Rubber composition and pneumatic tire using same

Abstract

To provide a rubber composition having excellent durability while maintaining high fuel efficiency, and a pneumatic tire using the rubber composition.SOLUTION: A rubber composition contains silica, a sulfur-containing silane coupling agent, and alkyl alkoxysilane in a diene rubber. A force curve measurement with an atomic force microscope is conducted to determine deformations of rubber components in a vulcanized sample of the rubber composition when elongating the sample by 200%. The proportion of a rubber component having a smaller deformation than its weighted average value is 65 vol.% or more in the rubber components.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, there has been a demand for further improvement in durability of rubber products such as tires. In response to this issue, for example, Patent Document 1 describes that durability can be improved by using a specific silane coupling agent.

[0003] Patent Document 2 describes that by blending silica and two or more types of silane coupling agents, one of which is a compound whose main chain skeleton is polyethylene glycol or polypropylene glycol and which has an alkoxysilyl group at its terminal, a rubber composition for tire treads can be obtained that has a good balance of low electrical resistance, low rolling resistance performance (fuel economy), wet grip performance, mechanical strength, and processability.

[0004] However, there is room for further improvement in durability. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5212782 [Patent Document 2] Patent No. 3908368 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-260920 [Patent Document 4] Patent No. 4930661 Summary of the Invention [Problem to be solved by the invention]

[0006] Furthermore, when the flexibility of the rubber composition is increased in order to improve durability, there is a risk that fuel economy may deteriorate.

[0007] In view of the above, an object of the present invention is to provide a rubber composition that maintains low fuel consumption and is excellent in durability, and a pneumatic tire using the same.

[0008] Patent Document 3 describes that the use of a specific silane coupling agent can provide excellent low heat buildup, wear resistance, and wet grip performance, and Patent Document 4 describes that the combined use of a sulfur-containing silane coupling agent and an alkyltriethoxysilane can suppress silica aggregation and viscosity increase, making it possible to produce a tire with excellent wet performance and rolling resistance, but does not evaluate durability. [Means for solving the problem]

[0009] The rubber composition according to the present invention is a rubber composition comprising a diene rubber, silica, a sulfur-containing silane coupling agent, and an alkylalkoxysilane, and is obtained by measuring the force curve with an atomic force microscope to determine the amount of deformation of the rubber component in a sample obtained by vulcanizing the rubber composition and elongating it by 200%, and the proportion of rubber components with an amount of deformation less than the weighted average value is 65 vol% or more of the rubber component.

[0010] The content of the silica may be 5 to 150 parts by mass relative to 100 parts by mass of the diene rubber, the content of the sulfur-containing silane coupling agent may be 2 to 15% by mass relative to the content of the silica, and the content of the alkylalkoxysilane may be 10 to 700 mol% relative to the content of the sulfur-containing silane coupling agent.

[0011] The sulfur-containing silane coupling agent may have a sulfide group.

[0012] The alkylalkoxysilane may be a compound represented by formula (1). [ka] However, in formula (1), R 1 represents an alkyl group having 3 to 20 carbon atoms.

[0013] The pneumatic tire according to the present invention is manufactured using the above rubber composition. [Effects of the Invention]

[0014] The rubber composition of the present invention provides excellent durability while maintaining fuel economy. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a histogram of the deformation amount of the rubber component obtained by measuring Example 1 with an atomic force microscope. [Figure 2] 1 is a histogram of the deformation amount of the rubber component obtained by measuring Comparative Example 1 with an atomic force microscope. DETAILED DESCRIPTION OF THE INVENTION

[0016] Matters relating to the implementation of the present invention will be described in detail below.

[0017] The rubber composition according to the present embodiment contains a diene rubber, silica, a sulfur-containing silane coupling agent, and an alkylalkoxysilane.

[0018] The diene rubber according to the present embodiment is not particularly limited, and examples thereof 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), butyl rubber (IIR), etc. The diene rubber also encompasses those whose terminals or main chains have been modified as necessary (for example, terminal-modified SBR), and those whose properties have been modified to impart desired characteristics (for example, modified NR).

