Rubber composition and rubber product

Abstract

The present invention addresses the problem of providing a rubber composition that achieves both thermal deterioration resistance and fracture resistance. The solution to this problem is a rubber composition characterized by including a diene rubber (A), a heterocyclic compound (B) that has a six-membered aromatic heterocyclic ring, a metal salt (C) (with the exception of metal oxides, metal carbonates, and fatty acid metal salts having 10 or more carbon atoms), an organic peroxide (D), and a carbon black (E). The mass ratio (D / C) of the organic peroxide (D) to the metal salt (C) is preferably 0.1-10.

Description

Rubber composition and rubber product

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

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

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

[0004] JP 2011-225717 A

[0005] However, although crosslinking with organic peroxides is excellent in heat deterioration resistance, it has lower fracture resistance (strength) than sulfur crosslinking, and there is room for improvement in fracture resistance.

[0006] Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional art and to provide a rubber composition that satisfies both heat degradation resistance and fracture resistance.A further object of the present invention is to provide a rubber product that satisfies both heat degradation resistance and fracture resistance.

[0007] The rubber composition and rubber product of the present invention that solve the above problems are summarized as follows.

[0008] [1] A rubber composition comprising: a diene rubber (A); a heterocyclic compound (B) having a six-membered aromatic heterocycle; a metal salt (C) (excluding metal oxides, metal carbonates, and metal salts of fatty acids having 10 or more carbon atoms); an organic peroxide (D); and carbon black (E).

[0009] [2] The rubber composition according to [1], wherein the mass ratio (D / C) of the organic peroxide (D) to the metal salt (C) is 0.1 to 10.

[0010] [3] The rubber composition according to [1] or [2], wherein the heterocyclic compound (B) has at least one heterocycle 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.

[0011] [4] The rubber composition according to [3], wherein the heterocyclic compound (B) has a triazine ring or a tetrazine ring.

[0012] [5] The heterocyclic compound (B) is represented by the following general formula (1): [In the formula, X １ and X ２ are each independently a pyridyl group or a pyrimidinyl group, and Y １ and Y ２ are each independently a single bond or a divalent hydrocarbon group.

[0013] [6] The rubber composition according to any one of [1] to [5], wherein the metal salt (C) contains at least one metal selected from the group consisting of transition metals and zinc.

[0014] [7] The rubber composition according to any one of [1] to [6], wherein the metal salt (C) is at least one selected from the group consisting of metal halide salts, metal acrylate salts, and metal methacrylate salts.

[0015] [8] The rubber composition according to any one of [1] to [7], further comprising zinc oxide (F).

[0016] [9] The rubber composition according to any one of [1] to [8], further comprising silica (G).

[0017]

[10] The rubber composition according to any one of [1] to [9], wherein the diene rubber (A) is modified with the heterocyclic compound (B).

[0018]

[11] The rubber composition according to any one of [1] to

[10] , wherein the diene rubber (A) has a weight average molecular weight (Mw) of 10,000 to 3,000,000.

[0019]

[12] The rubber composition according to any one of [1] to

[11] , wherein the bond dissociation energy between the metal salt (C) and the heterocyclic compound (B) is 100 kJ / mol or more.

[0020]

[13] A rubber product selected from the group consisting of a tire, a rubber crawler, and a seismic isolation rubber, characterized in that it contains the rubber composition according to any one of [1] to

[12] .

[0021] According to the present invention, it is possible to provide a rubber composition that has both heat degradation resistance and fracture resistance, and also to provide a rubber product that has both heat degradation resistance and fracture resistance.

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

[0023] <Rubber Composition> The rubber composition of the present invention is characterized by containing a diene rubber (A), a heterocyclic compound (B) having a six-membered aromatic heterocycle, a metal salt (C) (excluding metal oxides, metal carbonates, and metal salts of fatty acids having 10 or more carbon atoms), an organic peroxide (D), and carbon black (E).

