Rubber composition and pneumatic tire using the same

Abstract

To provide a rubber composition capable of improving conflicting performances with regard to a rolling resistance and wet grip performance, and also to provide a pneumatic tire using the same.SOLUTION: A rubber composition includes silica in diene rubber. In the rubber composition, by using a pulse method NMR device with a solid echo method, each spin-spin relaxation time of an unvulcanized specimen composed of the diene rubber and a specimen obtained by vulcanizing the rubber composition is measured at 25°C, and a relaxation curve (free induction decay curve) obtained by the unvulcanized specimen is divided into two components of a component (S0) with shorter relaxation time and a component (L0) with longer relaxation time, and a relaxation curve (free induction decay curve) obtained by the vulcanized specimen is divided into two components of a component (S) with shorter relaxation time and a component (L) with longer relaxation time, then a weighted mean value (T0) of the relaxation time of the component (S0) and the relaxation time of the component (L0) and a relaxation time (TS) of the component (S) satisfy TS / T0≥0.26. A volume (VS) of the component (S) and a volume (VL) of the component (L) satisfy VS / VL≥0.26.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a rubber composition and a pneumatic tire using the same. [Background technology]

[0002] In recent years, environmental considerations have become a social requirement, and the demand for fuel-efficient vehicles has increased. Given this situation, there is a need to develop materials with low rolling resistance for automobile tires, particularly for the tire tread that contacts the ground. Furthermore, from the perspective of improving vehicle safety, there is a demand for improved braking performance on wet roads (wet grip performance).

[0003] To address these challenges, for example, Patent Document 1 describes that when a material contains three types of rubber components and two types of silica, and the dispersion ratio of silica in each rubber component is within a predetermined range, it is possible to achieve a high level of wet performance, abrasion resistance, and low rolling resistance simultaneously.

[0004] Furthermore, Patent Document 2 describes that when the Rs, which indicates the ratio of the restraining phase of a rubber reinforced with silica and a silane coupling agent as measured by pulsed NMR, is within a predetermined range, excellent low hysteresis loss, wet skid resistance, and abrasion resistance can be achieved while ensuring sufficient processability.

[0005] Thus, various proposals have been made to improve wet grip performance and rolling resistance performance. However, wet grip performance and rolling resistance performance are mutually exclusive properties; improving one leads to a decrease in the other. Therefore, there is a need to improve the other while suppressing the deterioration of one (improvement of mutually exclusive properties).

[0006] In the rubber composition described in Patent Document 1, a rubber component with a low Tg is arranged around the silica. In order to achieve such a configuration, it was necessary to standardize the modification of the rubber component and the mixing method of the components to be blended. Furthermore, the rubber component near the silica interface is restricted by the silica, and there is a risk that it cannot absorb stress caused by external stimuli sensitively, and there was room for improvement in the trade-off performance between rolling resistance and wet grip performance.

[0007] In Patent Document 2, the relaxation time of the polymer is not mentioned. When the restraint of the polymer is too strong, there is a risk that it cannot absorb stress caused by external stimuli sensitively, and there was room for improvement in the trade-off performance between rolling resistance and wet grip performance.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] In view of the above points, an object of the present invention is to provide a rubber composition that improves the trade-off performance between rolling resistance and wet grip performance, and a pneumatic tire using the same.

Means for Solving the Problems

[0010] The rubber composition according to the present invention is a rubber composition containing silica in a diene rubber. At 25°C, using a pulsed NMR apparatus, by the solid echo method, the spin-spin relaxation times of an unvulcanized sample composed of the above diene rubber and a sample obtained by vulcanizing the above rubber composition are measured respectively. The relaxation curve (free induction decay curve) obtained from the above unvulcanized sample is separated into two components: a component (S0) with a short relaxation time and a component (L0) with a long relaxation time. The relaxation curve (free induction decay curve) obtained from the above vulcanized sample is separated into two components: a component (S) with a short relaxation time and a component (L) with a long relaxation time. The weighted average value (T0) of the relaxation time of component (S0) and the relaxation time of component (L0), and the relaxation time (T S ) satisfy T S / T0≥0.26, and the volume (V S ) of component (S) and the volume (V L ) of component (L) satisfy V S / V L ≥0.26.

[0011] The rubber composition according to the present invention can further contain a sulfur-containing silane coupling agent and an alkylalkoxysilane.