[0019] In one embodiment, the diene rubber preferably includes at least one selected from the group consisting of natural rubber, styrene-butadiene rubber, and butadiene rubber. More preferably, the diene rubber includes styrene-butadiene rubber. For example, 100 parts by mass of the diene rubber preferably includes 50 parts by mass or more of styrene-butadiene rubber, more preferably 70 parts by mass or more of styrene-butadiene rubber, and may include styrene-butadiene rubber alone.

[0020] The styrene butadiene rubber may be, for example, solution-polymerized styrene butadiene rubber (SSBR) or emulsion-polymerized styrene butadiene rubber (ESBR). As the styrene butadiene rubber, modified styrene butadiene rubber (e.g., amine-modified SBR or tin-modified SBR) whose terminals or main chain have been modified as necessary may also be used.

[0021] The silica according to the present embodiment is not particularly limited, but wet silica such as wet precipitation silica or wet gel silica is preferably used. The content of silica is preferably 5 to 150 parts by mass, more preferably 30 to 100 parts by mass, per 100 parts by mass of the diene rubber.

[0022] The sulfur-containing silane coupling agent according to the present embodiment is a silane coupling agent containing a sulfur atom in the molecule, and various sulfur-containing silane coupling agents that are compounded together with silica in rubber compositions can be used.

[0023] Specific examples of sulfur-containing silane coupling agents include: Sulfide silanes (bis-silane-based sulfide silane coupling agents) such as bis(3-triethoxysilylpropyl) tetrasulfide, bis(3-triethoxysilylpropyl) disulfide, bis(2-triethoxysilylethyl) tetrasulfide, bis(4-triethoxysilylbutyl) disulfide, bis(3-trimethoxysilylpropyl) tetrasulfide, and bis(2-trimethoxysilylethyl) disulfide; 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 "VP Si363" manufactured by Evonik Degussa (wherein m is an average of 1, n is an average of 2, and k is an average of 5); Examples include protected mercaptosilanes (i.e., silane compounds having a thiol ester structure in which the mercapto group is protected with an acyl group) such as 3-octanoylthio-1-propyltriethoxysilane (formula: CH3(CH2)6C(=O)S-(CH2)3-Si(OC2H5)3) and 3-propionylthiopropyltrimethoxysilane. These sulfur-containing silane coupling agents can be used alone or in combination of two or more.

[0024] Among these, sulfur-containing silane coupling agents are preferably sulfide silanes having a sulfide group, more preferably those having a disulfide group.

[0025] The content of the sulfur-containing silane coupling agent relative to the content of silica is preferably 2 to 15 mass%, more preferably 2 to 10 mass%, and even more preferably 2 to 8 mass%. That is, the total amount of the sulfur-containing silane coupling agent relative to 100 mass parts of silica is preferably 2 to 15 mass parts, more preferably 2 to 10 mass parts, and even more preferably 2 to 8 mass parts.

[0026] The alkylalkoxysilane according to this embodiment may be an alkyldialkoxysilane, but is preferably an alkyltrialkoxysilane. The alkylalkoxysilane preferably has an alkyl group having 3 to 20 carbon atoms, and specifically, an alkyltriethoxysilane represented by the following formula (1) is preferably used. In formula (1), R 1 represents an alkyl group having 3 to 20 carbon atoms. [ka]

[0027] The content of the alkylalkoxysilane is preferably 10 to 700 mol %, more preferably 15 to 300 mol %, based on the content of the sulfur-containing silane coupling agent.

[0028] In addition to the above-mentioned components, the rubber composition according to the present embodiment may contain compounding chemicals such as reinforcing fillers, process oils, softeners, plasticizers, waxes, antioxidants, sulfur, and vulcanization accelerators that are commonly used in the rubber industry, within normal ranges.

[0029] 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, and is, for example, 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 is mainly composed of silica, and the content of carbon black is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of diene rubber.

[0030] The rubber composition according to this embodiment can be prepared by kneading in a conventional manner using a commonly used mixer such as a Banbury mixer, kneader, or roll. In a preferred embodiment, in the first mixing stage, the alkylalkoxysilane, vulcanizing agent, and additives other than the vulcanization accelerator are added to the diene rubber and mixed at 80 to 120°C for 3 to 7 minutes. Then, in the second mixing stage, the alkylalkoxysilane is added to the resulting mixture and mixed at 80 to 120°C for 2 to 5 minutes. Finally, in the final mixing stage, the vulcanizing agent and vulcanization accelerator are added to the resulting mixture to prepare the rubber composition. When the alkylalkoxysilane is added and mixed in the second mixing stage, the proportion of rubber components that deform easily (flexible) tends to increase.