[0024] In the rubber composition of the present invention, a heterocyclic compound (B) is added to the main chain of a diene rubber (A). Furthermore, a metal salt (C) is coordinately bonded to the heterocyclic compound (B) portion added to the main chain of the diene rubber (A) to form a complex. The metal salt (C) 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 salt (C), the crosslinked rubber composition contains both a crosslink due to a coordinate bond of the metal 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, the crosslink due to a coordinate bond is a reversible crosslink 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). Meanwhile, when the rubber composition of the present invention is subjected to strain (particularly in a high strain region), the crosslinks due to coordination bonds are cleaved, resulting in high hysteresis loss. Furthermore, energy dissipation due to the cleavage of the crosslinks (i.e., sacrificial fracture of the crosslinks due to coordination bonds) can improve fracture resistance, thereby achieving fracture resistance (strength) equal to or greater than that of conventional sulfur crosslinks. Furthermore, the rubber composition of the present invention contains carbon black (E), which improves reinforcing properties and further improves fracture resistance. 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 crosslinking using only an organic peroxide.

[0025] --Diene Rubber (A)-- The rubber composition of the present invention contains a diene rubber (A). By including the diene rubber (A), the rubber composition can form a crosslinked structure together with the heterocyclic compound (B) and the metal salt (C).

[0026] The diene rubber (A) is a rubber containing units derived from a diene monomer (diene units) and may further contain units derived from a copolymerizable comonomer. The units derived from the diene monomer enable crosslinking (vulcanization) of the diene rubber and also enable it to exhibit rubber-like elongation and strength. Note that, although the diene rubber is usually present in a crosslinked state in the crosslinked rubber, a portion of it may not be crosslinked. 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. Specific examples of the aromatic vinyl compounds include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, o,p-dimethylstyrene, o-ethylstyrene, m-ethylstyrene, and p-ethylstyrene. Examples of the diene rubber (A) include natural rubber (NR), synthetic isoprene rubber (IR), styrene-butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), etc. These diene rubbers (A) may be used alone or as a blend of two or more.

[0027] In the rubber composition of the present invention, the diene rubber (A) preferably has a weight average molecular weight (Mw) of 10,000 to 3,000,000. When the weight average molecular weight (Mw) of the diene rubber (A) is 10,000 or more, the fracture resistance of the rubber composition is improved, and when it is 3,000,000 or less, the workability in kneading the rubber composition is improved. From the viewpoint of the fracture resistance of the rubber composition, the weight average molecular weight (Mw) of the diene rubber (A) is more preferably 100,000 or more, and even more preferably 120,000 or more. From the viewpoint of the workability in kneading the rubber composition, it is even more preferably 2,000,000 or less, and even more preferably 1,800,000 or less. In this specification, the weight average molecular weight (Mw) of the diene rubber (A) is determined by gel permeation chromatography (GPC) using polystyrene as a standard substance.

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

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

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

[0031] Furthermore, it is preferable that a pyridyl group or a pyrimidinyl group be bonded to the triazine ring or the tetrazine ring of the compound having a triazine ring or a tetrazine ring, and it is even more preferable that two pyridyl groups or two pyrimidinyl groups be bonded. When a pyridyl group or a pyrimidinyl group is bonded to the triazine ring or the tetrazine ring, the heterocyclic compound (B) and the metal salt (C) are more easily complexed, the bond dissociation energy is more easily increased, and a crosslinked structure with even higher strength can be formed. 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 salt (C) are more easily complexed, the bond dissociation energy is more easily increased, and a crosslinked structure with even higher strength can be formed. The pyridyl group may be a 2-pyridyl group, a 3-pyridyl group, or a 4-pyridyl group, but a 2-pyridyl group is preferred. The pyrimidinyl group may be a 2-pyrimidinyl group, a 4-pyrimidinyl group, or a 5-pyrimidinyl group.

[0032] The heterocyclic compound (B) is represented by the following general formula (1): [In the formula, 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. It is more preferable that the compound represented by general formula (1) is represented by the following formula: The compound represented by general formula (1) easily undergoes a Diels-Alder reaction with the diene rubber (A), and is easily combined with the metal salt (C) to form a crosslink through a coordinate bond. Furthermore, the compound represented by general formula (1) and the metal 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.

[0033] In the above general formula (1), X １ and X ２ are each independently a pyridyl group or a pyrimidinyl group. １ and X ２is preferably a pyridyl group. The pyridyl group may be a 2-pyridyl group, a 3-pyridyl group, or a 4-pyridyl group, with a 2-pyridyl group being preferred. The pyrimidinyl group may be a 2-pyrimidinyl group, a 4-pyrimidinyl group, or a 5-pyrimidinyl group.

