Rubber composition and rubber product

Abstract

To provide a rubber composition which achieves both thermal deterioration resistance and fracture resistance.SOLUTION: The rubber composition contains a diene rubber (A), a heterocyclic compound (B) having a six-membered aromatic heterocyclic ring, a metal halide salt (C), and an organic peroxide (D). The mass ratio (D / C) of the organic peroxide (D) to the metal halide salt (C) is preferably 0.1-10. The heterocyclic compound (B) preferably has at least one heterocyclic ring selected from the group consisting of a pyridine ring, a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, and a tetrazine ring.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Generally, rubber compositions with excellent fracture resistance (strength) are used in rubber products such as tires, rubber crawlers, and seismic isolation rubber. Such rubber compositions usually contain diene rubber and sulfur, and the sulfur crosslinks the diene rubber to ensure fracture resistance (strength). Here, sulfur crosslinking occurs between the diene rubbers through monosulfide bonds (-S-), disulfide bonds (-SS-), and polysulfide bonds (-SS-). x -S-, where x is 1 or more), and generally has high strength. However, among sulfur crosslinks, polysulfide bonds have low bond dissociation energy, so when diene rubber is crosslinked with sulfur, the polysulfide bonds are cleaved by heat, and in the process of recombination, the network density of the crosslink increases, hardening the crosslinked rubber and reducing the breaking strength, elongation, etc.

[0003] In response to this, a technology is known in which an organic peroxide is used as a crosslinking agent instead of sulfur (see Patent Document 1 below). When an organic peroxide is used as a crosslinking agent, diene rubbers can be crosslinked via -CC- bonds, etc., and since the -CC- bonds have large bond dissociation energy, they are difficult to cleave even when heat is applied, resulting in high resistance to heat degradation. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-225717 Summary of the Invention [Problem to be solved by the invention]

[0005] However, although crosslinking with organic peroxides is excellent in heat deterioration resistance, it has lower fracture resistance (strength) than sulfur crosslinking, and there is room for improvement in fracture 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 has both heat degradation resistance and fracture resistance. Another object of the present invention is to provide a rubber product that has both heat degradation resistance and fracture 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 a six-membered aromatic heterocycle; a metal halide salt (C); an organic peroxide (D); The present invention is characterized by comprising: The rubber composition of the present invention can achieve both heat degradation resistance and fracture resistance.

[0009] In a preferred embodiment of the rubber composition of the present invention, the mass ratio (D / C) of the organic peroxide (D) to the metal halide salt (C) is 0.1 to 10. In this case, the rubber composition has a better balance between heat degradation resistance and fracture resistance.

[0010] In another preferred embodiment of the rubber composition of the present invention, the heterocyclic compound (B) has at least one heterocyclic ring selected from the group consisting of a pyridine ring, a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, and a tetrazine ring. Heterocyclic compounds having a pyridine ring, a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, or a tetrazine ring have high reactivity with the diene rubber (A) and are likely to form crosslinks by coordinate bonds in combination with the metal halide salt (C).

[0011] Here, the heterocyclic compound (B) preferably has a triazine ring or a tetrazine ring. A heterocyclic compound having a triazine ring or a tetrazine ring has higher reactivity with the diene rubber (A) and is more likely to form a crosslink by a coordinate bond in combination with the metal halide salt (C).

[0012] 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 more preferably represented by the following formula: The compound represented by general formula (1) readily undergoes a Diels-Alder reaction with the diene rubber (A), and is more likely to form crosslinks by coordinate bonds in combination with the metal halide salt (C).

[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 improves the mechanical properties and electrical conductivity of the rubber composition and also makes the rubber composition less susceptible to adhesion.

[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 fracture 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 fracture resistance.

[0017] 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.

[0018] 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 fracture resistance and workability during kneading of the rubber composition.

[0019] 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, and in this case, crosslinking by coordinate bonds has sufficient strength in a low strain region.

[0020] 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 heat degradation resistance and fracture resistance. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide a rubber composition that has both heat degradation resistance and fracture resistance. Furthermore, according to the present invention, it is possible to provide a rubber product that has both heat degradation resistance and fracture resistance. DETAILED DESCRIPTION OF THE INVENTION

[0022] The rubber composition and rubber product of the present invention will be described in detail below by way of example based on embodiments thereof.

[0023] <Rubber composition> The rubber composition of the present invention is characterized by comprising a diene rubber (A), a heterocyclic compound (B) having a six-membered aromatic heterocycle, a metal halide salt (C), and an organic peroxide (D).

