JP7803744B2 - Rubber composition and rubber product - Google Patents

Description

The present invention relates to a rubber composition and a rubber product.

Generally, rubber products such as tires, rubber crawlers, and seismic isolation rubber use rubber compositions with excellent fracture resistance (strength). These rubber compositions typically contain diene rubber and sulfur, and the sulfur crosslinks the diene rubber to ensure fracture resistance (strength). Sulfur crosslinking occurs between diene rubbers via monosulfide bonds (-S-), disulfide bonds (-S-S-), or polysulfide bonds (-S-S _x -S-, where x is 1 or greater), and generally provides high strength. However, among sulfur crosslinks, polysulfide bonds have low bond dissociation energy. Therefore, when diene rubber is crosslinked with sulfur, the polysulfide bonds are cleaved by heat, and during the recombination process, the network density of the crosslink increases, hardening the crosslinked rubber and resulting in reduced breaking strength, elongation, and the like.

In response to this, a technology is known that uses organic peroxides instead of sulfur as crosslinking agents (see Patent Document 1 below). When organic peroxides are used as crosslinking agents, diene rubbers can be crosslinked via -C-C- bonds, etc., and because these -C-C- bonds have high bond dissociation energy, they are difficult to cleave even when heat is applied, resulting in high resistance to heat degradation.

JP 2011-225717 A

However, although crosslinking with organic peroxides has excellent resistance to thermal degradation, it has lower fracture resistance (strength) than sulfur crosslinking, and there is room for improvement in fracture resistance.

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.

The gist of the present invention, which solves the above problems, is as follows:

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.

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.

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).

Here, it is preferable that the heterocyclic compound (B) has a triazine ring or a tetrazine ring. Heterocyclic compounds having a triazine ring or a tetrazine ring have higher reactivity with the diene rubber (A) and, in combination with the metal halide salt (C), are more likely to form crosslinks through coordinate bonds.

The heterocyclic compound (B) is a compound represented by the following general formula (1):
[wherein ^X1 and ^X2 each independently represent a pyridyl group or a pyrimidinyl group, and ^Y1 and ^Y2 each independently represent a single bond or a divalent hydrocarbon group.] The compound represented by general formula (1) easily 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).

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. Metal halide salts containing a transition metal and/or zinc are likely to complex with the heterocyclic compound (B).

The rubber composition of the present invention preferably further contains zinc oxide (E). In this case, the mechanical properties and electrical conductivity of the rubber composition are improved, and the rubber composition is less likely to adhere to other surfaces.

The rubber composition of the present invention preferably further contains carbon black (F). In this case, the reinforcing properties of the rubber composition are improved, further improving fracture resistance.

The rubber composition of the present invention preferably further contains silica (G). In this case, the reinforcement properties of the rubber composition are improved, further improving fracture resistance.

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 multiple diene rubbers (A) can be crosslinked simply by complexing multiple heterocyclic compound (B) moieties with the metal halide salt (C) to form coordinate bonds.

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. In this case, the fracture resistance and workability during kneading of the rubber composition are improved.

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. In this case, crosslinking due to coordinate bonds has sufficient strength in the low strain region.

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.

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.

The rubber composition and rubber product of the present invention will be described in detail below, based on examples of the present invention.

<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).

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) portion 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 a crosslink formed by a coordinate bond due to the metal halide salt (C) and a crosslinked structure (e.g., a C-C bond) resulting from the organic peroxide (D) (Dual Cross Link: DCL). Here, the crosslinked structure (e.g., a C-C bond) resulting from the organic peroxide (D) is a crosslink that is resistant to cleavage even when heat is applied and is resistant to thermal morphological changes. On the other hand, crosslinking by coordinate 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 (C-C 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), crosslinks due to coordination bonds are cleaved, resulting in high hysteresis loss, and fracture resistance can be improved due to energy dissipation caused by the cleavage of crosslinks (i.e., sacrificial fracture of 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.

--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).

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 in the crosslinked rubber is usually present in a crosslinked state, 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.

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. 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.
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.

--Heterocyclic compound (B) having a six-membered aromatic heterocycle--
The rubber composition of the present invention includes 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.

Examples of the six-membered aromatic heterocycle include nitrogen-containing aromatic heterocycles such as pyridine rings, pyrimidine rings, pyridazine rings, pyrazine rings, triazine rings, and tetrazine rings, as well as aromatic heterocycles in which the nitrogen in the nitrogen-containing aromatic heterocycles is replaced with phosphorus. Among these, pyridine rings, pyrimidine rings, pyridazine rings, pyrazine rings, triazine rings, and tetrazine rings are preferred. Heterocyclic compounds having a pyridine ring, pyrimidine ring, pyridazine ring, pyrazine ring, triazine ring, or tetrazine ring are highly reactive with diene rubber (A) and readily form crosslinks via coordinate bonds in combination with metal halide salt (C).