[0034] In the above general formula (1), Y １ and Y ２ are each independently a single bond or a divalent hydrocarbon group. Here, examples of the divalent hydrocarbon group include an alkylene group, an alkenylene group, and an arylene group. More specifically, examples of the alkylene group include a methylene group, an ethylene group, a trimethylene group, and a tetramethylene group. Examples of the alkenylene group include a vinylene group, a propenylene group, and a butenylene group. Examples of the arylene group include a phenylene group, a tolylene group, and a naphthylene group. From the viewpoint of ease of synthesis, Y １ and Y ２ is preferably a single bond (i.e., X is not attached to the tetrazine ring). １ and X ２ is preferably directly bonded).

[0035] Here, X in the general formula (1) １ and X ２ is a pyridyl group, and Y １ and Y ２ is preferably a single bond. In this case, the compound of formula (1) is easily available, and is particularly likely to form a complex with the metal salt (C), and the bond dissociation energy is particularly likely to be high, making it possible to form a crosslinked structure with even higher strength.

[0036] The compounds represented by the general formula (1) include 3,6-di(2-pyridyl)-1,2,4,5-tetrazine, 3,6-di(3-pyridyl)-1,2,4,5-tetrazine, 3,6-di(4-pyridyl)-1,2,4,5-tetrazine, 3,6-di(2-pyridylmethyl)-1,2,4,5-tetrazine, 3,6-di(2-pyridylethyl)-1,2,4,5-tetrazine, 3-(2-pyridyl)-1,2,4,5-tetrazine, lysylmethyl)-6-(2-pyridylethyl)-1,2,4,5-tetrazine, 3,6-di(2-pyrimidinyl)-1,2,4,5-tetrazine, 3,6-di(4-pyrimidinyl)-1,2,4,5-tetrazine, 3,6-di(5-pyrimidinyl)-1,2,4,5-tetrazine, and the like. Among these, 3,6-di(2-pyridyl)-1,2,4,5-tetrazine is preferred.

[0037] The content of the heterocyclic compound (B) in the rubber composition is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less, per 100 parts by mass of the diene rubber (A). When the content of the heterocyclic compound (B) is 0.1 parts by mass or more per 100 parts by mass of the diene rubber (A), crosslinking by coordinate bonds increases, and in a high strain region, the crosslinking by coordinate bonds cleaves, and energy dissipation by sacrificial fracture further improves the fracture resistance of the rubber composition. Furthermore, when the content of the heterocyclic compound (B) is 10 parts by mass or less per 100 parts by mass of the diene rubber (A), a crosslinked rubber with sufficient elastomeric properties is easily obtained.

[0038] The diene rubber (A) is preferably modified with the heterocyclic compound (B). When the diene rubber (A) is modified with the heterocyclic compound (B), the main chains of the diene rubbers (A) can be crosslinked simply by complexing the heterocyclic compound (B) moieties with the metal salt (C) described below to form coordinate bonds. Here, the modification of the diene rubber (A) with the heterocyclic compound (B) may be performed at the compounding stage of the rubber composition. Alternatively, prior to compounding the rubber composition, the diene rubber (A) may be modified with the heterocyclic compound (B) in advance, and the diene rubber (A) modified with the heterocyclic compound (B) may be compounded with the metal salt (C) or the like at the compounding stage of the rubber composition to crosslink the main chains of the diene rubbers (A).

[0039] When the diene rubber (A) is modified with the heterocyclic compound (B), the heterocyclic compound (B) is preferably bonded in an amount of 0.01 to 10 mol%, more preferably 0.02 to 8 mol%, even more preferably 0.03 to 5 mol%, and particularly preferably 0.03 to 3 mol%, 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 are cleaved, and energy dissipation due to sacrificial fracture further improves the fracture resistance of the rubber composition. Furthermore, when the heterocyclic compound (B) is bonded in an amount of 10 mol% or less relative to the monomer units in the diene rubber (A), a crosslinked rubber with sufficient elastomeric properties is easily obtained.

[0040] --Metal Salt (C)-- The rubber composition of the present invention contains a metal salt (C) (excluding metal oxides, metal carbonates, and metal salts of fatty acids having 10 or more carbon atoms). The metal 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.

