Rubber composition and rubber product

Abstract

To provide a rubber composition which achieves both fuel economy and crack propagation resistance.SOLUTION: The rubber composition contains: a diene rubber (A); a heterocyclic compound (B) having at least one heterocyclic ring selected from the group consisting of a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, and a tetrazine ring; and a metal halide salt (C). The rubber composition preferably further contains sulfur (D). The mass ratio (D / C) of the sulfur (D) to the metal halide salt (C) is preferably 0.1-10.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] BACKGROUND ART Conventionally, in order to improve the durability of rubber products such as tires, rubber crawlers, and seismic isolation rubber, rubber compositions having excellent crack propagation resistance have been required.

[0003] Meanwhile, in connection with the recent trend toward global carbon dioxide emission regulations accompanying growing interest in environmental issues, there is an increasing demand for improved fuel efficiency in automobiles. To meet such demands, tire performance is also being sought that requires reduced rolling resistance. In general, by applying a low heat buildup rubber composition to tires, tire rolling resistance can be reduced, thereby achieving improved fuel efficiency in automobiles. Furthermore, by applying a low heat buildup rubber composition to rubber products other than tires, such as rubber crawlers and seismic isolation rubber, hysteresis loss can be reduced, thereby achieving improved fuel efficiency. For example, Patent Documents 1 and 2 listed below disclose rubber compositions containing diene rubber, a filler such as carbon black or silica, and a tetrazine compound. By introducing the tetrazine compound into the main chain of the diene rubber, the dispersibility of the filler is improved, thereby improving the fuel economy of the rubber composition. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-107506 [Patent Document 2] Japanese Patent Application Publication No. 2020-176229 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in general, the fuel economy and crack propagation resistance of a rubber composition are in a trade-off relationship, and although the rubber compositions disclosed in Patent Documents 1 and 2 have improved fuel economy, there is room for improvement in crack propagation resistance.

[0006] Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional technology and to provide a rubber composition that achieves both fuel economy and crack propagation resistance. Another object of the present invention is to provide a rubber product that combines fuel economy and crack growth resistance. [Means for solving the problem]

[0007] The gist and configuration of the present invention to solve the above problems is as follows.

[0008] The rubber composition of the present invention comprises: a diene rubber (A); a heterocyclic compound (B) having at least one heterocycle selected from the group consisting of a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, and a tetrazine ring; a metal halide salt (C); The present invention is characterized by comprising: The rubber composition of the present invention can achieve both fuel economy and crack propagation resistance.

[0009] The rubber composition of the present invention preferably further contains sulfur (D), which further improves the fuel economy and crack propagation resistance of the rubber composition.

[0010] Here, the mass ratio (D / C) of the sulfur (D) to the metal halide salt (C) is preferably 0.1 to 10. In this case, the balance between fuel economy and crack propagation resistance of the rubber composition becomes better.

[0011] In a preferred embodiment of the rubber composition of the present invention, the heterocyclic compound (B) has a triazine ring or a tetrazine ring. The heterocyclic compound having a triazine ring or a tetrazine ring has high reactivity with the main chain of the diene rubber (A) and is likely to form a crosslink by a coordinate bond in combination with the metal halide salt (C).

[0012] Here, the heterocyclic compound (B) is represented by the following general formula (1): [ka] [where, X 1 and X 2 are each independently a pyridyl group or a pyrimidinyl group, and Y 1 and Y 2 are each independently a single bond or a divalent hydrocarbon group. The compound represented by general formula (1) is easily subjected to a Diels-Alder reaction with the main chain of the diene rubber (A), and is easily combined with the metal halide salt (C) to further form crosslinks by coordinate bonds.

[0013] In another preferred embodiment of the rubber composition of the present invention, the metal halide salt (C) contains at least one metal selected from the group consisting of transition metals and zinc. The metal halide salt containing a transition metal and / or zinc is likely to form a complex with the heterocyclic compound (B).

[0014] The rubber composition of the present invention preferably further contains zinc oxide (E), which further improves the fuel economy and crack propagation resistance of the rubber composition.

[0015] The rubber composition of the present invention preferably further contains carbon black (F), which improves the reinforcing properties of the rubber composition and further improves the crack propagation resistance.

[0016] The rubber composition of the present invention preferably further contains silica (G), which improves the reinforcing properties of the rubber composition and further improves the crack propagation resistance.

[0017] The rubber composition of the present invention preferably further contains an organic peroxide (H), which further improves the fuel economy and crack propagation resistance of the rubber composition.

[0018] In another preferred embodiment of the rubber composition of the present invention, the diene rubber (A) is modified with the heterocyclic compound (B). In this case, the main chains of the diene rubbers (A) can be crosslinked simply by complexing the heterocyclic compound (B) moieties with the metal halide salt (C) to form coordinate bonds.

[0019] In the rubber composition of the present invention, the diene rubber (A) preferably has a weight average molecular weight (Mw) of 10,000 to 3,000,000, which improves the fuel economy and workability during kneading of the rubber composition.

[0020] In another preferred embodiment of the rubber composition of the present invention, the bond dissociation energy between the metal halide salt (C) and the heterocyclic compound (B) is 100 kJ / mol or more, which results in sufficient strength in a low strain region and can sufficiently improve the fuel economy of the rubber composition.

