Rubber composition and tire

Abstract

To provide a rubber composition excellent in stain resistance and excellent in ozone resistance and anti-thermal aging properties, and to provide a tire produced using the same.SOLUTION: The rubber composition contains 100 pts.mass of a diene rubber, 0.1 pt.mass or more and less than 5 pts.mass of eumelanin, and 0.1-20 pts.mass of an antioxidant containing no nitrogen atom.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] BACKGROUND ART Conventionally, rubber compositions containing an amine-based antioxidant (for example, N-phenyl-1-naphthylamine) as an antioxidant have been known (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-095806 Summary of the Invention [Problem to be solved by the invention]

[0004] On the other hand, rubber compositions containing conventional amine-based antioxidants may discolor to brown or the like during use (inadequate contamination resistance). Furthermore, the inventors of the present invention have studied the above rubber compositions and found that although they have excellent resistance to oxidative degradation due to ozone (ozone oxidative degradation) (ozone resistance), they may have insufficient resistance to oxidative degradation due to heat (thermooxidative degradation) (antiaging properties).

[0005] In view of the above circumstances, an object of the present invention is to provide a rubber composition that is excellent in contamination resistance, ozone resistance, and heat aging resistance, and a tire manufactured using the same. [Means for solving the problem]

[0006] As a result of extensive research into the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by using eumelanin in combination with a specific anti-aging agent, and have thus arrived at the present invention. That is, the present inventors have found that the above problems can be solved by the following configuration.

[0007] (1) A rubber composition containing 100 parts by mass of a diene rubber, 0.1 to 5 parts by mass of eumelanin, and 0.1 to 20 parts by mass of an antioxidant not containing a nitrogen atom. (2) The rubber composition according to (1) above, wherein the antioxidant is at least one selected from the group consisting of monophenol-based antioxidants and bisphenol-based antioxidants. (3) The rubber composition according to (1) or (2), wherein Y / X is 0.3 or more and 3 or less, where X is the part by mass of the eumelanin and Y is the part by mass of the antioxidant relative to 100 parts by mass of the diene rubber. (4) A tire manufactured using the rubber composition according to any one of (1) to (3) above. [Effects of the Invention]

[0008] As will be described below, the present invention can provide a rubber composition that is excellent in contamination resistance, ozone resistance, and heat aging resistance, as well as a tire manufactured using the same. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a partial cross-sectional schematic view showing an example of an embodiment of a tire of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] The rubber composition of the present invention will be described below. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. Each component may be used alone or in combination of two or more. When two or more components are used in combination, the content of the components refers to the total content unless otherwise specified. Furthermore, excellent stain resistance, ozone resistance, and anti-aging properties are also collectively referred to as "excellent effects of the present invention."

[0011] [I] Rubber composition The rubber composition of the present invention (hereinafter also referred to as "the composition of the present invention") is The rubber composition contains 100 parts by mass of diene rubber, 0.1 to 5 parts by mass of eumelanin, and 0.1 to 20 parts by mass of an antioxidant not containing a nitrogen atom.

[0012] Each component contained in the composition of the present invention will be described below.

[0013] [Diene rubber] The diene rubber contained in the composition of the present invention is not particularly limited. The diene rubber may be modified with an alkoxy group, an alkoxysilyl group, or the like. The composition of the present invention may contain one diene rubber or two or more diene rubbers.

[0014] [Specific example] Specific examples of the diene rubber include natural rubber (NR), butadiene rubber (BR), aromatic vinyl-conjugated diene copolymer rubber, isoprene rubber (IR), acrylonitrile-butadiene copolymer rubber (NBR), butyl rubber (IIR), halogenated butyl rubber (Br-IIR, Cl-IIR), chloroprene rubber (CR), etc. Examples of the aromatic vinyl-conjugated diene copolymer rubber include styrene-butadiene rubber (SBR), styrene-isoprene copolymer rubber, butyl rubber, etc.

[0015] [Molecular weight] The weight average molecular weight (Mw) of the diene rubber is not particularly limited, but in order to obtain better effects of the present invention, it is preferably 100,000 to 5,000,000, more preferably 200,000 to 3,000,000, and even more preferably 300,000 to 2,000,000.

[0016] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are values ​​calculated as standard polystyrene obtained by gel permeation chromatography (GPC) measurement.

[0017] [Eumelanin] The compositions of the present invention contain eumelanin. Eumelanin is a type of melanin (melanin pigment) containing a dihydroxyindole derivative, and is a natural black pigment. Eumelanin is found in large amounts in the ink of cephalopods such as squid and octopus.