[0041] The metal salt (C) excludes metal oxides, metal carbonates, and metal salts of fatty acids having 10 or more carbon atoms. Metal oxides, metal carbonates, and metal salts of fatty acids having 10 or more carbon atoms are unlikely to form coordinate bonds (complex) with the heterocyclic compound (B) moiety attached to the diene rubber (A) chain. Therefore, by using a metal salt (C) other than these, sufficient crosslinking by coordinate bonds can be formed. Here, examples of metal oxides include zinc oxide, silica, alumina, etc. Examples of metal carbonates include calcium carbonate, etc. Regarding metal salts of fatty acids having 10 or more carbon atoms, examples of fatty acids having 10 or more carbon atoms include palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, etc. Examples of metal salts of fatty acids having 10 or more carbon atoms include zinc salts, potassium salts, calcium salts, sodium salts, magnesium salts, etc. of the fatty acids.

[0042] The metal salt (C) preferably contains at least one metal selected from the group consisting of transition metals and zinc. Metal salts containing a transition metal and / or zinc are likely to complex with the heterocyclic compound (B). Examples of transition metals include elements in Groups 7 to 11 of the periodic table. Specific 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. Examples of elements in Group 11 of the periodic table include copper. Elements in Groups 7 to 11 of the periodic table and zinc tend to form a strong bond with the heterocyclic compound (B). Furthermore, when the metal salt (C) contains an element in 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 salt (C) is not particularly limited and may be any valence that each element can have, but is preferably divalent or greater.

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

[0044] Examples of the metal salt (C) include metal halides, metal sulfates, metal nitrates, metal acrylates, and metal methacrylates, and among these, metal halides, metal acrylates, and metal methacrylates are preferred. Metal halides, metal acrylates, and metal methacrylates are easy to handle and easily form bonds with the heterocyclic compound (B). The form of the metal salt (C) is not particularly limited, and may be, for example, a hydrate.

[0045] Examples of the metal halide salt include metal fluorides, metal chlorides, metal bromides, and metal iodides, and among these, metal chlorides are preferred because they are easy to handle and can easily form a bond with the heterocyclic compound (B).

[0046] Specific examples of the metal salt (C) include FeCl ２ , FeCl ２ ・4H ２ O, FeCl ３ , FeCl ３ ・6H ２ O, ZnCl ２ , CuCl, CuCl ２ , CuBr, zinc diacrylate, zinc dimethacrylate, etc. The metal salt (C) may be a single type or a combination of two or more types.

[0047] The content of the metal salt (C) is preferably 0.1 to 30 parts by mass, more preferably 0.1 to 15 parts by mass, even more preferably 0.1 to 10 parts by mass, and particularly preferably 0.1 to 5 parts by mass, per 100 parts by mass of the diene rubber (A). When the content of the metal salt (C) is 0.1 part by mass or more per 100 parts by mass of the diene rubber (A), crosslinks due to coordinate bonds increase, and in a high strain region, the crosslinks due to coordinate bonds are cleaved, and energy dissipation due to sacrificial fracture further improves the fracture resistance of the rubber composition. Furthermore, when the content of the metal 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.

[0048] In the rubber composition of the present invention, the bond dissociation energy between the metal salt (C) and the heterocyclic compound (B) is preferably 100 kJ / mol or more, more preferably 200 kJ / mol or more, even more preferably 240 kJ / mol or more, and preferably 500 kJ / mol or less. When the bond dissociation energy is 100 kJ / mol or more, the crosslinks formed by the coordinate bonds have sufficient strength in the low strain region. When the bond dissociation energy is 500 kJ / mol or less, the crosslinks formed by the coordinate bonds between the metal salt (C) and the heterocyclic compound (B) are easily cleaved 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.

[0049] Here, in the present invention, the bond dissociation energy between the metal 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 salt (C) and the heterocyclic compound (B) form ionic aggregates. Gaussian 09 or GRRM14 can be used to calculate the bond dissociation energy.

[0050] For example, crosslinking by coordinate bonds can be formed by mixing (kneading) the diene rubber (A), the heterocyclic compound (B), and the metal salt (C). Here, it is preferable that the conditions for kneading, such as temperature and time, be appropriately selected depending on the types and reactivities of the diene rubber (A), heterocyclic compound (B), and metal salt (C) used.

