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

Abstract

To provide a metal-rubber composite having excellent adhesiveness between a metal and a rubber and improved durability of a rubber part.SOLUTION: A metal-rubber composite 10 includes metals 1 and rubber 2 at least a part of which is bonded to the metals 1, wherein the rubber 2 is made of a rubber composition containing rubber components (A), carbon black (B), sulfurs (C), and peroxides (D), and the surfaces of the metals 1 are treated with a solvent (i) of pH7 or less.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 on the rubber side, 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 a steel wire / rubber composite formed by applying a solution containing a cobalt metal salt to a zinc-plated steel wire, then coating the wire with a rubber composition that does not contain a cobalt metal salt, and vulcanizing the resulting steel wire. Patent Document 2 below also discloses a rubber-to-metal adhesion promoter comprising a specific metal salt, a rubber composition containing such an adhesion promoter, and a tire having a steel cord / rubber composite comprising the rubber composition and a steel cord. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-324753 [Patent Document 2] International Publication No. 2016 / 039375 Summary of the Invention [Problem to be solved by the invention]

[0004] Meanwhile, in recent years, with the advancement in performance of rubber articles such as the above-mentioned tires, it has become necessary to prevent failures due to deterioration of the adhesive interface between the metal member and the rubber even when the rubber article is exposed to a deteriorating environment during actual use. In response to this demand, there is a demand for improvements in the durability of the rubber itself. In contrast to this, the above-mentioned Patent Documents 1 and 2 aim to improve the adhesiveness between the metal member and the rubber, but there is room for improvement in the durability of the rubber itself.

[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 that has excellent adhesion between the metal and rubber and improved durability of the rubber portion. 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 is made of a rubber composition containing a rubber component (A), carbon black (B), sulfur (C), and a peroxide (D), A metal-rubber composite, characterized in that the metal has a surface treated with a solution (i) having a pH of 7 or less. The metal-rubber composite of the present invention described in [1] above has excellent adhesion between the metal and the rubber, and the durability of the rubber portion is improved.

[0008] [2] The metal-rubber composite according to [1], wherein the surface of the metal is treated with an organic acid (i-1). The metal-rubber composite described in [2] above has further improved adhesion between the metal and the rubber.

[0009] [3] The metal-rubber composite according to [1] or [2], wherein the surface of the metal is further treated with an amine-based rust inhibitor (ii). The metal-rubber composite described in [3] above has further improved adhesion between the metal and the rubber.

[0010] [4] The metal-rubber composite according to any one of [1] to [3], wherein the content of the sulfur (C) in the rubber composition is 4 parts by mass or less per 100 parts by mass of the rubber component (A). The metal-rubber composite described in [4] above has a further improved durability of the rubber portion, and in particular, the breaking elongation of the rubber portion after deterioration is further improved.

[0011] [5] The metal-rubber composite according to any one of [1] to [4], wherein the mass ratio (C / D) of the sulfur (C) to the peroxide (D) in the rubber composition is 0.5 to 2.5. The metal-rubber composite described in [5] above has further improved durability of the rubber portion.

[0012] [6] The metal-rubber composite according to any one of [1] to [5], wherein the rubber composition further contains a metal acrylate or a derivative thereof (E). The metal-rubber composite described in [6] above has improved adhesion between the metal and the rubber.

[0013] [7] The metal-rubber composite according to any one of [1] to [6], wherein the rubber composition further contains zinc diacrylate or a derivative thereof (E1). The metal-rubber composite described in [7] above has further improved adhesion between the metal and the rubber.

[0014] [8] The metal-rubber composite according to [6], wherein the mass ratio (D / E) of the peroxide (D) to the metal acrylate or its derivative (E) in the rubber composition is 0.5 or more. The metal-rubber composite described in [8] above has further improved durability of the rubber portion.

[0015] [9] The metal-rubber composite according to [7], wherein the mass ratio (D / E1) of the peroxide (D) to the zinc diacrylate or its derivative (E1) in the rubber composition is 0.5 or more. The metal-rubber composite described in [9] above has further improved durability of the rubber portion.