[0021] The rubber product of the present invention is a rubber product selected from the group consisting of a tire, a rubber crawler, and a seismic isolation rubber, and is characterized by containing the above-mentioned rubber composition. The rubber product of the present invention can achieve both fuel economy and crack growth resistance. [Effects of the Invention]

[0022] According to the present invention, it is possible to provide a rubber composition that achieves both fuel economy and crack growth resistance. Furthermore, according to the present invention, it is possible to provide a rubber product that achieves both fuel economy and crack growth resistance. DETAILED DESCRIPTION OF THE INVENTION

[0023] The rubber composition and rubber product of the present invention will be described in detail below by way of example based on embodiments thereof.

[0024] <Rubber composition> The rubber composition of the present invention is characterized by comprising a diene rubber (A), a heterocyclic compound (B) having at least one heterocycle selected from the group consisting of a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, and a tetrazine ring, and a metal halide salt (C).

[0025] As described above, in rubber compositions, fuel economy and crack propagation resistance are usually in a trade-off relationship. For example, when sulfur is compounded into a rubber composition to crosslink it and the network density of the sulfur crosslink is reduced, the crack propagation resistance improves but the fuel economy decreases. In order to resolve this trade-off, the present inventors have conducted extensive research and found that it is important to control the strain dependency in the development of hysteresis loss.

[0026] In the rubber composition of the present invention, a heterocyclic compound (B) is added to the main chain of a diene rubber (A). Here, the metal halide salt (C) easily complexes with the heterocyclic compound (B). Therefore, the metal halide salt (C) forms a coordinate bond with the heterocyclic compound (B) added to the main chain of the diene rubber (A) to form a complex. The metal halide salt (C) then forms multiple coordinate bonds, resulting in crosslinking of multiple diene rubbers (A). Here, the crosslinking by the coordinate bond is a reversible crosslink in which bonding (crosslinking) and dissociation (cleavage) are reversible. Furthermore, while the bond is weaker than the sulfur crosslinking in general crosslinked rubbers, the rubber composition has sufficient strength in a low strain range even when strain is applied. In the rubber composition of the present invention, in a low strain region, the network density is maintained high by crosslinking due to coordination bonds, thereby reducing hysteresis loss and improving fuel economy. On the other hand, in a high strain region, the rubber composition of the present invention has crosslinks due to coordination bonds cleaved, resulting in high hysteresis loss, and also has improved crack propagation resistance due to energy dissipation caused by the cleavage of crosslinks (i.e., sacrificial fracture of crosslinks due to coordination bonds). Therefore, the rubber composition of the present invention can achieve high levels of both fuel economy and crack propagation resistance, which cannot be achieved by conventional crosslinking using only sulfur.

[0027] --Diene rubber (A)-- The rubber composition of the present invention contains a diene rubber (A). When the rubber composition contains the diene rubber (A), it becomes possible to form a crosslinked structure together with the heterocyclic compound (B) and the metal halide salt (C).

[0028] The diene rubber (A) is a rubber containing units derived from a diene monomer (diene units), and may further contain units derived from a copolymerizable comonomer. The diene monomer-derived units enable the diene rubber to be crosslinked (vulcanized) and to exhibit rubber-like elongation and strength. While the diene rubber is usually present in a crosslinked state in the crosslinked rubber, some of the diene rubber may be uncrosslinked. Specific examples of diene monomers (diene compounds) include 1,3-butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene. On the other hand, examples of the copolymerizable comonomer include aromatic vinyl compounds, such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, o,p-dimethylstyrene, o-ethylstyrene, m-ethylstyrene, and p-ethylstyrene. Examples of the diene rubber (A) include natural rubber (NR), synthetic isoprene rubber (IR), styrene-butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), etc. These diene rubbers (A) may be used alone or as a blend of two or more.

[0029] In the rubber composition of the present invention, the diene rubber (A) preferably has a weight average molecular weight (Mw) of 10,000 to 3,000,000. When the weight average molecular weight (Mw) of the diene rubber (A) is 10,000 or more, the fuel economy of the rubber composition is improved, and when it is 3,000,000 or less, the workability in kneading the rubber composition is improved. From the viewpoint of the fuel economy of the rubber composition, the weight average molecular weight (Mw) of the diene rubber (A) is more preferably 100,000 or more, and even more preferably 120,000 or more. Furthermore, from the viewpoint of the workability in kneading the rubber composition, it is more preferably 2,000,000 or less, and even more preferably 1,800,000 or less.

[0030] --Heterocyclic Compound (B)-- The rubber composition of the present invention includes a heterocyclic compound (B) having at least one heterocyclic ring selected from the group consisting of a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, and a tetrazine ring. The pyrimidine ring, the pyridazine ring, the pyrazine ring, the triazine ring, and the tetrazine ring each have a plurality of nitrogen atoms in the ring, and can form coordinate bonds with a plurality of metal halide salts (C). Furthermore, the heterocyclic compound (B) can crosslink a plurality of diene rubbers (A) together with the metal halide salts (C). In the present invention, the heterocyclic compound (B) is not used as a dispersant for the filler, but is used as a coordination site for the metal halide salt (C), thereby forming crosslinks through coordinate bonds. As a result, in the low strain region, the network density is maintained high through crosslinks through coordinate bonds, thereby improving fuel efficiency. On the other hand, in the high strain region, energy dissipation due to the cleavage of crosslinks through coordinate bonds improves crack propagation resistance.

[0031] The heterocyclic compound (B) preferably has a triazine ring or a tetrazine ring. Compounds having a triazine ring or a tetrazine ring have high reactivity with the main chain of the diene rubber (A) and are likely to form crosslinks by coordinate bonds in combination with the metal halide salt (C).