Here, the heterocyclic compound (B) preferably has a triazine ring or a tetrazine ring. Heterocyclic compounds having a triazine ring or a tetrazine ring have higher reactivity with the diene rubber (A) and, in combination with the metal halide salt (C), are more likely to form crosslinks through coordinate bonds.

In addition, it is preferable that a pyridyl group or a pyrimidinyl group is 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 are 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. In addition, 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.

The heterocyclic compound (B) is represented by the following general formula (1):
[wherein ^X1 and ^X2 are each independently a pyridyl group or a pyrimidinyl group, and ^Y1 and ^Y2 are each independently a single bond or a divalent hydrocarbon group.] It is more preferable that the compound represented by general formula (1) is easily subjected to a Diels-Alder reaction with the diene rubber (A), and is easily combined with the metal halide salt (C) to form a crosslink through a coordinate bond. Furthermore, the compound represented by general formula (1) and the metal halide salt (C) are particularly easily complexed, and the bond dissociation energy is particularly likely to be high, allowing the formation of a crosslinked structure with even greater strength.

In the general formula (1), ^X1 and ^X2 are each independently a pyridyl group or a pyrimidinyl group. From the viewpoint of ease of synthesis, ^X1 and ^X2 are preferably pyridyl groups. 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. Furthermore, the pyrimidinyl group may be a 2-pyrimidinyl group, a 4-pyrimidinyl group, or a 5-pyrimidinyl group.

In the general formula (1), ^Y1 and ^Y2 are each independently a single bond or a divalent hydrocarbon group. Examples of the divalent hydrocarbon group include alkylene groups, alkenylene groups, and arylene groups. More specifically, examples of the alkylene group include methylene groups, ethylene groups, trimethylene groups, and tetramethylene groups. Examples of the alkenylene group include vinylene groups, propenylene groups, and butenylene groups. Examples of the arylene group include phenylene groups, tolylene groups, and naphthylene groups. From the viewpoint of ease of synthesis, it is preferable that ^Y1 and ^Y2 are single bonds (i.e., it is preferable that ^X1 and ^X2 are directly bonded to the tetrazine ring).

Here, it is preferred that ^X1 and ^X2 in the general formula (1) are pyridyl groups and ^Y1 and ^Y2 are single bonds. 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 have particularly high bond dissociation energy, thereby enabling the formation of a crosslinked structure with even higher strength.

The compounds represented by the above 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, Examples include 3,6-di(2-pyridylmethyl)-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, and 3,6-di(5-pyrimidinyl)-1,2,4,5-tetrazine. Of these, 3,6-di(2-pyridyl)-1,2,4,5-tetrazine is preferred.

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, and even 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), crosslinking by coordinate bonds increases, and in the high strain region, the crosslinking by coordinate bonds cleaves, 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.

The diene rubber (A) is preferably modified with the heterocyclic compound (B). When the diene rubber (A) is modified with the heterocyclic compound (B), multiple heterocyclic compound (B) moieties can crosslink the main chains of multiple diene rubbers (A) simply by complexing 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 rubber composition compounding stage. Alternatively, the diene rubber (A) may be modified with the heterocyclic compound (B) before compounding the rubber composition, and the diene rubber (A) modified with the heterocyclic compound (B) may then be compounded with the metal halide salt (C) or the like at the rubber composition compounding stage to crosslink the main chains of multiple diene rubbers (A).

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 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 diene rubber (A), crosslinks due to coordinate bonds increase, and in the high strain region, the crosslinks due to coordinate bonds cleave. 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 relative to the monomer units in the diene rubber (A), a crosslinked rubber with sufficient elastomeric properties is easily obtained.

--Metal halide salt (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 restored.

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.
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 may be any valence that each element can have, but is preferably divalent or greater.

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), allowing for the formation of a stronger crosslinked structure. The valence of the iron ion is preferably divalent (Fe ²⁺ ) or trivalent (Fe ³⁺ ).

The metal halide salt (C) may be a metal fluoride salt, a metal chloride salt, a metal bromide salt, or a metal iodide salt, with metal chloride salts being preferred. Metal chloride salts are easy to handle and readily 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.

Specific examples of the metal halide salt (C) include FeCl ₂ , _FeCl 2.4H ₂ O, FeCl ₃ , FeCl _{3.6H 2} O, ZnCl ₂ , CuCl, CuCl ₂ , CuBr, etc. The metal halide salt (C) may be used alone or in combination of two or more.

The content of the metal halide salt (C) is preferably in the range of 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 parts by mass or more per 100 parts by mass of the diene rubber (A), crosslinks due to coordinate bonds increase, and in the high strain region, the crosslinks due to coordinate bonds are cleaved. 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.