[0051] As an example, 3,6-di(2-pyridyl)-1,2,4,5-tetrazine is used as the heterocyclic compound (B), and zinc chloride (ZnCl ２ The reaction scheme of the modification of the diene rubber (A) and the coordination bond crosslinking (complexation) of the modified diene rubber when the diene rubber (A) is used 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, an oxidized form, or the like.

[0052] As shown in the upper part of the reaction scheme, in one embodiment of the present invention, a modified diene rubber is produced by the Diels-Alder reaction of a diene rubber (A) and a heterocyclic compound (B). In this embodiment, nitrogen is eliminated during the Diels-Alder reaction, but any other reaction may be used for the modification reaction.

[0053] 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 salt (C) are complexed to produce a diene rubber crosslinked by a coordinate bond (complexed diene rubber). Note that, although the above reaction scheme shows a mode in which a nitrogen atom in the tetrazine residue, a nitrogen atom of a pyridyl group bonded to the tetrazine residue, and a zinc ion are complexed, the diene rubber crosslinked by a coordinate bond can take various crosslinking modes.

[0054] --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 salt (C), the crosslinked rubber composition contains both crosslinks due to coordinate bonds formed by the metal 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 the cleavage of the crosslinks due to coordinate bonds improves fracture resistance.

[0055] 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 the organic peroxide (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.

[0056] 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 caused by 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 having sufficient elastomeric properties is easily obtained.

[0057] Here, the mass ratio (D / C) of the organic peroxide (D) to the metal salt (C) is 0.1 to 10. When the mass ratio (D / C) of the organic peroxide (D) to the metal 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 salt (C) is more preferably within the range of 0.1 to 8, and even more preferably within the range of 0.1 to 6.

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

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

[0060] The content of the carbon black (E) in the rubber composition is preferably 2 parts by mass or more, more preferably 5 parts by mass or more, and preferably 100 parts by mass or less, more preferably 90 parts by mass or less, per 100 parts by mass of the diene rubber (A). When the content of the carbon black (E) 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. Also, when the content of the carbon black (E) is 100 parts by mass or less per 100 parts by mass of the diene rubber (A), the workability in kneading the rubber composition is further improved.

[0061] --Zinc oxide (F)-- The rubber composition of the present invention preferably further contains zinc oxide (F). When the rubber composition contains zinc oxide (F), the mechanical properties of the rubber composition are improved. Furthermore, when the rubber composition contains zinc oxide (F), 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 (F), the rubber composition is less likely to adhere to other materials.

[0062] The content of the zinc oxide (F) in the rubber composition is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and preferably 30 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 zinc oxide (F) is in the range of 0.1 parts 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 conductivity of the rubber composition are further improved, and the rubber composition becomes more resistant to adhesion. The mass ratio (F / C) of zinc oxide (F) to metal salt (C) is preferably in the range of 0.1 to 50, more preferably 1 to 20.

[0063] --Silica (G)-- The rubber composition of the present invention preferably further contains silica (G). When the rubber composition contains silica (G), the reinforcement properties of the rubber composition are improved, and the fracture resistance is further improved.

[0064] Examples of the silica (G) include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc. These silicas (G) may be used alone or in combination of two or more.

[0065] The content of the silica (G) in the rubber composition is preferably 2 parts by mass or more, more preferably 5 parts by mass or more, and preferably 100 parts by mass or less, more preferably 90 parts by mass or less, per 100 parts by mass of the diene rubber (A). When the content of silica (G) is 2 parts by mass or more per 100 parts by mass of the diene rubber (A), the reinforcement properties of the rubber composition are further improved, and the fracture resistance is further improved. 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 (E / G) of carbon black (E) to silica (G) is preferably in the range of 0.02 to 50, more preferably 0.05 to 20.

[0066] --Other-- In addition to the diene rubber (A), heterocyclic compound (B), metal salt (C), organic peroxide (D), carbon black (E), zinc oxide (F), and silica (G) described above, 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 blended within ranges that do not impair the objects of the present invention. Commercially available products can be suitably used as these compounding agents.

[0067] Examples of the antioxidant include N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), 2,2,4-trimethyl-1,2-dihydroquinoline polymer (TMDQ), 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline (AW), N,N'-diphenyl-p-phenylenediamine (DPPD), etc. The content of the antioxidant is not particularly limited, and is preferably in the range of 0.1 to 5 parts by mass, and more preferably 0.5 to 4 parts by mass, per 100 parts by mass of the diene rubber (A).