[0032] Here, the triazine ring or tetrazine ring of the compound having a triazine ring or tetrazine ring preferably has a pyridyl group or a pyrimidinyl group bonded thereto, and more preferably has two pyridyl groups or two pyrimidinyl groups bonded thereto. When a pyridyl group or a pyrimidinyl group is bonded to the triazine ring or the tetrazine ring, the heterocyclic compound (B) and the metal halide salt (C) are more likely to form a complex, the bond dissociation energy is more likely to be increased, and a crosslinked structure with higher strength can be formed. Furthermore, when two pyridyl groups or two pyrimidinyl groups are bonded to the triazine ring or the tetrazine ring, the heterocyclic compound (B) and the metal halide salt (C) are more likely to form a complex, the bond dissociation energy is more likely to be increased, and a crosslinked structure with higher strength can be formed. The pyridyl group may be a 2-pyridyl group, a 3-pyridyl group, or a 4-pyridyl group, with a 2-pyridyl group being preferred.The pyrimidinyl group may be a 2-pyrimidinyl group, a 4-pyrimidinyl group, or a 5-pyrimidinyl group.

[0033] The heterocyclic compound (B) is represented by the following general formula (1): [ka] [where, X 1 and X 2 are each independently a pyridyl group or a pyrimidinyl group, and Y 1 and Y 2 are each independently a single bond or a divalent hydrocarbon group. The compound represented by general formula (1) is preferably represented by the formula:

[0023] . The compound represented by general formula (1) readily undergoes a Diels-Alder reaction with the main chain of the diene rubber (A), and readily combines with the metal halide salt (C) to form further crosslinks through coordinate bonds. Furthermore, the compound represented by general formula (1) and the metal halide salt (C) are particularly susceptible to complexation, which tends to increase the bond dissociation energy, thereby enabling the formation of a crosslinked structure with even greater strength.

[0034] In the above general formula (1), X 1 and X 2are each independently a pyridyl group or a pyrimidinyl group. From the viewpoint of ease of synthesis, X 1 and X 2 is preferably a pyridyl group. The pyridyl group may be a 2-pyridyl group, a 3-pyridyl group, or a 4-pyridyl group, with a 2-pyridyl group being preferred. The pyrimidinyl group may be a 2-pyrimidinyl group, a 4-pyrimidinyl group, or a 5-pyrimidinyl group.

[0035] In the above general formula (1), Y 1 and Y 2 are each independently a single bond or a divalent hydrocarbon group. Here, examples of the divalent hydrocarbon group include an alkylene group, an alkenylene group, and an arylene group. More specifically, examples of the alkylene group include a methylene group, an ethylene group, a trimethylene group, and a tetramethylene group. Examples of the alkenylene group include a vinylene group, a propenylene group, and a butenylene group. Examples of the arylene group include a phenylene group, a tolylene group, and a naphthylene group. From the viewpoint of ease of synthesis, Y 1 and Y 2 is preferably a single bond (i.e., X is not attached to the tetrazine ring). 1 and X 2 is preferably directly bonded).

[0036] Here, X in the general formula (1) 1 and X 2 is a pyridyl group, and Y 1 and Y 2 is preferably a single bond. In this case, the compound of formula (1) is easily available, and is particularly likely to form a complex with the metal halide salt (C), which tends to increase the bond dissociation energy, thereby enabling the formation of a crosslinked structure with even greater strength.

[0037] The compounds represented by the general formula (1) include 3,6-di(2-pyridyl)-1,2,4,5-tetrazine, 3,6-di(3-pyridyl)-1,2,4,5-tetrazine, 3,6-di(4-pyridyl)-1,2,4,5-tetrazine, 3,6-di(2-pyridylmethyl)-1,2,4,5-tetrazine, 3,6-di(2-pyridylethyl)-1,2,4,5-tetrazine, 3-(2-pyridyl)-1,2,4,5-tetrazine, lysylmethyl)-6-(2-pyridylethyl)-1,2,4,5-tetrazine, 3,6-di(2-pyrimidinyl)-1,2,4,5-tetrazine, 3,6-di(4-pyrimidinyl)-1,2,4,5-tetrazine, 3,6-di(5-pyrimidinyl)-1,2,4,5-tetrazine, and the like. Among these, 3,6-di(2-pyridyl)-1,2,4,5-tetrazine is preferred.

[0038] The content of the heterocyclic compound (B) in the rubber composition is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less, per 100 parts by mass of the diene rubber (A). When the content of the heterocyclic compound (B) is 0.1 parts by mass or more per 100 parts by mass of the diene rubber (A), the network density of the coordinate bond crosslinks is increased, the hysteresis loss in the low strain region is further reduced, and the fuel economy of the rubber composition is improved. Furthermore, when the content of the heterocyclic compound (B) is 10 parts by mass or less per 100 parts by mass of the diene rubber (A), a crosslinked rubber with sufficient elastomeric properties is easily obtained.

[0039] The diene rubber (A) is preferably modified with the heterocyclic compound (B). When the diene rubber (A) is modified with the heterocyclic compound (B), the main chains of the diene rubbers (A) can be crosslinked simply by complexing the heterocyclic compound (B) moieties with the metal halide salt (C) described below to form coordinate bonds. Here, the modification of the diene rubber (A) with the heterocyclic compound (B) may be performed at the compounding stage of the rubber composition. Alternatively, the diene rubber (A) may be modified with the heterocyclic compound (B) in advance prior to compounding the rubber composition, and the diene rubber (A) modified with the heterocyclic compound (B) may be compounded with the metal halide salt (C) or the like at the compounding stage of the rubber composition to crosslink the main chains of the diene rubbers (A).

