Rubber composition for tire treads, and tire

Abstract

The present invention addresses the problem of providing: a rubber composition for tire treads which has excellent mixability and extrudability and with which tires having excellent steering stability, rolling performance, and wet performance are obtained; and a tire produced using the rubber composition for the tire treads. This rubber composition for tire treads comprises 100 parts by mass of a diene-based rubber including 30 parts by mass or more of a modified styrene / butadiene rubber, 70-140 parts by mass of silica, and a specific silane coupling agent. The modified styrene / butadiene rubber in GPC gives a molecular weight distribution curve which has a unimodal shape, and has a PDI less than 1.7. The content of the silane coupling agent is 8-20 mass% with respect to the content of the silica. The Tg is -50°C or higher. The rubber composition for tire treads is obtained by mixing the diene-based rubber with silica and, after the temperature of the mixture system has reached 80-120°C, mixing a silane coupling agent therewith.

Description

Rubber composition for tire treads and tires

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

[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.

[0003] Patent No. 7339580

[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, blending processability 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 demands that are likely to increase further in the future, it is desirable to further improve processability and rolling performance when made into tires.

[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.

[0007] The inventors of the present invention, after diligently studying the above problems, discovered that the above 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 of the present invention discovered that the above problems can be solved with the following configuration.

[0008] (1) A rubber composition for a tire tread, containing 100 parts by mass of a diene rubber containing 30 parts by mass or more of a modified styrene-butadiene rubber, 70 to 140 parts by mass of silica, and a silane coupling agent represented by the following formula (1), wherein the modified styrene-butadiene rubber has a unimodal molecular weight distribution curve in gel permeation chromatography (GPC) and a molecular weight distribution (PDI) of less than 1.7, the content of the silane coupling agent is 8 to 20% by mass with respect to the content of the silica, and the glass transition temperature is -50°C or higher, and the rubber composition for a tire tread is obtained by mixing the diene rubber and the silica and then mixing the silane coupling agent after the temperature of the mixture system reaches 80°C or higher and 120°C or lower. (C ２ , ２ｋ＋１ , ２ , ２ｍ , ｋ , ３ , ｍ , ２ , ２ H ２ｎ＋１ O) ３ Si - C ｍ H ２ｍ -S - CO - C ｋ H ２ｋ＋１ (1) In formula (1), n is 2, m is 3, and k is 7. (2) The silica is 50 to 80 parts by mass of silica 1 having a CTAB of 140 m ２ / g or more and less than 180 m ２ / g, and 180 m of CTAB ２ / g or more and 220 m ２(1) The tire tread rubber composition according to (1) above, comprising 20 to 60 parts by mass of silica 2 which is less than 1 / g. (3) The tire tread rubber composition according to (1) or (2) above, further comprising an alkyltriethoxysilane represented by formula (I) described later, wherein the content of the alkyltriethoxysilane is 0.1 to 20% by mass relative to the content of the silica. (4) The tire tread rubber composition according to any one of (1) to (3) above, wherein the diene rubber comprises 10 to 20 parts by mass of natural rubber. (5) The tire tread rubber composition according to any one of (1) to (4) above, wherein the diene rubber comprises 10 to 20 parts by mass of modified butadiene rubber. (6) The tire tread rubber composition according to any one of (1) to (5) above, wherein the diene rubber comprises 10 to 20 parts by mass of modified styrene-butadiene rubber different from the modified styrene-butadiene rubber. (7) A tire manufactured using the tire tread rubber composition described in any of (1) to (6) above as the tire tread.

[0009] As shown below, the present invention provides 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.

[0010] This is a schematic partial cross-sectional view showing an example of an embodiment of the tire of the present invention.

[0011] The rubber composition for tire treads of the present invention is described below. In this specification, numerical ranges expressed using "~" mean a range that includes the values ​​written before and after "~" as the lower and upper limits. In addition, each component may be used alone or in combination of two or more. Here, when two or more components are used in combination, the content of that component refers to the total content unless otherwise specified. In particular, when the 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 referred to as "total silica content." Furthermore, with respect to the rubber composition for tire treads, the handling stability, rolling performance, and wet performance when made into a tire are 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") contains 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 silane coupling agent represented by formula (1) described later, wherein the modified styrene-butadiene rubber has a unimodal molecular weight distribution curve 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 content of silica (total silica amount), and the glass transition temperature is -50°C or higher, and is obtained by mixing the diene rubber and the silica, and then mixing the 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 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 called "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 tends to aggregate with other polymers and does not mix well with silica. Therefore, if these components and a silane coupling agent are mixed at the same time, coupling between the two occurs in a state where the dispersibility of silica is insufficient. On the other hand, in the case of the composition of the present invention, the diene rubber containing the specific SBR and silica are mixed first, and then the silane coupling agent is mixed after the temperature reaches a specific range, so coupling occurs in a state of sufficient dispersion. In addition, because a specific silane coupling agent is used as the silane coupling agent, 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 to be able to obtain the desired properties.

