JP2023126042A - Rubber composition and rubber product - Google Patents

Abstract

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

Description

TECHNICAL FIELD The present invention relates to rubber compositions and rubber products.

Conventionally, in order to improve the durability of rubber products such as tires, rubber crawlers, and seismic isolation rubber, there has been a demand for rubber compositions with excellent crack growth resistance.

On the other hand, in conjunction with the recent movement toward carbon dioxide emission regulations around the world as a result of increased interest in environmental issues, there is an increasing demand for lower fuel efficiency in automobiles. In order to meet these demands, there is a need to reduce rolling resistance in terms of tire performance.Generally, by applying a low heat generation rubber composition to tires, the rolling resistance of tires can be reduced. It is possible to achieve lower fuel consumption in automobiles. Furthermore, by applying a low heat generation rubber composition to rubber products other than tires, such as rubber crawlers and seismic isolation rubber, hysteresis loss can be reduced and fuel efficiency can be achieved.
For example, Patent Documents 1 and 2 listed below disclose rubber compositions containing a diene rubber, a filler such as carbon black or silica, and a tetrazine compound. By introducing the filler into the filler and improving the dispersibility of the filler, the fuel efficiency of the rubber composition is improved.

JP 2021-107506 Publication Japanese Patent Application Publication No. 2020-176229

However, in general, there is an antinomic relationship between the fuel efficiency and crack growth resistance of a rubber composition, and the rubber compositions disclosed in Patent Documents 1 and 2 have improved fuel economy, but crack growth resistance. There is room for improvement in gender.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the problems of the prior art described above and to provide a rubber composition that has both low fuel consumption and crack growth resistance.
A further object of the present invention is to provide a rubber product that is both fuel efficient and crack growth resistant.

The gist of the present invention for solving the above problems is as follows.

The rubber composition of the present invention is
diene rubber (A);
A heterocyclic compound (B) having at least one heterocycle selected from the group consisting of a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, and a tetrazine ring;
a metal halide salt (C),
It is characterized by including.
The rubber composition of the present invention can achieve both fuel efficiency and crack growth resistance.

It is preferable that the rubber composition of the present invention further contains sulfur (D). In this case, the fuel efficiency and crack growth resistance of the rubber composition are further improved.

Here, the mass ratio (D/C) of the sulfur (D) and the metal halide salt (C) is preferably 0.1 to 10. In this case, the rubber composition has a better balance between fuel efficiency and crack growth resistance.

In a preferred example of the rubber composition of the present invention, the heterocyclic compound (B) has a triazine ring or a tetrazine ring. A heterocyclic compound having a triazine ring or a tetrazine ring has high reactivity with the main chain of the diene rubber (A), and when combined with a halogenated metal salt (C), tends to form a crosslink through a coordinate bond. .

［式中、Ｘ^１及びＸ^２は、それぞれ独立してピリジル基又はピリミジニル基であり、Ｙ^１及びＹ^２は、それぞれ独立して単結合又は二価の炭化水素基である。］で表されることが好ましい。一般式（１）で表される化合物は、ジエン系ゴム（Ａ）の主鎖とのディールス・アルダー反応が進行し易く、ハロゲン化金属塩（Ｃ）と組み合わさって、配位結合による架橋を更に形成し易い。 Here, the heterocyclic compound (B) has the following general formula (1):

[Wherein, 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. ] is preferably represented. The compound represented by the general formula (1) easily undergoes a Diels-Alder reaction with the main chain of the diene rubber (A), and when combined with the metal halide salt (C), crosslinking through coordination bonds occurs. Furthermore, it is easy to form.

In another preferred embodiment of the rubber composition of the present invention, the halogenated metal salt (C) contains at least one metal selected from the group consisting of transition metals and zinc. A halogenated metal salt containing a transition metal and/or zinc is easily complexed with the heterocyclic compound (B).

It is preferable that the rubber composition of the present invention further contains zinc oxide (E). In this case, the fuel efficiency and crack growth resistance of the rubber composition are further improved.

It is preferable that the rubber composition of the present invention further contains carbon black (F). In this case, the reinforcing properties of the rubber composition are improved, and the crack propagation resistance is further improved.

It is preferable that the rubber composition of the present invention further contains silica (G). In this case, the reinforcing properties of the rubber composition are improved, and the crack propagation resistance is further improved.

It is preferable that the rubber composition of the present invention further contains an organic peroxide (H). In this case, the fuel efficiency and crack growth resistance of the rubber composition are further improved.