[0040] When the diene rubber (A) is modified with the heterocyclic compound (B), the heterocyclic compound (B) is preferably bonded in an amount of 0.01 to 10 mol%, more preferably 0.02 to 8 mol%, even more preferably 0.03 to 5 mol%, and particularly preferably 0.03 to 3 mol%, relative to the monomer units in the main chain of the diene rubber (A). When the heterocyclic compound (B) is bonded in an amount of 0.01 mol% or more relative to the monomer units in the main chain of the diene rubber (A), the network density of the coordinate bond crosslinks increases, further reducing hysteresis loss in the low strain region and improving the fuel economy of the rubber composition. Furthermore, when the heterocyclic compound (B) is bonded in an amount of 10 mol% or less relative to the monomer units in the main chain of the diene rubber (A), a crosslinked rubber with sufficient elastomeric properties is easily obtained.

[0041] --Metal halide salts (C)-- The rubber composition of the present invention contains a metal halide salt (C). The metal halide salt (C) is easy to handle and easily forms a bond with the heterocyclic compound (B). The metal halide salt (C) forms coordinate bonds with multiple heterocyclic compounds (B), thereby crosslinking multiple diene rubbers (A). Here, the crosslinking by coordinate bonds is a reversible crosslink in which bonding (crosslinking) and dissociation (cleavage) are reversible, and the bond dissociation energy is relatively low, so that even if the bond is broken by an external stimulus, it can be reversibly regenerated.

[0042] The metal halide salt (C) preferably contains at least one metal selected from the group consisting of transition metals and zinc. A metal halide salt containing a transition metal and / or zinc is likely to form a complex with the heterocyclic compound (B). Examples of transition metals include elements in groups 7 to 11 of the periodic table. Specifically, examples of elements in Group 7 of the periodic table include manganese and rhenium. Examples of elements in Group 8 of the periodic table include iron, ruthenium, and osmium. Furthermore, examples of elements in Group 9 of the periodic table include cobalt, rhodium, and iridium. Examples of elements in Group 10 of the periodic table include nickel, palladium, and platinum. Furthermore, examples of elements in Group 11 of the periodic table include copper. Elements of Groups 7 to 11 of the periodic table tend to bond strongly with the heterocyclic compound (B). Furthermore, when the metal halide salt (C) contains an element of Group 8 of the periodic table, the bond with the heterocyclic compound (B) tends to be even stronger. The valence of the metal ions in the metal halide salt (C) is not particularly limited and can be any valence that each element can have, but is preferably divalent or greater.

[0043] The metal halide salt (C) particularly preferably contains iron, zinc, or copper. Iron ions, zinc ions, and copper ions are likely to form particularly strong bonds with the heterocyclic compound (B), and can form a stronger crosslinked structure. The valence of the iron ion is divalent (Fe 2+) or trivalent (Fe 3+ ) is preferred.

[0044] Examples of the metal halide salt (C) include metal fluorides, metal chlorides, metal bromides, and metal iodides, among which metal chlorides are preferred. Metal chlorides are easy to handle and also easily form bonds with the heterocyclic compound (B). The form of the metal halide salt (C) is not particularly limited, and may be, for example, a hydrate.

[0045] Specific examples of the metal halide salt (C) include FeCl2, FeCl2·4H2O, FeCl3, FeCl3·6H2O, ZnCl2, CuCl, CuCl2, CuBr, etc. The metal halide salt (C) may be a single type or a combination of two or more types.

[0046] The content of the metal halide salt (C) is preferably 0.1 to 30 parts by mass, more preferably 0.1 to 15 parts by mass, even more preferably 0.1 to 10 parts by mass, and particularly preferably 0.1 to 5 parts by mass, per 100 parts by mass of the diene rubber (A). When the content of the metal halide salt (C) is 0.1 part by mass or more per 100 parts by mass of the diene rubber (A), the network density of the coordinate bond crosslinks increases, the hysteresis loss in the low strain region further decreases, and the fuel economy of the rubber composition improves. Furthermore, when the content of the metal halide salt (C) is 30 parts by mass or less per 100 parts by mass of the diene rubber (A), a crosslinked rubber with sufficient elastomeric properties is easily obtained.

[0047] In the rubber composition of the present invention, the bond dissociation energy between the metal halide salt (C) and the heterocyclic compound (B) is preferably 100 kJ / mol or more, more preferably 200 kJ / mol or more, even more preferably 240 kJ / mol or more, and preferably 500 kJ / mol or less. When the bond dissociation energy is 100 kJ / mol or more, sufficient strength is obtained in a low strain region, and the fuel economy of the rubber composition can be sufficiently improved. When the bond dissociation energy is 500 kJ / mol or less, crosslinks formed by coordinate bonds between the metal halide salt (C) and the heterocyclic compound (B) are easily cleaved in a high strain region, and energy dissipation due to the cleavage of the crosslinks can further improve the crack propagation resistance of the rubber composition.

[0048] In the present invention, the bond dissociation energy between the metal halide salt (C) and the heterocyclic compound (B) is a value calculated in vacuum at the MO6 / 6-31G(d,p) / / B3PW91-D3 / 6-31G(d,p) level or the MO6 / 6-31G(d,p) level, and is a calculated value for a structure in which the heterocyclic compound (B) is bonded to the diene rubber (A). It is assumed that the metal halide salt (C) and the heterocyclic compound (B) form ionic aggregates. Gaussian09 or GRRM14 can be used to calculate the bond dissociation energy.