[0016]

[10] The metal-rubber composite according to any one of [1] to [9], wherein the mass ratio (C / D) of the sulfur (C) to the peroxide (D) in the rubber composition is 0.5 or more and less than 2.0. The metal-rubber composite described in

[10] above has further improved durability of the rubber portion.

[0017]

[11] The metal-rubber composite according to [6] or [8], wherein the mass ratio (D / E) of the peroxide (D) to the metal acrylate or its derivative (E) in the rubber composition is 0.5 to 3. The metal-rubber composite described in

[11] above has further improved durability of the rubber portion.

[0018]

[12] The metal-rubber composite according to [7] or [9], wherein the mass ratio (D / E1) of the peroxide (D) to the zinc diacrylate or its derivative (E1) in the rubber composition is 0.5 to 3. The metal-rubber composite described in

[12] above has further improved durability of the rubber portion.

[0019]

[13] The metal-rubber composite according to any one of [1] to

[12] , wherein the rubber component (A) contains an isoprene-skeleton rubber (A1). The metal-rubber composite described in

[13] above has further improved adhesion between the metal and the rubber.

[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 having excellent adhesion between the metal and the rubber and improved durability of the rubber portion. 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 in this metal-rubber composite is made of a rubber composition containing a rubber component (A), carbon black (B), sulfur (C), and a peroxide (D), and the metal has a surface treated with a solution (i) having a pH of 7 or less.

[0028] In the metal-rubber composite of this embodiment, the adhesion (particularly initial adhesion) between the metal and rubber is improved by treating the metal surface with solution (i) having a pH of 7 or less. The mechanism by which the adhesion (particularly initial adhesion) between the metal and rubber is improved is not limited to a particular theory, but is presumed to be as follows. Generally, metal components may have lubricants and rust inhibitors attached to their surfaces for ease of handling and to protect the metal from corrosion. It is believed that these lubricants and rust inhibitors form a coating that inhibits adhesion between the metal component and rubber. Furthermore, if the metal component has a plating layer on its surface, oxides of metals such as copper and zinc that make up the plating layer form a coating on the surface of the metal component, inhibiting adhesion between the metal component and rubber. Therefore, it is believed that the adhesion between the metal and rubber (particularly, initial adhesion) can be improved by removing at least a portion of the coating present on the surface of the metal component. In the metal-rubber composite of this embodiment, pretreating the metal surface with solution (i) having a pH of 7 or less removes at least a portion of the coating present on the metal surface, and also moderately activates the metal surface to a state suitable for adhesion with rubber, thereby improving the adhesion between the metal and rubber (particularly, initial adhesion).

[0029] The rubber composition constituting the rubber portion of the metal-rubber composite of this embodiment contains sulfur (C) and peroxide (D) as crosslinking agents, and the rubber portion of the composite contains sulfur crosslinks and crosslinked structures (C-C bonds, etc.) resulting from the peroxide. Here, the sulfur crosslinks and the crosslinked structures resulting from the peroxide contribute to improving the durability of the rubber portion of the composite. The rubber composition constituting the rubber portion of the metal-rubber composite of this embodiment also contains carbon black (B), which improves the reinforcing properties of the rubber portion of the composite and contributes to improving the durability of the rubber portion of the composite. Therefore, the metal-rubber composite of this embodiment has excellent adhesion between the metal and the rubber, and also has improved durability of the rubber portion.

[0030] 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.

[0031] (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.

[0032] 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.

[0033] - Treatment with solution (i) of pH 7 or less - The metal 1 is characterized in that the surface thereof is treated with a solution (i) having a pH of 7 or less. Treating the surface of the metal 1 with a solution (i) having a pH of 7 or less improves the adhesion (particularly the initial adhesion) between the metal and the rubber.

[0034] Examples of methods for contacting the surface of metal 1 with solution (i) having a pH of 7 or less include spraying solution (i) having a pH of 7 or less onto metal 1 and immersing metal 1 in solution (i) having a pH of 7 or less. Surface treatment of metal 1 with solution (i) having a pH of 7 or less may be performed multiple times. For example, spraying solution (i) having a pH of 7 or less onto metal 1 may be repeated multiple times, or metal 1 may be immersed in solution (i) having a pH of 7 or less, washed with water, or the like, and then immersed again in solution (i) having a pH of 7 or less.

