Rubber composition and method for producing the same

Abstract

To provide a rubber composition having excellent thermal aging resistance, crack propagation resistance and ozone resistance, and a method for producing the same.SOLUTION: A rubber composition contains a diene rubber 100 pts.mass, a phenylene diamine-based age resister 0.5-5 pts.mass, and an aliphatic thiol 0.1-5 pts.mass which has at least one group selected from the group consisting of an ester group and an ether group.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber composition and a method for producing the same. [Background technology]

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

[0003] [Patent Document 1] Patent Publication No. 2021-046554 Summary of the Invention [Problem to be solved by the invention]

[0004] Recently, with the increasing demand for higher safety levels, further improvements in heat aging resistance, crack propagation resistance and ozone resistance are required. When the present inventors studied the rubber composition described in Patent Document 1, it became clear that further improvement is desirable in consideration of demands that are likely to increase in the future.

[0005] In view of the above circumstances, an object of the present invention is to provide a rubber composition having excellent heat aging resistance, crack propagation resistance and ozone resistance, and a method for producing the same. [Means for solving the problem]

[0006] As a result of intensive research into the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by using a phenylenediamine-based antioxidant and an aliphatic thiol having a specific structure in specific amounts in combination, and have 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, 0.5 to 5 parts by mass of a phenylenediamine antioxidant, and 0.1 to 5 parts by mass of an aliphatic thiol having at least one group selected from the group consisting of an ester group and an ether group. (2) The rubber composition according to (1) above, wherein the molar ratio of the aliphatic thiol to the phenylenediamine-based antioxidant is 0.5 to 2. (3) The rubber composition according to (1) or (2) above, wherein the aliphatic thiol has an XlogP of 0.5 to 5. (4) The rubber composition according to any one of (1) to (3) above, further comprising 10 to 150 parts by mass of at least one filler selected from the group consisting of carbon black and silica. (5) The rubber composition according to any one of (1) to (4) above, wherein the aliphatic thiol has only one mercapto group. (6) A method for producing a rubber composition, which obtains the rubber composition according to any one of (1) to (5) above, The rubber composition further contains a vulcanizing agent, A method for producing a rubber composition, comprising simultaneously mixing the aliphatic thiol and the vulcanizing agent. [Effects of the Invention]

[0008] As will be described below, the present invention can provide a rubber composition excellent in heat aging resistance, crack propagation resistance, and ozone resistance, and a method for producing the same. DETAILED DESCRIPTION OF THE INVENTION

[0009] The rubber composition of the present invention and the method for producing 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.

[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, 0.5 to 5 parts by mass of a phenylenediamine antioxidant, and 0.1 to 5 parts by mass of an aliphatic thiol having at least one group selected from the group consisting of an ester group and an ether group (hereinafter also referred to as "specific aliphatic thiol").

[0011] It is generally known that polymers such as diene rubbers are deteriorated by radicals. Here, when radicals are generated in the composition of the present invention, the phenylenediamine-based antioxidant contained in the composition reacts with the radicals, deactivating them and suppressing deterioration of the diene rubber. On the other hand, when the phenylenediamine-based antioxidant reacts with the radicals, it becomes a diimine through oxidation and is no longer able to react with the radicals. In this case, if a large amount of radicals is generated, the suppression of deterioration of the diene rubber may be insufficient. In contrast, the composition of the present invention contains a specific aliphatic thiol in addition to a phenylenediamine-based antioxidant. It is believed that the specific aliphatic thiol reacts with the diimine-formed phenylenediamine-based antioxidant, regenerating hydrogen atoms on the nitrogen atoms of the diimine and restoring anti-aging properties. As a result, the rubber composition of the present invention is believed to exhibit extremely excellent heat-resistant anti-aging properties and crack propagation resistance. Furthermore, the specific aliphatic thiol has relatively high polarity because it contains at least one group selected from the group consisting of an ester group and an ether group, and because it is aliphatic, it has a relatively low melting point. Therefore, a portion of the specific aliphatic thiol precipitates on the surface to form a thin film, which is believed to contribute to excellent ozone resistance.

