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 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 70 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, further improvement in durability has been required for rubber products such as tires. In response to this problem, 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 containing silica in a diene rubber, and is obtained by measuring a force curve using 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 smaller than the weighted average value is 70 vol% or more of the rubber component.

[0010] The rubber composition according to the present invention may further contain a nitrogen-containing alkoxysilane and an alkylalkoxysilane.

[0011] The content of the silica may be 5 to 150 parts by mass per 100 parts by mass of the diene rubber, the total content of the nitrogen-containing alkoxysilane and alkylalkoxysilane may be 3 to 15 mass% relative to the content of silica, and the content of the nitrogen-containing alkoxysilane may be 10 to 80 mol% of the total content of the nitrogen-containing alkoxysilane and alkylalkoxysilane.

[0012] The nitrogen-containing alkoxysilane may have at least one substituent selected from the group consisting of an amino group, a ureido group, an isocyanate group, a cyano group, an azido group, and an amide group.

[0013] 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.

[0014] The pneumatic tire according to the present invention is manufactured using the above rubber composition. [Effects of the Invention]

[0015] The rubber composition of the present invention provides excellent durability while maintaining fuel economy. [Brief explanation of the drawings]

[0016] [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

[0017] Matters relating to the implementation of the present invention will be described in detail below.

[0018] The rubber composition according to this embodiment contains silica in a diene rubber.

[0019] 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).

[0020] 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.

[0021] 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.

[0022] 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 not particularly limited, but is preferably 5 to 150 parts by mass, more preferably 30 to 100 parts by mass, per 100 parts by mass of diene rubber.

[0023] The rubber composition according to the present embodiment may further contain a nitrogen-containing alkoxysilane and an alkylalkoxysilane.

[0024] Nitrogen-containing alkoxysilane is the alkoxysilane that contains nitrogen in its molecule.As nitrogen-containing alkoxysilane, for example, can be mentioned the compound that has functional group selected from the group consisting of amino group, ureido group, isocyanate group, cyano group, azide group and amide group, and the alkoxy group that is bonded to silicon atom, and can be mentioned the compound that has nitrogen atom in its molecule among those that are generally called silane coupling agents.

[0025] Specific examples of nitrogen-containing alkoxysilanes include aminoalkoxysilanes such as 3-aminopropylalkoxysilane (e.g., 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane), and 3-(2-aminoethylamino)propylalkoxysilane (e.g., 3-(2-aminoethylamino)propyltriethoxysilane, 3-(2-aminoethylamino)propyltrimethoxysilane, 3-(2-aminoethylamino)propylmethyldimethoxysilane); ureidoalkoxysilanes such as 3-ureidopropylalkoxysilanes (e.g., 3-ureidopropyltriethoxysilane, 3-ureidopropyltrimethoxysilane, 3-ureidopropylmethyldimethoxysilane, 3-ureidopropylmethyldiethoxysilane), 2-ureidoethylalkoxysilanes (e.g., 2-ureidoethyltrimethoxysilane, 2-ureidoethyltriethoxysilane, 2-ureidoethylmethyldimethoxysilane), and ureidomethylalkoxysilanes (e.g., ureidomethyltrimethoxysilane, ureidomethylmethyldimethoxysilane, ureidomethyltriethoxysilane, ureidomethylmethyldiethoxysilane); Examples of the isocyanate alkoxysilane include 3-isocyanatepropylalkoxysilane (e.g., 3-isocyanatepropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, 3-isocyanatepropyltripropoxysilane), 2-isocyanateethylalkoxysilane (e.g., 2-isocyanateethyltrimethoxysilane, 2-isocyanateethyltriethoxysilane), isocyanatemethylalkoxysilane (e.g., isocyanatemethyltrimethoxysilane, isocyanatemethyltriethoxysilane), cyanoalkoxysilane (e.g., 3-cyanopropyltrimethoxysilane, 3-cyanopropyltriethoxysilane), azidoalkylsilane (e.g., 3-azidopropyltriethoxysilane, 3-azidopropyltrimethoxysilane, 11-azidoundecyltrimethoxysilane), and alkylsilylamide acid (e.g., triethoxysilylpropylmaleamic acid). These can be used alone or in combination of two or more.