[0035] In this embodiment, solution (i) having a pH of 7 or less is used as a treatment liquid for surface treatment of metal 1. When metal-rubber composites 10 are continuously produced, or when metal 1 is immersed in solution (i), washed with water, or the like, and then immersed again in solution (i), the pH of solution (i) may fluctuate due to elution of metal from the surface of metal 1 or contamination with water. Therefore, if solution (i) is a buffer solution, it is advantageous because the pH is less likely to fluctuate, and solution (i) preferably contains a weak acid and its salt. From the viewpoint of using solution (i) as a buffer solution, the acid contained in solution (i) is preferably acetic acid, and the metal component contained in solution (i) is preferably sodium or potassium.

[0036] The pH of the solution (i) is 7 or less. If the pH exceeds 7, it becomes difficult to remove the coating present on the surface of the metal 1, and the adhesion between the metal and the rubber (particularly, the initial adhesion) is not sufficiently improved. Furthermore, the pH of the solution (i) is preferably 5 or more. If the pH of the solution (i) is 5 or more, adverse effects on the surface of the metal 1 can be suppressed, and corrosion of the metal 1 and deterioration of its durability can be prevented. From the viewpoints of the adhesion between the metal and the rubber (particularly, the initial adhesion) and the durability of the metal 1, the pH of the solution (i) is preferably 5.2 to 7.0, more preferably 5.4 to 6.8, and even more preferably 6.0 to 6.8. If the pH of the solution (i) is 6.0 to 6.8, the adhesion after leaving the treated mixture is also good.

[0037] The solution (i) preferably contains at least one acid, and more preferably contains an organic acid. The acid contained in the solution (i) is not particularly limited, but from the viewpoints of adhesion between the metal and the rubber (particularly initial adhesion) and durability of the metal 1, a weak acid is preferred, and an acid having an acid dissociation constant (pKa) of 4 or more and 8 or less is preferred, such as acetic acid, phthalic acid, succinic acid, citric acid, phosphoric acid, carbonic acid, etc. These acids may be used alone or in combination of two or more.

[0038] Specific examples of the solution (i) include acetic acid-sodium acetate buffer solution, potassium hydrogen phthalate-sodium hydroxide buffer solution, sodium citrate-sodium hydroxide buffer solution, succinic acid-sodium tetraborate buffer solution, sodium dihydrogen phosphate-disodium hydrogen phosphate buffer solution, etc. Among these, acetic acid-sodium acetate buffer solution is preferred.

[0039] The surface of the metal 1 is preferably treated with an organic acid (i-1). Examples of the organic acid include acetic acid, phthalic acid, succinic acid, and citric acid, with acetic acid being preferred. Treating the surface of the metal 1 with the organic acid (i-1) suppresses adverse effects on the surface of the metal 1, preventing corrosion and deterioration of the durability of the metal 1, while removing at least a portion of the coating present on the surface of the metal 1. Furthermore, the surface of the metal 1 is suitably activated to a state suitable for adhesion to rubber, further improving the adhesion (particularly the initial adhesion) between the metal 1 and the rubber 2.

[0040] If necessary, a metal salt, an alcohol, or the like may be added to the solution (i) as long as the effect of the present invention is not impaired. The metal salt is not particularly limited as long as it has high solubility in water, and examples thereof include metal chlorides, metal carbonates, metal nitrates, metal sulfates, metal acetates, metal citrates, metal gluconates, metal acetylacetonates, etc. Among these, metal acetates are preferred. The metal constituting the metal salt is preferably a metal with an ionization tendency lower than that of zinc and higher than that of copper. Examples of such metals include chromium (Cr), iron (Fe), cadmium (Cd), cobalt (Co), nickel (Ni), tin (Sn), and lead (Pb). Among these, cobalt is preferred. Cobalt is sometimes compounded into the rubber composition constituting rubber 2 as an adhesion promoter to improve adhesion. However, depending on the amount of cobalt contained in rubber 2, this can reduce the durability of the rubber itself against heat, moisture, and oxidation. However, by having such cobalt present on the surface of metal 1, the cobalt content in rubber 2 can be reduced, and compounding costs can be reduced while effectively suppressing deterioration in the physical properties of rubber 2. The concentration of the metal salt is usually 0.001 to 1 mol / L, preferably 0.005 to 0.5 mol / L, and more preferably 0.01 to 0.2 mol / L.