In another preferred example 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 plurality of diene rubbers (A) can be crosslinked simply by complexing the plurality of heterocyclic compound (B) moieties with the halide metal salt (C) to form a coordinate bond. I can do it.

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 fuel efficiency of the rubber composition and the workability in kneading 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, the rubber composition will have sufficient strength in the low strain region, and the fuel efficiency of the rubber composition can be sufficiently improved.

Further, 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 can achieve both low fuel consumption and crack growth resistance.

According to the present invention, it is possible to provide a rubber composition that has both low fuel consumption and crack growth resistance.
Further, according to the present invention, it is possible to provide a rubber product that has both low fuel consumption and crack growth resistance.

Below, the rubber composition and rubber product of the present invention will be illustrated and explained in detail based on the embodiments thereof.

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

As mentioned above, in a rubber composition, fuel efficiency and crack growth resistance are usually in a trade-off relationship. For example, if a rubber composition is crosslinked by adding sulfur to lower the network density of the sulfur crosslinks, crack propagation resistance improves, but fuel efficiency decreases. In order to solve this trade-off, the present inventors conducted extensive studies and found that strain-dependent control of the expression of hysteresis loss is important.

In the rubber composition of the present invention, the heterocyclic compound (B) is added to the main chain of the diene rubber (A). Here, the halogenated metal salt (C) easily complexes with the heterocyclic compound (B). Therefore, the halogenated metal salt (C) coordinates to the heterocyclic compound (B) moiety added to the main chain of the diene rubber (A) to form a complex. Then, the halogenated metal salt (C) forms a plurality of coordination bonds, thereby crosslinking the plurality of diene rubbers (A). Here, the crosslinking by coordination bond is a reversible crosslinking in which bonding (crosslinking) and dissociation (cleavage) are reversible, and it is a weaker bond than the sulfur crosslinking in general crosslinked rubber, but the rubber composition Even if an object is subjected to strain, it has sufficient strength in a low strain region.
The rubber composition of the present invention can reduce hysteresis loss and improve fuel efficiency by maintaining a high network density through crosslinking through coordination bonds in the low strain region. On the other hand, in the rubber composition of the present invention, the crosslinks due to coordination bonds are cleaved in the high strain region, resulting in high hysteresis loss, and the energy generated by the cleavage of the crosslinks (that is, sacrificial destruction of the crosslinks due to coordination bonds) Due to the dissipation, crack propagation resistance can be improved.
Therefore, the rubber composition of the present invention can achieve both high fuel efficiency and crack growth resistance, which cannot be achieved by conventional crosslinking using only sulfur.

--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 halogenated metal salt (C).

The diene rubber (A) is a rubber containing units derived from diene monomers (diene units), and may further contain units derived from copolymerizable comonomers.
The units derived from the diene monomer enable crosslinking (vulcanization) of the diene rubber, and can also exhibit rubber-like elongation and strength. In the crosslinked rubber, the diene rubber usually exists in a crosslinked state, but a portion thereof may not be crosslinked. Specific examples of the diene monomer (diene compound) include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, and the like.
On the other hand, examples of the copolymerizable comonomer include aromatic vinyl compounds. Specific examples of the aromatic vinyl compound include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, o,p-dimethylstyrene, o-ethylstyrene, m-ethylstyrene, and p-ethylstyrene. etc.
Examples of the diene rubber (A) include natural rubber (NR), synthetic isoprene rubber (IR), styrene-butadiene rubber (SBR), butadiene rubber (BR), and chloroprene rubber (CR). 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 fuel efficiency of the rubber composition is improved, and when it is 3,000,000 or less, the kneading of the rubber composition is improved. Improves work efficiency. From the viewpoint of fuel efficiency 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. In addition, from the viewpoint of workability in kneading the rubber composition, it is more preferably 2,000,000 or less, and even more preferably 1,800,000 or less.

--Heterocyclic compound (B) --
The rubber composition of the present invention contains a heterocyclic compound (B) having at least one heterocycle selected from the group consisting of a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, and a tetrazine ring. The pyrimidine ring, pyridazine ring, pyrazine ring, triazine ring, and tetrazine ring have a plurality of nitrogen atoms in the ring, and can coordinately bond with a plurality of halogenated metal salts (C). Further, the heterocyclic compound (B) can crosslink a plurality of diene rubbers (A) together with the halogenated metal salt (C).
In the present invention, the heterocyclic compound (B) is not used as a dispersant for the filler, but is used as a coordination site for the metal halide salt (C), thereby forming a crosslink by coordination bonds. Thereby, in the low strain region, the network density can be maintained high through crosslinking through coordination bonds, thereby improving fuel efficiency. On the other hand, in a high strain region, crack propagation resistance can be improved due to energy dissipation due to cleavage of crosslinks due to coordination bonds.

