Rubber composition

Abstract

To provide a rubber composition which is excellent in stain resistance and exhibits anti-aging properties equivalent or superior to those of a rubber composition containing a conventional amine-based antioxidant.SOLUTION: The rubber composition contains: 100 pts.mass of a diene rubber; and 0.1-20 pts.mass of a substituted indole which has a melting point of 200°C or lower and is a compound represented by the following formula (1). In the formula (1), R1-R7 each independently represent a hydrogen atom or a substituent, provided that at least one of R1-R7 is a substituent.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber composition. [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 (they may have insufficient stain resistance).

[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 and exhibits antiaging properties equal to or better than those of rubber compositions containing conventional amine-based antiaging agents. [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 blending a specific compound in a predetermined amount, 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 and 0.1 to 20 parts by mass of a substituted indole having a melting point of 200°C or less and being a compound represented by formula (1) described below. (2) The rubber composition according to (1) above, wherein at least one of R2 and R3 in formula (1) above is a substituent having a carbon atom at the bonding position. (3) The rubber composition according to (1) or (2) above, wherein at least one of R4 to R7 in the formula (1) above is a substituent having an oxygen atom at the bonding position. (4) The rubber composition according to any one of (1) to (3) above, wherein R2 in the formula (1) above contains an aromatic ring. (5) The above substituted indole 14 The rubber composition according to any one of the above (1) to (4), wherein the decay rate of C per gram per minute is 0.1 dpm / gC or more. [Effects of the Invention]

[0008] As will be described below, the present invention can provide a rubber composition that is excellent in stain resistance and exhibits antiaging properties equal to or better than those of rubber compositions containing conventional amine-based antiaging agents. DETAILED DESCRIPTION OF THE INVENTION

[0009] 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. In addition, the term "excellent anti-aging properties" refers to rubber compositions that exhibit anti-aging properties equal to or greater than those of rubber compositions containing conventional amine-based anti-aging agents. Furthermore, excellent stain resistance and anti-aging properties are also referred to as "excellent effects of the present invention."

[0010] 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 a diene rubber and 0.1 to 20 parts by mass of a substituted indole (hereinafter also referred to as "specific compound") having a melting point of 200°C or less and being a compound represented by formula (1) described below.

[0011] It is believed that the composition of the present invention, which has such a constitution, solves the above-mentioned problems. The reason for this is not clear, but is thought to be as follows.

[0012] The inventors have found through their research that there is a correlation between the HOMO energy level and / or LUMO energy level of a compound and its antiaging properties. While the reason for this is unclear, it is believed that the ease of reaction with oxygen and ozone, which cause deterioration, is related to the energy level. As mentioned above, amine-based antiaging agents such as N-phenyl-1-naphthylamine are known to have the effect of suppressing deterioration, and the energy level of a substituted indole (specific compound) is close to that of an amine-based antiaging agent. Furthermore, since the melting point of the specific compound is limited to a specific temperature or below, it has excellent compatibility with diene rubbers. As a result, it is believed that the specific compound exhibits antiaging properties equivalent to or superior to those of an amine-based antiaging agent. Furthermore, by adopting preferred embodiments such as Preferred Aspects 1 to 3 described below, the energy level of the specific compound can be made even closer to that of an amine-based antiaging agent. Furthermore, unlike amine-based antioxidants such as N-phenyl-1-naphthylamine, the specific compound does not have a structure in which the amino group is sandwiched between aromatic rings, and therefore is less likely to form a resonance structure (which can lead to discoloration) even if a hydrogen atom is abstracted. From the above viewpoints, it is believed that the composition of the present invention containing the specific compound exhibits excellent stain resistance and anti-aging properties.

[0013] Each component contained in the composition of the present invention will be described below.

[0014] [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.

[0015] [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.

[0016] [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.

[0017] 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.

[0018] [Specific compound] The composition of the present invention contains a substituted indole (specific compound) that has a melting point of 200° C. or lower and is a compound represented by the following formula (1):

[0019] [ka] (1)

[0020] In formula (1), R1 to R7 each independently represent a hydrogen atom or a substituent (for example, specific examples described below), provided that at least one of R1 to R7 is a substituent.