[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 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] [Phenylenediamine-based antioxidant] The phenylenediamine-based antioxidant contained in the composition of the present invention refers to an antioxidant having an aromatic ring with two secondary amines as substituents in its molecular structure.

[0018] [Specific example] Specific examples of phenylenediamine-based antioxidants include N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD), N-phenyl-N'-(1-methylheptyl)-p-phenylenediamine, N-phenyl-N'-isopropyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, etc. Among these, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD) is preferred because it provides better effects of the present invention.

[0019] [Content] In the composition of the present invention, the content of the phenylenediamine-based antioxidant is 0.5 to 5 parts by mass relative to 100 parts by mass of the diene rubber, and is preferably 1 to 4 parts by mass, since this provides better effects of the present invention.

[0020] [Specific Aliphatic Thiols] The specific aliphatic thiol contained in the composition of the present invention is an aliphatic thiol containing at least one group (hereinafter also referred to as "specific group") selected from the group consisting of an ester group and an ether group. Here, the aliphatic thiol is an aliphatic hydrocarbon having a mercapto group. The specific aliphatic thiol is a compound consisting of a specific group, a mercapto group, and an aliphatic hydrocarbon group. For example, the specific aliphatic thiol 1 (methoxybutyl mercaptopropionate) described below is a compound consisting of a specific group (-C(=O)O-, -O-), a mercapto group (-SH), and an aliphatic hydrocarbon group (-C2H4-, -C2H4CH(CH3)-, CH3).

[0021] [Specific group] The specific aliphatic thiol has at least one group (specific group) selected from the group consisting of an ester group and an ether group. Here, the ester group is a group represented by -C(=O)O-. An ether group is a group represented by -O-. Here, two aliphatic hydrocarbon groups are bonded to the oxygen atom of the ether group. Therefore, ether groups are distinguished from ester groups.

[0022] The specific aliphatic thiol preferably has an ester group as the specific group, and more preferably has both an ester group and an ether group as the specific group, for the reason that the effects of the present invention are more excellent.

[0023] [Mercapto group] The mercapto group is a group represented by -SH. The specific aliphatic thiol preferably has only one mercapto group, because this provides better effects of the present invention.

[0024] [Aliphatic hydrocarbon group] The aliphatic hydrocarbon group may be linear, branched, or cyclic. The aliphatic hydrocarbon group may be either saturated or unsaturated, but is preferably saturated because this provides a better effect of the present invention. The number of carbon atoms in the aliphatic hydrocarbon group is not particularly limited, but is preferably 1 to 30, as this provides better effects of the present invention.

[0025] [Molecular weight] The molecular weight of the specific aliphatic thiol is not particularly limited, but is preferably 80 to 1000, more preferably 100 to 500, even more preferably 120 to 300, and particularly preferably 160 to 200, for reasons of better effects of the present invention.

[0026] [XlogP] The XlogP of the specific aliphatic thiol is not particularly limited, but is preferably 0 to 5, more preferably 0.5 to 5, and even more preferably 0.1 to 2, for reasons of better effects of the present invention.

[0027] For XlogP: First, logP means the common logarithm of the partition coefficient P, a physical property that quantitatively represents how a compound is distributed in equilibrium in a two-phase system of oil (n-octanol in this case) and water. A larger number indicates a more hydrophobic compound, and a smaller number indicates a more hydrophilic compound, so it can be used as an index to represent the hydrophilicity or hydrophobicity of a compound.

[0028] logP=log(Coil / Cwater) Coil = molar concentration in oil phase Cwater = molar concentration in the aqueous phase

[0029] Generally, logP can be determined by experimental measurements using n-octanol and water. However, in this specification, we use XlogP, an approach consisting of an atom-based linear sum and correction terms. XlogP can be calculated using the software "XLogP" (available from the Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, http: / / WWW.sio-ccbg.ac.cn / software / xlogp3 / ). The calculation results are published in the PubChem database (http: / / pubchem.ncbi.nlm.nih.gov / #).

