Rubber composition and pneumatic tire

Abstract

To provide a rubber composition using a natural product as a substitute for a vulcanization accelerator, which is excellent in rubber physical properties such as vulcanization characteristics (maximum torque) of a rubber composition and tensile strength at cutting when formed into a vulcanized rubber and to provide a pneumatic tire comprising at least the vulcanized rubber of the rubber composition.SOLUTION: There is provided a rubber composition comprising a diene-based rubber, sulfur and a nitrogen-containing alkaloid compound having a melting point of 200°C or less. The nitrogen-containing alkaloid compound preferably is a compound having a tertiary amine structure. The mass ratio (A / B) of the content A of the nitrogen-containing alkaloid compound in the rubber composition to the content B of sulfur is preferably 0.2 to 2.0. The nitrogen-containing alkaloid compound preferably is at least one selected from the group consisting of gramine, pseudopelletierine, hordenine and tetrahydropalmatine.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] In recent years, companies have been required to work on the Sustainable Development Goals (SDGs), regardless of the application, such as pneumatic tires. The SDGs consist of 17 goals, one of which is SDG 12-2 (Ensure that natural resources are managed sustainably and used efficiently by 2030).

[0003] The following Patent Document 1 describes a method for producing an antioxidant, which includes a step of converting glucose into benzoic acid or a benzoic acid derivative by a microorganism, or extracting benzoic acid or a benzoic acid derivative from a plant, and a step of converting the obtained benzoic acid or benzoic acid derivative into aniline or an aniline derivative.

[0004] Patent Document 2 listed below describes a method for producing an antioxidant, which comprises the steps of obtaining 2-aminobenzoic acid by hydrolyzing indigo extracted from a plant, obtaining aniline by decarboxylating the obtained 2-aminobenzoic acid, and synthesizing an amine-based antioxidant or a benzimidazole-based antioxidant from the obtained aniline.

[0005] Patent Document 3 listed below describes a vulcanization accelerator synthesized from biological resources including plant resources, and characterized in that the Δ14C value is −75% to −225%. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-83288 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-222575 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-34598 Summary of the Invention [Problem to be solved by the invention]

[0007] Although there are techniques for compounding natural products into rubber compositions, such as those described in Patent Documents 1 to 3, there are few techniques aimed at significantly improving the physical properties of the vulcanized rubber finally obtained from the rubber composition, and as far as the inventors know, there are no reported examples of using natural products while taking into consideration their interaction with sulfur in the vulcanization process.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a rubber composition which uses a natural product as an alternative compounding agent to a vulcanization accelerator, and which has excellent rubber physical properties such as vulcanization characteristics (maximum torque) of the rubber composition and tensile strength at break when vulcanized, and to provide a pneumatic tire which includes at least vulcanized rubber of the rubber composition. [Means for solving the problem]

[0009] The above problems can be solved by the following constitution: The present invention relates to a rubber composition (1) characterized by containing a diene rubber, sulfur, and a nitrogen atom-containing alkaloid compound having a melting point of 200°C or less.

[0010] In the rubber composition (1), the nitrogen atom-containing alkaloid compound is preferably a rubber composition (2) having a tertiary amine structure.

[0011] In the rubber composition (1) or (2), a rubber composition (3) is preferred in which the mass ratio (A / B) of the content A of the nitrogen atom-containing alkaloid compound to the content B of the sulfur in the rubber composition is 0.2 to 2.0.

[0012] In any of the rubber compositions (1) to (3), a rubber composition (4) is preferred in which the nitrogen atom-containing alkaloid compound is at least one selected from the group consisting of gramine, pseudopelletierine, hordenine, and tetrahydropalmatine.

[0013] The present invention also relates to a pneumatic tire (5) comprising at least the vulcanized rubber of the rubber compositions (1) to (4). [Effects of the Invention]