[0021] The above-mentioned substituent is preferably a hydrocarbon group which may contain a heteroatom, for the reason that the effects of the present invention are more excellent. Examples of the hydrocarbon group include aliphatic hydrocarbon groups, aromatic hydrocarbon groups (aryl groups), and combinations thereof. The aliphatic hydrocarbon group may be linear, branched, or cyclic. Specific examples of the aliphatic hydrocarbon group include linear or branched alkyl groups (particularly having 1 to 30 carbon atoms), linear or branched alkenyl groups (particularly having 2 to 30 carbon atoms), and linear or branched alkynyl groups (particularly having 2 to 30 carbon atoms). Examples of the aromatic hydrocarbon group include aromatic hydrocarbon groups having 6 to 18 carbon atoms, such as phenyl, tolyl, xylyl, and naphthyl. R1 is preferably an alkyl group because the effects of the present invention are more excellent. The number of carbon atoms in the alkyl group is preferably 1 to 10, and more preferably 1 to 5, because the effects of the present invention are more excellent. A carbon atom in the alkyl group may be substituted with -O-, -C(=O)-, -C(=O)-O-, -OC(=O)-O-, -S-, -S(=O)-, -SO2-, -NR- (R: hydrogen atom or substituent (for example, specific examples will be described later)), or a group formed by combining these groups.

[0022] For the reason that the effects of the present invention are more excellent, the above-mentioned substituent is also preferably a group represented by *-LR (hereinafter also referred to as a "specific substituent"), where L represents a single bond or a divalent linking group, R represents a hydrocarbon group, and * represents a bonding position. Examples of the divalent linking group represented by L include a divalent aliphatic hydrocarbon group (particularly an alkylene group), a divalent aromatic hydrocarbon group (particularly an arylene group), -O-, -C(=O)-, -C(=O)-O-, -OC(=O)-O-, -S-, -S(=O)-, -SO2-, -NR- (R: hydrogen atom or a substituent (for example, specific examples will be described later)), and groups combining these. Specific examples of the hydrocarbon group represented by R are as described above.

[0023] For the reason that the effects of the present invention are more excellent, the above-mentioned substituent is also preferably a group represented by *-LX, where L represents a single bond or a divalent linking group, X represents a substituent (for example, specific examples described below), and * represents the bonding position. Specific examples of the divalent linking group represented by L are as described above.

[0024] [Preferred embodiment 1] For the reason that the effects of the present invention are more excellent, the specific compound is preferably an embodiment in which at least one of R2 and R3 in formula (1) is a substituent having a carbon atom at the bonding position (hereinafter also referred to as "preferred embodiment 1").

[0025] [Preferred embodiment 2] The specific compound is preferably an embodiment in which at least one of R4 to R7 in formula (1) is a substituent having an oxygen atom at the bonding position (hereinafter also referred to as "preferred embodiment 2"), because the effects of the present invention are more excellent.

[0026] [Preferred embodiment 3] The specific compound preferably has an aspect in which R2 in formula (1) contains an aromatic ring (hereinafter also referred to as "preferred aspect 3"), because this provides better effects of the present invention.

[0027] Preferred Embodiment 4 The specific compound is preferably derived from a natural product, since this will provide a more excellent effect of the present invention. Whether or not the specific compound is derived from a natural product can be determined, for example, by 14 This can be determined by C dating. of a specific compound14 The decay rate of C per gram per minute is preferably 0.1 dpm / gC or more, because the effect of the present invention is more excellent. 14 The C decay rate per gram per minute is measured by accelerator mass spectrometry (AMS) and liquid scintillation counting method (LSC).

[0028] [Melting point] The melting point of the specific compound is 200°C or less. The melting point is preferably 150°C or lower, and more preferably 130°C or lower, because the effects of the present invention are more excellent. There is no particular lower limit to the melting point, but because the effects of the present invention are more excellent, it is preferably 30°C or higher, more preferably 50°C or higher, and even more preferably 70°C or higher. The melting point is measured at 1 atmosphere.

[0029] [Content] In the composition of the present invention, the content of the specific compound is 0.1 to 20 parts by mass relative to 100 parts by mass of the diene rubber. The content is preferably 0.5 to 10 parts by mass, more preferably 1 to 5 parts by mass, for the reason that the effects of the present invention are more excellent.