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. Furthermore, 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 more likely to cleave in the high strain region, and the energy dissipation caused by the cleavage of the crosslinks further improves the fracture resistance of the rubber composition.

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 M06/6-31G(d,p)//B3PW91-D3/6-31G(d,p) level or the M06/6-31G(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 believed that the metal halide salt (C) and the heterocyclic compound (B) form ionic aggregates. Gaussian 09 or GRRM14 can be used to calculate this bond dissociation energy.

For example, crosslinking through 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 to select appropriate kneading conditions, such as temperature and time, depending on the types and reactivities of the diene rubber (A), heterocyclic compound (B), and metal halide salt (C) used.

As an example, the reaction scheme of 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 (ZnCl ₂ ) is used as the metal halide salt (C) is shown below. Note that the structure of the modified diene rubber shown here is one assumed example and is not limited thereto. For example, the modified diene rubber may be an isomer due to tautomerism or an oxidized form.

As shown in the upper part of the reaction scheme above, in one embodiment of the present invention, a modified diene rubber is produced by a Diels-Alder reaction between 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.

Furthermore, 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). Note that 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, but the diene rubber crosslinked by a coordinate bond can take various crosslinking forms.

--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 formed by the metal halide salt (C) and crosslinked structures (C-C bonds, etc.) resulting from the organic peroxide (D) (Dual Cross Link: DCL). The crosslinked structures (C-C bonds, etc.) resulting from the organic peroxide (D) are resistant to cleavage even when heat is applied, and are crosslinks that are resistant to thermal morphological changes, thereby 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 cleavage of the crosslinks due to coordinate bonds improves fracture resistance.

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, 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-butylperoxylaurate, tert-butylperoxy-2-ethylhexanate, 1,1, Examples of organic peroxides (D) include 3,3-tetramethylbutylperoxy-2-ethylhexanoate, tert-hexylperoxy-2-ethylhexanoate, tert-butylperoxy-2-ethylhexanoate, tert-butylperoxyacetate, 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 alone or in combination of two or more.

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, even more preferably 0.5 parts by mass or more, and preferably 30 parts by mass or less, even more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less, per 100 parts by mass of the diene rubber (A). 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.

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 better. 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 in the range of 0.1 to 8, and even more preferably in the range of 0.1 to 6.

--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.

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 the 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 to 50, more preferably 1 to 20.

--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.

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

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 properties of the rubber composition are 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 of the rubber composition during kneading is further improved.

--Silica (G)--
The rubber composition of the present invention preferably further contains silica (G). When the rubber composition contains silica (G), the reinforcement property of the rubber composition is improved, and the fracture resistance is further improved.

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

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.

--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 a range that does not impair the object of the present invention. Commercially available products can be suitably used as these compounding agents.

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), and N,N'-diphenyl-p-phenylenediamine (DPPD). The amount of the antioxidant is not particularly limited, but is preferably in the range of 0.1 to 5 parts by mass, and more preferably 0.5 to 4 parts by mass, per 100 parts by mass of the diene rubber (A).

Examples of the wax include paraffin wax and microcrystalline wax. There are no particular restrictions on the amount of the wax, but it is preferably in the range of 0.1 to 5 parts by mass, and more preferably 1 to 4 parts by mass, per 100 parts by mass of the diene rubber (A).

--Method for producing rubber composition--
The method for producing the rubber composition is not particularly limited. For example, the rubber composition can be produced 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 then kneading, heating, extruding, or the like.

The conditions for the kneading are not particularly limited, and various conditions such as the input volume of the kneading device, rotor rotation speed, ram pressure, kneading temperature, kneading time, and type of kneading device can be selected appropriately depending on the purpose. Examples of kneading devices include Banbury mixers, intermixes, kneaders, rolls, and the like that are typically used to knead rubber compositions.

There are no particular restrictions on the conditions for the heat-in process, and conditions such as the heat-in process temperature, heat-in process time, and heat-in process equipment can be selected appropriately depending on the purpose. Examples of such heat-in process equipment include heat-in rolls typically used for heat-in process of rubber compositions.

There are no particular restrictions on the extrusion conditions, and various conditions such as extrusion time, extrusion speed, extrusion equipment, and extrusion temperature can be selected appropriately depending on the purpose. Examples of extrusion equipment include extruders typically used for extruding rubber compositions. The extrusion temperature can be determined appropriately.

