Metal-rubber composite, hose, rubber crawler, and tire

Abstract

To provide a metal-rubber composite improved in initial adhesiveness and wet heat adhesiveness.SOLUTION: A metal-rubber composite 10 includes a metal 1 and a rubber 2 at least partially bonded to the metal 1, wherein the rubber 2 is formed of a rubber composition containing a rubber component containing an isoprene-based rubber and a butadiene-based rubber, a heterocyclic compound 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 at least one metal salt selected from the group consisting of a metal halide, a metal acrylate, a metal methacrylate, and a metal acetate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a metal-rubber composite, a hose, a rubber crawler, and a tire. [Background technology]

[0002] Generally, in rubber articles that require strength, such as hoses, rubber crawlers, and tires, composites of metal members and rubber (hereinafter referred to as "metal-rubber composites") are used to reinforce the rubber and improve its strength and durability. In order for such metal-rubber composites to exhibit high strength and durability over a long period of time, it is necessary to strongly bond the metal and rubber. Conventionally, in order to directly bond the metal and rubber by vulcanization, an adhesion promoter has been compounded in the rubber, and organic acid cobalt salts such as cobalt stearate and cobalt versatate have been commonly used as the adhesion promoter. However, concerns have arisen about the environmental impact of organic acid cobalt salts, and there is a demand for the development of rubber that does not contain cobalt salts. In response to this demand, Patent Document 1 below discloses an adhesion promoter for rubber and metal that consists of a specific metal salt. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2016 / 039375 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the inventors have conducted research and found that the adhesion promoter described in Patent Document 1 is not necessarily effective enough in promoting adhesion between metal and rubber, and that it is necessary to further improve the adhesion between metal and rubber, particularly the initial adhesion and the adhesion after moist heat aging (hereinafter referred to as "moisture and heat adhesion"), without using a cobalt salt.

[0005] Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional technology and to provide a metal-rubber composite having improved adhesion between the metal and the rubber, particularly improved initial adhesion and wet heat adhesion. Another object of the present invention is to provide a hose, a rubber crawler, and a tire that are equipped with such a metal-rubber composite and have excellent durability. [Means for solving the problem]

[0006] The metal-rubber composite, hose, rubber crawler, and tire of the present invention that solve the above problems are outlined below.

[0007] [1] A metal-rubber composite comprising a metal and a rubber at least partially adhered to the metal, The rubber a rubber component including an isoprene skeleton rubber and a butadiene rubber; 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; at least one metal salt selected from the group consisting of metal halide salts, metal acrylate salts, metal methacrylate salts, and metal acetate salts; A metal-rubber composite comprising a rubber composition comprising: The metal-rubber composite of the present invention described in [1] above has improved adhesion between the metal and the rubber, particularly improved initial adhesion and wet heat adhesion.

[0008] [2] The metal-rubber composite according to [1], wherein the content of the isoprene skeleton rubber is 75 parts by mass or more per 100 parts by mass of the rubber component. In the metal-rubber composite described in [2] above, the strength of the rubber portion is further improved, and the initial adhesiveness and adhesiveness under heat and humidity between the metal and rubber are further improved.

[0009] [3] The metal-rubber composite according to [1] or [2], wherein the rubber composition contains butadiene rubber as the butadiene-based rubber. In the metal-rubber composite described in [3] above, the processability (workability in kneading) of the rubber composition that constitutes the rubber portion is further improved.

[0010] [4] The metal-rubber composite according to any one of [1] to [3], wherein the heterocyclic compound has a triazine ring or a tetrazine ring. In the metal-rubber composite described in [4] above, the heterocyclic compound has high reactivity with the main chain of the rubber component, and is likely to form crosslinks by coordinate bonds in combination with the metal salt.

[0011] [5] The heterocyclic compound is represented by the following general formula (1): [ka] [where, X 1 and X 2 are each independently a pyridyl group or a pyrimidinyl group, and Y 1 and Y 2 are each independently a single bond or a divalent hydrocarbon group.]. The metal-rubber composite according to any one of [1] to [4], In the metal-rubber composite described in [5] above, the compound represented by general formula (1) easily undergoes a Diels-Alder reaction with isoprene-based rubber and butadiene-based rubber, and when combined with a metal salt, it easily forms further crosslinks through coordinate bonds.

[0012] [6] The metal-rubber composite according to any one of [1] to [5], wherein the content of the heterocyclic compound in the rubber composition is 0.01 to 5 parts by mass per 100 parts by mass of the rubber component. The metal-rubber composite described in [6] above can achieve a high degree of compatibility between the strength and elastomer properties of the rubber portion.

[0013] [7] The metal-rubber composite according to any one of [1] to [6], wherein the metal salt includes a metal methacrylate. In the metal-rubber composite described in [7] above, the metal methacrylate is easy to handle and also easy to form a bond with the heterocyclic compound.

[0014] [8] The metal is a steel cord consisting of a plurality of steel filaments, The metal-rubber composite according to any one of [1] to [7], wherein the N atoms on the surface of the steel cord are 2 atomic % or more and 60 atomic % or less, and the Cu / Zn ratio is 1 or more and 4 or less. The metal-rubber composite described in [8] above has further improved initial adhesion and heat and humidity adhesion between the metal and rubber.

[0015] [9] The steel cord is made by twisting together a plurality of steel filaments having brass plating on the circumferential surface, The metal-rubber composite according to [8], wherein the brass plating has a composition of 40 to 80 mass % of Cu and 20 to 60 mass % of Zn. According to the metal-rubber composite described in [9] above, the adhesion between the steel cord and the rubber can be further improved.

[0016]

[10] The metal-rubber composite according to [8] or [9], wherein the steel cord is surface-treated with a buffer solution having a pH of 5.0 to 7.2 and with one or more triazole compounds selected from 1,2,4-triazole, 1,2,3-triazole, 3-amino-1,2,4-triazole, 4-amino-1,2,4-triazole, benzotriazole, tolyltriazole, and 3-mercapto-1,2,4-triazole. According to the metal-rubber composite described in

[10] above, the adhesion between the steel cord and the rubber can be further improved.