[0026] The alkylalkoxysilane according to this embodiment may be an alkyldialkoxysilane, but is preferably an alkyltrialkoxysilane. As the alkylalkoxysilane, one having an alkyl group having 3 to 20 carbon atoms is preferred, 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 total content of the nitrogen-containing alkoxysilane and alkylalkoxysilane relative to the silica content is preferably 3 to 15 mass%, more preferably 3 to 10 mass%, and even more preferably 3 to 8 mass%. That is, the total amount of the nitrogen-containing alkoxysilane and alkylalkoxysilane relative to 100 mass parts of silica is preferably 3 to 15 mass parts, more preferably 3 to 10 mass parts, and even more preferably 3 to 8 mass parts.

[0028] The content of the nitrogen-containing alkoxysilane in the total content of the nitrogen-containing alkoxysilane and the alkylalkoxysilane is preferably 10 to 80 mol %, more preferably 10 to 60 mol %, and even more preferably 20 to 50 mol %.

[0029] In addition to the above-mentioned components, the rubber composition according to the present embodiment can be appropriately compounded with compounding chemicals such as reinforcing fillers, process oils, softeners, plasticizers, waxes, antioxidants, sulfur, vulcanization accelerators, etc., which are generally used in the rubber industry, within the usual range. Note that, although a sulfur-containing silane coupling agent, which is usually compounded when silica is compounded, may be compounded, in one embodiment, it is preferable not to compound a sulfur-containing silane coupling agent.

[0030] 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 filler contains silica as a main component, 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.

[0031] The carbon black is not particularly limited, and various known types can be used. The content of carbon black is preferably 5 to 100 parts by mass, more preferably 20 to 80 parts by mass, per 100 parts by mass of diene rubber.

[0032] The rubber composition according to the present embodiment can be prepared by kneading in a conventional manner using a commonly used mixer such as a Banbury mixer, kneader, roll, etc. In the first mixing stage, additives other than the vulcanizing agent and vulcanization accelerator are added and mixed with the diene rubber, and then in the final mixing stage, the vulcanizing agent and vulcanization accelerator are added and mixed with the resulting mixture to prepare the rubber composition.

[0033] The rubber composition according to this embodiment is such that the amount of deformation of the rubber component in a sample vulcanized from the rubber composition when elongated by 200% is determined by force curve measurement using an atomic force microscope, and the proportion of rubber components with deformation amounts less than the average value is 70 vol% or more of the rubber component. In other words, an increase in the proportion of rubber components with large deformation amounts (flexible) shifts the average value toward the larger deformation side. 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 amounts less than the 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.

[0034] 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.

[0035] 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]

[0036] Examples of the present invention will be shown below, but the present invention is not limited to these examples.

[0037] According to the formulations (parts by mass) listed in Tables 1 to 5, the rubber components were masticated for 30 seconds using a Daihan lab mixer (300 cc). Then, silica, a sulfur-containing silane coupling agent, a nitrogen-containing alkoxysilane, an alkylalkoxysilane, zinc oxide, and stearic acid were added and mixed for 240 seconds, after which the mixture was discharged. The discharged rubber composition was then added to a lab mixer, kneaded for 180 seconds, and then discharged. Furthermore, the discharged rubber composition, sulfur, and a vulcanization accelerator were added to the lab mixer, kneaded 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.

[0038] Details of each component in Tables 1 to 5 are as follows. S-SBR: JSR Corporation "HPR350", terminal amine-modified S-SBR Silica: "Nipsil AQ" manufactured by Tosoh Corporation Zinc oxide: "Zinc oxide No. 3" manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Kao Corporation's "Lunac S-20" Sulfur-containing silane coupling agent: "Si75" manufactured by Evonik Japan Co., Ltd. Nitrogen-containing alkoxysilane 1: Amino group-containing, "3-aminopropyltriethoxysilane" manufactured by Tokyo Chemical Industry Co., Ltd. Nitrogen-containing alkoxysilane 2: Ureido group-containing, "3-ureidopropyltriethoxysilane" manufactured by Tokyo Chemical Industry Co., Ltd., 40 to 52 mass% methanol solution Nitrogen-containing alkoxysilane 3: Isocyanate group-containing, "3-isocyanatepropyltriethoxysilane" manufactured by Tokyo Chemical Industry Co., Ltd. Alkylalkoxysilane 1: "Octadecyltriethoxysilane" manufactured by Tokyo Chemical Industry Co., Ltd. Alkylalkoxysilane 2: "Propyltriethoxysilane" manufactured by Tokyo Chemical Industry Co., Ltd. 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.