For example, in the first stage of kneading, a diene rubber (A), a heterocyclic compound (B), and various other components selected as needed 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) and an organic peroxide (D), and various other components selected as needed are blended and kneaded to complex the diene rubber (A) modified with the heterocyclic compound (B), forming a crosslinked structure through coordinate bonds while also forming a crosslinked structure (e.g., C-C bonds) due to the organic peroxide (D). This method of producing a rubber composition offers excellent productivity because it can form crosslinked structures through coordinate bonds and crosslinked structures (e.g., C-C bonds) due to the organic peroxide (D) during the production of the rubber composition (kneading of the rubber composition).

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 previously prepared modified diene rubber may be kneaded with optional compounding ingredients in the first stage of kneading. 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 may be blended and kneaded to complex the diene rubber (A) modified with the heterocyclic compound (B), forming a crosslinked structure via coordinate bonds while also forming a crosslinked structure (e.g., C-C bonds) resulting from the organic peroxide (D). This method of producing a rubber composition also allows for the easy formation of a crosslinked structure via coordinate bonds and a crosslinked structure (e.g., C-C bonds) resulting from the organic peroxide (D), and also offers excellent productivity.

<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.

--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 obtain a green tire. The green tire is then heated and vulcanized in a conventional manner to produce a desired tire (e.g., a pneumatic tire).

--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.

--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.

The present invention will be explained in more detail below using examples, but the present invention is not limited to the following examples in any way.

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

(1) Method for measuring 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: HLC-8321GPC/HT manufactured by Tosoh Corporation, column: HT-806M × 2 manufactured by Showa Denko K.K., detector: differential refractometer (RI)) using monodisperse polystyrene as a standard. The measurement temperature is 40°C.

<Production and Evaluation of Rubber Composition>
Using a conventional Banbury mixer, rubber compositions were produced 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.

--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 at 100°C for 48 hours in air. The rate of change before and after heat degradation was calculated as an absolute value from the modulus value at 100% strain of the test piece immediately after preparation and the modulus value at 100% strain of the heat-aged test piece.
The smaller the rate of change before and after thermal degradation, the more excellent the resistance to thermal degradation.

(3) Evaluation method of fracture resistance (strength) The fracture energy obtained from the tensile test 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 of Comparative Example 4 as a control (index value 100). A larger index value indicates a larger fracture energy and better fracture resistance.

--Carbon black-blended 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 the test piece thermally aged at 100°C for 48 hours in air. The rate of change before and after heat degradation was calculated as an absolute value 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.

(5) Evaluation method for fracture resistance (crack resistance) Rectangular test pieces with a hole drilled in the center were prepared from the rubber composition, and the test pieces were subjected to a dc/dn test (measured using a Shimadzu Servo Pulser at a frequency of 5 Hz, 40°C, and at least two stress levels for each formulation using a constant stress test). The crack growth rate was calculated when the common logarithm of the tear energy [J/ ^m2 ] after 2,000 repetitions reached 4.0. The crack growth rate obtained by the above process was normalized by the reciprocal of the formulation data of each example, with the formulation data of Comparative Example 6 set as the control (index value 100). A larger index value indicates a lower crack growth rate and better fracture resistance.

(6) Method for Calculating 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)) is a value calculated in vacuum at the M06/6-31G(d,p)//B3PW91-D3/6-31G(d,p) level or the M06/6-31G(d,p) level, and is a calculated value for a structure in which the heterocyclic compound (B) is bonded to the diene rubber (A). Note that 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 determined under the M06/6-31G(d,p) level of theory, gas phase conditions.

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.

*1 SBR: Styrene-butadiene rubber, manufactured by Asahi Kasei Corporation, trade 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: manufactured by New Japan Chemical Co., Ltd., trade 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, trade 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., trade name "Suncerer CM-G"
*10 Zinc chloride: ZnCl ₂ , manufactured by Tokyo Chemical Industry Co., Ltd. *11 Carbon black: ISAF grade, manufactured by Asahi Carbon Co., Ltd., trade name "Asahi #78"
*12 Vulcanization accelerator 2: Ouchi Shinko Chemical Industry Co., Ltd., product name "Nocceler TOT-N"

Tables 1 and 2 show that the rubber compositions of the examples according to the present invention achieve both heat degradation resistance and fracture resistance.

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

Claims (9)

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):
[wherein X1 ^and X2 ^each independently represent a pyridyl group or a pyrimidinyl group, and Y1 ^and Y2 ^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 . The rubber composition according to claim 1, wherein the mass ratio (D/C) of the organic peroxide (D) to the metal halide salt (C) is 0.1 to 10. The rubber composition according to claim 1 or 2 , wherein the metal halide salt (C) contains zinc. The rubber composition according to any one of claims 1 to 3 , further comprising zinc oxide (E). The rubber composition according to any one of claims 1 to 4 , further comprising carbon black (F). The rubber composition according to any one of claims 1 to 5 , further comprising silica (G). 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. 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. 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 .