[0017]

[11] The metal-rubber composite according to any one of [8] to

[10] , wherein the steel filaments have an N element content of 60 mass ppm or more, a C element content of 0.7 to 1.0 mass%, a Cu element content of 0.01 to 0.4 mass%, and a Cr element content of 0.05 to 0.3 mass%. The metal-rubber composite described in

[11] above is preferable from an environmental point of view.

[0018]

[12] The metal-rubber composite according to

[11] , wherein the steel filaments have a Cu element content of 0.05 to 0.4 mass %. The metal-rubber composite described in

[12] above is more preferable from an environmental point of view.

[0019]

[13] The metal-rubber composite according to any one of [8] to

[12] , wherein the steel filaments have a diameter of 0.15 mm to 0.6 mm. In the metal-rubber composite described in

[13] above, the durability of the steel cord is high.

[0020]

[14] A hose comprising the metal-rubber composite material according to any one of [1] to

[13] . The hose of the present invention described in

[14] above has excellent durability.

[0021]

[15] A rubber crawler comprising the metal-rubber composite according to any one of [1] to

[13] . The rubber crawler track of the present invention described in

[15] above has excellent durability.

[0022]

[16] A tire comprising the metal-rubber composite material according to any one of [1] to

[13] . The tire of the present invention described in

[16] above has excellent durability. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide a metal-rubber composite body having improved adhesion between the metal and the rubber, particularly improved initial adhesion and wet heat adhesion. Furthermore, according to the present invention, it is possible to provide a hose, a rubber crawler, and a tire that are equipped with such a metal-rubber composite and have excellent durability. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a schematic cross-sectional view of one embodiment of the metal-rubber composite of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] The metal-rubber composite, hose, rubber crawler, and tire of the present invention will be described in detail below by way of example based on embodiments thereof.

[0026] <Definition> The compounds described herein may be derived in part or in whole from fossil sources, biological sources such as plant sources, recycled sources such as used tires, or a mixture of two or more of fossil, biological, and recycled sources.

[0027] <Metal-rubber composite> The metal-rubber composite of this embodiment includes a metal and a rubber at least partially adhered to the metal. The rubber is made of a rubber composition including a rubber component containing an isoprene-skeleton rubber and a butadiene-based rubber, 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, and at least one metal salt selected from the group consisting of a metal halide salt, a metal acrylate salt, a metal methacrylate salt, and a metal acetate salt.

[0028] In the rubber portion of the metal-rubber composite of this embodiment, a heterocyclic compound is added to the rubber component. Furthermore, metal salts are easily complexed with the heterocyclic compound portion added to the rubber component. Therefore, in the rubber portion of the metal-rubber composite of this embodiment, the metal salt forms a coordinate bond with the heterocyclic compound portion added to the rubber component to form a complex. The metal salt then forms multiple coordinate bonds, thereby crosslinking the molecular chains of multiple rubber components. Here, the crosslinking by the coordinate bond is a reversible crosslink in which bonding (crosslinking) and dissociation (cleavage) are reversible, and although it is a weaker bond than the sulfur crosslinking in typical crosslinked rubbers, it still has sufficient strength. Furthermore, by including a metal salt in the rubber portion of the metal-rubber composite of this embodiment, adhesion to the metal is improved without the need for an organic acid cobalt salt. Furthermore, by including a metal salt in the rubber portion of the metal-rubber composite of this embodiment, the metal salt in the rubber portion of the composite interacts with the metal portion of the composite, improving the moisture-heat adhesion (moisture-heat degradation resistance of the adhesion) between the rubber portion and the metal portion, and also achieving a balance with other adhesive properties (initial adhesion, etc.). Therefore, the metal-rubber composite of this embodiment has improved adhesion between the metal portion and the rubber portion, particularly improved initial adhesion and wet heat adhesion.

[0029] Next, a metal-rubber composite according to one embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a schematic cross-sectional view of one embodiment of the metal-rubber composite of the present invention. The metal-rubber composite 10 shown in Fig. 1 comprises a metal 1 and a rubber 2 at least partially adhered to the metal 1. Although the metal 1 of the metal-rubber composite 10 shown in FIG. 1 has a circular cross section, the shape of the metal of the metal-rubber composite of the present invention is not particularly limited.

[0030] (metal) The metal (metal member) 1 of the metal-rubber composite 10 serves as a reinforcing material for the metal-rubber composite 10, improving the strength of rubber articles comprising the metal-rubber composite. The metal 1 is not particularly limited and can take various shapes. In this embodiment, the metal 1 is a metal cord. The metal cord is preferably made of a plurality of twisted metal filaments (also called metal wires or metal steel wires) or a single metal filament. The metal filament is not particularly limited, but examples thereof include wire materials such as iron, steel (stainless steel), lead, aluminum, copper, brass, bronze, Monel metal alloy, nickel, and zinc. In a preferred embodiment of the present invention, the metal 1 is a steel cord. When the metal 1 is a steel cord, it can be easily deformed into a desired shape, resulting in excellent productivity of the metal-rubber composite 10.

[0031] The surface of the metal 1 is preferably plated. The plating is not particularly limited, but examples thereof include zinc plating, copper plating, and brass plating, from the viewpoint of adhesion between the metal 1 and the rubber 2, and among these, zinc plating and brass plating are preferred. When the metal 1 is zinc plated or brass plated, the adhesion between the metal 1 and the rubber 2 is further improved. When the metal 1 is plated, the plated layer is also included in the metal.

[0032] The metal 1 is preferably a steel cord made up of a plurality of steel filaments. The number of steel filaments constituting the steel cord may be two or more, with no particular upper limit.