The heterocyclic compound (B) preferably has a triazine ring or a tetrazine ring. A compound having a triazine ring or a tetrazine ring has high reactivity with the main chain of the diene rubber (A), and when combined with the metal halide salt (C), easily forms a crosslink through a coordinate bond.

Here, it is preferable that a pyridyl group or a pyrimidinyl group is bonded to the triazine ring or tetrazine ring of the compound having the triazine ring or tetrazine ring, and it is further preferable that two pyridyl groups or pyrimidinyl groups are bonded to the triazine ring or tetrazine ring of the compound having the triazine ring or tetrazine ring. preferable. When a pyridyl group or pyrimidinyl group is bonded to the triazine ring or tetrazine ring, the heterocyclic compound (B) and the metal halide salt (C) are more likely to be complexed, and the bond dissociation energy is likely to increase, A crosslinked structure with higher strength can be formed. In addition, when two pyridyl groups or pyrimidinyl groups are bonded to the triazine ring or tetrazine ring, the heterocyclic compound (B) and the metal halide salt (C) are more easily complexed, and the bond dissociation energy is can easily become even higher, and a crosslinked structure with even higher strength can be formed.
Note that the pyridyl group may be a 2-pyridyl group, a 3-pyridyl group, or a 4-pyridyl group, but a 2-pyridyl group is preferable. Furthermore, the pyrimidinyl group may be a 2-pyrimidinyl group, a 4-pyrimidinyl group, or a 5-pyrimidinyl group.

［式中、Ｘ^１及びＸ^２は、それぞれ独立してピリジル基又はピリミジニル基であり、Ｙ^１及びＹ^２は、それぞれ独立して単結合又は二価の炭化水素基である。］で表されることが好ましい。一般式（１）で表される化合物は、ジエン系ゴム（Ａ）の主鎖とのディールス・アルダー反応が進行し易く、ハロゲン化金属塩（Ｃ）と組み合わさって、配位結合による架橋を更に形成し易い。また、一般式（１）で表される化合物とハロゲン化金属塩（Ｃ）とは、特に錯化し易く、結合解離エネルギーが特に高くなり易く、より一層強度の高い架橋構造を形成できる。 The heterocyclic compound (B) has the following general formula (1):

[Wherein, 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. ] is preferably represented. The compound represented by the general formula (1) easily undergoes a Diels-Alder reaction with the main chain of the diene rubber (A), and when combined with the metal halide salt (C), crosslinking through coordination bonds occurs. Furthermore, it is easy to form. Further, the compound represented by the general formula (1) and the metal halide salt (C) are particularly easy to complex, and the bond dissociation energy is particularly easy to increase, so that a crosslinked structure with even higher strength can be formed.

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 are preferably pyridyl groups. The pyridyl group may be a 2-pyridyl group, a 3-pyridyl group, or a 4-pyridyl group, but a 2-pyridyl group is preferable. Furthermore, the pyrimidinyl group may be a 2-pyrimidinyl group, a 4-pyrimidinyl group, or a 5-pyrimidinyl group.

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, an arylene group, and the like. More specifically, examples of alkylene groups include methylene group, ethylene group, trimethylene group, tetramethylene group, etc., examples of alkenylene groups include vinylene group, propenylene group, butenylene group, etc., and examples of arylene group include , phenylene group, tolylene group, naphthylene group, etc. From the viewpoint of ease of synthesis, Y ¹ and Y ² are preferably single bonds (that is, it is preferable that X ¹ and X ² are directly bonded to the tetrazine ring).

Here, it is preferable that X ¹ and X ² in the above general formula (1) are pyridyl groups, and Y ¹ and Y ² are single bonds. In this case, the compound of formula (1) is easily available, and it is particularly easy to complex with the metal halide salt (C), and the bond dissociation energy is particularly easy to increase, so that a crosslinked structure with even higher strength can be formed. .

Examples of the compound 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-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, 3,6-di(5-pyrimidinyl) )-1,2,4,5-tetrazine, and among 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, based on 100 parts by mass of the diene rubber (A). , and preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less. When the content of the heterocyclic compound (B) is 0.1 parts by mass or more based on 100 parts by mass of the diene rubber (A), the network density of the coordinate bond crosslinks becomes high, and the low strain region The hysteresis loss is further reduced, and the fuel efficiency of the rubber composition is improved. Further, when the content of the heterocyclic compound (B) is 10 parts by mass or less based on 100 parts by mass of the diene rubber (A), a crosslinked rubber having sufficient elastomer properties can be easily obtained.