[0041] The time during which the metal 1 is in contact with the solution (i) (referred to as the "surface treatment time") can be adjusted appropriately depending on the pH of the solution (i), and is usually in the range of 0.5 to 20 seconds, preferably 1 to 15 seconds. When the pH of the solution (i) is low, the surface treatment time can be short. When the pH of the solution (i) is high, the surface treatment time can be long. In other words, when the pH of the solution (i) is high, it is easy to change the degree of surface treatment of the metal 1 by adjusting the surface treatment time. In addition, the treatment temperature with the solution (i) is preferably 10 to 40°C, more preferably 15 to 30°C.

[0042] - Treatment with amine-based rust inhibitor (ii) - It is preferable that the surface of the metal 1 is further treated with an amine-based rust inhibitor (ii). As described above, the surface of the metal 1 is activated by treating the surface with the solution (i) having a pH of 7 or less, but further treating the surface of the metal 1 with the amine-based rust inhibitor (ii) adjusts the activity of the surface of the metal 1 and makes it more suitable for adhesion to the rubber 2, thereby further improving the adhesion between the metal 1 and the rubber 2, and in particular, improving the adhesion after moist heat aging is expected.

[0043] The amine-based rust inhibitor (ii) contains an amine compound having a rust-preventing effect. The amine-based rust inhibitor (ii) is preferably an aqueous solution of a triazole compound. Examples of the aqueous solution of the triazole compound include an aqueous solution of one or more triazole compounds selected from benzotriazole, tolyltriazole, 1,2,4-triazole, 1,2,3-triazole, 3-amino-1,2,4-triazole, 4-amino-1,2,4-triazole, and 3-mercapto-1,2,4-triazole. Among these, it is preferable to use water-soluble solutions of 1,2,4-triazole, 1,2,3-triazole, 3-amino-1,2,4-triazole, and 4-amino-1,2,4-triazole. The concentration of the aqueous triazole solution is preferably 0.1 to 5 g / L. The treatment time with the amine-based rust inhibitor (ii) varies depending on the concentration, but is usually in the range of 0.5 to 30 seconds, preferably 1 to 15 seconds. The treatment temperature with the amine-based rust inhibitor (ii) is preferably 10 to 40°C, more preferably 15 to 30°C.

[0044] (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 (A), carbon black (B), sulfur (C), and peroxide (D).

[0045] -Rubber component (A)- The rubber composition used for the rubber 2 contains a rubber component (A), which provides rubber elasticity to the rubber 2. The rubber component (A) is preferably a diene rubber, and examples of the diene rubber include isoprene-based rubber, butadiene rubber (BR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), halogenated butyl rubber (Cl-IIR, Br-IIR, etc.), and ethylene-propylene rubber (EPR, EPDM). The rubber component (A) may also contain a non-diene rubber, such as fluororubber, silicone rubber, or urethane rubber. These rubber components (A) may be used alone or as a blend of two or more.

[0046] The rubber component (A) preferably contains an isoprene skeleton rubber (A1). The isoprene skeleton rubber (A1) is a rubber whose main skeleton is an isoprene unit, and specific examples thereof include natural rubber (NR) and synthetic isoprene rubber (IR). A rubber 2 made of a rubber composition containing the isoprene skeleton rubber (A1) as the rubber component (A) has excellent adhesion to a metal 1. Therefore, by using a rubber composition containing the isoprene skeleton rubber (A1) as the rubber 2, the adhesion between the metal 1 and the rubber 2 is further improved. Furthermore, by using a rubber composition containing the isoprene skeleton rubber (A1) as the rubber 2, the strength of the rubber 2 can also be improved. The proportion of the isoprene skeleton rubber (A1) in the rubber component (A) is preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass.

[0047] -Carbon black (B)- The rubber composition used for the rubber 2 contains carbon black (B). By applying a rubber composition containing carbon black (B) to the rubber 2, the reinforcing properties of the rubber 2 are improved, and the durability of the rubber 2 is improved.