[0033] The content of N (nitrogen) atoms on the surface of the steel cord is preferably 2 atomic % or more and 60 atomic % or less, and the Cu / Zn ratio is preferably 1 or more and 4 or less, on a mass basis. It is more preferable that the content of N atoms on the surface of the steel cord is 2.1 atomic % or more and 55.0 atomic % or less, and the Cu / Zn ratio is 1.1 or more and 3.5 or less. By making the proportion of N atoms on the surface of the steel cord 2 atomic % or more, initial adhesion to the rubber (coating rubber) 2 is improved, and also treat retention is improved. Furthermore, by making the proportion of N atoms on the surface of the steel cord 60 atomic % or less, sufficient initial adhesion to the rubber 2 can be ensured. Furthermore, by making the Cu / Zn ratio on the surface of the steel cord 1 or more, initial adhesion to the rubber 2 is improved, and by making it 4 or less, initial adhesion to the rubber 2 is good and sufficient heat-and-moisture adhesion is also achieved. Therefore, when the N atoms on the surface of the steel cord are 2 atomic % or more and 60 atomic % or less and the Cu / Zn ratio is 1 or more and 4 or less, the initial adhesion and wet heat adhesion between the metal 1 and the rubber 2 can be further improved.

[0034] The N (nitrogen) atoms on the surface of the steel cord can be adjusted to 2 atomic % or more and 60 atomic % or less by suitably combining, for example, a treatment with a triazole compound (rust inhibitor), specifically, a surface treatment such as contacting with an aqueous solution of a triazole compound. The Cu / Zn ratio on the surface of the steel cord can be adjusted to be 1 or more and 4 or less by, for example, performing a treatment in which the pH of the acidic buffer solution and the concentration of the triazole aqueous solution are suitably combined. The lower the pH, the higher the Cu / Zn ratio of the steel cord that can be obtained.

[0035] Examples of the acidic buffer solution include acetate buffer, phosphate buffer, citrate buffer, etc., having a pH of 5.0 to 7.2, with acetate buffer solution having a pH of 5.0 to 7.2 being preferred. If the pH is less than 5.0, it becomes difficult to achieve a Cu / Zn ratio of 4 or less, and if the pH exceeds 7.2, it becomes difficult to achieve a Cu / Zn ratio of 1 or more. The surface treatment time with this buffer solution can be, for example, 0.5 to 20 seconds when an acetate buffer solution having a pH of 5.0 to 7.2 is used.

[0036] Examples of the triazole aqueous solution include aqueous solutions of one or more triazole compounds selected from 1,2,4-triazole, 1,2,3-triazole, 3-amino-1,2,4-triazole, 4-amino-1,2,4-triazole, benzotriazole, tolyltriazole, and 3-mercapto-1,2,4-triazole. Among these, aqueous solutions of 1,2,4-triazole, 1,2,3-triazole, 3-amino-1,2,4-triazole, and 4-amino-1,2,4-triazole are preferred. The concentration of the triazole aqueous solution is preferably 0.01 to 20 g / L. The treatment time varies depending on the concentration, but can be 0.1 to 30 seconds.

[0037] The steel cord is preferably surface-treated with a buffer solution having a pH of 5.0 to 7.2 and with one or more triazole compounds selected from 1,2,4-triazole, 1,2,3-triazole, 3-amino-1,2,4-triazole, 4-amino-1,2,4-triazole, benzotriazole, tolyltriazole, and 3-mercapto-1,2,4-triazole. A steel cord that has been surface-treated with such a buffer solution and then with a triazole compound can further improve adhesion to the rubber 2.

[0038] In this specification, the "surface" refers to a surface region extending to a depth of 5 nm radially inward of the steel filaments. The measurement of N atoms and Cu / Zn ratio on the surface of the steel cord is carried out by measuring the surface of the steel cord after it has been obtained, and after it has been subjected to cleaning treatment, drying, etc. as necessary, but before it is coated with rubber (rubber composition) 2. In this specification, the measurement of N atoms on the surface of the steel cord refers to measurement of N atoms on the surface of the steel cord measured by X-ray photoelectron spectroscopy (XPS), and the measurement of the Cu / Zn ratio on the surface of the steel cord refers to measurement of the Cu / Zn ratio on the surface of the steel cord by the photoelectron spectroscopy.

[0039] The steel filaments preferably have a plated layer formed on their surfaces by a conventional method, and the plated layer is not particularly limited, but examples thereof include a zinc plated layer, a copper plated layer, a brass plated layer, etc. Among these, a brass plated layer is preferred from the viewpoints of initial adhesion to the rubber 2 and adhesiveness under moist heat. The bulk brass plating composition constituting the brass plating layer preferably contains 40 to 80 mass % Cu (copper) and 20 to 60 mass % Zn (zinc), and more preferably 55 to 70 mass % Cu and 30 to 45 mass % Zn, from the viewpoints of workability of the steel cord and adhesion to the rubber 2. A steel cord made by twisting together a plurality of steel filaments having brass plating on their circumferential surfaces, and having the brass plating composition of 40 to 80 mass % Cu and 20 to 60 mass % Zn, can further improve adhesion to the rubber 2.

[0040] The steel filaments preferably have a diameter of 0.15 mm to 0.6 mm. When the diameter of the steel filaments is 0.15 mm or more, they have excellent strength and durability, and are therefore less likely to break during wire drawing. Furthermore, when the diameter of the steel filaments is 0.6 mm or less, for example, when a steel cord is applied to a tire, the steel filaments in the steel cord can follow the deformation of the tire, making them less likely to break (high durability) and also advantageously lightweight. Furthermore, steel cords using steel filaments with a diameter of 0.15 mm to 0.6 mm are highly durable.

[0041] From the viewpoint of durability, the steel filament has a diameter of X (mm) and a tensile strength of Y (MPa) that satisfies the following formula: 4000-2000X≦Y≦4500-2000X Here, the tensile strength of the filament is determined in accordance with the provisions of ISO 17832:2009.

[0042] From the viewpoint of fatigue resistance, the hardness of the surface layer of the steel filament is preferably 90 to 110% of the hardness of the inner layer, and particularly preferably 100%. The hardness can be measured, for example, by Vickers hardness. The surface layer of the filament refers to the layer from the outermost surface to a depth of 0.01 mm, and the area inside refers to the inner layer of the filament. The hardness can be measured in a region 0.005 mm deep from the outermost surface for the surface layer, and in a region 0.04 mm deep for the inner layer.