[0024] 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). Furthermore, since the rubber composition of the present invention contains an organic peroxide (D) along with the metal halide salt (C), the crosslinked rubber composition contains both crosslinks due to coordinate bonds formed by the metal halide salt (C) and crosslinked structures (e.g., C-C bonds) resulting from the organic peroxide (D) (dual crosslink: DCL). Here, the crosslinked structures (e.g., C-C bonds) resulting from the organic peroxide (D) are resistant to cleavage and thermal deformation even when heat is applied. On the other hand, crosslinking by coordination bonds is a reversible crosslinking in which bonding (crosslinking) and dissociation (cleavage) are reversible. The rubber composition of the present invention can improve heat degradation resistance due to the crosslinked structure (CC bond, etc.) resulting from the organic peroxide (D). On the other hand, when the rubber composition of the present invention is subjected to strain (particularly in a high strain region), the crosslinks due to coordination bonds are cleaved, resulting in high hysteresis loss, and the fracture resistance can be improved due to energy dissipation caused by the cleavage of the crosslinks (i.e., sacrificial fracture of the crosslinks due to coordination bonds), thereby achieving fracture resistance (strength) equal to or greater than that of conventional sulfur crosslinks. Therefore, the rubber composition of the present invention can achieve both heat degradation resistance and fracture resistance, which cannot be achieved by conventional crosslinking using only sulfur or by using only a crosslinked structure resulting from an organic peroxide.

[0025] --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).

[0026] 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.

[0027] 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 fracture resistance 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 fracture resistance 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. 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. In this specification, the weight average molecular weight (Mw) of the diene rubber (A) is determined by gel permeation chromatography (GPC) using polystyrene as a standard substance.

[0028] --Heterocyclic compound (B) having a six-membered aromatic heterocycle-- The rubber composition of the present invention contains a heterocyclic compound (B) having a six-membered aromatic heterocycle. The six-membered aromatic heterocycle has a heteroatom in the ring and can form a coordinate bond with a metal halide salt (C). Furthermore, the heterocyclic compound (B) having a six-membered aromatic heterocycle can crosslink multiple diene rubbers (A) together with the metal halide salt (C). Here, examples of the heteroatom in the six-membered aromatic heterocycle include a nitrogen atom and a phosphorus atom.

[0029] Examples of the six-membered aromatic heterocycle include nitrogen-containing aromatic heterocycles such as pyridine ring, pyrimidine ring, pyridazine ring, pyrazine ring, triazine ring, and tetrazine ring, and aromatic heterocycles in which the nitrogen in the nitrogen-containing aromatic heterocycle is replaced with phosphorus. Among these, pyridine ring, pyrimidine ring, pyridazine ring, pyrazine ring, triazine ring, and tetrazine ring are preferred. Heterocyclic compounds having a pyridine ring, pyrimidine ring, pyridazine ring, pyrazine ring, triazine ring, or tetrazine ring have high reactivity with the diene rubber (A) and are easily combined with the metal halide salt (C) to form crosslinks by coordinate bonds.

[0030] Here, the heterocyclic compound (B) preferably has a triazine ring or a tetrazine ring. A heterocyclic compound having a triazine ring or a tetrazine ring has higher reactivity with the diene rubber (A) and is more likely to form a crosslink by a coordinate bond in combination with the metal halide salt (C).

[0031] Furthermore, it is preferable that a pyridyl group or a pyrimidinyl group be bonded to the triazine ring or the tetrazine ring of the compound having a triazine ring or a tetrazine ring, and it is even more preferable that two pyridyl groups or two pyrimidinyl groups be bonded. 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 easily complexed, the bond dissociation energy is more easily 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 easily complexed, the bond dissociation energy is more easily 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.

[0032] 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 2are each independently a single bond or a divalent hydrocarbon group. It is more preferable that the compound represented by general formula (1) is represented by the following formula: The compound represented by general formula (1) easily undergoes a Diels-Alder reaction with the diene rubber (A) and, in combination with the metal halide salt (C), easily forms a crosslink through a coordinate bond. Furthermore, the compound represented by general formula (1) and the metal halide salt (C) are particularly likely to form a complex, which tends to increase the bond dissociation energy, thereby forming a crosslinked structure with even greater strength.

[0033] In the above general formula (1), X 1 and X 2 are 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.

[0034] 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).

[0035] Here, X in the general formula (1) 1 and X 2 is a pyridyl group, and Y 1 and Y 2is 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.

[0036] 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.

[0037] 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), crosslinks due to coordinate bonds increase, and in a high strain region, the crosslinks due to coordinate bonds are cleaved, and energy dissipation due to sacrificial fracture further improves the fracture resistance of the rubber composition. 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.

[0038] 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).