[0048] Examples of the carbon black (B) include GPF, FEF, HAF, ISAF, and SAF grade carbon blacks. These carbon blacks (B) may be used alone or in combination of two or more.

[0049] The content of the carbon black (B) in the rubber composition is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 50 parts by mass or more, and preferably 120 parts by mass or less, even more preferably 100 parts by mass or less, and even more preferably 80 parts by mass or less, per 100 parts by mass of the rubber component (A). When the content of the carbon black (B) is 10 parts by mass or more per 100 parts by mass of the rubber component (A), the reinforcing properties of the rubber 2 are further improved, and the durability of the rubber 2 is further improved. Furthermore, when the content of the carbon black (B) is 120 parts by mass or less per 100 parts by mass of the rubber component (A), the workability in kneading the rubber composition is further improved.

[0050] -Sulfur(C)- The rubber composition used for the rubber 2 contains sulfur (C). When the rubber composition used for the rubber 2 contains sulfur (C), sulfur crosslinks are present in the rubber 2, and the durability of the rubber 2 is improved.

[0051] The sulfur (C) is not particularly limited, and various types of sulfur can be used, such as ordinary sulfur (soluble sulfur (powdered sulfur) and the like), insoluble sulfur, and oil treat sulfur can also be used. Here, insoluble sulfur is sulfur insoluble in carbon disulfide (amorphous polymeric sulfur), and soluble sulfur (powdered sulfur) is sulfur soluble in carbon disulfide.

[0052] The content of the sulfur (C) in the rubber composition is preferably 0.1 part by mass or more, more preferably 0.5 parts by mass or more, even more preferably 1 part by mass or more, and preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 4 parts by mass or less, per 100 parts by mass of the rubber component (A). When the content of sulfur (C) is 0.1 part by mass or more per 100 parts by mass of the rubber component (A), the network density due to the sulfur is improved, and the durability of the rubber 2 is further improved. When the content of sulfur (C) is 10 parts by mass or less per 100 parts by mass of the rubber component (A), a crosslinked rubber with sufficient elastomeric properties is obtained, and the elongation at break of the rubber 2 is improved. When the content of sulfur (C) is 4 parts by mass or less per 100 parts by mass of the rubber component (A), the durability of the rubber 2 is further improved, and in particular, the elongation at break of the rubber 2 after aging is further improved. Although reducing the content of sulfur (C) improves the durability of the rubber 2 after deterioration, there is a risk that the adhesion to ordinary metal members may deteriorate. However, in the metal-rubber composite 10 of this embodiment, as described above, by combining the metal 1 whose surface has been treated with the solution (i) having a pH of 7 or less with the rubber 2, the adhesion between the metal 1 and the rubber 2 can be made sufficiently excellent.

[0053] -Peroxide (D)- The rubber composition used for the rubber 2 contains a peroxide (D). When the rubber composition used for the rubber 2 contains the peroxide (D), a crosslinked structure (such as a C-C bond) resulting from the peroxide (D) is present in the rubber 2, and the durability of the rubber 2 is improved.

[0054] The peroxide (D) may be either an organic peroxide or an inorganic peroxide, but is preferably an organic peroxide. Here, the organic peroxide is not particularly limited, but examples thereof include tert-butyl hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, cumene hydroperoxide, p-menthane hydroperoxide, diisopropylbenzene hydroperoxide, dicumyl peroxide, di-tert-butyl peroxide, di-tert-hexyl peroxide, diisopropylbenzene hydroperoxide, tert-butylcumyl peroxide, di(2-tert-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, perbenzoic acid, benzoyl peroxide, 1,1-bis(1,1-dimethylethylperoxy)cyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, Examples of peroxyl groups include 1,1-bis(tert-hexylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-hexylperoxy)cyclohexane, 2,2-bis(4,4-di-(tert-butylperoxy)cyclohexyl)propane, n-butyl-4,4-di-(tert-butylperoxy)valerate, tert-butyl peroxylaurate, tert-butylperoxy-2-ethylhexanate, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, tert-hexylperoxy-2-ethylhexanoate, tert-butylperoxy-2-ethylhexanoate, tert-butyl peroxyacetate, cyclohexanone peroxide, acetylacetone peroxide, diisopropyl peroxydicarbonate, and di(4-tert-butylcyclohexyl)peroxydicarbonate. Examples of inorganic peroxides include hydrogen peroxide, sodium persulfate, potassium persulfate, ammonium persulfate, etc. These peroxides (D) may be used alone or in combination of two or more.