[0018] [Content] In the composition of the present invention, the content of eumelanin is 0.1 parts by mass or more and less than 5 parts by mass per 100 parts by mass of the diene rubber. The content is preferably 0.5 to 4.5 parts by mass, and more preferably 1 to 4 parts by mass, because this provides better effects of the present invention.

[0019] When the composition of the present invention contains carbon black, the ratio of the eumelanin content to the carbon black content is preferably 0.1 to 20 mass%, more preferably 1 to 10 mass%, even more preferably 2 to 8 mass%, and particularly preferably 3 to 7 mass%, because this provides better effects of the present invention.

[0020] [Specific anti-aging agent] The composition of the present invention contains an antioxidant that does not contain a nitrogen atom (hereinafter also referred to as a "specific antioxidant"). Examples of the specific antioxidant include phenol-based antioxidants, sulfur-based antioxidants, and phosphorus-based antioxidants. Examples of the phenol-based antiaging agent include monophenol-based antiaging agents such as 2,6-di-tert-butyl-4-methylphenol and styrenated phenol; and bisphenol-based antiaging agents such as 2,2'-methylene-bis(4-methyl-6-tert-butylphenol), 2,2'-methylene-bis(4-ethyl-6-tert-butylphenol), 4,4'-butylidene-bis(3-methyl-6-tert-butylphenol), and 4,4'-thio-bis(3-methyl-6-tert-butylphenol). Examples of sulfur-based antioxidants include dilauryl thiodipropionate. Examples of phosphorus-based antioxidants include tris(nonylphenyl)phosphite. The specific antioxidant is preferably a phenolic antioxidant, and more preferably at least one selected from the group consisting of monophenolic antioxidants and bisphenolic antioxidants, because this provides better effects of the present invention.

[0021] [Content] In the composition of the present invention, the content of the specific antioxidant is 0.1 to 20 parts by mass based on 100 parts by mass of the diene rubber. The content is preferably 0.5 to 10 parts by mass, and more preferably 1 to 5 parts by mass, because this provides better effects of the present invention.

[0022] When the composition of the present invention contains carbon black, the ratio of the content of the specific antioxidant to the content of carbon black is preferably 0.1 to 20 mass%, more preferably 1 to 10 mass%, and even more preferably 4 to 9 mass%, because the effects of the present invention are more excellent.

[0023] [Y / X] When the parts by mass of the eumelanin and the parts by mass of the antioxidant are represented by X and Y, respectively, relative to 100 parts by mass of the diene rubber, Y / X is preferably 0.1 or more and 10 or less, more preferably 0.3 or more and 3 or less, and even more preferably 0.5 or more and 2.5 or less, for reasons of better effects of the present invention.

[0024] X+Y X+Y is preferably 1 to 20, more preferably 2 to 10, and even more preferably 3 to 7, because the effects of the present invention are more excellent.

[0025] [Preferred embodiment] When the composition of the present invention contains carbon black, the ratio of the total content of the eumelanin and the specific antioxidant to the content of carbon black is preferably 2 to 40 mass%, more preferably 5 to 20 mass%, and even more preferably 10 to 15 mass%, for reasons of better effects of the present invention.

[0026] [Optional ingredients] The composition of the present invention may further contain other components (optional components) as needed, provided that the effects and purposes of the composition are not impaired. Examples of the optional components include various additives commonly used in rubber compositions, such as fillers (e.g., silica, carbon black), silane coupling agents, terpene resins (e.g., aromatic modified terpene resins), thermally expandable microcapsules, zinc oxide (zinc white), stearic acid, antioxidants, waxes, processing aids, oils, liquid polymers, thermosetting resins, vulcanizing agents (e.g., sulfur), and vulcanization accelerators.

[0027] [Carbon black] The composition of the present invention preferably contains carbon black, as this provides better effects of the present invention. The carbon black is not particularly limited, and various grades such as SAF-HS, SAF, ISAF-HS, ISAF, ISAF-LS, IISAF-HS, HAF-HS, HAF, HAF-LS, and FEF can be used. The nitrogen adsorption specific surface area (N2SA) of the carbon black is not particularly limited, but is preferably 50 to 200 m for the reason that the effect of the present invention is more excellent. 2 / g, and 70 to 150m 2 / g is more preferred. Here, the nitrogen adsorption specific surface area (N2SA) is the amount of nitrogen adsorbed onto the surface of carbon black measured according to JIS K6217-2:2001 "Part 2: Determination of specific surface area - Nitrogen adsorption method - Single point method."