[0030] [Content] In the composition of the present invention, the content of the specific aliphatic thiol is 0.1 to 5 parts by mass relative to 100 parts by mass of the diene rubber, and is preferably 1 to 3 parts by mass, since this provides better effects of the present invention.

[0031] The molar ratio of the specific aliphatic thiol to the phenylenediamine-based antioxidant (specific aliphatic thiol / phenylenediamine-based antioxidant) is preferably 0.5 to 2, and more preferably 0.8 to 1.2, for reasons of better effects of the present invention.

[0032] [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 other than the above-mentioned phenylenediamine-based antioxidants, waxes, processing aids, oils, liquid polymers, thermosetting resins, vulcanizing agents (e.g., sulfur), and vulcanization accelerators.

[0033] The composition of the present invention preferably contains 10 to 150 parts by mass of at least one filler selected from the group consisting of carbon black and silica.

[0034] [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."

[0035] The content of the carbon black is not particularly limited, but in order to obtain better effects of the present invention, it is preferably 1 to 100 parts by mass, and more preferably 30 to 60 parts by mass, per 100 parts by mass of the diene rubber.

[0036] [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 above-mentioned specific aliphatic thiol, vulcanizing agent, and vulcanization accelerator at a high temperature (preferably 100 to 155°C), cool the mixture, and then mix the specific aliphatic thiol, vulcanizing agent, and vulcanization accelerator, because the effects of the present invention are more excellent in the resulting rubber composition. The composition of the present invention can be vulcanized or crosslinked under conventionally known vulcanization or crosslinking conditions.

[0037] [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 treads). [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, all components other than specific aliphatic thiols 1 to 5, comparative thiol 1, reactants, sulfur, and vulcanization accelerator were mixed in a 1.8 L internal mixer at 130°C for 5 minutes, and a masterbatch was released. Then, specific aliphatic thiols 1 to 5, comparative thiol 1, reactants, sulfur, and vulcanization accelerator were added to the masterbatch, and the mixture was mixed at 80°C using an open roll to produce each rubber composition.

[0040] 〔evaluation〕 The resulting rubber compositions (unvulcanized) were evaluated as follows.

[0041] <Heat aging resistance> Each of the resulting rubber compositions (unvulcanized) was press-vulcanized in a mold (15 cm × 15 cm × 0.2 cm) at 150°C for 30 minutes to produce a vulcanized rubber sheet. The resulting vulcanized rubber sheet was then left in a 70°C environment for 168 hours. Thereafter, JIS No. 3 dumbbell-shaped test specimens (2 mm thick) were punched out according to JIS K6251:2010, and the tensile strength (elongation at break) was evaluated at a temperature of 20°C and a pulling rate of 500 mm / min. The results are shown in Table 1. The results are expressed as an index, with Comparative Example 2 being 100. A larger index indicates better heat aging resistance.

[0042] <Crack propagation resistance> Vulcanized rubber sheets were prepared as described above, and the crack growth length (crack propagation) of the resulting vulcanized rubber sheets after 100,000 flexing cycles was measured in accordance with JIS K6260. The reciprocal of the crack growth is shown in Table 1. The results are expressed as an index, with the reciprocal of Comparative Example 2 being 100. The larger the index, the better the crack growth resistance. Note that Comparative Examples 1 and 4 broke during the test, so the crack growth could not be measured.

[0043] <Ozone resistance> A vulcanized rubber sheet was prepared as described above. The resulting vulcanized rubber sheet was placed in an ozone bath (50°C, 100 pphm) and allowed to stand at 40% elongation for 48 hours. The vulcanized rubber sheet was then observed and evaluated according to the following criteria. The results are shown in Table 1. From the viewpoint of ozone resistance, 1 is preferable. 1: No cracks were visible to the naked eye, but were visible under a 10x magnifying glass. 2: Small cracks (less than 1 mm) were observed with the naked eye. 3: Relatively large cracks (approximately 1 mm) were observed with the naked eye. 4: Deep, large cracks (1-3 mm) were observed with the naked eye.