The diene rubber (A) is preferably modified with the heterocyclic compound (B). When the diene rubber (A) is modified with a heterocyclic compound (B), a plurality of heterocyclic compound (B) moieties are complexed with the metal halide salt (C) described below to form a coordinate bond. By simply doing this, the main chains of a plurality of diene rubbers (A) can be crosslinked. Here, the modification of the diene rubber (A) with the heterocyclic compound (B) may be carried out at the stage of compounding the rubber composition. Furthermore, prior to blending the rubber composition, the diene rubber (A) is modified with the heterocyclic compound (B) in advance, and the diene rubber (A) modified with the heterocyclic compound (B) is mixed with the diene rubber (A). In the step of compounding the rubber composition, the main chains of the plurality of diene rubbers (A) may be crosslinked by compounding with a halogenated metal salt (C) or the like.

When the diene rubber (A) is modified with the heterocyclic compound (B), the heterocyclic compound (B) has a It is preferably bound 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 even more preferably 0.03 to 3 mol%. It is particularly preferable that When the heterocyclic compound (B) is bonded in an amount of 0.01 mol% or more to the monomer unit in the main chain of the diene rubber (A), the network density of the coordination bond crosslinks becomes high, The hysteresis loss in the low strain region is further reduced, and the fuel efficiency of the rubber composition is improved. Furthermore, when the heterocyclic compound (B) is bonded in an amount of 10 mol% or less to the monomer units in the main chain of the diene rubber (A), a crosslinked rubber having sufficient elastomeric properties cannot be obtained. easy.

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

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

It is particularly preferable that the metal halide salt (C) contains iron, zinc or copper. Iron ions, zinc ions, and copper ions tend to bond particularly strongly with the heterocyclic compound (B), and can form a stronger crosslinked structure. Note that the valence of the iron ion is preferably divalent (Fe ²⁺ ) or trivalent (Fe ³⁺ ).

Further, examples of the metal halide salt (C) include metal fluoride, metal chloride, metal bromide, metal iodide, etc. Among these, metal chloride is preferred. Metal chloride salts are easy to handle and are also easy to 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 _FeCl2 , _FeCl2.4H2O , _FeCl3 , _FeCl3.6H2O , _ZnCl2 , CuCl, _CuCl2 , CuBr, and the like. Further, 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 in the range of 0.1 to 15 parts by mass, based on 100 parts by mass of the diene rubber (A). Preferably, the range is from 0.1 to 10 parts by weight, even more preferably from 0.1 to 5 parts by weight. When the content of the metal halide salt (C) is 0.1 parts by mass or more based on 100 parts by mass of the diene rubber (A), the network density of the coordinate bond crosslinks becomes high, and the low strain region The hysteresis loss is further reduced, and the fuel efficiency of the rubber composition is improved. Further, when the content of the metal halide salt (C) is 30 parts by mass or less based on 100 parts by mass of the diene rubber (A), a crosslinked rubber having sufficient elastomer properties can be 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, and preferably 200 kJ/mol or more. It is more preferable that it is, even more preferably that it is 240 kJ/mol or more, and it is more preferable that it is 500 kJ/mol or less. When the bond dissociation energy is 100 kJ/mol or more, the rubber composition has sufficient strength in the low strain region, and the fuel efficiency of the rubber composition can be sufficiently improved. Further, if the bond dissociation energy is 500 kJ/mol or less, the crosslink due to the coordinate bond between the metal halide salt (C) and the heterocyclic compound (B) is likely to be cleaved in the high strain region. The crack propagation resistance of the rubber composition can be further improved due to energy dissipation due to the cleavage of the crosslinks.

Here, in the present invention, the bond dissociation energy between the metal halide salt (C) and the heterocyclic compound (B) is M06/6-31G(d,p)//B3PW91-D3/6-31G (d, p) level or M06/6-31G (d, p) level, a value calculated in vacuum, and a calculated value in a structure in which the heterocyclic compound (B) is combined with the diene rubber (A) It is. Note that the metal halide salt (C) and the heterocyclic compound (B) are considered to form an ionic aggregate. Gaussian09 or GRRM14 can be used to calculate the bond dissociation energy.

For example, by mixing (kneading) the diene rubber (A), the heterocyclic compound (B), and the halogenated metal salt (C), a crosslink by a coordinate bond can be formed. In kneading, conditions such as temperature and time are appropriately selected depending on the type and reactivity of the diene rubber (A), heterocyclic compound (B), and metal halide salt (C) used. It is preferable.