[0030] [Specific examples of substituents] Specific examples of the substituent in this specification include a halogeno group (halogen atom), an alkyl group (for example, a tert-butyl group) (including a cycloalkyl group, a bicycloalkyl group, and a tricycloalkyl group), an alkenyl group (including a cycloalkenyl group and a bicycloalkenyl group), an alkynyl group, an aryl group, a heterocyclic group (which may also be called a heterocyclic group), a cyano group, a hydroxy group, a nitro group, a carboxy group, a formyl group, an alkoxy group, an aryloxy group, a silyloxy group, a heterocyclic oxy group, an acyloxy group, a carbamoyl group, a carbamoyloxy group, an alkoxycarbonyloxy group, an aryloxycarbonyloxy group, an amino group (including an anilino group), an ammonio group, a dialkylamino group, an acylamino group, and an aminocarbonylamino group. Examples of substituents include an alkoxycarbonylamino group, an aryloxycarbonylamino group, a sulfamoylamino group, an alkyl or arylsulfonylamino group, a mercapto group, an alkylthio group, an arylthio group, a heterocyclic thio group, a sulfamoyl group, a sulfo group, an alkyl or arylsulfinyl group, an alkyl or arylsulfonyl group, an acyl group, an aryloxycarbonyl group, an alkoxycarbonyl group, an aryl or heterocyclic azo group, an imido group, a phosphino group, a phosphinyl group, a phosphinyloxy group, a phosphinylamino group, a phosphono group, a silyl group, a hydrazino group, a ureido group, a boronic acid group (-B(OH)), a phosphato group (-OPO(OH)), a sulfato group (-OSOH), and other known substituents.

[0031] [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.

[0032] [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."

[0033] <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.

[0034] 〔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.

[0035] 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.

[0036] <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.

[0037] [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.

[0038] [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). [Example]

[0039] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0040] [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.

[0041] [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.

[0042] [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.

[0043] [Breaking strength retention rate and 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 breaking strength and breaking elongation were 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 breaking strength and breaking elongation. The breaking strength retention rate and breaking elongation retention rate were then calculated as follows. The results are shown in Table 1. Breaking strength retention rate (%) = Breaking strength after aging test / Breaking strength before aging test × 100 Breaking elongation retention rate (%) = Breaking elongation after aging test / Breaking elongation before aging test × 100 Higher breaking strength retention and breaking elongation retention indicate better anti-aging properties. If the breaking strength retention is 80% or more and the breaking elongation is 75% or more, it can be said that the rubber composition exhibits anti-aging properties equal to or better than those of a rubber composition containing a conventional amine-based anti-aging agent.

[0044] [Table 1]

[0045] The temperatures listed in Table 1 represent the melting points of the components.

[0046] [Naphthylamine, indole, tryptophan, and compounds 1 to 7] Among the components in Table 1, naphthylamine, indole, tryptophan, and compounds 1 to 7 are as follows. Note that naphthylamine, indole, and tryptophan do not fall under the above-mentioned specific compounds, but compounds 1 to 7 fall under the above-mentioned specific compounds. In addition, compounds 1 to 7 are 14 The decay rate of C per gram per minute is 0.1 dpm / gC or more.

[0047] Naphthylamine: the following compound (melting point: 62°C) [ka]

[0048] Indole: the following compound (melting point: 52°C) [ka]

[0049] When indole is applied to formula (1), all of R1 to R7 become hydrogen atoms, and therefore it does not fall under the category of the above-mentioned specific compounds.

[0050] Tryptophan: The following compound (melting point: decomposes at 289°C) [ka]

[0051] Although tryptophan is a compound represented by formula (1), it does not fall under the category of the above-mentioned specific compounds because its melting point exceeds 200°C.

[0052] Compound 1: Melatonin (compound shown below, melting point: 117°C) [ka]

[0053] Compound 1 is a compound represented by formula (1). In formula (1), R3 is *-C2H4-NH-C(=O)-CH3 (*: bonding position), R5 is a methoxy group, and R1 to R2, R4, and R6 to R7 are hydrogen atoms. Compound 1 has a melting point of 200°C or lower. Therefore, Compound 1 corresponds to the above-mentioned specific compound.

[0054] Compound 2: ethyl 3-indoleacetate (compound shown below, melting point: 44-45°C) [ka]

[0055] Compound 2 is a compound represented by formula (1). In formula (1), R3 is *-CH2-C(=O)-O-C2H5 (*: bonding position), and R1 to R2 and R4 to R7 are hydrogen atoms. Compound 2 has a melting point of 200°C or lower. Therefore, compound 2 falls under the category of the specific compound described above.