[0044] [Table 1]

[0045] Details of each component in Table 1 are as follows: Natural rubber: Natural rubber Phenylenediamine antioxidant: N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD) Specific aliphatic thiol 1: methoxybutyl mercaptopropionate (structure below) (XlogP: 1.6) [ka] Specific aliphatic thiol 2: Methyl mercaptopropionate (structure below) (XlogP: 0.8) [ka] Specific aliphatic thiol 3: methoxybutyl thioglycolate (structure below) (XlogP: 1.1) [ka] Specific aliphatic thiol 4: 2-ethylhexyl mercaptopropionate (structure below) (XlogP: 3.5) [ka] Specific aliphatic thiol 5: 2-(2-ethoxyethoxy)ethanethiol (structure below) (XlogP: 0.6) [ka] Comparison thiol 1: mercaptopropionic acid (structure below) (XlogP: 0.4) [ka] Reactant: reaction product of the specific aliphatic thiol 2 (methyl mercaptopropionate) and the phenylenediamine antioxidant (6PPD) (structure below) [ka] 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) Sulfur: Oil-treated sulfur (Karuizawa Refinery Co., Ltd.) Vulcanization accelerator: Sancerer NS-G (manufactured by Sanshin Chemical Industry Co., Ltd.)

[0046] In Table 1, the XlogP column indicates the XlogP of the specific aliphatic thiols 1 to 5 or comparative thiol 1 used in each example.

[0047] As can be seen from Table 1, compared to Comparative Example 1, which contained neither a phenylenediamine-based antioxidant nor a specific aliphatic thiol, Comparative Examples 2 and 3, which contained a phenylenediamine-based antioxidant but no specific aliphatic thiol, and Comparative Example 4, which contained a phenylenediamine-based antioxidant but no specific aliphatic thiol (contained a thiol other than the specific aliphatic thiol), Examples 1 to 5, which used a phenylenediamine-based antioxidant and a specific aliphatic thiol in combination in specific amounts, exhibited excellent heat aging resistance, crack propagation resistance, and ozone resistance. Among them, Examples 1 to 4, in which the specific aliphatic thiol had an ester group, exhibited better heat aging resistance. Among them, Examples 1 to 2 and Example 4, in which the specific aliphatic thiol had a group represented by -R-SH (R is an aliphatic hydrocarbon group having two or more carbon atoms), exhibited even better heat aging resistance. Among them, Example 1, in which the specific aliphatic thiol had an ether group, exhibited even better heat aging resistance and crack propagation resistance.

Claims

1. The rubber composition contains 100 parts by mass of a diene rubber, 0.5 to 5 parts by mass of a phenylenediamine antioxidant, and 0.1 to 5 parts by mass of a specific aliphatic thiol, which is a compound comprising at least one group selected from the group consisting of an ester group and an ether group, a mercapto group, and an aliphatic hydrocarbon group, A rubber composition characterized in that the specific aliphatic thiol has only one mercapto group.

2. 2. The rubber composition according to claim 1, wherein a molar ratio of the specific aliphatic thiol to the phenylenediamine-based antioxidant is 0.5 to 2.

3. The rubber composition according to claim 1 or 2, wherein the specific aliphatic thiol has an XlogP of 0.5 to 5.

4. The rubber composition according to any one of claims 1 to 3, further comprising 10 to 150 parts by mass of at least one filler selected from the group consisting of carbon black and silica.

5. A method for producing a rubber composition, which obtains the rubber composition according to any one of claims 1 to 4, comprising: The rubber composition further contains a vulcanizing agent, A method for producing a rubber composition, comprising simultaneously mixing the specific aliphatic thiol and the vulcanizing agent.

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