[0028] <Content> When the composition of the present invention contains carbon black, the content thereof is not particularly limited, but in order to obtain better effects of the present invention, the content thereof is preferably 2 to 100 parts by mass, and more preferably 20 to 50 parts by mass, per 100 parts by mass of the diene rubber described above.

[0029] 〔silica〕 The composition of the present invention preferably contains silica, since this provides a more excellent effect of the present invention. The silica is not particularly limited, and any conventionally known silica can be used. Examples of the 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 used alone or in combination of two or more types.

[0030] The cetyltrimethylammonium bromide (CTAB) adsorption specific surface area of ​​the silica (hereinafter, "CTAB adsorption specific surface area" may be simply referred to as "CTAB") is not particularly limited, but for the reason that the effect of the present invention is more excellent, it is preferably 100 to 300 m 2 / g, and 150 to 200m 2 / g is more preferred. Here, the CTAB adsorption specific surface area is a value measured in accordance with JIS K6430:2008, Appendix G.

[0031] <Content> When the composition of the present invention contains silica, the content thereof is not particularly limited, but in order to obtain better effects of the present invention, the content thereof is preferably 10 to 150 parts by mass, and more preferably 50 to 100 parts by mass, per 100 parts by mass of the diene rubber described above.

[0032] [Manufacturing method] The method for producing the composition of the present invention is not particularly limited, and specific examples thereof include a method of kneading the above-mentioned components using known methods and devices (e.g., a Banbury mixer, a kneader, a roll, etc.). When the composition of the present invention contains a vulcanizing agent (e.g., sulfur) and a vulcanization accelerator, it is preferable to first mix the components other than the vulcanizing agent and vulcanization accelerator at a high temperature (preferably 100 to 155°C), cool the mixture, and then mix the vulcanizing agent and vulcanization accelerator, because this will provide a more excellent effect of the present invention in the resulting composition. The composition of the present invention can be vulcanized or crosslinked under conventionally known vulcanization or crosslinking conditions.

[0033] [Application] The composition of the present invention is suitable for use as a rubber material. For example, it is suitable for use in tires (particularly pneumatic tires), conveyor belts, hoses, vibration-proof materials, rubber rolls, outer covers for railway vehicles, etc. Among these, it is particularly suitable for use in tires (particularly tire treads).

[0034] [II] Tires The tire of the present invention is a tire manufactured using the composition of the present invention described above. The tire of the present invention is preferably a pneumatic tire, and can be filled with air, an inert gas such as nitrogen, or other gases.

[0035] 1 shows a partial cross-sectional schematic view of a tire representing one example of an embodiment of the tire of the present invention, although the tire of the present invention is not limited to the embodiment shown in FIG.

[0036] In FIG. 1, reference numeral 1 denotes a bead portion, reference numeral 2 denotes a sidewall portion, and reference numeral 3 denotes a tire tread portion. Between the pair of left and right bead portions 1, a carcass layer 4 with fiber cords embedded therein is mounted, and the ends of this carcass layer 4 are folded back and wrapped around the bead core 5 and bead filler 6 from the inside to the outside of the tire. In the tire tread portion 3, a belt layer 7 is disposed on the outer side of the carcass layer 4 around the entire circumference of the tire. In addition, a rim cushion 8 is disposed in the bead portion 1 at the portion that comes into contact with the rim. At least one of the reference numerals 2 to 3, 5 to 6, and 8 (preferably reference numeral 3) is formed from the composition of the present invention described above.

[0037] The tire of the present invention can be manufactured, for example, by a conventionally known method. The gas to be filled into the tire can be normal air or air with an adjusted oxygen partial pressure, or an inert gas such as nitrogen, argon, or helium. [Example]

[0038] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0039] [Production of rubber composition] The components in Table 1 below were mixed in the composition (parts by mass) shown in the same table. Specifically, first, the components in Table 1 other than sulfur and the vulcanization accelerator were mixed in a 1.8 L internal mixer at 130°C for 5 minutes, and a masterbatch was discharged. Then, sulfur and the vulcanization accelerator were added to the masterbatch, and the mixture was mixed using an open roll at 80°C to produce each rubber composition.

[0040] [evaluation] The obtained rubber composition was press-vulcanized at 150° C. for 30 minutes to prepare a vulcanized rubber sheet, which was then evaluated as follows.