[0068] Examples of the wax include paraffin wax, microcrystalline wax, etc. The content of the wax is not particularly limited, but is preferably in the range of 0.1 to 5 parts by mass, more preferably 1 to 4 parts by mass, per 100 parts by mass of the diene rubber (A).

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

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

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

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

[0073] For example, in the first stage of kneading, a diene rubber (A), a heterocyclic compound (B), carbon black (E), and various components appropriately selected as necessary are blended and kneaded to form a mixture containing a modified diene rubber in which the heterocyclic compound (B) is bonded to the diene rubber (A), and in the second or subsequent stage of kneading, a metal salt (C) and an organic peroxide (D), and various components appropriately selected as necessary are blended and kneaded to complex the diene rubber (A) modified with the heterocyclic compound (B), forming a crosslinked structure due to a coordinate bond while also forming a crosslinked structure (C-C bond, etc.) due to the organic peroxide (D). Such a method for producing a rubber composition is excellent in productivity because it can form a crosslinked structure due to a coordinate bond and a crosslinked structure (C-C bond, etc.) due to the organic peroxide (D) during the production of the rubber composition (kneading of the rubber composition).

[0074] 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 in a first stage of kneading, the previously prepared modified diene rubber, carbon black (E), and any compounding ingredients may be kneaded together. In a second or subsequent stage of kneading, a metal salt (C), an organic peroxide (D), and various components appropriately selected as necessary may be blended and kneaded to complex the diene rubber (A) modified with the heterocyclic compound (B), forming a crosslinked structure due to a coordinate bond while also forming a crosslinked structure (C-C bond, etc.) due to the organic peroxide (D). This method for producing a rubber composition also makes it possible to easily form a crosslinked structure due to a coordinate bond and a crosslinked structure (C-C bond, etc.) due to the organic peroxide (D), and also provides excellent productivity.

[0075] <Rubber Product> 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 rubber composition described above. Because the rubber product of the present invention contains the rubber composition described above, it has excellent heat degradation resistance and fracture resistance.

[0076] --Tire-- When the rubber product of the present invention is a tire, the application portion of the tire to the rubber composition of the present invention is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include the tread, base tread, sidewall, side reinforcing rubber, and bead filler. Conventional methods can be used to manufacture the tire. For example, components typically used in tire manufacturing, such as a carcass layer, belt layer, and tread layer composed of an unvulcanized rubber composition and / or cords, are laminated on a tire building drum, and the drum is removed to obtain a green tire. The green tire can then be heated and vulcanized according to a conventional method to manufacture a desired tire (e.g., a pneumatic tire).

[0077] --Rubber Track-- In one embodiment, when the rubber product of the present invention is a rubber track, the rubber track 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 track, but is preferably used in the main rubber layer, particularly the lugs, due to its excellent crack propagation resistance.

[0078] --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 that is 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.

[0079] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0080] <Analysis of Diene Rubber> The weight average molecular weight (Mw) of the diene rubber is measured by the following method.

[0081] (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.

[0082] <Production and Evaluation of Rubber Compositions> Rubber compositions were produced using a conventional Banbury mixer according to the formulation shown in Table 1. 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 salt (C) and heterocyclic compound (B) was also measured by the following method.

[0083] (2) Evaluation method for heat degradation resistance (modulus change rate after heat degradation) For Examples 1 and 2, ring-shaped test pieces were prepared from the rubber composition, and a tensile test (measured using a universal tensile tester manufactured by Tensilon Corporation at a tensile speed of 300 mm / min) was performed on the test piece immediately after preparation and on the test piece thermally aged in air at 100°C for 48 hours. The absolute value of the change in modulus before and after heat degradation was calculated from the modulus value at 300% strain of the test piece immediately after preparation and the modulus value at 300% strain of the thermally aged test piece. For Comparative Examples 1 to 4, JIS No. 7 test pieces were prepared from the rubber composition, and a tensile test (measured using a universal tensile tester manufactured by Instron Corporation at a tensile speed of 200 mm / min) was performed on the test piece immediately after preparation and on the test piece thermally aged in air at 100°C for 48 hours. The absolute value of the change in modulus before and after thermal degradation 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. Note that although the test machine, shape of the test piece, and measurement conditions are partially different between the examples and comparative examples, the results of the change in modulus before and after thermal degradation are reproducible. The smaller the change rate before and after thermal degradation, the better the resistance to thermal degradation.