[0014] While it may be theoretically possible to measure the difference in silica dispersibility using an electron microscope, in practice, this 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 the prior art has a vast number of possibilities, it is impossible to uniquely determine a statistically significant number. Therefore, finding such an indicator and its value, and directly identifying the features of the present invention by the structure or properties of the material, is not at all practical.

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

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

[0019] [Modifying Groups] The modifying groups that a particular SBR may have are not particularly limited, but specific examples include alkoxysilyl groups and amino groups (for example, -NR) ２ Examples of such groups include hydroxyl groups, carboxyl groups, etc., where R represents a hydrogen atom or substituent. Among these, alkoxysilyl groups are preferred because they exhibit superior effects compared to the present invention.

[0020] Examples of the above alkoxysilyl group include -Si(OR1) ｎ (R2) ３－ｎ Examples of groups are those represented as follows: (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 its 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 has a unimodal molecular weight distribution curve when measured by gel permeation chromatography (GPC), and its molecular weight distribution (PDI) is less than 1.7. A unimodal molecular weight distribution curve indicates high molecular uniformity and homogeneous distribution 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. A molecular weight distribution (PDI) of less than 1.7 indicates high molecular uniformity and homogeneous distribution within the diene rubber, similar to a unimodal molecular weight distribution curve. For reasons that the effects of the present invention are superior, 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, for example: Apparatus: Gel permeation chromatography [GPC: HLC-8020, manufactured by Tosoh Corporation] Column: GMH-HR-H, manufactured by Tosoh Corporation (two columns connected in series) Measurement temperature: 40°C Carrier gas: Helium Flow rate: 5 mmol / L Sample: 10 mg dissolved in 10 mL of THF (tetrahydrofuran) Injection volume: 10 μL 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 the specific SBR is not particularly limited, but from the reason that the effects of the present invention are more excellent, 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 the specific SBR is not particularly limited, but from the reason that the effects of the present invention are more excellent, it is preferably -60 to -10 °C, and more preferably -40 to -20 °C. The above Tg can be adjusted, for example, by the amount of styrene or vinyl. In the present specification, the glass transition temperature (Tg) is measured using a differential scanning calorimeter (DSC) at a heating rate of 10 °C / min and calculated by the midpoint method.

[0027] [Content] The content of the specific SBR is 30 parts by mass or more in 100 parts by mass of the diene rubber. Among them, from the reason that the effects of the present invention are more excellent, it is preferably 50 parts by mass or more, and more preferably 60 parts by mass or more. The upper limit is not particularly limited, but from the reason that the effects of the present invention are more excellent, it is preferably 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 rubbers] The diene rubber may contain diene rubbers other than the specific SBR. Examples of such diene rubbers include styrene-butadiene rubber (SBR) other than the 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), chloroprene rubber (CR), and the like.

[0029] [Natural rubber] The diene rubber preferably contains natural rubber (NR) from the reason that the effects of the present invention are more excellent.

[0030] <Content> The content 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 reason that the effects of the present invention are superior.

[0031] [Modified Butadiene Rubber] For the diene rubber, it is preferable to include modified butadiene rubber (modified BR) because the effects of the present invention are superior.

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

[0033] <Content> The content 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 reason that the effects of the present invention are superior.

[0034] [Modified styrene-butadiene rubber different from specific SBR] The diene rubber preferably contains modified styrene-butadiene rubber different from specific SBR because it provides superior effects in the present invention.

[0035] <Modifying Groups> Specific examples and preferred embodiments of 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 the specified 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 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 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 silica may be one type of silica used alone, or two or more types of silica may be used in combination.

[0039] [CTAB] The specific surface area of ​​the above silica adsorbed with cetyltrimethylammonium bromide (CTAB) (hereinafter, "CTAB adsorption specific surface area" will also be simply 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 is / g, and 150 to 200m ２ It is more preferable that the value is / 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] For better effects of the present invention, silica is preferred when CTAB is 140 m ２ / g or more 180m ２ 50 to 80 parts by mass of silica 1 (hereinafter also simply referred to as "silica 1") which is less than 1 / g, and 180 m 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 1g / g.

[0042] [3] Specific Silane Coupling Agent 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) ３ Si-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, it is preferable that the content be 12 to 18% by mass for which the effects of the present invention are superior.

[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 Components The compositions 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, stearic acid, antioxidants, waxes, processing aids, liquid polymers, vulcanizing agents (e.g., sulfur), vulcanization accelerators, vulcanization activators, and various other additives commonly used in rubber compositions.