[0049] For example, crosslinking by coordinate bonds can be formed by mixing (kneading) the diene rubber (A), the heterocyclic compound (B), and the metal halide salt (C). Here, it is preferable that the conditions for kneading, such as temperature and time, be appropriately selected depending on the types and reactivities of the diene rubber (A), heterocyclic compound (B), and metal halide salt (C) used.

[0050] As an example, the reaction scheme for the modification of diene rubber (A) and the coordination bond crosslinking (complexation) of the modified diene rubber when 3,6-di(2-pyridyl)-1,2,4,5-tetrazine is used as the heterocyclic compound (B) and iron chloride (FeCl2) is used as the metal halide salt (C) is shown below. Note that the structure of the modified diene rubber shown here is one possible example and is not limited thereto. For example, it may be an isomer due to tautomerism or an oxidized form. [ka]

[0051] As shown in the upper part of the reaction scheme, in one embodiment of the present invention, a modified diene rubber is produced by a Diels-Alder reaction between the main chain of the diene rubber (A) and the heterocyclic compound (B). In this embodiment, nitrogen is eliminated during the Diels-Alder reaction, but any other reaction may be used for the modification reaction.

[0052] As shown in the lower part of the above reaction scheme, in one embodiment of the present invention, the modified diene rubber and the metal halide salt (C) are complexed to produce a diene rubber crosslinked by a coordinate bond (complexed diene rubber). While the above reaction scheme shows a complexation between the nitrogen atom in the tetrazine residue, the nitrogen atom of the pyridyl group bonded to the tetrazine residue, and an iron ion, the diene rubber crosslinked by a coordinate bond can take various crosslinking forms.

[0053] --Sulfur (D)-- The rubber composition of the present invention preferably further contains sulfur (D). When the rubber composition contains sulfur (D) together with the metal halide salt (C), the rubber composition after crosslinking contains both crosslinks due to coordinate bonds of the metal halide salt (C) and sulfur crosslinks (Dual Cross Link: DCL). In a low strain region, the network density is maintained at a high level by both the crosslinks due to coordinate bonds and the sulfur crosslinks, thereby further reducing hysteresis loss and further improving fuel economy. On the other hand, in a high strain region, the strength of the rubber composition (also referred to as a "crosslinked rubber composition" or "crosslinked rubber") is improved and crack propagation resistance is further improved by the presence of sulfur crosslinks in addition to energy dissipation due to cleavage of crosslinks due to coordinate bonds.

[0054] The content of the sulfur (D) in the rubber composition is preferably 0.1 part by mass or more, more preferably 0.3 part by mass or more, and preferably 30 parts by mass or less, more preferably 10 parts by mass or less, per 100 parts by mass of the diene rubber (A). When the content of sulfur (D) is 0.1 part by mass or more per 100 parts by mass of the diene rubber (A), the network density due to the sulfur is improved, and fuel economy is further improved. Furthermore, when the content of sulfur (D) is 30 parts by mass or less per 100 parts by mass of the diene rubber (A), a crosslinked rubber with sufficient elastomeric properties is easily obtained.

[0055] Here, the mass ratio (D / C) of the sulfur (D) to the metal halide salt (C) is preferably 0.1 to 10. When the mass ratio (D / C) of the sulfur (D) to the metal halide salt (C) is within the range of 0.1 to 10, the balance between fuel economy and crack propagation resistance of the rubber composition is improved. From the viewpoint of the balance between fuel economy and crack propagation resistance of the rubber composition, the mass ratio (D / C) of the sulfur (D) to the metal halide salt (C) is more preferably within the range of 0.1 to 8, and even more preferably within the range of 0.1 to 6.

[0056] --Zinc Oxide(E)-- The rubber composition of the present invention preferably further contains zinc oxide (E). When the rubber composition contains zinc oxide (E) together with the metal halide salt (C), the fuel economy and crack propagation resistance of the rubber composition are further improved.

[0057] The content of the zinc oxide (E) in the rubber composition is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, and is preferably 30 parts by mass or less, and more preferably 10 parts by mass or less, per 100 parts by mass of the diene rubber (A). When the content of zinc oxide (E) is in the range of 0.1 part by mass or more and 30 parts by mass or less per 100 parts by mass of the diene rubber (A), the fuel economy and crack propagation resistance of the rubber composition are further improved. The mass ratio (E / C) of zinc oxide (E) to metal halide salt (C) is preferably in the range of 0.1-50, more preferably 1-20.

[0058] --Carbon Black (F)-- The rubber composition of the present invention preferably further contains carbon black (F). When the rubber composition contains carbon black (F), the reinforcing properties of the rubber composition are improved, and the crack propagation resistance is further improved.

[0059] Examples of the carbon black (F) include GPF, FEF, HAF, ISAF, and SAF grade carbon blacks. These carbon blacks (F) may be used alone or in combination of two or more.

[0060] The content of the carbon black (F) in the rubber composition is preferably 2 parts by mass or more, more preferably 5 parts by mass or more, and preferably 100 parts by mass or less, more preferably 90 parts by mass or less, per 100 parts by mass of the diene rubber (A). When the content of the carbon black (F) is 2 parts by mass or more per 100 parts by mass of the diene rubber (A), the reinforcement property of the rubber composition is further improved, and the crack propagation resistance is further improved. Furthermore, when the content of the carbon black (F) is 100 parts by mass or less per 100 parts by mass of the diene rubber (A), the fuel economy of the rubber composition is further improved.