[0012] The content of the above silica is 5 to 150 parts by mass with respect to 100 parts by mass of the diene rubber. The content of the above sulfur-containing silane coupling agent is 3 to 15% by mass with respect to the content of silica. The content of the above alkylalkoxysilane can be 10 to 300 mol% with respect to the sulfur-containing silane coupling agent.

[0013] The above sulfur-containing silane coupling agent can have a sulfide group.

[0014] The above alkylalkoxysilane can be a compound represented by the formula (1).

Chemical formula

[0015] The pneumatic tire according to the present invention shall be manufactured using the above-mentioned rubber composition. [Effects of the Invention]

[0016] The rubber composition of the present invention can improve the trade-off performance between rolling resistance and wet grip performance. [Brief explanation of the drawing]

[0017] [Figure 1] A graph showing the T2 relaxation curve of the rubber in Example 1, and the results of fitting and separating it. [Modes for carrying out the invention]

[0018] The following describes in detail matters related to the implementation of the present invention.

[0019] The rubber composition according to this embodiment contains silica in a diene rubber.

[0020] The diene rubber according to this embodiment is not particularly limited, but examples include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), and butyl rubber (IIR). Furthermore, the concept of diene rubber also includes those with modified ends or main chains as needed (e.g., end-modified SBR) and those modified to impart desired properties (e.g., modified NR).

[0021] In one embodiment, the diene rubber preferably contains at least one selected from the group consisting of natural rubber, styrene-butadiene rubber, and butadiene rubber. More preferably, the diene rubber contains styrene-butadiene rubber. For example, 100 parts by mass of the diene rubber preferably contains 50 parts by mass or more of styrene-butadiene rubber, more preferably 70 parts by mass or more of styrene-butadiene rubber, or it may contain styrene-butadiene rubber alone.

[0022] As the styrene-butadiene rubber, for example, solution-polymerized styrene-butadiene rubber (SSBR) or emulsion-polymerized styrene-butadiene rubber (ESBR) may be used. As the styrene-butadiene rubber, modified styrene-butadiene rubber with modified ends or main chain (for example, amine-modified SBR or tin-modified SBR) may be used as needed.

[0023] The silica in this embodiment is not particularly limited, but wet silica such as wet sedimentation silica or wet gel silica is preferably used. The silica content is preferably 5 to 150 parts by mass, and more preferably 30 to 100 parts by mass, per 100 parts by mass of diene rubber.

[0024] The rubber composition according to this embodiment may further contain a sulfur-containing silane coupling agent and an alkylalkoxysilane.

[0025] The sulfur-containing silane coupling agent according to this embodiment is a silane coupling agent containing sulfur atoms in its molecule, and various sulfur-containing silane coupling agents that are compounded together with silica in a rubber composition can be used.

[0026] Specific examples of sulfur-containing silane coupling agents include: Sulfide silanes such as bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)disulfide (bis-silane-based sulfide silane coupling agents); 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyldimethylmethoxysilane, mercaptoethyltriethoxysilane, formula: HS-(CH2)3-Si(OC2H5) m (O(C2H4O) k -C 13 H 27 ) n mercaptosilanes such as Evonik Degussa's "VP Si363" (where m = average 1, n = average 2, k = average 5) represented by; Protected mercaptosilanes such as 3-octanoylthio-1-propyltriethoxysilane (formula: CH3(CH2)6C(=O)S-(CH2)3-Si(OC2H5)3), 3-propionylthiopropyltrimethoxysilane, etc. (that is, silane compounds having a thiol ester structure in which the mercapto group is protected by an acyl group), etc. These sulfur-containing silane coupling agents can be used either singly or in combination of two or more.

[0027] Among these, as the sulfur-containing silane coupling agent, sulfide silanes having a sulfide group are preferred, and more preferably those having a disulfide group.

[0028] The content of the sulfur-containing silane coupling agent is preferably 2 to 15% by mass, more preferably 2 to 10% by mass, and even more preferably 2 to 8% by mass, relative to the silica content. In other words, the total amount of sulfur-containing silane coupling agent is preferably 2 to 15 parts by mass, more preferably 2 to 10 parts by mass, and even more preferably 2 to 8 parts by mass, per 100 parts by mass of silica.