[0031] The rubber composition according to this embodiment is such that the deformation of the rubber component in a vulcanized sample of the rubber composition is measured by force curve measurement using an atomic force microscope when the sample is elongated by 200%, and the proportion of rubber components with deformation less than the weighted average value is 65 vol% or more of the rubber component. In other words, an increase in the proportion of rubber components with high deformation (flexible) shifts the weighted average value toward the side with high deformation. Therefore, the flexibility of the rubber composition as a whole is increased, and excellent durability is likely to be obtained. The upper limit of the proportion of rubber components with deformation less than the weighted average value is not particularly limited, but is preferably 90 vol% or less, more preferably 85 vol% or less, and even more preferably 80 vol% or less.

[0032] The conditions for the rubber composition and the measurement conditions when measuring the force curve with an atomic force microscope will be described in the Examples section below.

[0033] The rubber composition thus obtained can be applied to various parts of tires, such as the tread and sidewall of pneumatic tires of various sizes and applications, such as tires for passenger cars and large tires for trucks and buses. That is, the rubber composition can be molded into a predetermined shape by a conventional method, for example, extrusion processing, and combined with other components to produce a green tire, which can then be vulcanized and molded at, for example, 140°C to 180°C, thereby producing a pneumatic tire. Among these, use as a tire tread compound is particularly preferred. [Example]

[0034] Examples of the present invention will be shown below, but the present invention is not limited to these examples.

[0035] According to the formulations (parts by mass) listed in Tables 1 to 3, the rubber components were masticated for 30 seconds at 100°C using a Daihan lab mixer (300cc). Then, silica, a silane coupling agent, zinc oxide, and stearic acid were added and kneaded at 100°C for 240 seconds, after which the mixture was discharged. The discharged rubber composition and alkylalkoxysilane were then added to the lab mixer, kneaded at 100°C for 180 seconds, and then discharged. The discharged rubber composition, sulfur, and vulcanization accelerator were then added to the lab mixer, kneaded at 100°C for 60 seconds, and then discharged. The resulting unvulcanized rubber composition was sheeted using a two-roll mill to a thickness of 2 mm, and then subjected to a vulcanization press at 160°C for 20 minutes to obtain a vulcanized sample.

[0036] Details of each component in Tables 1 to 3 are as follows. S-SBR1: Asahi Kasei Corporation's "Tufden 2000", unmodified S-SBR S-SBR2: JSR Corporation "HPR350", terminal amine-modified S-SBR Silica: "Nipsil AQ" manufactured by Tosoh Corporation Sulfur-containing silane coupling agent 1: "Si75" manufactured by Evonik Japan Co., Ltd. Sulfur-containing silane coupling agent 2: "VP Si363" manufactured by Evonik Japan Co., Ltd. Alkylalkoxysilane 1: "Propyltriethoxysilane" manufactured by Tokyo Chemical Industry Co., Ltd. Alkylalkoxysilane 2: "Octadecyltriethoxysilane" manufactured by Tokyo Chemical Industry Co., Ltd. Zinc oxide: "Zinc oxide No. 3" manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Kao Corporation's "Lunac S-20" Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator 1: "Soxinol CZ" manufactured by Sumitomo Chemical Co., Ltd. Vulcanization accelerator 2: "Noccela D" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0037] The obtained vulcanized sample was subjected to force curve measurement using an atomic force microscope. Specifically, the vulcanized rubber sample was stretched to 200% and the force curve was measured at 128 points x 128 points in a 3 μm x 3 μm square using a cantilever AC-240TS-R3 (spring constant: 1.7 N / m) under the following measurement conditions to measure the ease of deformation when force was applied at each point. <Measurement conditions> Measurement frequency: 10Hz Push-in force: 2nN

[0038] Since the filler hardly deforms, the deformation of the rubber component can be calculated by subtracting the volume fraction of the filler from the parts with the least deformation. A histogram of the deformation of the rubber component was created as shown in Figures 1 and 2.