[0061] --Silica (G)-- The rubber composition of the present invention preferably further contains silica (G). When the rubber composition contains silica (G), the reinforcing properties of the rubber composition are improved, and the crack propagation resistance is further improved.

[0062] Examples of the silica (G) include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc. These silicas (G) may be used alone or in combination of two or more.

[0063] The content of the silica (G) in the rubber composition is preferably 2 parts by mass or more, more preferably 5 parts by mass or more, and preferably 100 parts by mass or less, more preferably 90 parts by mass or less, per 100 parts by mass of the diene rubber (A). When the content of silica (G) is 2 parts by mass or more per 100 parts by mass of the diene rubber (A), the reinforcement properties of the rubber composition are further improved, and the crack propagation resistance is further improved. Furthermore, when the content of silica (G) is 100 parts by mass or less per 100 parts by mass of the diene rubber (A), the fuel economy of the rubber composition is further improved. The mass ratio (F / G) of carbon black (F) to silica (G) is preferably in the range of 0.02 to 50, more preferably in the range of 0.05 to 20.

[0064] --Organic peroxide (H)-- The rubber composition of the present invention preferably further contains an organic peroxide (H). When the rubber composition contains the organic peroxide (H) together with the metal halide salt (C), the crosslinked rubber composition contains crosslinks due to coordinate bonds of the metal halide salt (C) and crosslinked structures (e.g., C-C bonds) due to the organic peroxide (H) (dual crosslink: DCL). In the low strain region, the network density is maintained high by both the crosslinks due to coordinate bonds and the crosslinked structures due to the organic peroxide (H), thereby further reducing hysteresis loss and improving fuel economy. Meanwhile, in the high strain region, the crack propagation resistance is further improved by the presence of crosslinked structures due to the organic peroxide (H) in addition to energy dissipation due to the cleavage of crosslinks due to coordinate bonds.

[0065] The organic peroxide (H) is not particularly limited, but examples thereof include tert-butyl hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, cumene hydroperoxide, p-menthane hydroperoxide, diisopropylbenzene hydroperoxide, dicumyl peroxide, di-tert-butyl peroxide, di-tert-hexyl peroxide, diisopropylbenzene hydroperoxide, tert-butylcumyl peroxide, di(2-tert-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, perbenzoic acid, benzoyl peroxide, 1,1-bis(1,1-dimethylethylperoxy)cyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, Examples of peroxyl groups include 1,1-bis(tert-hexylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-hexylperoxy)cyclohexane, 2,2-bis(4,4-di-(tert-butylperoxy)cyclohexyl)propane, n-butyl-4,4-di-(tert-butylperoxy)valerate, tert-butyl peroxylaurate, tert-butylperoxy-2-ethylhexanate, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, tert-hexylperoxy-2-ethylhexanoate, tert-butylperoxy-2-ethylhexanoate, tert-butyl peroxyacetate, cyclohexanone peroxide, acetylacetone peroxide, diisopropyl peroxydicarbonate, and di(4-tert-butylcyclohexyl)peroxydicarbonate. These organic peroxides (H) may be used singly or in combination of two or more.

[0066] The content of the organic peroxide (H) in the rubber composition is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, and preferably 30 parts by mass or less, more preferably 20 parts by mass or less, per 100 parts by mass of the diene rubber (A). When the content of the organic peroxide (H) is 0.1 part by mass or more per 100 parts by mass of the diene rubber (A), the network density of the crosslinked structure resulting from the organic peroxide (H) is improved, further improving fuel economy. Furthermore, when the content of the organic peroxide (H) is 30 parts by mass or less per 100 parts by mass of the diene rubber (A), a crosslinked rubber with sufficient elastomeric properties is easily obtained. The mass ratio (D / H) of the organic peroxide (H) to the sulfur (D) is preferably in the range of 0.003-300, more preferably 0.01-100.

[0067] --others-- In addition to the diene rubber (A), heterocyclic compound (B), metal halide salt (C), sulfur (D), zinc oxide (E), carbon black (F), silica (G), and organic peroxide (H), the rubber composition of the present invention may contain compounding agents commonly used in the rubber industry, such as softeners, stearic acid, wax, antioxidants, silane coupling agents, adhesion inhibitors (fatty acid metal salts), and vulcanization accelerators, which may be appropriately selected and blended within ranges that do not impair the objects of the present invention. Commercially available products can be suitably used as these compounding agents.

[0068] Examples of the vulcanization accelerator include sulfenamide vulcanization accelerators, guanidine vulcanization accelerators, thiazole vulcanization accelerators, thiuram vulcanization accelerators, and dithiocarbamate vulcanization accelerators. Among these, sulfenamide vulcanization accelerators are preferred. These vulcanization accelerators may be used alone or in combination of two or more. The content of the vulcanization accelerator is not particularly limited, and is preferably in the range of 0.1 to 5 parts by mass, more preferably 0.3 to 3 parts by mass, per 100 parts by mass of the diene rubber (A).

[0069] --Method of manufacturing rubber composition-- The method for producing the rubber composition is not particularly limited, but the rubber composition can be produced, for example, by blending various components appropriately selected as necessary with the diene rubber (A), heterocyclic compound (B), and metal halide salt (C) described above, and kneading, heating, extruding, etc.