[0084] (3) Evaluation method of fracture resistance (crack resistance) A rectangular test piece with a hole drilled in the center was prepared from the rubber composition, and the tear energy [J / m] after 2000 repetitions was measured in a dc / dn test using the test piece (measured using a Shimadzu Servo Pulser at a frequency of 5 Hz, 40°C, and at two or more stress levels for each formulation by a constant stress test). ２ The crack growth rate was calculated when the common logarithm of [(log(√{square root over ( ...

[0085] (4) Method for Calculating Bond Dissociation Energy The bond dissociation energy between the metal salt (C) (specifically, the metal ion of the metal 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.

[0086] For the rubber composition produced in Example 1, the bond dissociation energy between the metal salt (C) [zinc chloride] and the heterocyclic compound (B) [3,6-di(2-pyridyl)-1,2,4,5-tetrazine] is 172.0 kJ / mol. For the rubber composition produced in Example 2, the bond dissociation energy between the metal salt (C) [zinc dimethacrylate] and the heterocyclic compound (B) [3,6-di(2-pyridyl)-1,2,4,5-tetrazine] is 111.9 kJ / mol.

[0087]

[0088] * 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 Carbon black: ISAF grade, manufactured by Asahi Carbon Co., Ltd., trade name "Asahi # 78" * 4 Stearic acid: Manufactured by New Japan Chemical Co., Ltd., trade name "Stearic Acid 50s" * 5 Antiaging agent: Antiaging agent 6PPD, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine, manufactured by Sumitomo Chemical Co., Ltd., trade name "Antigen 6C" * 6 Wax: Manufactured by Seiko Chemical Co., Ltd., trade name "Santite" * 7 Sulfur: Manufactured by Hosoi Chemical Industry Co., Ltd., trade name "HK200-5" * 8 Organic peroxide: Dicumyl peroxide (DCP), NOF Corporation, trade name "Percumyl D" *9 Zinc oxide: Zinc oxide, Hakusui Tech Co., Ltd., "Zinc oxide type 2" *10 Vulcanization accelerator 1: Sanshin Chemical Industry Co., Ltd., trade name "Suncerer CM-G" *11 Vulcanization accelerator 2: Ouchi Shinko Chemical Industry Co., Ltd., trade name "Noccela TOT-N" *12 Zinc chloride: ZnCl ２ , manufactured by Tokyo Chemical Industry Co., Ltd. *13 Zinc dimethacrylate: manufactured by CRAY VALLEY, trade name "DYMALINK 708"

[0089] It can be seen from Table 1 that the rubber compositions of the examples according to the present invention are able to achieve both heat degradation resistance and fracture resistance.

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

Claims

1. a diene rubber (A); a heterocyclic compound (B) having a six-membered aromatic heterocycle; a metal salt (C) (excluding metal oxides, metal carbonates, and metal salts of fatty acids having 10 or more carbon atoms); an organic peroxide (D); Carbon black (E), A rubber composition comprising:

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

3. The rubber composition according to claim 1, wherein 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.

4. The rubber composition according to claim 3 , wherein the heterocyclic compound (B) has a triazine ring or a tetrazine ring.

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

6. The rubber composition according to claim 1, wherein the metal salt (C) contains at least one metal selected from the group consisting of transition metals and zinc.

7. The rubber composition according to claim 1, wherein the metal salt (C) is at least one selected from the group consisting of metal halide salts, metal acrylate salts, and metal methacrylate salts.

8. The rubber composition according to claim 1, further comprising zinc oxide (F).

9. The rubber composition according to claim 1, further comprising silica (G).

10. The rubber composition according to claim 1, wherein the diene rubber (A) is modified with the heterocyclic compound (B).

11. 2. The rubber composition according to claim 1, wherein the diene rubber (A) has a weight average molecular weight (Mw) of 10,000 to 3,000,000.

12. The rubber composition according to claim 1, wherein a bond dissociation energy between the metal salt (C) and the heterocyclic compound (B) is 100 kJ / mol or more.

13. 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 claim 1.

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