[0041] [Stain resistance] The appearance of the obtained vulcanized rubber sheet (6 x 6 inches) was visually observed after one month of outdoor exposure, and the stain resistance was evaluated according to the following criteria: ◯ indicates excellent stain resistance. ○: No discoloration was observed. ×: Discoloration was observed.

[0042] [Ozone resistance] The vulcanized rubber sheets were exposed to ozone (ozone concentration: 100 pphm (100 × 10 -8 ), temperature: 0°C, strain: 40%). Fixed-point observations were made 24 hours, 48 ​​hours, 72 hours, and 96 hours after the start of ozone exposure to check for the presence or absence of fracture. The time at which fracture was first observed is shown in Table 1. If no fracture was observed after 96 hours, it was recorded as "no fracture." It is preferable that the period be 96 hours or longer.

[0043] [Breaking elongation retention rate] From the obtained vulcanized rubber sheet, JIS No. 3 dumbbell-shaped test pieces (thickness: 2 mm) were punched out in accordance with JIS K6251:2010, and the elongation at break was evaluated under conditions of a temperature of 20°C and a tensile speed of 500 mm / min. The vulcanized rubber sheets were also subjected to an aging test (left to stand in an environment of 80°C for 240 hours) and similarly evaluated for elongation at break. The elongation at break retention rate was then calculated as follows. The results are shown in Table 1. Breaking elongation retention rate (%) = Breaking elongation after aging test / Breaking elongation before aging test × 100 A higher breaking elongation retention rate means better anti-aging properties. The breaking elongation rate is preferably 80% or more.

[0044] [Table 1]

[0045] Details of each component in Table 1 are as follows: Natural rubber: Natural rubber Carbon black: Show Black N234 (manufactured by Showa Cabot Corporation) Zinc oxide: Three types of zinc oxide (manufactured by Seido Chemical Industry Co., Ltd.) Stearic acid: Beads Stearic Acid YR (manufactured by NOF Corporation) Oil: Process oil Naphthylamine: the following compounds [ka] Eumelanin: Eumelanin (squid ink pigment) Antioxidant 1 (monophenolic): BHT (compound below) [ka] Antioxidant 2 (bisphenol type): p-TBp14 (compound below) [ka] Sulfur: Oil-treated sulfur (Karuizawa Refinery Co., Ltd.) Vulcanization accelerator TBBS: Sancerer NS-G (manufactured by Sanshin Chemical Industry Co., Ltd.)

[0046] [Summary of Table 1] As can be seen from Table 1, Examples 1 to 7, which used eumelanin in combination with a specific antioxidant, exhibited excellent stain resistance, ozone resistance, and anti-aging properties. Comparing Examples 1 and 2 with Examples 4 to 7 (comparison between the embodiments in which antioxidant 1 was used as the specific antioxidant), Examples 1 and 2 and Examples 4 to 6, in which Y / X was 0.3 or more and 3 or less, exhibited more excellent antiaging properties. Among these, Examples 4 and 5, in which Y / X was 1 or more and 2.5 or less, exhibited even more excellent antiaging properties. Furthermore, a comparison between Examples 1 and 2 (comparison between embodiments in which only the type of specific antioxidant is different) showed that Example 2, in which the specific antioxidant was a bisphenol-based antioxidant, exhibited superior antiaging properties.

[0047] On the other hand, Comparative Example 2, which contained eumelanin but no specific antioxidant, had insufficient antiaging properties. Comparative Example 3, which contained a specific antioxidant but no eumelanin, had insufficient ozone resistance and antiaging properties. Comparative Example 1, which used only naphthylamine, a nitrogen-containing antioxidant, had insufficient stain resistance and antiaging properties. [Explanation of symbols]

[0048] 1 Bead section 2 Sidewall 3 Tire tread 4 carcass layers 5 bead core 6 Bead filler 7 Belt Layer 8 Rim Cushion

Claims

1. A rubber composition comprising 100 parts by mass of a diene rubber, 0.1 parts by mass or more but less than 5 parts by mass of eumelanin, and 0.1 to 20 parts by mass of an antioxidant not containing a nitrogen atom.

2. The rubber composition according to claim 1, wherein the antioxidant is at least one selected from the group consisting of monophenol-based antioxidants and bisphenol-based antioxidants.

3. 2. The rubber composition according to claim 1, wherein Y / X is 0.3 or more and 3 or less, where X is the part by mass of the eumelanin and Y is the part by mass of the antioxidant relative to 100 parts by mass of the diene rubber.

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

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