[0043] The steel filaments preferably have an N (nitrogen) content of 60 mass ppm or more, a C (carbon) content of 0.7 to 1.0 mass%, a Cu (copper) content of 0.01 to 0.4 mass%, and a Cr (chromium) content of 0.05 to 0.3 mass%. Such steel filaments are preferable from an environmental perspective because they do not require advanced refining. The steel filaments preferably have iron as their main component and an Fe (iron) content of 98 mass% or more.

[0044] The steel filaments preferably have an N (nitrogen) content of 60 ppm by mass or more. Steel filaments with an N content of 60 ppm by mass or more are preferable from an environmental perspective because they do not require advanced refining. Furthermore, from the viewpoint of durability, the N content of the steel filaments is preferably 200 ppm by mass or less, more preferably less than 90 ppm by mass. When a steel cord is used as a reinforcing material in a tire, the steel cord is subjected to loads from various directions during tire manufacture and use. Therefore, the steel filaments constituting the steel cord are required to have excellent torsional durability as one indicator of durability. Steel filaments with an N content of less than 90 ppm by mass are particularly excellent in torsional durability.

[0045] The steel filaments preferably have a C (carbon) content of 0.7 to 1.0% by mass, more preferably 0.7 to 0.85% by mass. Steel filaments with a C content within this range are preferable from an environmental perspective because they do not require advanced refining. Furthermore, steel filaments with a C content of 0.85% by mass or less have high ductility and can prevent breakage even when processed into steel filaments with a small diameter. Therefore, steel filaments with a C content of 0.7 to 0.85% by mass are less likely to break and have high durability.

[0046] The steel filaments preferably have a Cu (copper) content of 0.01 to 0.4 mass%, more preferably 0.05 to 0.4 mass%. Recycled iron with a Cu content within this range is preferable from an environmental perspective because it does not require advanced refining. Furthermore, a steel cord using steel filaments with a Cu content of 0.05 to 0.4 mass% is even more preferable from an environmental perspective.

[0047] The steel filaments preferably have a Cr (chromium) content of 0.05 to 0.3 mass %. Recycled iron with a Cr content within this range is preferable from an environmental perspective because it does not require advanced refining.

[0048] (rubber) The rubber (rubber portion of the composite) 2 of the metal-rubber composite 10 is made of a rubber composition containing a rubber component including an isoprene skeleton rubber and a butadiene-based rubber, 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, and at least one metal salt selected from the group consisting of a metal halide salt, a metal acrylate salt, a metal methacrylate salt, and a metal acetate salt.

[0049] -Rubber component- The rubber component of the rubber composition used for the rubber 2 contains an isoprene skeleton rubber and a butadiene-based rubber. The rubber composition used for the rubber 2 contains the isoprene skeleton rubber and the butadiene-based rubber, which allows the rubber composition to form a crosslinked structure together with the metal salt and the heterocyclic compound.

[0050] The isoprene-skeleton rubber is a rubber whose main skeleton is isoprene units, and specific examples include natural rubber (NR), synthetic isoprene rubber (IR), etc. When the rubber component contains an isoprene-skeleton rubber, the strength of the rubber composition can be improved, and the strength of the rubber part of a composite to which the rubber composition is applied and the adhesion between the rubber part and the metal part can also be improved.

[0051] The content of the isoprene skeleton rubber is preferably 75 parts by mass or more per 100 parts by mass of the rubber component. Furthermore, the content of the isoprene skeleton rubber is preferably 95 parts by mass or less per 100 parts by mass of the rubber component, more preferably 90 parts by mass or less, and even more preferably 85 parts by mass or less. When the content of the isoprene skeleton rubber is 75 parts by mass or more per 100 parts by mass of the rubber component, the strength of the rubber portion (rubber composition) of the composite is further improved, and the adhesion between the metal portion and the rubber portion, particularly the initial adhesion and the adhesion under wet heat can be further improved.

[0052] The butadiene rubber refers to a rubber containing a unit derived from butadiene as a monomer unit, and is a type of diene rubber. Examples of the butadiene rubber include butadiene rubber (BR) and aromatic vinyl compound-butadiene copolymer rubber (e.g., styrene-butadiene rubber (SBR)). When the rubber composition contains butadiene rubber, the processability (workability in kneading) of the rubber composition is improved.

[0053] The rubber composition used for the rubber 2 preferably contains butadiene rubber as the butadiene-based rubber. When the rubber composition contains butadiene rubber together with the isoprene skeleton rubber, the processability (workability in kneading) of the rubber composition is further improved.

[0054] The amount of the butadiene rubber is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, the amount of the butadiene rubber is preferably 25 parts by mass or less, per 100 parts by mass of the rubber component. When the amount of the butadiene rubber is 5 parts by mass or more, per 100 parts by mass of the rubber component, the processability (workability during kneading) of the rubber composition is improved.

[0055] The rubber component of the rubber composition used for the rubber 2 may contain other rubbers in addition to the isoprene-based rubber and the butadiene-based rubber. Examples of such other rubbers include chloroprene rubber (CR), ethylene-propylene rubber (EPR, EPDM), fluororubber, silicone rubber, and urethane rubber. The content of these other rubbers is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less, per 100 parts by mass of the rubber component.

[0056] -Heterocyclic compounds- The rubber composition used for the rubber 2 includes a heterocyclic compound having at least one heterocyclic ring selected from the group consisting of a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, and a tetrazine ring. The pyrimidine ring, the pyridazine ring, the pyrazine ring, the triazine ring, and the tetrazine ring each have multiple nitrogen atoms in the ring, and can form coordinate bonds with multiple metal salts. Furthermore, the heterocyclic compound, together with the metal salt, can crosslink molecular chains of multiple rubber components.

[0057] The heterocyclic compound preferably has a triazine ring or a tetrazine ring. Compounds having a triazine ring or a tetrazine ring have high reactivity with the main chain of the rubber component and are likely to form crosslinks by coordinate bonds in combination with a metal salt.