[0070] The conditions for the kneading are not particularly limited, and various conditions such as the input volume of the kneading device, the rotation speed of the rotor, the ram pressure, the kneading temperature, the kneading time, the type of kneading device, etc. can be appropriately selected depending on the purpose. Examples of the kneading device include a Banbury mixer, an intermix, a kneader, a roll, etc. that are usually used for kneading rubber compositions.

[0071] The conditions for the heat-in are not particularly limited, and various conditions such as the heat-in temperature, heat-in time, and heat-in device can be appropriately selected depending on the purpose. Examples of the heat-in device include a heat-in roll mill typically used for heat-in of rubber compositions.

[0072] The extrusion conditions are not particularly limited, and various conditions such as extrusion time, extrusion speed, extrusion device, and extrusion temperature can be appropriately selected depending on the purpose. Examples of the extrusion device include an extruder typically used for extruding rubber compositions. The extrusion temperature can be appropriately determined.

[0073] For example, in the first stage of kneading, a diene rubber (A), a heterocyclic compound (B), and various other components appropriately selected as necessary are blended and kneaded to form a mixture containing a modified diene rubber in which the heterocyclic compound (B) is bonded to the main chain of the diene rubber (A), and in the second or subsequent stages of kneading, a metal halide salt (C) and various other components appropriately selected as necessary are blended and kneaded to complex the diene rubber (A) modified with the heterocyclic compound (B), thereby forming a crosslinked structure through a coordinate bond. This method for producing a rubber composition is excellent in productivity because the crosslinked structure through a coordinate bond can be formed during the production of the rubber composition (kneading of the rubber composition).

[0074] Alternatively, for example, a modified diene rubber having a heterocyclic compound (B) bonded to the main chain of a diene rubber (A) may be prepared in advance, and the modified diene rubber may be kneaded with optional compounding ingredients in a first stage of kneading. In a second or subsequent stage of kneading, a metal halide salt (C) and various components appropriately selected as necessary may be added and kneaded to complex the diene rubber (A) modified with the heterocyclic compound (B), thereby forming a crosslinked structure through a coordinate bond. This method for producing a rubber composition also allows for the easy formation of a crosslinked structure through a coordinate bond, and is also excellent in productivity.

[0075] Although there have been several reports of crosslinking using compounds containing polar groups, the compounds containing polar groups are generally introduced as monomers during polymer synthesis, and strict kneading conditions are required when crosslinking is to be formed during kneading of the rubber composition. In contrast, the rubber composition of the present invention has the advantage that crosslinking can be easily formed during kneading of the rubber composition, and no special kneading conditions are required.

[0076] <Rubber products> The rubber product of the present invention is a rubber product selected from the group consisting of tires, rubber crawlers, and seismic isolation rubber, and is characterized by containing the above-mentioned rubber composition. The rubber product of the present invention contains the above-mentioned rubber composition and is therefore excellent in fuel economy and crack growth resistance.

[0077] --tire-- When the rubber product of the present invention is a tire, the application portion of the tire to which the rubber composition of the present invention is applied is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include the tread, base tread, sidewall, side reinforcing rubber, and bead filler. The tire can be manufactured by a conventional method. For example, components typically used in tire manufacturing, such as a carcass layer, a belt layer, and a tread layer, each composed of an unvulcanized rubber composition and / or cords, are laminated on a tire-building drum in this order, and the drum is removed to form a green tire. The green tire is then heated and vulcanized in a conventional manner to manufacture a desired tire (e.g., a pneumatic tire).

[0078] --Rubber Tracks-- In one embodiment, when the rubber product of the present invention is a rubber crawler, the rubber crawler comprises steel cords, an intermediate rubber layer covering the steel cords, a core bar disposed on the intermediate rubber layer, and a main rubber layer surrounding the intermediate rubber layer and the core bar, and further has a plurality of lugs on the contact surface side of the main rubber layer. Here, the rubber composition of the present invention may be used in any part of the rubber crawler, but is preferably used in the main rubber layer, particularly the lugs, due to its excellent crack propagation resistance.

[0079] --Seismic isolation rubber-- When the rubber product of the present invention is a seismic isolation rubber, in one embodiment, the seismic isolation rubber comprises a laminate in which soft layers and hard layers are alternately laminated, and a plug press-fitted into a hollow portion formed in the center of the laminate. In one embodiment, the above-described rubber composition of the present invention can be used for at least one of the soft layer and the plug. [Example]

[0080] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0081] <Method for measuring weight average molecular weight (Mw) of diene rubber> The weight average molecular weight was determined by gel permeation chromatography (GPC) measurement under the following conditions, and expressed as a value converted into standard polystyrene. GPC: HLC-8320GPC manufactured by Tosoh Corporation; Column: 2 x TSKgel G4000HXL manufactured by Tosoh Corporation (column temperature 40°C); Mobile phase: tetrahydrofuran (flow rate: 1 ml / min); Detector: differential refractometer (a multi-wavelength detector (detection wavelength: 254 nm) was further connected); Standard material: TSK standard polystyrene manufactured by Tosoh Corporation.

[0082] <Production and Evaluation of Rubber Composition> Rubber compositions were produced using a conventional Banbury mixer according to the compounding recipes shown in Table 1. The resulting rubber compositions were evaluated for fuel economy and crack growth resistance by the following methods. The bond dissociation energy between the compounded metal halide salt (C) and heterocyclic compound (B) was measured by the following method.

