Rubber composition and pneumatic tire using the same

Abstract

To provide: a rubber composition excellent in fracture characteristics while maintaining hardness; and a pneumatic tire using the same.SOLUTION: The rubber composition contains, based on 100 pts.mass of a diene-based rubber, 0.1 to 10 pts.mass of a thioester-based compound represented by the general formula (1) defined by A-COS-(CH2)n-SCO-A (A are each an alkyl group or aromatic hydrocarbon group having 1 to 10 carbon atoms, and may be the same as or different from each other, and n is an integer from 1 to 6).SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] In recent years, for rubber products such as tires, further improvement in fracture properties has been demanded to improve durability. In response to such problems, the use of multiple crosslinking agents has been considered.

[0003] For example, in Patent Document 1, it is described that by using 1,6-bis(N,N-dibenzylthiocarbamoyldithio)hexane in addition to sulfur as a crosslinking agent, reversion and heat aging properties can be improved.

[0004] Also, in Patent Document 2, it is described that by using 1,8-bis(thiobenzoate)octane in addition to sulfur as a crosslinking agent, toughness can be improved.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, for 1,6-bis(N,N-dibenzylthiocarbamoyldithio)hexane of Patent Document 1, there is room for improvement in fracture properties, and for 1,8-bis(thiobenzoate)octane of Patent Document 2, there is a problem that the hardness decreases.

[0007] In view of the above, the present invention aims to provide a rubber composition that can improve fracture characteristics while maintaining hardness, and a pneumatic tire using the same.

[0008] Although Patent Document 3 describes the use of a blocked mercaptosilane coupling agent in a tire rubber composition, it does not describe the fracture characteristics. [Means for solving the problem]

[0009] The rubber composition according to the present invention contains 0.1 to 10 parts by mass of a thioester compound represented by the following general formula (1) per 100 parts by mass of diene rubber. A-COS-(CH2) n -SCO-A ···(1) However, in formula (1), A is an alkyl group or aromatic hydrocarbon group having 1 to 10 carbon atoms, and these may be the same or different, and n is an integer from 1 to 6.

[0010] The above thioester compound can be defined as the compound represented by n=6 in formula (1).

[0011] The above rubber composition may contain 0.1 to 10 parts by mass of sulfur per 100 parts by mass of diene rubber.

[0012] The pneumatic tire according to the present invention shall be manufactured using the above-mentioned rubber composition. [Effects of the Invention]

[0013] According to the rubber composition of the present invention, excellent fracture properties can be obtained while maintaining hardness. [Modes for carrying out the invention]

[0014] The following describes in detail matters related to the implementation of the present invention.

[0015] The rubber composition according to this embodiment contains 0.1 to 10 parts by mass of a thioester compound represented by the following general formula (1) per 100 parts by mass of diene rubber. A-COS-(CH2) n -SCO-A ···(1) However, in formula (1), A is an alkyl group or aromatic hydrocarbon group having 1 to 10 carbon atoms, and may be the same or different, and n is an integer from 1 to 6, preferably an integer from 3 to 6, and more preferably 6.

[0016] The rubber composition according to this embodiment contains a diene rubber as a rubber component, and the type 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).

[0017] The thioester compound according to this embodiment is not particularly limited as long as it is represented by the general formula (1) above. In general formula (1), A is not particularly limited as long as it is an alkyl group or aromatic compound having 1 to 10 carbon atoms, and since the thioester group is decomposed and released as a carboxylic acid during the crosslinking reaction, it does not affect the crosslinking structure. In general formula (1), A may be a linear alkyl group such as a methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, or n-decyl group; it may be a branched alkyl group such as an isopropyl group, isobutyl group, t-butyl group, isopentyl group, neopentyl group, isohexyl group, isoheptyl group, isooctyl group, 2-ethylhexyl group, isononyl group, or isodecyl group; it may be an alicyclic alkyl group such as a cyclopropyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, cyclooctyl group, or tricyclodecyl group; or it may be an aromatic hydrocarbon group such as a phenyl group, phenethyl group, or benzyl group.

[0018] The content of the thioester compound is not particularly limited as long as it is between 0.1 and 10 parts by mass per 100 parts by mass of diene rubber, but is preferably between 0.1 and 5 parts by mass, and more preferably between 0.1 and 3 parts by mass. When the content of the thioester compound is within the above range, excellent hardness and fracture properties are easily obtained.