[0058] Furthermore, it is preferable that a pyridyl group or a pyrimidinyl group is bonded to the triazine ring or the tetrazine ring of the compound having a triazine ring or a tetrazine ring, and it is even more preferable that two pyridyl groups or two pyrimidinyl groups are bonded to the triazine ring or the tetrazine ring. When a pyridyl group or a pyrimidinyl group is bonded to the triazine ring or the tetrazine ring, the heterocyclic compound and the metal salt are more easily complexed, and a crosslinked structure with higher strength can be formed. Furthermore, when two pyridyl groups or two pyrimidinyl groups are bonded to the triazine ring or the tetrazine ring, the heterocyclic compound and the metal salt are more easily complexed, and a crosslinked structure with higher strength can be formed. The pyridyl group may be a 2-pyridyl group, a 3-pyridyl group, or a 4-pyridyl group, with a 2-pyridyl group being preferred.The pyrimidinyl group may be a 2-pyrimidinyl group, a 4-pyrimidinyl group, or a 5-pyrimidinyl group.

[0059] The heterocyclic compound is represented by the following general formula (1): [ka] [where, X 1 and X 2 are each independently a pyridyl group or a pyrimidinyl group, and Y 1 and Y 2are each independently a single bond or a divalent hydrocarbon group. It is more preferable that the compound represented by general formula (1) is represented by the following formula: The compound represented by general formula (1) easily undergoes a Diels-Alder reaction with isoprene-based rubber and butadiene-based rubber, and when combined with a metal salt, easily forms a crosslink through a coordinate bond. Furthermore, the compound represented by general formula (1) and a metal salt are particularly likely to form a complex, allowing the formation of a crosslinked structure with even greater strength.

[0060] In the above general formula (1), X 1 and X 2 are each independently a pyridyl group or a pyrimidinyl group. From the viewpoint of ease of synthesis, X 1 and X 2 is preferably a pyridyl group. The pyridyl group may be a 2-pyridyl group, a 3-pyridyl group, or a 4-pyridyl group, with a 2-pyridyl group being preferred. The pyrimidinyl group may be a 2-pyrimidinyl group, a 4-pyrimidinyl group, or a 5-pyrimidinyl group.

[0061] 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).

[0062] Here, X in the general formula (1) 1 and X 2 is a pyridyl group, and Y 1 and Y 2is preferably a single bond. In this case, the compound of formula (1) is easily available, and is particularly easy to complex with metal salts, allowing the formation of a crosslinked structure with even greater strength.

[0063] Examples of the compound represented by the general formula (1) include 3,6-di(2-pyridyl)-1,2,4,5-tetrazine (the compound is also called "3,6-di(pyridin-2-yl)-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 ...

[0033] Examples of the 3-(2-pyridylmethyl)-6-(2-pyridylethyl)-1,2,4,5-tetrazine include 3,6-di(2-pyrimidinyl)-1,2,4,5-tetrazine, 3,6-di(4-pyrimidinyl)-1,2,4,5-tetrazine, and 3,6-di(5-pyrimidinyl)-1,2,4,5-tetrazine. Among these, 3,6-di(2-pyridyl)-1,2,4,5-tetrazine is preferred.

[0064] The content of the heterocyclic compound in the rubber composition used for the rubber 2 is preferably 0.01 to 5 parts by mass per 100 parts by mass of the rubber component. When the content of the heterocyclic compound is 0.01 part by mass or more per 100 parts by mass of the rubber component, the network density of the coordinate bond crosslinks increases, improving the strength of the rubber 2. When the content of the heterocyclic compound is 5 parts by mass or less per 100 parts by mass of the rubber component, the rubber 2 is likely to have sufficient rubber elasticity (elastomeric properties). When the content of the heterocyclic compound is 0.01 to 5 parts by mass per 100 parts by mass of the rubber component, the strength and elastomeric properties of the rubber 2 can be highly compatible. From the viewpoint of the strength of rubber 2, the content of the heterocyclic compound is more preferably 0.1 parts by mass or more, and even more preferably 0.5 parts by mass or more, per 100 parts by mass of the rubber component. Also, from the viewpoint of the rubber elasticity of rubber 2, the content of the heterocyclic compound is more preferably 4 parts by mass or less, and even more preferably 3 parts by mass or less, per 100 parts by mass of the rubber component.

[0065] The rubber component is preferably modified with the heterocyclic compound. When the rubber component is modified with the heterocyclic compound, the main chains of the rubber components can be crosslinked simply by complexing the heterocyclic compound moieties with a metal salt described below to form coordinate bonds. Here, the modification of the rubber component with the heterocyclic compound may be performed at the compounding stage of the rubber composition. Alternatively, the rubber component may be modified with the heterocyclic compound in advance prior to compounding the rubber composition, and the rubber component modified with the heterocyclic compound (also referred to as "modified rubber") may be compounded with a metal salt or the like at the compounding stage of the rubber composition to crosslink the main chains of the rubber components.

[0066] When the rubber component is modified with the heterocyclic compound, the heterocyclic compound is preferably bonded in an amount of 0.01 to 10 mol%, more preferably 0.02 to 8 mol%, even more preferably 0.03 to 5 mol%, and particularly preferably 0.03 to 3 mol%, based on the monomer units in the rubber component. When the heterocyclic compound is bonded in an amount of 0.01 mol% or more based on the monomer units in the rubber component, the network density of the coordinate bond crosslinks increases, improving the strength of the rubber 2. Furthermore, when the heterocyclic compound is bonded in an amount of 10 mol% or less based on the monomer units in the rubber component, a rubber (crosslinked rubber) 2 with sufficient elastomeric properties is easily obtained.

[0067] -Metal salts- The rubber composition used for the rubber 2 contains at least one metal salt selected from the group consisting of metal halide salts, metal acrylate salts, metal methacrylate salts, and metal acetate salts. The metal salt forms coordinate bonds with multiple heterocyclic compounds, thereby crosslinking multiple rubber components. Here, the crosslinking by coordinate bonds is reversible, in that bonding (crosslinking) and dissociation (cleavage) are reversible, and even if it is broken by an external stimulus, it can be reversibly restored. The metal halide salt, metal acrylate salt, metal methacrylate salt, and metal acetate salt are easy to handle and easily form a bond with the heterocyclic compound. The form of the metal salt is not particularly limited, and may be, for example, a hydrate.