[0014] The rubber composition according to the present invention contains, in addition to a diene rubber, sulfur and a nitrogen-containing alkaloid compound having a melting point of 200°C or lower. When sulfur and a nitrogen-containing alkaloid compound coexist, the nitrogen atoms in the alkaloid compound nucleophilically attack the sulfur chains during the crosslinking reaction, resulting in cleavage of the sulfur chains. When a nitrogen-containing alkaloid compound having a melting point of 200°C or lower is used, it melts quickly in the diene rubber during vulcanization, resulting in excellent dispersibility in the diene rubber. As a result, uniform sulfur crosslinking progresses in the diene rubber, improving the rubber's physical properties, such as the vulcanization characteristics (maximum torque) of the rubber composition and the tensile strength at break of the vulcanized rubber. When the nitrogen-containing alkaloid compound has a tertiary amine structure, the tertiary amine structure does not form hydrogen bonds and is highly hydrophobic, resulting in excellent dispersibility in the hydrophobic diene rubber. This further improves the rubber's physical properties, such as the vulcanization characteristics (maximum torque) of the rubber composition and the tensile strength at break of the vulcanized rubber. In particular, when the nitrogen atom-containing alkaloid compound is at least one selected from the group consisting of gramine, pseudopelletierine, hordenine, and tetrahydropalmatine, these alkaloid compounds have a lower melting point than other alkaloid compounds and are particularly excellent in dispersibility in diene rubber during vulcanization, which can particularly improve the vulcanization characteristics of the rubber composition and the rubber properties of the vulcanized rubber.

[0015] As described above, in the rubber composition according to the present invention, the nitrogen-containing alkaloid compound contributes to improving dispersibility while increasing the crosslinkability of sulfur chains. In particular, it is preferable that the mass ratio (A / B) of the nitrogen-containing alkaloid compound content A to the sulfur content B in the rubber composition is 0.2 to 2.0, since this can particularly improve the vulcanization characteristics of the rubber composition and the rubber properties of the vulcanized rubber.

[0016] The vulcanized rubber of the rubber composition according to the present invention has improved rubber physical properties such as maximum torque and tensile strength at break, and is therefore particularly useful for pneumatic tires. DETAILED DESCRIPTION OF THE INVENTION

[0017] The rubber composition according to the present invention contains a diene rubber and a sulfur- and nitrogen-atom-containing alkaloid compound.

[0018] The diene rubber is not particularly limited, and examples thereof include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer, styrene-isoprene-butadiene copolymer rubber, etc. These may be used alone or in combination of two or more.

[0019] The sulfur may be any ordinary sulfur for rubber, such as powdered sulfur, precipitated sulfur, insoluble sulfur, highly dispersible sulfur, etc. In the rubber composition according to the present invention, when the total amount of the diene rubber is taken as 100 parts by mass, the content of the vulcanizing agent is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass.

[0020] Nitrogen atom-containing alkaloid compounds are mainly found in plants, and in the present invention, examples thereof include gramine (melting point 132°C), pseudopelletierine (melting point 46°C), hordenine (melting point 118°C), tetrahydropalmatine (melting point 150°C), caffeine (melting point 238°C), 3-(3,4-dihydroxyphenyl)-L-alanine (melting point 278°C), nicotine (melting point -80°C), sparteine (melting point 31°C), matrine (melting point 76°C), proxyphylline (melting point 136°C), cytisine (melting point 156°C), bicuculline (melting point 197°C), norharman (melting point 201°C), cinchonidine (melting point 206°C), cordycepin (melting point 226°C), tryptanthrin (melting point 266°C), ℃), indirubin (melting point 350℃), etc. can be used. However, if the melting point of the nitrogen-atom-containing alkaloid compound is too high, the degree of melting in the diene rubber may decrease during vulcanization, and in that case, dispersibility in the diene rubber tends to deteriorate. Therefore, in the present invention, it is preferable to use a nitrogen-atom-containing alkaloid compound with a melting point of 200℃ or less, and it is more preferable to use a nitrogen-atom-containing alkaloid compound with a melting point of 180℃ or less. In the present invention, the melting point of the nitrogen-atom-containing alkaloid compound is a value measured by differential scanning calorimetry (DSC) in accordance with JIS K6220.

[0021] In the rubber composition according to the present invention, when the total amount of the diene rubber is taken as 100 parts by mass, the content of the nitrogen atom-containing alkaloid compound is preferably 0.1 to 15 parts by mass, more preferably 0.5 to 10 parts by mass.

[0022] The rubber composition according to the present invention is characterized by the combined use of sulfur and a nitrogen-containing alkaloid compound. It is preferable that the mass ratio (A / B) of the nitrogen-containing alkaloid compound content A to the sulfur content B in the rubber composition is 0.2 to 2.0, more preferably 0.4 to 1.8, because this can particularly improve the rubber physical properties such as maximum torque and tensile strength at break when vulcanized.