[0039] 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%, based on the monomer units in the diene rubber (A). When the heterocyclic compound (B) is bonded in an amount of 0.01 mol% or more based on the monomer units in the diene rubber (A), crosslinks due to coordinate bonds increase, and in the high strain region, the crosslinks due to coordinate bonds are cleaved, and energy dissipation due to sacrificial fracture further improves the fracture resistance of the rubber composition. Furthermore, when the heterocyclic compound (B) is bonded in an amount of 10 mol% or less based on the monomer units in the diene rubber (A), a crosslinked rubber with sufficient elastomeric properties is easily obtained.

[0040] --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.

[0041] 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. The elements of Groups 7 to 11 of the periodic table and zinc tend to bond strongly with the heterocyclic compound (B). When the metal halide salt (C) contains an element of Groups 8 or 11 of the periodic table or zinc, 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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), crosslinks due to coordinate bonds increase, and in a high strain region, the crosslinks due to coordinate bonds are cleaved, and energy dissipation due to sacrificial fracture further improves the fracture resistance of the rubber composition. 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.

[0046] 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, the crosslinks formed by the coordinate bonds have sufficient strength in the low strain region. When the bond dissociation energy is 500 kJ / mol or less, the crosslinks formed by the coordinate bonds between the metal halide salt (C) and the heterocyclic compound (B) are easily cleaved in the high strain region, and the energy dissipation due to the cleavage of the crosslinks further improves the fracture resistance of the rubber composition.

[0047] 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.

[0048] 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.

[0049] 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 zinc chloride (ZnCl2) 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]

[0050] As shown in the upper part of the reaction scheme, in one embodiment of the present invention, a modified diene rubber is produced by the Diels-Alder reaction of a diene rubber (A) and a 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.

[0051] 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 a zinc ion, the diene rubber crosslinked by a coordinate bond can take various crosslinking forms.

[0052] --Organic peroxide (D)-- The rubber composition of the present invention contains an organic peroxide (D). By including the organic peroxide (D) in the rubber composition 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 (D) (dual crosslink: DCL). The crosslinked structures (e.g., C-C bonds) due to the organic peroxide (D) are resistant to cleavage even when heat is applied and are resistant to thermal morphological changes, contributing to improved heat degradation resistance of the rubber composition. Meanwhile, when strain is applied (particularly in the high strain region), energy dissipation due to the cleavage of the crosslinks due to coordinate bonds improves fracture resistance.

[0053] The organic peroxide (D) 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. Among these, dicumyl peroxide (DCP) is preferred as the organic peroxide (D). These organic peroxides (D) may be used singly or in combination of two or more.

[0054] The content of the organic peroxide (D) in the rubber composition is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, per 100 parts by mass of the diene rubber (A), and is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less. When the content of the organic peroxide (D) is 0.1 parts 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 (D) is improved, and heat degradation resistance is further improved. Furthermore, when the content of the organic peroxide (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 organic peroxide (D) to the metal halide salt (C) is 0.1 to 10. When the mass ratio (D / C) of the organic peroxide (D) to the metal halide salt (C) is within the range of 0.1 to 10, the balance between the heat degradation resistance and the fracture resistance of the rubber composition is improved. From the viewpoint of the balance between the heat degradation resistance and the fracture resistance of the rubber composition, the mass ratio (D / C) of the organic peroxide (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), the mechanical properties of the rubber composition are improved. Furthermore, when the rubber composition contains zinc oxide (E), the conductivity of the rubber composition is improved, and static electricity is less likely to accumulate during the production process of the rubber composition. Furthermore, when the rubber composition contains zinc oxide (E), the rubber composition is less likely to adhere to other materials.

[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 mechanical properties and electrical conductivity of the rubber composition are further improved, and the rubber composition becomes even less likely to adhere to other surfaces. 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 fracture 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 carbon black (F) is 2 parts by mass or more per 100 parts by mass of the diene rubber (A), the reinforcement of the rubber composition is further improved, and the fracture resistance is further improved. Furthermore, when the content of carbon black (F) is 100 parts by mass or less per 100 parts by mass of the diene rubber (A), the workability in kneading 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 fracture 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 of the rubber composition is further improved, and the fracture 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 workability in kneading 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] --others-- In addition to the diene rubber (A), heterocyclic compound (B), metal halide salt (C), organic peroxide (D), zinc oxide (E), carbon black (F), and silica (G), the rubber composition of the present invention may contain compounding agents commonly used in the rubber industry, such as softeners, stearic acid, antioxidants, waxes, silane coupling agents, and vulcanization accelerators, which may be appropriately selected and compounded within ranges that do not impair the objects of the present invention. Commercially available products can be suitably used as these compounding agents.