[0068] 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.

[0069] The metal salt preferably includes a metal methacrylate, which is easy to handle and also easy to form a bond with the heterocyclic compound.

[0070] The metal salt preferably contains at least one metal selected from the group consisting of transition metals and zinc. Metal salts containing transition metals and / or zinc are likely to form complexes with the heterocyclic compound. Examples of transition metals include elements in groups 7 to 11 of the periodic table. Specifically, examples of elements in Group 7 of the periodic table include manganese and rhenium. Examples of elements in Group 8 of the periodic table include iron, ruthenium, and osmium. Furthermore, examples of elements in Group 9 of the periodic table include cobalt, rhodium, and iridium. Examples of elements in Group 10 of the periodic table include nickel, palladium, and platinum. Furthermore, examples of elements in Group 11 of the periodic table include copper. Elements of Groups 7 to 11 of the periodic table and zinc tend to bond strongly with heterocyclic compounds. Furthermore, when the metal salt contains an element of Groups 8 or 11 of the periodic table or zinc, the bond with the heterocyclic compound tends to be even stronger. Furthermore, from the viewpoint of environmental consideration, it is preferable that the element is other than cobalt. Regarding the metal ions in the metal salt, the valence of the ions is not particularly limited and can have any valence that each element can have, but is preferably divalent or greater.

[0071] The metal salt particularly preferably contains iron, zinc, copper, or nickel. Iron ions, zinc ions, copper ions, and nickel ions are likely to form particularly strong bonds with the heterocyclic compound, and can form a stronger crosslinked structure. The valence of the iron ions is divalent (Fe 2+ ) or trivalent (Fe 3+ ) is preferred.

[0072] Specific examples of the metal salt include zinc diacrylate, zinc dimethacrylate (ZDMA), FeCl2, FeCl2·4H2O, FeCl3, FeCl3·6H2O, CuCl, CuCl2, CuBr, and Ni(CH3COO)2·4H2O. The metal salt may be a single type or a combination of two or more types. Among these, zinc dimethacrylate (ZDMA) is preferred as the metal salt. Zinc dimethacrylate (ZDMA) is easy to handle and particularly easily forms a bond with a heterocyclic compound.

[0073] The content of the metal salt 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, still more preferably 0.1 to 5 parts by mass, and particularly preferably 0.5 to 2 parts by mass, per 100 parts by mass of the rubber component. When the content of the metal salt is 0.1 part by mass or more per 100 parts by mass of the rubber component, crosslinking by coordinate bonds increases, improving the strength of the rubber 2. Also, the interaction between the metal salt in the rubber 2 and the metal 1 improves, improving the adhesion between the metal 1 and the rubber 2, particularly the initial adhesion and the adhesion under wet heat. When the content of the metal salt is 30 parts by mass or less per 100 parts by mass of the rubber component, it is easy to obtain a rubber (crosslinked rubber) 2 having sufficient elastomeric properties.

[0074] In the present embodiment, for example, crosslinking by coordinate bonds can be formed by mixing (kneading) the rubber component, the heterocyclic compound, and the metal salt. Here, it is preferable that the conditions for kneading, such as temperature and time, are appropriately selected depending on the types and reactivities of the rubber component, heterocyclic compound, and metal salt used.

[0075] As an example, the reaction scheme for modifying the rubber component and crosslinking (complexation) of the modified rubber when 3,6-di(2-pyridyl)-1,2,4,5-tetrazine is used as the heterocyclic compound and zinc dimethacrylate (ZDMA) is used as the metal salt is shown below. Note that the structure of the modified rubber shown here is one possible example and is not limited thereto. For example, it may be an isomer due to tautomerism or an oxidized form. [ka]

[0076] As shown in the upper part of the reaction scheme, in one embodiment, a modified rubber is produced by a Diels-Alder reaction between a rubber component and a heterocyclic compound. In this embodiment, nitrogen is eliminated during the Diels-Alder reaction, but any other reaction may be used for the modification reaction.

[0077] As shown in the lower part of the above reaction scheme, in one embodiment, the modified rubber and the metal salt are complexed to produce a rubber crosslinked by a coordinate bond (complexed rubber). Note that, although the above reaction scheme shows a mode in which the nitrogen atom in the tetrazine residue, the nitrogen atom of the pyridyl group bonded to the tetrazine residue, and the zinc ion are complexed, the rubber crosslinked by a coordinate bond can take various crosslinking modes.

[0078] -others- The rubber composition used for the rubber 2 may contain, in addition to the above-mentioned rubber components, heterocyclic compounds, and metal salts, compounding agents commonly used in the rubber industry, such as fillers (carbon black, silica, etc.), zinc oxide (zinc white), softeners, stearic acid, wax, antioxidants, silane coupling agents, vulcanization accelerators, vulcanizing agents, etc., which may be appropriately selected and compounded within a range that does not impair the object of the present invention. Commercially available products can be suitably used as these compounding agents.

[0079] Examples of the filler include carbon black, silica, clay, talc, calcium carbonate, and aluminum hydroxide, with carbon black being preferred. The carbon black is not particularly limited, and examples include GPF, FEF, HAF, ISAF, and SAF grade carbon black. The carbon black may also be recycled carbon black. The inclusion of a filler in the rubber 2 (rubber composition) improves the strength of the rubber 2.

[0080] The content of the filler is preferably in the range of 10 to 100 parts by mass per 100 parts by mass of the rubber component. When the content of the filler is 10 parts by mass or more per 100 parts by mass of the rubber component, the strength of the rubber 2 is further improved, and when the content is 100 parts by mass or less, the fuel economy of the rubber 2 is improved. From the viewpoint of the strength of the rubber 2, the content of the filler is more preferably 20 parts by mass or more, and even more preferably 40 parts by mass or more, per 100 parts by mass of the rubber component, and from the viewpoint of fuel economy, it is more preferably 80 parts by mass or less.

[0081] The content of the zinc oxide (zinc white) is not particularly limited, and is preferably in the range of 0.1 to 20 parts by mass, more preferably 1 to 15 parts by mass, and even more preferably 5 to 12 parts by mass, per 100 parts by mass of the rubber component.