As an example, 3,6-di(2-pyridyl)-1,2,4,5-tetrazine is used as the heterocyclic compound (B), and iron chloride (FeCl ₂ ) is used, the reaction scheme of modification of the diene rubber (A) and coordination bond crosslinking (complexation) of the modified diene rubber is shown below. Note that the structure of the modified diene rubber shown here is one possible example, and is not limited to this. For example, it may be an isomer due to tautomerism, an oxidized form, etc.

As described in the upper part of the above reaction scheme, in one embodiment of the present invention, a modified diene rubber is Produces rubber. In this embodiment, nitrogen is eliminated during the Diels-Alder reaction, but any other reaction may be used for the modification reaction.

Furthermore, as described in the lower part of the above reaction scheme, in one embodiment of the present invention, the modified diene rubber and the halogenated metal salt (C) are complexed, resulting in crosslinking through coordinate bonds. A complexed diene rubber (complexed diene rubber) is produced. In addition, in the above reaction scheme, the nitrogen atom in the tetrazine residue, the nitrogen atom of the pyridyl group bonded to the tetrazine residue, and the iron ion were shown to be complexed. The diene rubber can take various forms of crosslinking.

--Sulfur (D)--
It is preferable that the rubber composition of the present invention further contains sulfur (D). Since the rubber composition contains sulfur (D) together with the metal halide salt (C), the crosslinking due to coordination bonds due to the metal halide salt (C) and the sulfur crosslinking occur in the rubber composition after crosslinking. (Dual Cross Link: DCL). In the low strain region, by keeping the network density higher by both crosslinking by coordination bonds and sulfur crosslinking, hysteresis loss can be further reduced and fuel efficiency can be further improved. On the other hand, in the high strain region, in addition to energy dissipation due to cleavage of crosslinks due to coordination bonds, the presence of sulfur crosslinks causes the rubber composition (also referred to as "crosslinked rubber composition" or "crosslinked rubber"). ) is improved, and the crack growth resistance is further improved.

The content of the sulfur (D) in the rubber composition is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, based on 100 parts by mass of the diene rubber (A). The amount is preferably 30 parts by mass or less, and more preferably 10 parts by mass or less. When the content of sulfur (D) is 0.1 parts by mass or more based on 100 parts by mass of the diene rubber (A), the network density due to sulfur is improved and fuel efficiency is further improved. Further, when the content of sulfur (D) is 30 parts by mass or less based on 100 parts by mass of the diene rubber (A), a crosslinked rubber having sufficient elastomer properties can be easily obtained.

Here, the mass ratio (D/C) of the sulfur (D) and the metal halide salt (C) is preferably 0.1 to 10. When the mass ratio (D/C) of sulfur (D) and metal halide salt (C) is within the range of 0.1 to 10, the rubber composition has a better balance between fuel efficiency and crack growth resistance. Becomes good. From the viewpoint of the balance between fuel efficiency and crack growth resistance of the rubber composition, the mass ratio (D/C) of sulfur (D) and halogenated metal salt (C) is preferably in the range of 0.1 to 8. More preferably, the range is from 0.1 to 6, even more preferably.

--Zinc oxide (E)--
It is preferable that the rubber composition of the present invention further contains zinc oxide (E). When the rubber composition contains zinc oxide (E) together with the metal halide salt (C), the fuel efficiency and crack growth resistance of the rubber composition are further improved.

The content of the zinc oxide (E) in the rubber composition is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, based on 100 parts by mass of the diene rubber (A). , is preferably 30 parts by mass or less, and more preferably 10 parts by mass or less. When the content of zinc oxide (E) is in the range of 0.1 parts by mass or more and 30 parts by mass or less based on 100 parts by mass of the diene rubber (A), the fuel efficiency and crack resistance of the rubber composition are improved. Progressivity is further improved.
The mass ratio (E/C) between zinc oxide (E) and metal halide salt (C) is preferably in the range of 0.1 to 50, more preferably in the range of 1 to 20.

--Carbon black (F)--
It is preferable that the rubber composition of the present invention further contains carbon black (F). When the rubber composition contains carbon black (F), the reinforcing properties of the rubber composition are improved, and the crack growth 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.

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 100 parts by mass, based on 100 parts by mass of the diene rubber (A). The amount is preferably at most 90 parts by mass, more preferably at most 90 parts by mass. When the content of carbon black (F) is 2 parts by mass or more based on 100 parts by mass of the diene rubber (A), the reinforcing properties of the rubber composition are further improved, and the crack growth resistance is further improved. Improve further. Further, when the content of carbon black (F) is 100 parts by mass or less based on 100 parts by mass of the diene rubber (A), the fuel efficiency of the rubber composition is further improved.