[0065] Examples of the antioxidant include N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), 2,2,4-trimethyl-1,2-dihydroquinoline polymer (TMDQ), 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline (AW), N,N'-diphenyl-p-phenylenediamine (DPPD), etc. The content of the antioxidant is not particularly limited, and is preferably in the range of 0.1 to 5 parts by mass, more preferably 0.5 to 4 parts by mass, per 100 parts by mass of the diene rubber (A).

[0066] Examples of the wax include paraffin wax, microcrystalline wax, etc. The content of the wax is not particularly limited, but is preferably in the range of 0.1 to 5 parts by mass, more preferably 1 to 4 parts by mass, per 100 parts by mass of the diene rubber (A).

[0067] --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 the diene rubber (A), heterocyclic compound (B), metal halide salt (C), and organic peroxide (D) described above with various components appropriately selected as necessary, and kneading, heating, extruding, etc.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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 diene rubber (A). In the second or subsequent stages of kneading, a metal halide salt (C), an organic peroxide (D), and various other components appropriately selected as necessary are blended and kneaded to complex the diene rubber (A) modified with the heterocyclic compound (B), forming a crosslinked structure due to a coordinate bond while also forming a crosslinked structure (e.g., a C-C bond) due to the organic peroxide (D). This method for producing a rubber composition is excellent in productivity because it can form a crosslinked structure due to a coordinate bond and a crosslinked structure (e.g., a C-C bond) due to the organic peroxide (D) during the production of the rubber composition (kneading of the rubber composition).

[0072] Alternatively, for example, a modified diene rubber in which a heterocyclic compound (B) is bonded to 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), an organic peroxide (D), and various other components appropriately selected as necessary may be blended and kneaded to complex the diene rubber (A) modified with the heterocyclic compound (B), forming a crosslinked structure due to a coordinate bond while also forming a crosslinked structure (such as a C-C bond) due to the organic peroxide (D). This method for producing a rubber composition also makes it possible to easily form a crosslinked structure due to a coordinate bond and a crosslinked structure (such as a C-C bond) due to the organic peroxide (D), and also provides excellent productivity.

[0073] <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 therefore has excellent heat degradation resistance and fracture resistance.

[0074] --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).

[0075] --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.

[0076] --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]

[0077] 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.

[0078] <Analysis of Diene Rubber> The weight average molecular weight (Mw) of the diene rubber is measured by the following method.

[0079] (1) Measurement method of weight average molecular weight (Mw) The weight average molecular weight (Mw) of the diene rubber in terms of polystyrene is determined by gel permeation chromatography (GPC: Tosoh HLC-8321GPC / HT, columns: Showa Denko HT-806M × 2, detector: differential refractometer (RI)) using monodisperse polystyrene as a standard. The measurement temperature is 40°C.

[0080] <Production and Evaluation of Rubber Composition> Rubber compositions were produced using a conventional Banbury mixer according to the compounding recipes shown in Tables 1 and 2. The heat degradation resistance and fracture resistance of the resulting rubber compositions were evaluated 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.

[0081] --Rubber Compositions Without Carbon Black (Examples 1 to 3 and Comparative Examples 1 to 4)-- (2) Evaluation method for heat degradation resistance (modulus change rate after heat degradation) For Examples 1 to 3 and Comparative Examples 1 to 4, ring-shaped test pieces were prepared from the rubber compositions, and tensile tests (measured using a universal tensile machine manufactured by Tensilon Corporation at a tensile speed of 300 mm / min) were performed on the test pieces immediately after preparation and on test pieces thermally aged in air at 100°C for 48 hours. The absolute value of the change in modulus before and after thermal aging was calculated from the modulus value at 100% strain of the test piece immediately after preparation and the modulus value at 100% strain of the thermally aged test piece. The smaller the rate of change before and after thermal degradation, the more excellent the resistance to thermal degradation.

[0082] (3) Evaluation method for fracture resistance (strength) The fracture energy obtained from the tensile tests for Examples 1 to 3 and Comparative Examples 1 to 4 (measured using a universal tensile machine manufactured by Tensilon Corporation at a tensile speed of 300 mm / min) was normalized by setting the compounding data for Comparative Example 4 as a control (index value 100). A larger index value indicates a larger fracture energy and better fracture resistance.