[0083] (1) Evaluation method for fuel efficiency Test specimens were prepared from the rubber compositions and subjected to viscoelasticity testing using an ARES-G2 manufactured by TA Instruments under conditions of a frequency of 15 Hz, a shear strain of 3%, and a temperature of 30°C, to measure the loss tangent (tanδ) of the rubber compositions. The evaluation results were normalized by the reciprocal of the compounding data of each example, with the compounding data of Comparative Example 1 set as the control (index value 100). A larger index value indicates a smaller tanδ and better fuel economy.

[0084] (2) Evaluation method for crack propagation resistance A rectangular test piece with a hole in the center was prepared from the rubber composition, and in a dc / dn test using the test piece (measured at a frequency of 5 Hz, 40°C, and at least two stress levels for each compound using a Shimadzu Servo Pulser), the tear energy [J / m] after 1,950 repetitions was measured. 2 The crack growth rate was calculated when the common logarithm of [(log(√{square root over ( ...

[0085] (3) Calculation method of bond dissociation energy The bond dissociation energy between the metal halide salt (C) (specifically, the metal ion of the metal halide salt (C)) and the heterocyclic compound (B) (specifically, the functional group of the heterocyclic compound (B)) was calculated in vacuum at the MO6 / 6-31G(d,p) / / B3PW91-D3 / 6-31G(d,p) level or the MO6 / 6-31G(d,p) level, assuming a structure in which the heterocyclic compound (B) is bonded to the diene rubber (A). The metal ion and the functional group are considered to form ionic aggregates. Gaussian09 or GRRM14 can be used to calculate the bond dissociation energy. Here, the dissociation energy of the coordinate bond between the central metal and the tetrazine derivative was calculated under the MO6 / 6-31G(d,p) level of theory, gas phase conditions.

[0086] For the rubber compositions produced in Examples 1 to 9, the bond dissociation energy between the metal halide salt (C) [FeCl2·4H2O] and the heterocyclic compound (B) [3,6-di(2-pyridyl)-1,2,4,5-tetrazine] is 412.6 kJ / mol. Furthermore, for the rubber composition produced in Example 10, the bond dissociation energy between the metal halide salt (C) [ZnCl2] and the heterocyclic compound (B) [3,6-di(2-pyridyl)-1,2,4,5-tetrazine] is 172.0 kJ / mol.

[0087] [Table 1]

[0088] *1 SBR: Styrene-butadiene rubber with a bound styrene content of 10%, a 1,2 vinyl bond content of 42%, and a weight average molecular weight (Mw) of 386,982. *2 Carbon black: ISAF grade, manufactured by Asahi Carbon Co., Ltd., product name "Asahi #78" *3 Heterocyclic compound: 3,6-di(2-pyridyl)-1,2,4,5-tetrazine, manufactured by Tokyo Chemical Industry Co., Ltd. *4 Anti-adhesion agent: fatty acid metal salt *5 Sulfur: Hosoi Chemical Industry Co., Ltd., product name "HK200-5" *6 Vulcanization accelerator: The total amount of Sanshin Chemical Industry Co., Ltd.'s "Suncerer DM-TG" and "Suncerer NS-G." In all comparative examples and examples except for Examples 7 and 8, each component is blended in the same ratio. *7 Zinc oxide: Hakusui Tech Co., Ltd., "Zinc oxide type 2" *8 Iron chloride: FeCl2·4H2O, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. *9 Zinc chloride: ZnCl2, manufactured by Tokyo Chemical Industry Co., Ltd. *10 Other: The total amount of stearic acid, wax, and antioxidant 6PPD. The same amount of each ingredient is used in all comparative examples and examples.

[0089] It can be seen from Table 1 that the rubber compositions of the examples according to the present invention are able to achieve both fuel economy and crack growth resistance. [Industrial Applicability]

[0090] The rubber composition of the present invention can be used for rubber products such as tires, rubber crawlers, and seismic isolation rubber.

Claims

1. a diene rubber (A); a heterocyclic compound (B) having a triazine ring or a tetrazine ring; a metal halide salt (C); Including, the diene rubber (A) is modified with the heterocyclic compound (B), A rubber composition, characterized in that the metal halide salt (C) contains iron, zinc or copper.

2. The rubber composition according to claim 1, further comprising sulfur (D).

3. The rubber composition according to claim 2, wherein a mass ratio (D / C) of the sulfur (D) to the metal halide salt (C) is 0.1 to 10.

4. The heterocyclic compound (B) is represented by the following general formula (1): 【Chemistry 1】 [In the formula, X １ and X ２ are each independently a pyridyl group or a pyrimidinyl group, and Y １ and Y ２ and each independently represents a single bond or a divalent hydrocarbon group.

5. The rubber composition according to any one of claims 1 to 4, wherein the metal halide salt (C) contains zinc.

6. The rubber composition according to any one of claims 1 to 5, further comprising zinc oxide (E).

7. The rubber composition according to any one of claims 1 to 6, further comprising carbon black (F).

8. The rubber composition according to any one of claims 1 to 7, further comprising silica (G).

9. The rubber composition according to any one of claims 1 to 8, further comprising an organic peroxide (H).

10. The rubber composition according to any one of claims 1 to 9, wherein the diene rubber (A) has a weight average molecular weight (Mw) of 10,000 to 3,000,000.

11. The rubber composition according to any one of claims 1 to 10, wherein a bond dissociation energy between the metal halide salt (C) and the heterocyclic compound (B) is 100 kJ / mol or more.

12. A rubber product selected from the group consisting of a tire, a rubber crawler, and a seismic isolation rubber, A rubber product comprising the rubber composition according to any one of claims 1 to 11.

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