[0029] The alkylalkoxysilane in this embodiment may be an alkyldialkoxysilane, but alkyltrialkoxysilane is preferred. The alkylalkoxysilane is preferably one having an alkyl group with 3 to 20 carbon atoms, and specifically, an alkyltriethoxysilane represented by the following formula (1) is preferably used. In formula (1), R 1 This represents an alkyl group having 3 to 20 carbon atoms, preferably an alkyl group having 6 to 20 carbon atoms, and more preferably an alkyl group having 10 to 20 carbon atoms. [ka]

[0030] The alkylalkoxysilane content is preferably 10 to 300 mol%, more preferably 15 to 100 mol%, and even more preferably 15 to 50 mol%, relative to the content of the sulfur-containing silane coupling agent.

[0031] In addition to the components described above, the rubber composition according to this embodiment may contain, as appropriate, various chemicals commonly used in the rubber industry, such as reinforcing fillers, process oils, softeners, plasticizers, waxes, antioxidants, sulfur, and vulcanization accelerators, within a normal range.

[0032] The reinforcing filler may contain carbon black in addition to silica. That is, the reinforcing filler may be silica alone or a combination of carbon black and silica. The content of the reinforcing filler is not particularly limited, but is preferably 5 to 150 parts by mass, more preferably 30 to 100 parts by mass, and even more preferably 30 to 80 parts by mass, per 100 parts by mass of diene rubber. Preferably, the reinforcing filler has silica as its main component, and the carbon black content is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of diene rubber.

[0033] The rubber composition according to this embodiment can be prepared by kneading in accordance with conventional methods using a commonly used mixer such as a Banbury mixer, kneader, or roll. In a preferred embodiment, in the first mixing stage, the diene rubber is mixed with other additives except alkylalkoxysilane, vulcanizing agent, and vulcanization accelerator at 80 to 120°C for 3 to 7 minutes. Then, in the second mixing stage, alkylalkoxysilane is added to the resulting mixture and mixed at 80 to 120°C for 2 to 5 minutes. Finally, in the last mixing stage, the vulcanizing agent and vulcanization accelerator are added and mixed to the resulting mixture to prepare the rubber composition. When alkylalkoxysilane is added and mixed in the second mixing stage, it is easier to improve the trade-off performance between rolling resistance and wet grip performance.

[0034] In this embodiment, the spin-spin relaxation times of an unvulcanized sample made of the diene-based rubber and a sample of the rubber composition after vulcanization were measured at 25°C using a pulsed NMR spectrometer and the solid echo method. The relaxation curve (free induction decay curve) obtained from the unvulcanized sample was separated into two components: a component with a short relaxation time (S0) and a component with a long relaxation time (L0). The relaxation curve (free induction decay curve) obtained from the vulcanized sample was also separated into two components: a component with a short relaxation time (S) and a component with a long relaxation time (L). The weighted average value (T0) of the relaxation time of component (S0) and the relaxation time of component (L0) was then calculated. S ) and T S The volume of component (S) (V) satisfies / T0≧0.26.S ) and volume (V) of component (L) L ) and V S / V L The condition must satisfy ≥ 0.26.

[0035] In the short phase, rubber components that are more strongly constrained by silica have shorter relaxation times, while rubber components that are less strongly constrained have longer relaxation times. This ratio (T S The molecular mobility of the rubber composition can be evaluated by ratio T0. That is, the molecular mobility of the rubber composition can be evaluated by ratio T0. S The condition / T0≧0.26 is satisfied, and in the short layer, a certain amount of rubber component with weak restraint by silica is present, allowing for sensitive stress absorption in response to external stimuli, making it easier to improve the trade-off performance between rolling resistance and wet grip performance.

[0036] Furthermore, the rubber composition is ratio V S / V L The condition ≥ 0.26 is satisfied, and a certain amount of silica-bound rubber components are present in the rubber composition, making it easier to improve the conflicting performance of rolling resistance and wet grip performance in the rubber composition as a whole.

[0037] The conditions for the rubber composition when measuring pulsed NMR, the measurement conditions, and the methods for calculating the short phase fraction and long phase fraction are described in the examples below.

[0038] The rubber composition obtained in this way can be applied to various parts of pneumatic tires, such as the tread and sidewall, for various applications and sizes, including passenger car tires and large tires for trucks and buses. Specifically, the rubber composition can be molded into a predetermined shape by conventional methods, for example by extrusion, and combined with other parts to produce a green tire. After that, the green tire can be vulcanized at, for example, 140°C to 180°C to produce a pneumatic tire. Among these uses, its use as a compound for tire treads is particularly preferred. [Examples]

[0039] The following are examples of the present invention, but the present invention is not limited to these examples.