[0046] [Specific alkyltriethoxysilane] 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] 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 for the reason that 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 mixing the above-mentioned specific silane coupling agent after the temperature of the mixed system has risen to 80°C or higher and 120°C or lower (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 mixing system rises due to kneading, a specific silane coupling agent is mixed into the mixing system when the temperature of the mixing 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 system in mix 1. If the composition of the present invention contains a vulcanizing system, it is preferable to release the mixing system (masterbatch) from the mixer after mix 1 and mix 2, let it 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). Between the pair of left and right bead portions 1, a carcass layer 4 in which fiber cords are embedded is mounted, and the ends of this carcass layer 4 are folded back and wound up from the inside to the outside of the tire around the bead core 5 and bead filler 6. In the tire tread portion 3, a belt layer 7 is arranged around the entire circumference of the tire on the outside of the carcass layer 4. In the bead portion 1, a rim cushion 8 is arranged in the portion that 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.

[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 4 L stainless steel pressure vessels, vacuum-dried, were prepared. In the first pressure vessel, 6,922 g of cyclohexane, 85 g of the compound represented by the following chemical formula (i), and 60 g of tetramethylethylenediamine were added to prepare the first reaction solution. Simultaneously, in the second pressure vessel, 180 g of liquid 2.0 M n-butyllithium and 6,926 g of cyclohexane were added to prepare the second reaction solution. At this time, the molar ratio of the compound represented by chemical formula (i), n-butyllithium, and tetramethylethylenediamine was 1:1:1. With the pressure in each pressure vessel maintained at 7 bar, the first reaction solution was injected into the continuous reactor at an injection rate of 1.0 g / min through the first continuous channel and the second reaction solution at an injection rate of 1.0 g / min through the second continuous channel, 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]

[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), n-hexane at a rate of 47.0 kg / h, 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 containing 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 solution of IR1520 (manufactured by BASF) dissolved at 30% by mass was added to the polymerization solution discharged from the third reactor at a rate of 170 g / h as an antioxidant and 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 in GPC, and a molecular weight distribution (PDI) of 1.3.

[0062] [Reference Examples 1-3, Examples 1-18, Comparative Examples 1-3 and Comparative Examples 5-7] The comparative silane coupling agent and the components excluding the silane coupling agent from the components listed in Tables 1-5 below, 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 as a result of the mixing. When the internal temperature of the mixer reached 100°C, the comparative silane coupling agent or 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 mixed using an open roll under conditions of 100°C or less to obtain each rubber composition.

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

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

[0065] [Mixability] The obtained rubber composition was molded into a sheet, and the sheet surface was visually observed. The mixability was then evaluated according to the following criteria. The results are shown in Tables 1 to 5. A score of △ or higher is preferable, and a score of ○ is more preferable. ・○: Smooth surface with no irregularities and no cracks at the edges ・△: Smooth surface but with several cracks at the edges ・×: Irregularities and numerous cracks at the edges

[0066] [Extrudeability] The obtained rubber composition was molded into a predetermined shape by extrusion, and its extrudeability was evaluated according to the following criteria. The results are shown in Tables 1 to 5. A score of △ or higher is preferable, and a score of ○ is more preferable. ・○: Smooth surface with no irregularities and no cracks at the edges ・△: Smooth surface with several cracks at the edges ・×: Irregular surface with numerous cracks at the edges

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

[0068] [Rolling Performance] Using the rubber composition, test tires were prepared in tire size 245 / 40R19. The test tires were mounted on wheels with a rim size of 18 x 7.5J, and the air pressure was set to 210 kPa. Using an indoor drum testing machine (drum diameter: 1707 mm), the rolling resistance was measured when the tires were pressed against the drum with a load equivalent to 85% of the maximum load at the air pressure described in the JATMA Yearbook 2009 edition, and driven at a speed of 80 km / h (hour). 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, 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 to 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 prepared 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 (hour) was measured on a water-sprinkled asphalt road 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, 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 better wet performance. In practical terms, an index of 102 or higher is preferable.