[0082] Examples of the antioxidant include N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6C) and 2,2,4-trimethyl-1,2-dihydroquinoline polymer (TMDQ). These antioxidants may be used alone or in combination of two or more. The content of the antioxidant is not particularly limited, and is preferably in the range of 0.1 to 5 parts by mass, more preferably 1 to 4 parts by mass, per 100 parts by mass of the rubber component.

[0083] Examples of the vulcanization accelerator include sulfenamide vulcanization accelerators, guanidine vulcanization accelerators, thiazole vulcanization accelerators, thiuram vulcanization accelerators, and dithiocarbamate vulcanization accelerators. These vulcanization accelerators may be used alone or in combination of two or more. The content of the vulcanization accelerator is not particularly limited, and is preferably in the range of 0.1 to 5 parts by mass, more preferably 0.2 to 4 parts by mass, per 100 parts by mass of the rubber component.

[0084] The vulcanizing agent may be sulfur, etc. The content of the vulcanizing agent is preferably in the range of 1 to 10 parts by mass, more preferably 2 to 8 parts by mass, and even more preferably 3 to 7 parts by mass, in terms of sulfur content, per 100 parts by mass of the rubber component.

[0085] From the viewpoint of responding to future environmental regulations, the rubber composition used for rubber 2 preferably contains 0.01 parts by mass or less of a cobalt compound per 100 parts by mass of the rubber component, and more preferably does not contain a cobalt compound. Furthermore, because the addition of a cobalt compound accelerates thermal degradation of the rubber composition, it is desirable that the rubber composition does not contain a cobalt compound from the viewpoint of degradation resistance. Note that although a cobalt compound (or cobalt metal or cobalt ions derived from a cobalt compound) may migrate from the outside to rubber 2, it is preferable that a cobalt compound is not compounded at least when producing the rubber composition used for rubber 2.

[0086] -Method of manufacturing rubber composition- The method for producing the rubber composition used for the rubber 2 is not particularly limited, but for example, the rubber composition can be produced by blending the above-mentioned rubber component, heterocyclic compound, and metal salt with various components appropriately selected as necessary, and kneading, heating, extruding, etc.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] For example, in the first stage of kneading, a rubber component, a heterocyclic compound, and various other components appropriately selected as necessary are blended and kneaded to form a mixture containing a modified rubber in which the heterocyclic compound is bonded to the main chain of the rubber component, and in the second or subsequent stages of kneading, a metal salt and various other components appropriately selected as necessary are blended and kneaded to complex the rubber modified with the heterocyclic compound and form a crosslinked structure through a coordinate bond. Such a method for producing a rubber composition is excellent in productivity because a crosslinked structure through a coordinate bond can be formed during the production of the rubber composition (kneading of the rubber composition).

[0091] Alternatively, for example, a modified rubber having a heterocyclic compound bonded to the main chain of a rubber component may be prepared in advance, and in the first stage of kneading, the modified rubber prepared in advance may be kneaded with any compounding ingredients, and in the second or subsequent stages of kneading, a metal salt and various components appropriately selected as necessary may be blended and kneaded to complex the rubber modified with the heterocyclic compound and form a crosslinked structure by a coordinate bond. This method of producing a rubber composition also makes it possible to easily form a crosslinked structure by a coordinate bond and is also excellent in productivity.

[0092] (Metal-rubber composite manufacturing method) The metal-rubber composite 10 can be produced, for example, by subjecting a metal 1 (such as a cord) to a cleaning treatment as necessary, and then bonding the metal 1 to a rubber composition for the rubber 2. Here, examples of methods for bonding the metal 1 and the rubber 2 include a method in which the metal 1 and the rubber 2 are vulcanized and bonded under pressure and heat.

[0093] <hose> The hose of this embodiment is characterized by including the above-mentioned metal-rubber composite. The hose of this embodiment has excellent durability because it comprises the above-mentioned metal-rubber composite with high adhesion between the metal portion and the rubber portion. In one embodiment, the hose includes an inner rubber layer (inner tube rubber) located on the radially inner side, an outer rubber layer located on the radially outer side, and a metal reinforcing layer (metal 1) located between the inner rubber layer and the outer rubber layer. In one embodiment, the rubber composition for rubber 2 described above can be used for at least one of the inner rubber layer and the outer rubber layer.

[0094] <Rubber crawler> The rubber crawler track of this embodiment is characterized by including the above-mentioned metal-rubber composite. The rubber crawler of this embodiment has excellent durability because it includes the above-mentioned metal-rubber composite with high adhesion between the metal portion and the rubber portion. In one embodiment, the rubber track comprises steel cords (metal 1), an intermediate rubber layer covering the steel cords, a metal core (metal 1) disposed on the intermediate rubber layer, and a main rubber layer surrounding the intermediate rubber layer and the metal core, and further has a plurality of lugs on the contact surface side of the main rubber layer. Here, the rubber composition for rubber 2 described above may be used in any part of the rubber track.

[0095] <Tires> The tire of this embodiment is characterized by including the above-mentioned metal-rubber composite. The tire of this embodiment has excellent durability because it includes the above-mentioned metal-rubber composite with high adhesion between the metal portion and the rubber portion. The application site of the metal-rubber composite in a tire is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include the carcass, belt, and bead core. The tire can be manufactured by a conventional method. For example, components typically used in tire manufacturing, such as a carcass and belt (metal-rubber composite 10) made of an unvulcanized rubber composition and metal cords, and a tread made of an unvulcanized rubber composition, are laminated on a tire-building drum in this order, and the drum is removed to form a green tire. The green tire is then heated and vulcanized in a conventional manner to manufacture a desired tire (e.g., a pneumatic tire). [Example]

[0096] 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.

[0097] <Production of metal-rubber composite> As Metal 1, a zinc-plated steel wire having a diameter of 0.34 mm was prepared. Furthermore, a rubber composition was prepared according to the compounding recipe shown in Table 1 using a conventional Banbury mixer, and the resulting rubber composition was rolled into a rubber sheet having a thickness of 2 mm. Seven of the steel wires were arranged without any gaps, and the steel cord (metal 1) was covered from above and below with the rubber sheet (rubber 2) to prepare a treat reel (unvulcanized metal-rubber composite).

