization initiator) = 1:1 mol]. The temperature of the third reactor was maintained at 65°C. Subsequently, a 30% by mass solution of IR1520 (manufactured by BASF) was added to the polymerization solution discharged from the third reactor at a rate of 170 g / h as an antioxidant, and the mixture was stirred. The resulting polymer was placed in steam-heated hot water, stirred to remove the solvent, and modified SBR was obtained. The obtained modified SBR is also called modified SBR2.

[0061] Modified SBR2 is a styrene-butadiene rubber containing alkoxysilyl groups. It has a Tg of -31°C, a unimodal molecular weight distribution curve for GPC, and a molecular weight distribution (PDI) of 1.3.

[0062] [Criteria Examples 1-3, Examples 1-18, Comparative Examples 1-3 and Comparative Examples 5-7] The components listed in Tables 1-5 below, excluding the comparative silane coupling agent and the silane coupling agent, along with carbon black, oil, zinc oxide, stearic acid, and an antioxidant, were placed in a 1.8 L sealed mixer, and mixing was started at room temperature. The internal temperature of the mixer (temperature of the mixing system) rose during mixing. When the internal temperature of the mixer reached 100°C, the comparative silane coupling agent or the silane coupling agent listed in Tables 1-5 below was added to the mixing system, and mixing was continued. Subsequently, when the internal temperature of the mixer reached 160°C, the mixture (masterbatch) was removed from the mixer. Then, sulfur and a vulcanization accelerator were added to the masterbatch, and the mixture was obtained using an open roll under conditions below 100°C.

[0063] [Comparative Example 4] The rubber composition was obtained by following the same procedure as in the other examples described above, except that the silane coupling agent was mixed together with each component (except for sulfur and vulcanization accelerator) in the mixer, rather than being added later.

[0064] [evaluation] The following evaluations were performed on each of the obtained rubber compositions.

[0065] [Mixing processability] The obtained rubber composition was molded into a sheet, and its surface was visually inspected. The processability for mixing was then evaluated according to the following criteria. The results are shown in Tables 1-5. A score of △ or higher is preferable, and a score of ○ is even more preferable. • ○: A smooth surface without bumps or irregularities, and no cracks at the edges. •△: The surface is smooth, but there are several cracks on the edges. • ×: The surface is uneven and has numerous cracks on the edges.

[0066] [Extrusion processability] The obtained rubber composition was molded into a predetermined shape by extrusion, and its extrusion processability was evaluated according to the following criteria. The results are shown in Tables 1-5. A score of △ or higher is preferable, and a score of ○ is even more preferable. • ○: A smooth surface without bumps or irregularities, and no cracks at the edges. •△: The surface is smooth, but there are several cracks on the edges. • ×: The surface is uneven and has numerous cracks on the edges.

[0067] [Handling Stability] Using the rubber composition, test tires were fabricated in tire size 245 / 40R19. Four test tires were mounted on a passenger car with a 2300cc engine. A test driver conducted a subjective evaluation of the handling stability on a dry road surface. The handling stability was then evaluated according to the following criteria. The results are shown in Tables 1-5. A score of △ or higher is preferable, and a score of ○ is even more preferable. • ○: No delay in response to steering input. • △: Slight delay in response to steering input. • ×: Significant delay in response to steering input.

[0068] [Rolling performance] Using the rubber composition, test tires were fabricated in tire size 245 / 40R19. The test tire was mounted on a wheel with a rim size of 18 x 7.5J, the air pressure was set to 210 kPa, and the rolling resistance was measured when the tire was pressed against the drum with a load equivalent to 85% of the maximum load at the specified air pressure as described in the JATMA Yearbook 2009 edition, while the vehicle was driven at a speed of 80 km / h (hour) using an indoor drum testing machine (drum diameter: 1707 mm). The reciprocal of the measured value was then indexed with Reference Example 1 set to 100 for Examples 1-2, Comparative Examples 1-2, Examples 7, Examples 10, Examples 13 and 16; with Reference Example 2 set to 100 for Examples 3-4, Comparative Examples 3-6, Examples 9, Examples 12, Examples 15 and 18; and with Reference Example 3 set to 100 for Examples 5-6, Comparative Examples 7, Examples 8, Examples 11, Examples 14 and 17. The results are shown in Tables 1-5. A higher index indicates lower rolling resistance and superior rolling performance. In practical terms, an index of 105 or higher is preferable.