[0040] According to the formulations (parts by mass) listed in Tables 1 and 2, the rubber components were kneaded at 100°C for 30 seconds using a Daihan lab mixer (300cc). Silica, silane coupling agent, zinc oxide, and stearic acid were then added and kneaded at 100°C for 240 seconds before being discharged. Next, the discharged rubber composition and alkylalkoxysilane were added to the lab mixer and kneaded at 100°C for 180 seconds before being discharged. Furthermore, the discharged rubber composition, sulfur, and vulcanization accelerator were added to the lab mixer and kneaded for 60 seconds before being discharged. Using two rolls, the obtained unvulcanized rubber composition was sheeted to a thickness of 2 mm, and then vulcanized by pressing at 160°C for 20 minutes to obtain a vulcanized sample.

[0041] The details of each component in Tables 1 and 2 are as follows. • S-SBR: JSR Corporation's "SL563", terminally tin-modified • Silica: "Nip Seal AQ" manufactured by Tosoh Corporation • Sulfur-containing silane coupling agent: "Si75" manufactured by Evonik Japan Co., Ltd. • Alkylalkoxysilane 1: Propyltriethoxysilane manufactured by Tokyo Chemical Industry Co., Ltd. • Alkylalkoxysilane 2: "Hexyltriethoxysilane" manufactured by Tokyo Chemical Industry Co., Ltd. • Alkylalkoxysilane 3: Octadecyltriethoxysilane manufactured by Tokyo Chemical Industry Co., Ltd. • Zinc oxide: "Zinc Oxide No. 3" manufactured by Mitsui Mining & Smelting Co., Ltd. • Stearic acid: "Lunaq S-20" manufactured by Kao Corporation • Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industries, Ltd. • Vulcanization accelerator 1: "Soxinol CZ" manufactured by Sumitomo Chemical Co., Ltd. • Vulcanization accelerator 2: "Noxellar D" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0042] Pulse NMR measurements were performed on the obtained vulcanized samples. Specifically, using a JEOL JNM-MU25A at a measurement temperature of 25°C, approximately 1g of the sample cut into 1mm squares was placed in a 10mmΦ glass tube, and the relaxation time T2 was measured by the solid echo method. The obtained relaxation curve M(t) was approximated using the following equation to separate the relaxation time into two components, the short phase (S) and the long phase (L), and the T2 relaxation time (T) of each phase was calculated. S ·T L ), and component fraction (V S ·V L The following formula was calculated. Note that the Weibull coefficient (W) was assumed to be 1 in the calculation below.

number

[0043] Furthermore, the relaxation time of each rubber component (in this case, S-SBR alone) used in each rubber composition was measured in its unvulcanized state. The relaxation time was separated into two components, the short phase (S0) and the long phase (L0), from the relaxation curve M(t) obtained in the same manner as above, and the T2 relaxation time (T S ·T L ), and component fraction (V S ·V L The following formula was used to calculate the relaxation time of the two components. The weighted average of the relaxation times of the two components was calculated and defined as T0. The ratio (T) of the calculated T0 to the relaxation time of the short phase of the above vulcanized sample was calculated. S The value of / T0 was calculated.

[0044]

number

[0045] Furthermore, the rolling resistance and wet grip performance of the obtained vulcanized samples were evaluated, and the ratio of rolling resistance to wet grip performance was determined. The results are shown in Tables 1 and 2. The measurement methods for each evaluation are as follows.

[0046] • Rolling resistance (RR): Using a viscoelasticity testing machine manufactured by Ueshima Seisakusho, the loss coefficient tanδ was measured at a frequency of 10 Hz, static strain of 10%, dynamic strain of 1%, and temperature of 60°C. In Table 1, the value for Comparative Example 1-1 is set to 100, and in Table 2, the value for Comparative Example 2-1 is set to 100 as an index. A smaller index indicates better rolling resistance.

[0047] • Wet grip performance (wet): Using a viscoelasticity testing machine manufactured by Ueshima Seisakusho, the loss coefficient tanδ was measured at a frequency of 10 Hz, static strain of 10%, dynamic strain of 1%, and temperature of 0°C. In Table 1, the value for Comparative Example 1-1 is set to 100, and in Table 2, the value for Comparative Example 2-1 is set to 100 as an index. A larger index indicates better wet grip performance.