[0039] Further, a weighted average value of the deformation amount was calculated by the following formula, and the ratio of components with a deformation amount smaller than the weighted average value was calculated to obtain the deformation allowance of the rubber component. Weighted average value: (each deformation amount x frequency) / total frequency

[0040] 1 and 2, black bars indicate deformation amounts less than the weighted average, and gray bars indicate deformation amounts greater than the weighted average. Because the amount of deformation is not normally distributed, the weighted average shifts to the right (toward greater deformation) in the figures for rubber compositions such as Example 1, which are flexible and adapt well to deformation, and the proportion of components with deformation amounts less than the weighted average increases.

[0041] Furthermore, the obtained rubber compositions were evaluated for durability (tensile product and modulus change) and heat buildup performance, and the results are shown in Tables 1 to 3. The measurement methods for each evaluation were as follows.

[0042] Tensile product: A rubber sheet 1 mm thick was prepared using the resulting rubber composition and vulcanized at 160°C for 20 minutes. A tensile test (dumbbell No. 3) was conducted in accordance with JIS K 6251 using a Shimadzu autograph to measure tensile strength. The tensile strength at break Tb (MPa) and elongation at break Eb (%) were calculated, and the tensile product (Tb × Eb ÷ 100) was determined. Table 1 shows the value for Comparative Example 1-1, Table 2 shows the value for Comparative Example 2-1, and Table 3 shows the value for Comparative Example 3-1 as an index, with 100 representing the value. A larger value indicates a higher modulus and therefore better durability.

[0043] Modulus change rate: A 1 mm thick rubber sheet was made using the obtained rubber composition and vulcanized at 160°C for 20 minutes. The obtained vulcanized rubber sheet was punched out using an old JIS No. 4 dumbbell cutter to prepare samples. A tensile strength test was conducted on the obtained sample and a sample after fatigue at 50% elongation for 1 million cycles, and the modulus at 100% elongation was measured. The modulus before fatigue was set to 100, and the modulus after fatigue was calculated. The modulus change rate was calculated by subtracting the modulus after fatigue from the modulus before fatigue.

[0044] In Table 1, Comparative Example 1-1 was used as the standard, in Table 2 Comparative Example 2-1, and in Table 3 Comparative Example 3-1. Those with a larger tensile product and a smaller absolute value of modulus change were deemed to have good durability and were marked with "O", while those not meeting these conditions were deemed to have poor durability and were marked with "X".

[0045] Heat buildup performance: The rubber composition obtained was vulcanized at 160°C for 20 minutes, and the loss factor tanδ was measured for samples using a Shima Seisakusho viscoelasticity tester at a frequency of 10 Hz, static strain of 10%, dynamic strain of 1%, and a temperature of 60°C. The values ​​are expressed as an index, with the value for Comparative Example 1-1 in Table 1, the value for Comparative Example 2-1 in Table 2, and the value for Comparative Example 3-1 in Table 3 set at 100. The smaller the value, the better the fuel economy.

[0046] [Table 1]

[0047] [Table 2]

[0048] [Table 3]

[0049] The results are shown in Tables 1 to 3, and in each formulation, the Examples were superior in durability compared to the Comparative Examples, which served as the benchmark.

[0050] Furthermore, the formulations in Tables 1 and 2 were able to maintain heat generation performance compared to the comparative example, which served as a reference, and the formulation in Table 3 was superior in heat generation performance to the comparative example, which served as a reference. [Industrial Applicability]

[0051] The rubber composition of the present invention can be used for the treads, sidewalls, belts, carcasses, etc. of tires for passenger cars and large tires for trucks and buses.

Claims

1. A rubber composition containing a diene rubber, silica, a sulfur-containing silane coupling agent, and an alkylalkoxysilane, the sulfur-containing silane coupling agent is a bis-silane sulfide silane coupling agent, The content of the sulfur-containing silane coupling agent is 2 to 8 mass% relative to the content of the silica, A rubber composition, wherein a sample obtained by vulcanizing the rubber composition is stretched by 200% to determine the amount of deformation of the rubber component in the sample by force curve measurement using an atomic force microscope, and the proportion of rubber components whose deformation is smaller than the weighted average value is 65 vol% or more of the rubber component.

2. the content of the silica is 5 to 150 parts by mass per 100 parts by mass of the diene rubber, 2. The rubber composition according to claim 1, wherein the content of the alkylalkoxysilane is 10 to 700 mol % based on the content of the sulfur-containing silane coupling agent.

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

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

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