[0069] [Wet performance] Using the rubber composition, test tires were fabricated in tire size 245 / 40R19. Four test tires were mounted on a passenger car with an engine displacement of 2300cc, and the braking distance from an initial speed of 100 km / h (time) was measured on a water-sprayed asphalt surface. The reciprocal of the distance was then indexed with Reference Example 1 set to 100 for Examples 1-2, Comparative Examples 1-2, Examples 7, 10, 13, and 16; with Reference Example 2 set to 100 for Examples 3-4, Comparative Examples 3-6, Examples 9, 12, 15, and 18; and with Reference Example 3 set to 100 for Examples 5-6, Comparative Examples 7, 8, 11, 14, and 17. The results are shown in Tables 1-5. A higher index indicates better wet performance. In practical terms, an index of 102 or higher is preferable.

[0070] [Table 1] [Table 2] [Table 3] [Table 4]

[0071] [Table 5]

[0072] The details of each component in Tables 1-5 are as follows. • Modified SBR1: Styrene-butadiene rubber containing alkoxysilyl groups, manufactured by Zeon Corporation (NS560), with a Tg of -32°C. (Does not fall under the category of the specified SBR mentioned above.) • Modified SBR2: Modified SBR2 synthesized as described above (Modified SBR2 has a unimodal molecular weight distribution curve in GPC and its molecular weight distribution (PDI) is less than 1.7, therefore it falls under the category of the specified SBR described above). • Unmodified BR: Butadiene rubber, Nipol BR1220 manufactured by Nippon Zeon Co., Ltd., with a Tg of -105°C. • NR: Natural rubber, TSR20, Tg -65℃ Modified BR: Nipol BR1261 manufactured by Nippon Zeon Corporation, with a Tg of -95°C. • Modified SBR3: Terminal-modified styrene-butadiene rubber, HPR850 manufactured by ENEOS Material Co., Ltd. (Modifying group: Vinyl content: 59% by mass, Styrene content: 27% by mass) (Does not fall under the category of the specified SBR mentioned above) • Silica 1: Solvay ZEOSIL 1165MP, CTAB: 160m 2 / g(CTAB is 140m 2 / g or more 180m 2 (Since it is silica with a weight of less than / g, it falls under Silica 1 as described above.) • Silica 2: Evonik ULTRASIL 9100GR, CTAB: 200m 2 / g(CTAB is 180m 2 / g or more 220m 2(Since it is silica with a weight of less than / g, it corresponds to Silica 2 as described above.) • Comparative silane coupling agent: Si69 manufactured by Evonik Degussa, bis(triethoxysilylpropyl)tetrasulfide (not applicable to the specified silane coupling agent mentioned above) • Silane coupling agent: A silane coupling agent represented by formula (1) above, Momentive's NXT silane (corresponding to the specified silane coupling agent mentioned above) • Alkylsilane: Octyltriethoxysilane, KBE-3083 manufactured by Shin-Etsu Chemical Co., Ltd. (This is an alkyltriethoxysilane represented by formula (I) above, and therefore falls under the category of specific alkyltriethoxysilanes mentioned above.)

[0073] In Tables 1-5, the Tg column represents the glass transition temperature (Tg) [°C] of each rubber composition.

[0074] As can be seen from Tables 1 to 5, Examples 1 to 18, which contained predetermined amounts of specific SBR, silica, and specific silane coupling agents and satisfied condition A, showed excellent mixability, extrusionability, handling stability, rolling performance, and wet performance.