[0019] By using the above-mentioned thioester compounds, it is possible to improve fracture properties while maintaining hardness. Although the mechanism is not entirely clear, it can be hypothesized as follows: In rubber products, by introducing crosslinking chains that are moderately longer than those typically used in sulfur crosslinking, the reduction in hardness is suppressed while the flexibility of the rubber is improved, thereby improving fracture properties. Furthermore, the improved flexibility of the rubber also improves wet grip performance.

[0020] The rubber composition according to this embodiment may contain sulfur, and its content is preferably 0.1 to 10 parts by mass, more preferably 1 to 5 parts by mass, based on 100 parts by mass of the diene rubber. Examples of sulfur include sulfur components such as powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersed sulfur.

[0021] The rubber composition according to this embodiment may further contain a vulcanization accelerator, and its content is preferably 0.1 to 3 parts by mass, more preferably 0.2 to 3 parts by mass, based on 100 parts by mass of the diene rubber. Examples of the vulcanization accelerator include sulfenamide-based vulcanization accelerators, thiuram-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiourea-based vulcanization accelerators, guanidine-based vulcanization accelerators, and dithiocarbamate-based vulcanization accelerators.

[0022] In addition to the above components, the rubber composition according to this embodiment can be appropriately blended with compounding chemicals such as reinforcing fillers, process oils, softeners, plasticizers, waxes, and anti-aging agents commonly used in the normal rubber industry within a normal range.

[0023] It is preferable to use carbon black and / or silica as the reinforcing filler. That is, the reinforcing filler may be carbon black alone, silica alone, or a combination of carbon black and silica. Preferably, it is carbon black alone or a combination of carbon black and silica. The content of the reinforcing filler is not particularly limited, and for example, it is preferably 10 to 140 parts by mass, more preferably 20 to 100 parts by mass, and even more preferably 30 to 80 parts by mass, based on 100 parts by mass of the diene rubber.

[0024] The carbon black is not particularly limited, and various known varieties can be used. The content of the carbon black is preferably 5 to 100 parts by mass, more preferably 20 to 80 parts by mass, based on 100 parts by mass of the diene rubber.

[0025] While there are no particular limitations on the silica used, wet silica, such as wet sedimentation silica or wet gel silica, is preferably used. When silica is incorporated, its content is preferably 5 to 40 parts by mass, and more preferably 5 to 30 parts by mass, per 100 parts by mass of diene rubber.

[0026] 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. That is, for example, in the first mixing stage, the diene rubber can be mixed with other additives except for the thioester compound, vulcanizing agent, and vulcanization accelerator, and then, in the final mixing stage, the thioester compound, vulcanizing agent, and vulcanization accelerator can be added to the resulting mixture to prepare the rubber composition.

[0027] 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]

[0028] The following are examples of the present invention, but the present invention is not limited to these examples.

[0029] <Synthesis Example 1> Under a nitrogen atmosphere, 40 mL of acetonitrile, 2.4 g (20 mmol) of benzoic acid, 9.2 g (48 mmol) of p-toluenesulfonic acid chloride, and 9.8 g (120 mmol) of N-methylimidazole were added and stirred at room temperature for 1 hour. In a separate container, 1.5 g (10 mmol) of 1,6-hexanedithiol was dissolved in 20 mL of acetonitrile. This solution was added and stirred at room temperature for a further 3 hours. After the reaction was complete, water was added to the reaction mixture, and the mixture was extracted three times with dichloromethane. The resulting organic layer was washed with saturated brine, dehydrated using anhydrous magnesium sulfate, filtered, and then concentrated under reduced pressure. The concentrate obtained above was purified by silica gel column chromatography to obtain 3.4 g of 1,6-bis(thiobenzoic acid ester)hexane (yield 94%).

[0030] <Synthesis Example 2> Under a nitrogen atmosphere, 17 mL of dichloromethane, 1.5 g (10 mmol) of 1,6-hexanedithiol, 6.0 g (60 mmol) of isopropenyl acetate, and 150 mg (1 mmol) of trifluoromethanesulfonic acid were added and the mixture was stirred at room temperature for 1 hour. After the reaction was complete, potassium carbonate was added and the mixture was stirred for 30 minutes. The mixture was then diluted with ethyl acetate, filtered through Celite, and concentrated under reduced pressure. The concentrate obtained above was purified by silica gel column chromatography to obtain 2.2 g of 1,6-bis(thioacetate)hexane (yield 95%).