[0083] --Carbon Black-Compound Rubber Composition (Example 4 and Comparative Examples 5 to 8)-- (4) Evaluation method for heat degradation resistance (modulus change rate after heat degradation) For Example 4, ring-shaped test pieces were prepared from the rubber composition, and a tensile test (measured using a universal tensile machine manufactured by Tensilon Corporation at a tensile speed of 300 mm / min) was performed on the test piece immediately after preparation and on a test piece thermally aged in air at 100°C for 48 hours. The absolute value of the rate of change before and after thermal aging was calculated from the modulus value at 300% strain of the test piece immediately after preparation and the modulus value at 300% strain of the thermally aged test piece. For Comparative Examples 5 to 8, JIS No. 7 test pieces were prepared from the rubber compositions, and tensile tests (measured using a universal tensile tester manufactured by Instron at a tensile speed of 200 mm / min) were performed on the test pieces immediately after preparation and on test pieces thermally aged in air at 100°C for 48 hours. The absolute value of the rate of change before and after thermal aging was calculated from the modulus value at 300% strain of the test piece immediately after preparation and the modulus value at 300% strain of the thermally aged test piece. Although the test machine, the shape of the test specimen, and some of the measurement conditions are different between the examples and the comparative examples, the results of the modulus change rate before and after thermal degradation are reproducible. The smaller the rate of change before and after thermal degradation, the more excellent the resistance to thermal degradation.

[0084] (5) Evaluation method for fracture resistance (crack 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 2000 repetitions was measured. 2 The crack growth rate was calculated when the common logarithm of [(log(√{square root over ( ...

[0085] (6) 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 4, the bond dissociation energy between the metal halide salt (C) [zinc chloride] and the heterocyclic compound (B) [3,6-di(2-pyridyl)-1,2,4,5-tetrazine] is 172.0 kJ / mol.

[0087] [Table 1]

[0088] [Table 2]

[0089] *1 SBR: Styrene-butadiene rubber, manufactured by Asahi Kasei Corporation, product name "Tufden 2000R", weight average molecular weight (Mw) = 363,046 *2 Heterocyclic compound: 3,6-di(2-pyridyl)-1,2,4,5-tetrazine, manufactured by Tokyo Chemical Industry Co., Ltd. *3 Stearic acid: New Japan Chemical Co., Ltd., product name "Stearic Acid 50s" *4 Antioxidant: Antioxidant 6PPD, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine, manufactured by Sumitomo Chemical Co., Ltd., trade name "Antigen 6C" *5 Wax: Seiko Chemical Co., Ltd., product name "Suntite" *6 Sulfur: Hosoi Chemical Industry Co., Ltd., product name "HK200-5" *7 Organic peroxide: Dicumyl peroxide (DCP), manufactured by NOF Corporation, product name "Percumyl D *8 Zinc oxide: Zinc oxide, manufactured by Hakusui Tech, "Zinc oxide type 2" *9 Vulcanization accelerator 1: Sanshin Chemical Industry Co., Ltd., product name "Suncerer CM-G" *10 Zinc chloride: ZnCl2, manufactured by Tokyo Chemical Industry Co., Ltd. *11 Carbon black: ISAF grade, manufactured by Asahi Carbon Co., Ltd., product name "Asahi #78" *12 Vulcanization accelerator 2: Ouchi Shinko Chemical Industry Co., Ltd., product name "Noccela TOT-N"

[0090] It can be seen from Tables 1 and 2 that the rubber compositions of the examples according to the present invention are able to achieve both heat degradation resistance and fracture resistance. [Industrial Applicability]

[0091] 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 six-membered aromatic heterocycle; a metal halide salt (C); an organic peroxide (D); Including, the diene rubber (A) is modified with the heterocyclic compound (B), The heterocyclic compound (B) is represented by the following general formula (1): 【Chemistry 1】 [wherein X 1 and X 2 each independently represent a pyridyl group or a pyrimidinyl group, and Y 1 and Y 2 each independently represent a single bond or a divalent hydrocarbon group], A rubber composition, characterized in that the metal halide salt (C) contains iron, zinc or copper.

2. 2. The rubber composition according to claim 1, wherein a mass ratio (D / C) of the organic peroxide (D) to the metal halide salt (C) is 0.1 to 10.

3. The rubber composition according to claim 1 or 2, wherein the metal halide salt (C) contains zinc.

4. The rubber composition according to any one of claims 1 to 3, further comprising zinc oxide (E).

5. The rubber composition according to any one of claims 1 to 4, further comprising carbon black (F).

6. The rubber composition according to any one of claims 1 to 5, further comprising silica (G).

7. The rubber composition according to any one of claims 1 to 6, wherein the diene rubber (A) has a weight average molecular weight (Mw) of 10,000 to 3,000,000.

8. The rubber composition according to any one of claims 1 to 7, wherein a bond dissociation energy between the metal halide salt (C) and the heterocyclic compound (B) is 100 kJ / mol or more.

9. 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 8.

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