--Silica (G)--
It is preferable that the rubber composition of the present invention further contains silica (G). When the rubber composition contains silica (G), the reinforcing properties of the rubber composition are improved, and the crack growth resistance is further improved.

Examples of the silica (G) include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, and the like. 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 100 parts by mass, based on 100 parts by mass of the diene rubber (A). The following is preferable, and 90 parts by mass or less is more preferable. When the content of silica (G) is 2 parts by mass or more based on 100 parts by mass of the diene rubber (A), the reinforcing properties of the rubber composition are further improved, and the crack growth resistance is further improved. improves. Moreover, when the content of silica (G) is 100 parts by mass or less based on 100 parts by mass of the diene rubber (A), the fuel efficiency of the rubber composition is further improved.
The mass ratio (F/G) of carbon black (F) to silica (G) is preferably in the range of 0.02 to 50, more preferably in the range of 0.05 to 20.

--Organic peroxide (H)--
It is preferable that the rubber composition of the present invention further contains an organic peroxide (H). By containing the organic peroxide (H) together with the metal halide salt (C) in the rubber composition, the rubber composition after crosslinking can contain crosslinking due to coordination bonds due to the metal halide salt (C) and organic A crosslinked structure (CC bond, etc.) due to peroxide (H) is present (Dual Cross Link: DCL). In the low strain region, by keeping the network density higher due to both the crosslinking by coordination bonds and the crosslinking structure caused by organic peroxide (H), hysteresis loss is further reduced and fuel efficiency is improved. can be improved. On the other hand, in the high strain region, in addition to energy dissipation due to cleavage of crosslinks due to coordination bonds, the presence of a crosslinked structure caused by organic peroxide (H) further improves crack growth resistance.

The organic peroxide (H) is not particularly limited, but includes 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- Butyl peroxylaurate, tert-butylperoxy-2-ethylhexanate, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, tert-hexylperoxy-2-ethylhexanoate, tert- Examples include butylperoxy-2-ethylhexanoate, tert-butylperoxyacetate, cyclohexanone peroxide, acetylacetone peroxide, diisopropyl peroxydicarbonate, di(4-tert-butylcyclohexyl)peroxydicarbonate, and the like. These organic peroxides (H) may be used alone or in combination of two or more.

The content of the organic peroxide (H) in the rubber composition is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, based on 100 parts by mass of the diene rubber (A). , and preferably 30 parts by mass or less, more preferably 20 parts by mass or less. When the content of the organic peroxide (H) is 0.1 part by mass or more based on 100 parts by mass of the diene rubber (A), the network of the crosslinked structure due to the organic peroxide (H) Density is improved and fuel efficiency is further improved. Further, when the content of the organic peroxide (H) is 30 parts by mass or less based on 100 parts by mass of the diene rubber (A), a crosslinked rubber having sufficient elastomer properties can be easily obtained.
The mass ratio (D/H) of organic peroxide (H) to sulfur (D) is preferably in the range of 0.003 to 300, more preferably in the range of 0.01 to 100.

--others--
The rubber composition of the present invention includes the above-mentioned diene rubber (A), heterocyclic compound (B), halogenated metal salt (C), sulfur (D), zinc oxide (E), and carbon black (F). , silica (G), organic peroxide (H), compounding agents commonly used in the rubber industry, such as softeners, stearic acid, waxes, anti-aging agents, silane coupling agents, anti-adhesion agents ( Fatty acid metal salts), vulcanization accelerators, etc. may be appropriately selected and blended within a range that does not impede the object of the present invention. Commercially available products can be suitably used as these compounding agents.

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

--Production method of rubber composition--
The method for producing the rubber composition is not particularly limited, but for example, the above-mentioned diene rubber (A), heterocyclic compound (B), and metal halide salt (C) may be added as necessary. It can be manufactured by blending various components appropriately selected, kneading, heating, extruding, etc.

There are no particular restrictions on the conditions for the kneading, and various conditions such as the input volume of the kneading device, rotational speed of the rotor, ram pressure, etc., kneading temperature, kneading time, type of kneading device, etc. It can be selected as appropriate. Examples of the kneading device include a Banbury mixer, an intermix, a kneader, and a roll, which are usually used for kneading the rubber composition.

There are no particular limitations on the heating conditions, and various conditions such as heating temperature, heating time, heating device, etc. can be appropriately selected depending on the purpose. Examples of the heating device include a heating roll machine normally used for heating the rubber composition.