[0039] In Tables 1 to 5, the "proportion (molar ratio (%)) of nitrogen-containing alkoxysilane in the total amount of silane compounds" refers to the content (mol %) of nitrogen-containing alkoxysilane in the total content of nitrogen-containing alkoxysilane and alkylalkoxysilane. The blending amount of nitrogen-containing alkoxysilane 2 in Table 5 includes the amount of methanol in the product.

[0040] 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 an AC-240TS-R3 cantilever (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

[0041] 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.

[0042] 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

[0043] 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 value of a rubber composition such as Example 1, which is flexible and adapts well to deformation, shifts to the right side of the figure (the side with greater deformation), and the proportion of components with deformation amounts less than the weighted average increases.

[0044] Furthermore, the resulting rubber compositions were evaluated for durability (tensile product and modulus change) and heat buildup performance, and the results are shown in Tables 1 to 5. The measurement methods for each evaluation were as follows.

[0045] Tensile product: A 1 mm thick rubber sheet 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. The values ​​are expressed as an index, with the values ​​of Comparative Example 1-1 in Table 1, Comparative Example 2-1 in Table 2, Comparative Example 3-1 in Table 3, Comparative Example 4-1 in Table 4, and Comparative Example 5-1 in Table 5 being set at 100. A larger tensile product indicates a higher modulus and therefore better durability.

[0046] 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.

[0047] In Table 1, Comparative Example 1-1 was used as the standard, in Table 2 Comparative Example 2-1, in Table 3 Comparative Example 3-1, in Table 4 Comparative Example 4-1, and in Table 5 Comparative Example 5-1. 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 that did not meet these conditions were deemed to have poor durability and were marked with "X".

[0048] Heat buildup performance: The obtained rubber composition was vulcanized at 160°C for 20 minutes to obtain a sample, and the loss factor tanδ was measured 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 results are expressed as an index, with the value of Comparative Example 1-1 in Table 1, Comparative Example 2-1 in Table 2, Comparative Example 3-1 in Table 3, Comparative Example 4-1 in Table 4, and Comparative Example 5-1 in Table 5 being set at 100. The smaller the index, the better the fuel economy.

[0049] [Table 1]

[0050] [Table 2]

[0051] [Table 3]

[0052] [Table 4]

[0053] [Table 5]

[0054] The results are shown in Tables 1 to 5, and in each formulation, the Examples were superior in durability compared to the Comparative Examples, which served as the benchmark.

[0055] Furthermore, the formulations in Tables 1, 3, and 4 were able to maintain heat generation performance compared to the comparative examples, which served as the reference, and the formulations in Tables 2 and 5 were superior in heat generation performance to the comparative examples, which served as the reference. [Industrial Applicability]

[0056] 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 nitrogen-containing alkoxysilane, and an alkylalkoxysilane having an alkyl group having 3 to 20 carbon atoms, 100 parts by mass of the diene rubber contains 70 parts by mass or more of an amine-modified styrene-butadiene rubber, 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 of the force curve is 70 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, the total content of the nitrogen-containing alkoxysilane and the alkylalkoxysilane is 3 to 15 mass% relative to the content of the silica; 2. The rubber composition according to claim 1, wherein a content ratio of the nitrogen-containing alkoxysilane is 10 to 80 mol % of the total content of the nitrogen-containing alkoxysilane and the alkylalkoxysilane.

3. The rubber composition according to claim 1 or 2, wherein the nitrogen-containing alkoxysilane has at least one substituent selected from the group consisting of an amino group, a ureido group, an isocyanate group, a cyano group, an azido group, and an amide group.

4. The rubber composition according to any one of claims 1 to 3, 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.

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

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