[0075] A comparison of Examples 1-2, Examples 3-4, and Examples 5-6 (all comparisons of embodiments differing only in the content of modified SBR1 and modified SBR2) showed that Examples 1, 3, and 5, in which the content of modified SBR per 100 parts by mass of diene rubber was 50 parts by mass or more, exhibited superior wet performance. Furthermore, from a comparison between Example 5 and Example 8 (comparison of embodiments with different types and amounts of silica), it was found that silica and CTAB were 140m 2 / g or more 180m 2 50-80 parts by mass of silica 1 (less than / g) and 180m of CTAB 2 / g or more 220m 2 Example 8, which contained 20 to 60 parts by mass of silica 2 in a quantity of less than 1g, showed superior wet performance. Furthermore, comparisons between Example 7 and Example 10, Example 8 and Example 11, and Example 9 and Example 12 (all comparisons of embodiments where only the mass parts of unmodified BR and NR differed) showed that Examples 10-12, in which the diene rubber contained 10-20 parts by mass of natural rubber, exhibited superior wet performance. Furthermore, comparisons between Example 10 and Example 13, between Example 11 and Example 14, and between Example 12 and Example 15 (all comparisons between embodiments where only the mass parts of unmodified BR and modified BR differed) showed that Examples 13 to 15, in which the diene rubber contained 10 to 20 parts by mass of modified butadiene rubber, exhibited superior rolling performance and wet performance. Furthermore, comparisons between Example 13 and Example 16, between Example 14 and Example 17, and between Example 15 and Example 18 (all comparisons of embodiments where only the mass parts of modified SBR2 and modified SBR3 differed) showed that Examples 16 to 18, which contained 10 to 20 parts by mass of modified styrene-butadiene rubber different from the specified SBR, exhibited superior wet performance.

[0076] On the other hand, standard examples 1 to 3, which did not contain specific SBR, and comparative examples 1 and 7, which contained specific SBR but in amounts less than 30 parts by mass, exhibited insufficient rolling performance and wet performance. Furthermore, Comparative Example 4, which contained 30 parts by mass or more of a specific SBR but did not meet condition A (obtained by mixing a specific silane coupling agent with other components), exhibited insufficient mixability, rolling performance, and wet performance. Furthermore, Comparative Example 2, which contained less than 70 parts by mass of silica, exhibited insufficient wet performance. Furthermore, Comparative Example 3, which contained more than 140 parts by mass of silica, exhibited insufficient rolling performance. Furthermore, Comparative Example 6, which did not contain the specified silane coupling agent (but contained a silane coupling agent other than the specified silane coupling agent), and Comparative Example 5, which contained the specified silane coupling agent but whose silica content was less than 8% by mass, exhibited insufficient mixability, extrusionability, rolling performance, and wet performance. [Explanation of Symbols]

[0077] 1. Bead section 2 Sidewall section 3. Tire tread section 4. Carcass layer 5 Bead core 6. Bead Filler 7 Belt layer 8 Rim Cushion

Claims

1. It contains 100 parts by mass of a diene rubber containing 30 parts by mass or more of modified styrene-butadiene rubber, 70 to 140 parts by mass of silica, and a silane coupling agent represented by the following formula (1). The modified styrene-butadiene rubber has a unimodal molecular weight distribution curve obtained by gel permeation chromatography (GPC), and its molecular weight distribution (PDI) is less than 1.

7. The content of the silane coupling agent is 8 to 20% by mass relative to the silica content. A rubber composition for tire treads having a glass transition temperature of -50°C or higher, A rubber composition for tire treads obtained by mixing the diene-based rubber and the silica, and then mixing the silane coupling agent after the temperature of the mixture system has risen to 80°C or higher and 120°C or lower. (C ｎ H ２ｎ＋１ O) ３ Si-C ｍ H ２ｍ -----C ｋ H ２ｋ＋１ (1) In equation (1), n ​​is 2, m is 3, and k is 7.

2. The silica is 50 to 80 parts by mass of silica 1 in which CTAB is 140 m ２ / g or more and less than 180 m ２ / g, and 20 to 60 parts by mass of silica 2 in which CTAB is 180 m ２ / g or more and less than 220 m ２ / g, and the rubber composition for a tire tread according to claim 1.

3. Furthermore, it contains an alkyltriethoxysilane represented by the following formula (I), The rubber composition for tire treads according to claim 1, wherein the content of the alkyltriethoxysilane is 0.1 to 20% by mass relative to the content of the silica. 【Chemistry 1】 In formula (I), R １ represents an alkyl group with 7 to 20 carbon atoms, and Et represents an ethyl group.

4. The rubber composition for tire treads according to claim 1, wherein the diene rubber contains 10 to 20 parts by mass of natural rubber.

5. The tire tread rubber composition according to claim 1, wherein the diene rubber comprises 10 to 20 parts by mass of modified butadiene rubber.

6. The tire tread rubber composition according to claim 1, wherein the diene rubber comprises 10 to 20 parts by mass of a modified styrene-butadiene rubber different from the modified styrene-butadiene rubber.

7. A tire manufactured using the tire tread rubber composition described in any one of claims 1 to 6 as the tire tread.

Images