There are no particular limitations on the extrusion conditions, and 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 normally used for extruding rubber compositions. The extrusion temperature can be determined as appropriate.

For example, in the first step of kneading, the diene rubber (A), the heterocyclic compound (B), and various components selected as appropriate are blended and kneaded. ) A mixture containing a modified diene rubber in which a heterocyclic compound (B) is bonded to the main chain of By blending and kneading various components, the diene rubber (A) modified with the heterocyclic compound (B) can be complexed to form a crosslinked structure with coordinate bonds. This method for producing a rubber composition has excellent productivity because a crosslinked structure can be formed by coordination bonds during production of the rubber composition (kneading of the rubber composition).

Alternatively, for example, a modified diene rubber in which the heterocyclic compound (B) is bonded to the main chain of the diene rubber (A) is prepared in advance, and in the first stage of kneading, the modified diene rubber prepared in advance is Rubber and optional compounding agents are kneaded, and in the second and subsequent stages of kneading, the halogenated metal salt (C) and various components appropriately selected as necessary are blended and kneaded to form a complex compound. The diene rubber (A) modified with the cyclic compound (B) may be complexed to form a crosslinked structure by coordinate bonds. This method for producing a rubber composition also allows a crosslinked structure by coordination bonds to be easily formed, and is also excellent in productivity.

Although there have been several reports on the formation of crosslinks using compounds containing polar groups, generally, compounds containing polar groups are introduced as monomers during polymer synthesis, and when kneading rubber compositions, compounds containing polar groups are generally introduced as monomers. When forming crosslinks, strict kneading conditions are required. In contrast, the rubber composition of the present invention has the advantage that crosslinking can be easily formed during kneading of the rubber composition, and special kneading conditions are not required.

<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.
Since the rubber product of the present invention contains the above-mentioned rubber composition, it has excellent fuel efficiency and crack growth resistance.

--tire--
When the rubber product of the present invention is a tire, there are no particular restrictions on the areas to which the rubber composition of the present invention is applied in the tire, and can be appropriately selected depending on the purpose, such as the tread, base tread, sidewall, etc. , side reinforcement rubber, bead filler, etc.
A conventional method can be used to manufacture the tire. For example, members normally used in tire manufacturing, such as a carcass layer, a belt layer, and a tread layer made of an unvulcanized rubber composition and/or cord, are laminated one after another on a tire-building drum, and the drum is removed to form a green tire. do. Next, by heating and vulcanizing this green tire according to a conventional method, a desired tire (for example, a pneumatic tire) can be manufactured.

--Rubber crawler--
When the rubber product of the present invention is a rubber crawler, in one embodiment, the rubber crawler includes a steel cord, an intermediate rubber layer covering the steel cord, and a core metal disposed on the intermediate rubber layer. It includes a main rubber layer surrounding the intermediate rubber layer and the core metal, and further includes a plurality of lugs on the ground surface side of the main rubber layer. Although the rubber composition of the present invention may be used in any part of the rubber crawler, it is preferably used in the main rubber layer, particularly in the lugs, since it has 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 includes a laminate in which soft layers and hard layers are alternately laminated, and a hollow space formed at the center of the laminate. It has a plug that is press-fitted into the section. In one embodiment, the rubber composition of the present invention described above can be used for at least one of the soft layer and the plug.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to the Examples below.

<Method for measuring weight average molecular weight (Mw) of diene rubber>
The weight average molecular weight was measured by gel permeation chromatography (GPC) under the following conditions and was determined as a value in terms of standard polystyrene.
GPC: Tosoh Corporation HLC-8320GPC, Column: Tosoh Corporation TSKgel G4000HXL x 2 (column temperature 40°C), Mobile phase: Tetrahydrofuran (flow rate: 1ml/min), Detector: Differential refractometer (multi-wavelength detection) Standard material: TSK standard polystyrene manufactured by Tosoh Corporation.

<Manufacture and evaluation of rubber composition>
A rubber composition was produced using a conventional Banbury mixer according to the formulation shown in Table 1. The resulting rubber composition was evaluated for fuel efficiency and crack growth resistance using the following methods.
Further, the bond dissociation energy between the compounded metal halide salt (C) and the heterocyclic compound (B) was measured by the following method.

(1) Evaluation method for fuel efficiency A test piece was prepared from a rubber composition, and the viscoelasticity was evaluated using “ARES-G2” manufactured by TA Instruments under the conditions of a frequency of 15 Hz, a shear strain of 3%, and a temperature of 30°C. A test was conducted to measure the loss tangent (tan δ) of the rubber composition. The evaluation results were normalized by the reciprocal of the formulation data of each example, using the formulation data of Comparative Example 1 as a control (index value 100). The larger the index value, the smaller the tan δ and the better the fuel efficiency.