[0048] • Ratio of rolling resistance to wet grip performance (wet / RR): The tanδ value at 0°C, which represents wet grip performance, was divided by the tanδ value at 60°C, which represents rolling resistance performance. The obtained values ​​and their indices are shown in Tables 1 and 2. In each table, the indices are expressed with the value of Comparative Example 1 set to 100 in Table 1, and with the value of Comparative Example 2-1 set to 100 in Table 2. A larger value indicates an improvement in the trade-off performance between rolling resistance and wet grip performance.

[0049] [Table 1]

[0050] [Table 2]

[0051] The results are shown in Tables 1 and 2. Comparative Example 1-1 is an example in which a sulfur-containing silane coupling agent was used without the alkylalkoxysilane, and the T values ​​measured by pulsed NMR were obtained. S The value of / T0 is outside the specified range. Comparative Example 1-2 is an example in which an alkylalkoxysilane is incorporated without a sulfur-containing silane coupling agent, V S / V LThe value is outside the specified range. Comparative Example 1-2 showed a deterioration in the trade-off performance between rolling resistance and wet grip performance compared to Comparative Example 1-1.

[0052] On the other hand, Examples 1-1 to 1-9 are examples in which a sulfur-containing silane coupling agent and an alkylalkoxysilane were used in combination, and the T values ​​measured by pulsed NMR were measured. S The value of / T0 and V S / V L The value is within the predetermined range. These embodiments showed improved performance in the trade-off between rolling resistance and wet grip performance compared to Comparative Examples 1-1 and 1-2.

[0053] Comparative Example 2-1 is an example in which a sulfur-containing silane coupling agent was used without the alkylalkoxysilane, and the V measured by pulsed NMR S / V L The value is outside the specified range. Comparative Example 2-2 is an example in which an alkylalkoxysilane is incorporated without a sulfur-containing silane coupling agent, and V S / V L The value is outside the specified range. Compared to Comparative Example 2-1, Comparative Example 2-2 showed a deterioration in the trade-off performance between rolling resistance and wet grip performance.

[0054] On the other hand, Examples 2-1 to 2 to 8 are examples in which a sulfur-containing silane coupling agent and an alkylalkoxysilane were used in combination, and the T values ​​measured by pulsed NMR were measured. S The value of / T0 and V S / V L The value is within the predetermined range. These examples show improved performance in the trade-off between rolling resistance and wet grip performance compared to Comparative Examples 2-1 and 2-2. [Industrial applicability]

[0055] The rubber composition of the present invention can be used in the treads, sidewalls, belts, carcasses, etc., of passenger car tires and large tires such as those for trucks and buses.

Claims

1. An unvulcanized rubber composition containing diene rubber, silica, a sulfur-containing silane coupling agent, and an alkylalkoxysilane, The aforementioned diene rubber (100 parts by mass) contains 50 parts by mass or more of tin-modified styrene-butadiene rubber. The silica content is 5 to 150 parts by mass per 100 parts by mass of diene rubber. The content of the sulfur-containing silane coupling agent is 3 to 15% by mass relative to the silica content. The content of the alkylalkoxysilane is 10 to 300 mol% relative to the sulfur-containing silane coupling agent. At 25°C, the spin-spin relaxation times of an unvulcanized sample made of the diene-based rubber and a sample made by vulcanization of the rubber composition were measured using a pulsed NMR apparatus and the solid echo method. The relaxation curve (free induction decay curve) obtained from the unvulcanized sample is used for the component with the shortest relaxation time (S ０ ) and components with long relaxation times (L ０ ) is separated into two components, The relaxation curve (free induction decay curve) obtained from the vulcanized sample is separated into two components: a component with a short relaxation time (S) and a component with a long relaxation time (L). Ingredients (S ０ ) Relaxation time and component (L ０ ) Weighted mean of relaxation time (T ０ ) and the relaxation time (T) of component (S). Ｓ ) and T Ｓ / T ０ Satisfying ≥ 0.26, Volume (V Ｓ of component (S) and volume (V Ｌ of component (L) satisfy V Ｓ / V Ｌ ≧0.26, an unvulcanized rubber composition.

2. The unvulcanized rubber composition according to claim 1, wherein the sulfur-containing silane coupling agent has a sulfide group.

3. The unvulcanized rubber composition according to claim 1 or 2, wherein the alkylalkoxysilane is a compound represented by formula (1). 【Chemistry 1】 However, in equation (1), R １ This represents an alkyl group having 3 to 20 carbon atoms.

4. A pneumatic tire made using the unvulcanized rubber composition described in any one of claims 1 to 3.

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