[0023] The rubber composition according to the present invention may contain, in addition to the diene rubber and the sulfur- and nitrogen-atom-containing alkaloid compound, carbon black, silica, a silane coupling agent, a vulcanizing agent, a vulcanization accelerator, an antioxidant, stearic acid, a softener such as wax or oil, a processing aid, and the like.

[0024] Examples of carbon black that can be used include carbon blacks commonly used in the rubber industry, such as SAF, ISAF, HAF, FEF, and GPF, as well as conductive carbon blacks such as acetylene black and ketjen black. The rubber composition according to the present invention preferably contains 5 to 100 parts by mass of carbon black when the total amount of the rubber components is 100 parts by mass.

[0025] As the silica, wet silica, dry silica, sol-gel silica, surface-treated silica, etc., which are commonly used for rubber reinforcement, are used, and among these, wet silica is preferred.

[0026] When silica is contained as a filler, it is also preferable to contain a silane coupling agent. The silane coupling agent is not particularly limited as long as it contains sulfur in the molecule, and various silane coupling agents that are compounded together with silica in rubber compositions can be used. Examples of the silane include sulfide silanes such as bis(3-triethoxysilylpropyl)tetrasulfide (e.g., "Si69" manufactured by Degussa), bis(3-triethoxysilylpropyl)disulfide (e.g., "Si75" manufactured by Degussa), bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, and bis(2-trimethoxysilylethyl)disulfide; mercaptosilanes such as γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, mercaptopropylmethyldimethoxysilane, mercaptopropyldimethylmethoxysilane, and mercaptoethyltriethoxysilane; and protected mercaptosilanes such as 3-octanoylthio-1-propyltriethoxysilane and 3-propionylthiopropyltrimethoxysilane.

[0027] As described above, the nitrogen-atom-containing alkaloid compound acts as a vulcanization accelerator that accelerates the crosslinking reaction of sulfur, but the rubber composition according to the present invention may further contain a known vulcanization accelerator other than the nitrogen-atom-containing alkaloid compound. As the vulcanization accelerator other than the nitrogen-atom-containing alkaloid compound, vulcanization accelerators commonly used for rubber vulcanization, such as 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, may be used alone or in appropriate mixtures.

[0028] As the antiaging agent, antiaging agents commonly used for rubber, such as aromatic amine antiaging agents, amine-ketone antiaging agents, monophenol antiaging agents, bisphenol antiaging agents, polyphenol antiaging agents, dithiocarbamate antiaging agents, and thiourea antiaging agents, may be used alone or in appropriate mixtures.

[0029] The rubber composition according to the present invention can be obtained by kneading a diene rubber, a sulfur- and nitrogen-atom-containing alkaloid compound, carbon black, silica, a silane coupling agent, a vulcanizing agent, a vulcanization accelerator, zinc oxide, an antioxidant, a softener such as stearic acid or wax, a processing aid, and the like, using a kneading machine typically used in the rubber industry, such as a Banbury mixer, a kneader, or a roll.

[0030] The method for compounding the above-mentioned components is not particularly limited, and any of the following may be used: a method in which the compounding components other than the vulcanization compounding agents, such as the sulfur- and nitrogen-atom-containing alkaloid compound, are pre-mixed to form a master batch, and the remaining components are then added and further kneaded; a method in which the components are added in any order and kneaded; or a method in which all the components are added simultaneously and kneaded.

[0031] The vulcanized rubber of the rubber composition according to the present invention has improved vulcanization characteristics (maximum torque) of the rubber composition and improved rubber physical properties such as tensile strength at break when vulcanized, and is therefore particularly useful for pneumatic tires. [Example]

[0032] The present invention will be explained in more detail below by way of examples.

[0033] (Preparation of Rubber Composition for Tires) Rubber compositions for tires were prepared by compounding the rubber compositions of Examples 1 to 9 and Comparative Examples 1 to 5 with 100 parts by mass of the rubber component according to the compounding recipes in Tables 1 to 3 and kneading them using a conventional Banbury mixer. The compounding ingredients listed in Tables 1 to 3 are shown below.