[0056] Compound 3: 5-hydroxyindole (compound shown below, melting point: 107°C) [ka]

[0057] Compound 3 is a compound represented by formula (1). In formula (1), R5 is a hydroxy group, and R1 to R4 and R6 to R7 are hydrogen atoms. Compound 3 has a melting point of 200°C or lower. Therefore, compound 3 falls under the category of the specific compound described above.

[0058] Compound 4: 3-indoleethanol (compound shown below: melting point: 59°C) [ka]

[0059] Compound 4 is a compound represented by formula (1). In formula (1), R3 is *-C2H4-OH (*: bonding position), and R1 to R2 and R4 to R7 are hydrogen atoms. Compound 4 has a melting point of 200°C or lower. Therefore, compound 4 falls under the category of the specific compound described above.

[0060] Compound 5: 2-phenylindole (compound shown below, melting point: 192°C) [ka]

[0061] Compound 5 is a compound represented by formula (1). In formula (1), R2 is a phenyl group, and R1 and R3 to R7 are hydrogen atoms. Compound 5 has a melting point of 200°C or lower. Therefore, compound 5 falls under the category of the specific compound described above.

[0062] Compound 6: 7-benzyloxyindole (compound shown below, melting point: 73°C) [ka]

[0063] Compound 6 is a compound represented by formula (1). In formula (1), R7 is a benzyl group, and R1 to R6 are hydrogen atoms. Compound 6 has a melting point of 200°C or lower. Therefore, compound 6 falls under the category of the specific compound described above.

[0064] Compound 7: Indole-7-carboxaldehyde (compound shown below, melting point: 90°C) [ka]

[0065] Compound 7 is a compound represented by formula (1). In formula (1), R7 is a formyl group, and R1 to R6 are hydrogen atoms. Compound 7 has a melting point of 200°C or lower. Therefore, compound 7 falls under the category of the specific compound described above.

[0066] [About other ingredients] Other components 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 Sulfur: Oil-treated sulfur (Karuizawa Refinery Co., Ltd.) Vulcanization accelerator TBBS: Sancerer NS-G (manufactured by Sanshin Chemical Industry Co., Ltd.)

[0067] [Summary of Table 1] As can be seen from Table 1, Examples 1 to 7, which contained the specific compound, exhibited excellent stain resistance and anti-aging properties. In particular, Examples 1 to 4 and Example 6, in which the melting point of the specific compound was 150°C or less and the specific compound was one of Preferred Embodiments 1 to 3, exhibited even better anti-aging properties. Among these, Examples 1 to 2 and Example 6, in which at least one of R1 to R7 in Formula (1) was a specific substituent, exhibited higher retention of elongation at break. Among these, Examples 1 and 2, in which R3 in Formula (1) was a substituent, exhibited even higher retention of elongation at break.

[0068] On the other hand, Comparative Example 2, which used indole in which all of R1 to R7 in formula (1) are hydrogen atoms, and Comparative Example 3, which used tryptophan, a compound represented by formula (1) but with a melting point exceeding 200°C, had insufficient antiaging properties. Also, Comparative Example 1, which used Compound 1, a conventional amine-based antiaging agent, had insufficient stain resistance.

Claims

1. A rubber composition comprising 100 parts by mass of a diene rubber and 0.1 to 20 parts by mass of a substituted indole having a melting point of 200°C or less and being a compound represented by the following formula (1): 【Chemistry 1】 （１） In formula (1), R １ ~R ７ each independently represents a hydrogen atom or a substituent. １ ~R ７ At least one of the groups is a substituent.

2. R in the formula (1) ２ and R ３ The rubber composition according to claim 1, wherein at least one of the following is a substituent having a carbon atom at the bonding position:

3. R in the formula (1) ４ ~R ７ The rubber composition according to claim 1 or 2, wherein at least one of the following is a substituent having an oxygen atom at the bonding position.

4. R in the formula (1) ２ The rubber composition according to claim 1 or 2, wherein contains an aromatic ring.

5. of the substituted indole １４ 3. The rubber composition according to claim 1, wherein the decay rate of C per gram per minute is 0.1 dpm / gC or more.

Images