[0098] (1) Evaluation of initial adhesion The treated material prepared as described above was vulcanized at 145°C for 10 minutes to prepare a metal-rubber composite 10 (note that the vulcanization time was shorter than usual to clearly distinguish between the individual examples). Of the seven steel cords in the prepared metal-rubber composite 10, five cords, excluding the two cords at both ends, were peeled together, and the percentage of the rubber-covered area remaining on the steel cords was calculated as the rubber coverage (%). Table 1 shows the rubber coverage. A higher rubber coverage indicates better initial adhesion.

[0099] (2) Evaluation of wet heat adhesion The treated reel prepared as described above was left for 7 days in an air atmosphere at a temperature of 75°C and a relative humidity of 95%RH to allow for moist heat degradation. The treated reel after moist heat degradation was vulcanized at 145°C for 40 minutes to produce a metal-rubber composite 10. Of the seven steel cords in the prepared metal-rubber composite 10, five cords, excluding the two cords at both ends, were peeled together, and the percentage of the rubber-covered area remaining on the steel cords was calculated as the rubber coverage (%). Table 1 shows the rubber coverage. A higher rubber coverage indicates better moist heat adhesion.

[0100] [Table 1]

[0101] *1 NR: Natural rubber *2 IR: Synthetic isoprene rubber, manufactured by ENEOS Materials, product name "IR2200" *3 BR: Butadiene rubber, manufactured by Zeon Corporation, product name "NIPOL BR1220L" *4 Heterocyclic compound: 3,6-di(2-pyridyl)-1,2,4,5-tetrazine, manufactured by Tokyo Chemical Industry Co., Ltd. *5 Carbon black: Tokai Carbon Co., Ltd., Seast 300 (HAF-LS) *6 Zinc oxide: Hakusui Tech Co., Ltd., "Zinc oxide type 2" *7 Organic acid cobalt salt: DIC Corporation, product name "DICNATE NBC-2" *8 Sulfur: Eastman Chemical Company, Crystex HS OT-20 *9 ZDMA: Zinc methacrylate, manufactured by Cray Valley, product name "DYMALINK 708" *10 Vulcanization accelerator: Ouchi Shinko Chemical Industry Co., Ltd., product name "Noccela CZ-G" *11 Other chemicals: total amount of stearic acid, antioxidant, and retarder

[0102] From Table 1, it can be seen that the metal-rubber composite 10 of the example according to the present invention has high initial adhesion and high heat and moisture adhesion between the metal 1 and the rubber 2. [Industrial Applicability]

[0103] The metal-rubber composite of the present invention can be used for hoses, rubber crawlers, tires, etc.

[0104] [Contribution to the United Nations-led Sustainable Development Goals (SDGs)] The SDGs have been proposed to realize a sustainable society. One embodiment of the present invention is thought to be a technology that can contribute to the achievement of goals such as "No. 12 Responsible Consumption and Production" and "No. 13 Take concrete action against climate change." [Explanation of symbols]

[0105] 1: Metal 2: Rubber 10: Metal-rubber composite

Claims

1. A metal-rubber composite comprising a metal and a rubber at least partially adhered to the metal, The rubber a rubber component including an isoprene skeleton rubber and a butadiene rubber; 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; at least one metal salt selected from the group consisting of metal halide salts, metal acrylate salts, metal methacrylate salts, and metal acetate salts; A metal-rubber composite comprising a rubber composition comprising:

2. 2. The metal-rubber composite according to claim 1, wherein the content of the isoprene skeleton rubber is 75 parts by mass or more per 100 parts by mass of the rubber component.

3. 2. The metal-rubber composite according to claim 1, wherein the rubber composition contains a butadiene rubber as the butadiene-based rubber.

4. The metal-rubber composite according to claim 1, wherein the heterocyclic compound has a triazine ring or a tetrazine ring.

5. The heterocyclic compound 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 are each independently a single bond or a divalent hydrocarbon group.

6. 2. The metal-rubber composite according to claim 1, wherein the content of the heterocyclic compound in the rubber composition is 0.01 to 5 parts by mass per 100 parts by mass of the rubber component.

7. The metal-rubber composite according to claim 1 , wherein the metal salt comprises a metal methacrylate.

8. the metal is a steel cord consisting of a plurality of steel filaments, 2. The metal-rubber composite according to claim 1, wherein the N atoms on the surface of the steel cord are 2 atomic % or more and 60 atomic % or less, and the Cu / Zn ratio is 1 or more and 4 or less.

9. The steel cord is made by twisting together a plurality of steel filaments having brass-plated peripheral surfaces, The metal-rubber composite according to claim 8, wherein the brass plating has a composition of 40 to 80 mass % of Cu and 20 to 60 mass % of Zn.

10. The metal-rubber composite according to claim 8, wherein the steel cord has been surface-treated with a buffer solution having a pH of 5.0 to 7.2 and treated with one or more triazole compounds selected from 1,2,4-triazole, 1,2,3-triazole, 3-amino-1,2,4-triazole, 4-amino-1,2,4-triazole, benzotriazole, tolyltriazole, and 3-mercapto-1,2,4-triazole.

11. The steel filaments have an N element content of 60 ppm by mass or more, a C element content of 0.7 to 1.0% by mass, a Cu element content of 0.01 to 0.4% by mass, and a Cr element content of 0.05 to 0.3% by mass. The metal-rubber composite according to claim 8.

12. The metal-rubber composite according to claim 11, wherein the steel filaments have a Cu element content of 0.05 to 0.4 mass%.

13. The metal-rubber composite of claim 8, wherein the steel filaments have a diameter of 0.15 mm to 0.6 mm.

14. A hose comprising the metal-rubber composite material according to any one of claims 1 to 13.

15. A rubber crawler comprising the metal-rubber composite according to any one of claims 1 to 13.

16. A tire comprising a metal-rubber composite according to any one of claims 1 to 13.

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