[0034] (Diene rubber) Styrene-butadiene rubber (SBR (ESBR (emulsion-polymerized SBR))): Product name "SBR1502" (manufactured by ENEOS Materials Co., Ltd.) Natural rubber (NR): RSS#3 (sulfur) Product name: "Powdered sulfur" (manufactured by Tsurumi Chemical Industry Co., Ltd.) (Nitrogen atom-containing alkaloid compounds) Gramine (melting point 132°C): (Tokyo Chemical Industry Co., Ltd.) Pseudopelletierine (melting point 46°C): (Tokyo Chemical Industry Co., Ltd.) Hordenine (melting point 118°C): (Tokyo Chemical Industry Co., Ltd.) Tetrahydropalmatine (melting point 150°C): (Tokyo Chemical Industry Co., Ltd.) Caffeine (melting point 238°C): (Tokyo Chemical Industry Co., Ltd.) 3-(3,4-dihydroxyphenyl)-L-alanine (melting point 278°C): (Tokyo Chemical Industry Co., Ltd.) (Other compounding agents) Carbon black: Show Black N330T (manufactured by Cabot Japan) Zinc oxide: Product name "Zinc Oxide No. 3" (manufactured by Mitsui Mining & Smelting Co., Ltd.) Stearic acid: product name "Lunac S-20" (Kao Corporation) Vulcanization accelerator CZ: Product name "Noccela CZ-G" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)

[0035] The rubber compositions of Examples 1 to 9 and Comparative Examples 1 to 5 were vulcanized at 160°C under pressure using a metal plate as a mold to prepare vulcanized rubber samples. The vulcanization time was the 90% vulcanization time (t90) specified in JIS K6300-2 (measurement results for 60 minutes at 160°C).

[0036] <Vulcanization characteristics of rubber composition (maximum torque)> Tests were conducted based on JIS K6300-2. Measurements were conducted at 160°C for 60 minutes, and the maximum torque at that time was determined. For Examples 1 to 7, the value for Comparative Example 1 was expressed as an index of 100, for Example 8, the value for Comparative Example 4 was expressed as an index of 100, and for Example 9, the value for Comparative Example 5 was expressed as an index of 100. A larger value indicates better vulcanization characteristics (maximum torque) of the rubber composition.

[0037] <Tensile test (tensile strength at break when vulcanized rubber)> The test was carried out in accordance with JIS 6251. No. 7 dumbbells were used as test pieces. Examples 1 to 7 are expressed as an index with the value of Comparative Example 1 set to 100, Example 8 is expressed as an index with the value of Comparative Example 4 set to 100, and Example 9 is expressed as an index with the value of Comparative Example 5 set to 100. A larger value indicates better tensile strength at break when vulcanized into rubber.

[0038] [Table 1]

[0039] The compounding system in Table 1 is a system in which 100 parts by mass of styrene-butadiene rubber is compounded as the rubber component. The results in Table 1 show that the rubber compositions of Examples 1 to 7 have excellent vulcanization characteristics (maximum torque) and also have excellent tensile strength at break when made into vulcanized rubber.

[0040] [Table 2]

[0041] The compounding system in Table 2 is a system in which 100 parts by mass of natural rubber is compounded as the rubber component. The results in Table 2 show that the rubber composition of Example 8 has excellent vulcanization characteristics (maximum torque) and also has excellent tensile strength at break when made into vulcanized rubber.

[0042] [Table 3]

[0043] The compounding system in Table 3 is a system in which 50 parts by mass each of styrene-butadiene rubber and natural rubber are compounded as the rubber components. The results in Table 3 show that the rubber composition of Example 9 has excellent vulcanization characteristics (maximum torque) and also has excellent tensile strength at break when made into vulcanized rubber.

Claims

1. A rubber composition comprising a diene rubber, sulfur, and a nitrogen atom-containing alkaloid compound having a melting point of 200°C or less.

2. The rubber composition according to claim 1, wherein the nitrogen atom-containing alkaloid compound has a tertiary amine structure.

3. 2. The rubber composition according to claim 1, wherein a mass ratio (A / B) of a content A of the nitrogen atom-containing alkaloid compound to a content B of the sulfur in the rubber composition is 0.2 to 2.

0.

4. 2. The rubber composition according to claim 1, wherein the nitrogen atom-containing alkaloid compound is at least one selected from the group consisting of gramine, pseudopelletierine, hordenine, and tetrahydropalmatine.

5. A pneumatic tire comprising at least a vulcanized rubber of the rubber composition according to claim 1.

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