[0070]

[0071]

[0072] Details of each component in Tables 1 to 5 are as follows: ・Modified SBR1: Styrene butadiene rubber having an alkoxysilyl group, NS560 manufactured by Nippon Zeon Co., Ltd., Tg is -32°C. (Does not fall under the specified SBR mentioned above) ・Modified SBR2: Modified SBR2 synthesized as described above (Modified SBR2 falls under the specified SBR mentioned above because its GPC molecular weight distribution curve is unimodal and its molecular weight distribution (PDI) is less than 1.7) ・Unmodified BR: Butadiene rubber, Nipol BR1220 manufactured by Nippon Zeon Co., Ltd., Tg is -105°C. ・NR: Natural rubber, TSR20, Tg is -65°C ・Modified BR: Nipol BR1261 manufactured by Nippon Zeon Co., Ltd., Tg is -95°C. - Modified SBR3: Terminal-modified styrene-butadiene rubber, HPR850 manufactured by ENEOS Materials (modifying group: vinyl content: 59% by mass, styrene content: 27% by mass) (does not fall under the specified SBRs mentioned above) - Silica 1: ZEOSIL 1165MP manufactured by Solvay, CTAB: 160m ２ / g (CTAB is 140m) ２ / g or more 180m２ Since it is silica with a concentration of less than / g, it corresponds to 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 value of 0.1 / g or less, it corresponds to Silica 2 mentioned above.) Comparative silane coupling agent: Si69 manufactured by Evonik Degussa, bis(triethoxysilylpropyl)tetrasulfide (does not correspond to the specified silane coupling agent mentioned above) Silane coupling agent: Silane coupling agent represented by formula (1) mentioned above, NXT silane manufactured by Momentive (corresponds to the specified silane coupling agent mentioned above) Alkylsilane: Octyltriethoxysilane, KBE-3083 manufactured by Shin-Etsu Chemical Co., Ltd. (Since it is an alkyltriethoxysilane represented by formula (I) mentioned above, it corresponds to the specified alkyltriethoxysilane mentioned above)

[0073] In Tables 1 to 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 agent and satisfied condition A, showed excellent mixability, extrusionability, handling stability, rolling performance, and wet performance.

[0075] From 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), Examples 1, 3, and 5, in which the modified SBR content per 100 parts by mass of diene rubber was 50 parts by mass or more, showed superior wet performance. Furthermore, from a comparison of Examples 5 and 8 (comparisons of embodiments differing in the type and amount of silica), silica and CTAB were found to be of 140 m ２ / g or more 180m ２ 50 to 80 parts by mass of silica 1 which is less than 1 / g, and 180 m of CTAB ２ / g or more 220m ２Example 8, which contained 20 to 60 parts by mass of silica 2 at a concentration of less than 1 / g, showed superior wet performance. Furthermore, comparing Example 7 with Example 10, Example 8 with Example 11, and Example 9 with Example 12 (all comparisons of embodiments where only the parts by mass of unmodified BR and NR differed), Examples 10 to 12, in which the diene rubber contained 10 to 20 parts by mass of natural rubber, showed superior wet performance. Furthermore, comparing Example 10 with Example 13, Example 11 with Example 14, and Example 12 with Example 15 (all comparisons of embodiments where only the parts by mass of unmodified BR and modified BR differed), Examples 13 to 15, in which the diene rubber contained 10 to 20 parts by mass of modified butadiene rubber, showed 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, Reference Examples 1 to 3, which do not contain the specified SBR, and Comparative Examples 1 and 7, which contain the specified SBR but in amounts less than 30 parts by mass, exhibited insufficient rolling performance and wet performance. Furthermore, Comparative Example 4, which contains 30 parts by mass or more of the specified SBR but does not meet condition A (obtained by mixing the specified silane coupling agent with other components), exhibited insufficient mixability, rolling performance, and wet performance. Furthermore, Comparative Example 2, which has a silica content of less than 70 parts by mass, exhibited insufficient wet performance. Furthermore, Comparative Example 3, which has a silica content exceeding 140 parts by mass, exhibited insufficient rolling performance. Furthermore, Comparative Example 6, which does not contain the specified silane coupling agent (contains a silane coupling agent other than the specified silane coupling agent), and Comparative Example 5, which contains the specified silane coupling agent but in amounts less than 8% by mass relative to the silica content, exhibited insufficient mixability, extrusion processability, rolling performance, and wet performance.

[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. A tire tread rubber composition comprising 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), wherein the modified styrene-butadiene rubber has a unimodal molecular weight distribution curve 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 content of silica, and the glass transition temperature is -50°C or higher, the tire tread rubber composition obtained by mixing the diene rubber and the silica, and then mixing the 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) ３ Si-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 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. The tire tread rubber composition according to claim 1 or 2, further comprising an alkyltriethoxysilane represented by the following formula (I), wherein the content of the alkyltriethoxysilane is 0.1 to 20% by mass relative to the content of the silica. In formula (I), R １ represents an alkyl group with 7 to 20 carbon atoms, and Et represents an ethyl group.

4. The tire tread rubber composition according to any one of claims 1 to 3, wherein the diene rubber contains 10 to 20 parts by mass of natural rubber.

5. The tire tread rubber composition according to any one of claims 1 to 4, wherein the diene rubber comprises 10 to 20 parts by mass of modified butadiene rubber.

6. The tire tread rubber composition according to any one of claims 1 to 5, 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.

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