(2) Evaluation method of crack growth resistance A rectangular test piece with a hole in the center was prepared from the rubber composition, and a DC/DN test using the test piece (using Shimadzu's "Servo Pulsar") , at a frequency of 5 Hz and 40°C, measured by a constant stress test at stress levels of 2 or more for each formulation), the value obtained by taking the common logarithm of tearing energy [J/m ² ] at 1950 repetitions is 3.9 The crack growth rate was calculated when . The crack growth rate obtained by the above treatment was normalized by the reciprocal of the formulation data of each example, using the formulation data of Comparative Example 1 as a control (index value 100). The larger the index value, the lower the crack growth rate and the better the crack growth resistance.

(3) Calculation method of 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 heterocyclic compound The bond dissociation energy with the functional group of compound (B) is at the M06/6-31G(d,p)//B3PW91-D3/6-31G(d,p) level or the M06/6-31G(d,p ) level is a value calculated in vacuum, and is a calculated value in 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 an ionic aggregate. 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 M06/6-31G (d, p) level of theory, gas phase conditions.

Regarding the rubber compositions produced in Examples 1 to 9, the metal halide salt (C) [FeCl _{2.4H 2} O] and the heterocyclic compound (B) [3,6-di(2-pyridyl)-1, 2,4,5-tetrazine] is 412.6 kJ/mol.
Regarding the rubber composition produced in Example 10, the halogenated metal salt (C) [ZnCl ₂ ] 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 with a bound styrene content of 10%, a 1,2 vinyl bond content of 42%, and a weight average molecular weight (Mw) of 386,982 *2 Carbon black: ISAF grade, manufactured by Asahi Carbon Co., Ltd., product Name: “Asahi #78”
*3 Heterocyclic compound: 3,6-di(2-pyridyl)-1,2,4,5-tetrazine, manufactured by Tokyo Kasei Kogyo Co., Ltd. *4 Adhesion inhibitor: Fatty acid metal salt *5 Sulfur: Hosoi Chemical Co., Ltd. Manufactured by product name "HK200-5"
*6 Vulcanization accelerator: This is the total amount of Sanshin Kagaku Kogyo Co., Ltd., trade name "Suncella DM-TG" and Sanshin Kagaku Kogyo Co., Ltd., trade name "Suncella NS-G". All the comparative examples and examples except for the same ratio of each component *7 Zinc oxide: Manufactured by Hakusui Tech Co., Ltd., "Zinc oxide 2 types"
*8 Iron chloride: _FeCl2.4H2O , manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. *9 Zinc chloride: _ZnCl2 , manufactured by Tokyo Kasei Kogyo Co., Ltd. *10 Others: Total amount of stearic acid, _wax , and anti-aging agent 6PPD Yes, each component was mixed in the same amount in all comparative examples and examples.

From Table 1, it can be seen that the rubber compositions of Examples according to the present invention are able to achieve both low fuel consumption and crack growth resistance.

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

Claims (14)

diene rubber (A);
A heterocyclic compound (B) having at least one heterocycle selected from the group consisting of a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, and a tetrazine ring;
a metal halide salt (C),
A rubber composition comprising: The rubber composition according to claim 1, further comprising sulfur (D). The rubber composition according to claim 2, wherein the mass ratio (D/C) of the sulfur (D) and the metal halide salt (C) is 0.1 to 10. The rubber composition according to any one of claims 1 to 3, wherein the heterocyclic compound (B) has a triazine ring or a tetrazine ring. The heterocyclic compound (B) has the following general formula (1):

[Wherein, 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 rubber composition according to claim 4, which is represented by: The rubber composition according to any one of claims 1 to 5, wherein the halogenated metal salt (C) contains at least one metal selected from the group consisting of transition metals and zinc. The rubber composition according to any one of claims 1 to 6, further comprising zinc oxide (E). The rubber composition according to any one of claims 1 to 7, further comprising carbon black (F). The rubber composition according to any one of claims 1 to 8, further comprising silica (G). The rubber composition according to any one of claims 1 to 9, further comprising an organic peroxide (H). The rubber composition according to any one of claims 1 to 10, wherein the diene rubber (A) is modified with the heterocyclic compound (B). The rubber composition according to any one of claims 1 to 11, 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 12, wherein the 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 tires, rubber crawlers, and seismic isolation rubber,
A rubber product comprising the rubber composition according to any one of claims 1 to 13.