[0031] <Synthesis Example 3> Under a nitrogen atmosphere, 40 mL of acetonitrile, 2.4 g (20 mmol) of benzoic acid, 9.2 g (48 mmol) of p-toluenesulfonic acid chloride, and 9.8 g (120 mmol) of N-methylimidazole were added and stirred at room temperature for 1 hour. In a separate container, 1.8 g (10 mmol) of 1,8-octanedithiol was dissolved in 20 mL of acetonitrile. This solution was added and stirred at room temperature for a further 3 hours. After the reaction was complete, water was added to the reaction mixture, and the mixture was extracted three times with dichloromethane. The resulting organic layer was washed with saturated brine, dehydrated using anhydrous magnesium sulfate, filtered, and then concentrated under reduced pressure. The concentrate obtained above was purified by silica gel column chromatography to obtain 3.8 g (99% yield) of 1,8-bis(thiobenzoic acid ester)octyl.

[0032] Using a Banbury mixer, and following the formulation (parts by mass) shown in Table 1 below, first, in the first mixing stage, components excluding sulfur, vulcanization accelerator, and thioester compounds were added and mixed (discharge temperature = 160°C). Then, in the second mixing stage, sulfur, vulcanization accelerator, and thioester compounds were added and mixed to the resulting mixture (discharge temperature = 90°C) to prepare the rubber composition.

[0033] The details of each component in Table 1 are as follows: • Isoprene rubber: JSR Corporation "IR2200" • Carbon Black: "Show Black N330T" manufactured by Cabot Japan 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. • Thioester compound 1: 1,6-bis(thiobenzoic acid ester)hexane obtained in the above synthesis example 1. • Thioester compound 2: 1,6-bis(thioacetate)hexane obtained in the above synthesis example 2: • Thioester compound 3: 1,8-bis(thiobenzoic acid ester)octyl obtained in the above synthesis example 3. • Vulcanization accelerator: "Noxellar CZ-G" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0034] Using each of the obtained rubber compositions, vulcanized rubber samples were prepared by vulcanizing them at 160°C under pressure, with a metal plate as a mold. The vulcanization time was the 90% vulcanization time specified in JIS K6300-2.

[0035] • Hardness: In accordance with JIS K6253, the hardness was measured at 23°C using a Type A durometer and expressed as an index with the value of Comparative Example 1 set to 100. A higher index indicates higher hardness at room temperature.

[0036] • Tensile strength at break: Tensile tests were conducted in accordance with JIS K6251 (dumbbell-shaped, type 7) to measure the tensile strength at break, and the value was expressed as an index with the value of Comparative Example 1 set to 100. A higher index indicates superior fracture characteristics.

[0037] • Elongation at break: Tensile tests (dumbbell-shaped, type 7) were conducted in accordance with JIS K6251, and the elongation at break was measured. The value for Comparative Example 1 was set to 100, and the result was expressed as an index. A higher index indicates superior fracture characteristics.

[0038] • Wet grip performance: The loss coefficient tanδ was measured using a UBM E4000 rheospectrometer under the conditions of a frequency of 10 Hz, static strain of 10%, dynamic strain of 2%, and temperature of 0°C. The value was expressed as an index with the value of Comparative Example 1 set to 100. A larger index indicates a larger tanδ and superior wet grip performance.

[0039] [Table 1]

[0040] The results are shown in Table 1. Comparative Examples 2 and 3 used 1,8-bis(thiobenzoic acid ester)octyl as the thioester compound, and showed inferior hardness compared to Comparative Example 1.

[0041] On the other hand, Example 1 is an example in which a thioester compound with shorter carbon chains between thioesters was used than the thioester compounds used in Comparative Examples 2 and 3. Compared to Comparative Example 1, it maintained or improved hardness while improving fracture characteristics and wet grip performance. [Industrial applicability]

[0042] 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. A rubber composition containing 0.1 to 10 parts by mass of a thioester compound represented by the following general formula (1) per 100 parts by mass of diene rubber. A-COS-(CH ２ ) ｎ -SCO-A ・・・(1) However, in formula (1), A is an alkyl group or aromatic hydrocarbon group having 1 to 10 carbon atoms, and these may be the same or different, and n is an integer from 3 to 6.

2. The rubber composition according to claim 1, wherein the thioester compound is a compound represented by n=6 in formula (1).

3. The rubber composition according to claim 1, comprising 0.1 to 10 parts by mass of sulfur per 100 parts by mass of diene rubber.

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

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