[0055] The content of the peroxide (D) in the rubber composition is preferably 0.1 part by mass or more, more preferably 0.5 parts by mass or more, even more preferably 1 part by mass or more, and preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 4 parts by mass or less, per 100 parts by mass of the rubber component (A). When the content of the peroxide (D) is 0.1 part by mass or more per 100 parts by mass of the rubber component (A), the network density of the crosslinked structure resulting from the peroxide (D) is improved, and the durability of the rubber 2 is further improved. When the content of the peroxide (D) is 10 parts by mass or less per 100 parts by mass of the rubber component (A), a crosslinked rubber having sufficient elastomeric properties is obtained, and the elongation at break of the rubber 2 is further improved.

[0056] The mass ratio (C / D) of the sulfur (C) to the peroxide (D) in the rubber composition is preferably 0.5 to 2.5, and more preferably 0.5 or more and less than 2.0. When the mass ratio (C / D) of the sulfur (C) to the peroxide (D) is within the range of 0.5 to 2.5, the durability of the rubber 2 is further improved. Furthermore, when the mass ratio (C / D) of the sulfur (C) to the peroxide (D) is less than 2.0, the durability of the rubber 2, particularly the elongation at break after aging, is further improved. Therefore, by applying a rubber composition having a mass ratio (C / D) of the sulfur (C) to the peroxide (D) of 0.5 or more and less than 2.0 to the rubber 2, the durability of the rubber 2, particularly the elongation at break after aging, can be further improved. In addition, the mass ratio (C / D) of sulfur (C) to peroxide (D) is more preferably 1.99 or less, more preferably 1.98 or less, more preferably 1.97 or less, even more preferably 1.96 or less, and particularly preferably 1.95 or less, from the viewpoint of the breaking elongation after deterioration of rubber 2.

[0057] -Metal acrylate or its derivative (E)- The rubber composition used for the rubber 2 preferably further contains a metal acrylate or a derivative thereof (E). When the rubber composition used for the rubber 2 contains a metal acrylate or a derivative thereof (E), the adhesion between the metal 1 and the rubber 2 is improved, and the elastic modulus of the rubber 2 is also improved, further improving the durability of the rubber 2. Here, the metal acrylate is a metal salt of acrylic acid. The metal acrylate derivative is a compound in which the hydrogen atom in the metal salt of acrylic acid is substituted with a substituent, and the substituent can be an alkyl group such as a methyl group. The metal acrylate derivative can be, for example, a metal salt of methacrylic acid.

[0058] Examples of the metal constituting the metal acrylate or its derivative (E) include zinc, magnesium, calcium, etc. The valence of the metal ion in the metal acrylate or its derivative (E) is not particularly limited, and each element may have any valence, but is preferably divalent or greater.

[0059] Specific examples of the metal acrylate or derivative thereof (E) include zinc diacrylate, magnesium diacrylate, calcium diacrylate, zinc dimethacrylate, magnesium dimethacrylate, calcium dimethacrylate, etc. These metal acrylates or derivatives thereof (E) may be used alone or in combination of two or more.

[0060] The content of the metal acrylate or derivative thereof (E) in the rubber composition is preferably 0.1 part by mass or more, more preferably 0.3 part by mass or more, even more preferably 0.5 parts by mass or more, and preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 4 parts by mass or less, per 100 parts by mass of the rubber component (A). When the content of the metal acrylate or derivative thereof (E) is 0.1 part by mass or more per 100 parts by mass of the rubber component (A), the durability of the rubber 2 is further improved. When the content of the metal acrylate or derivative thereof (E) is 10 parts by mass or less per 100 parts by mass of the rubber component (A), a crosslinked rubber with sufficient elastomeric properties is obtained, and the breaking elongation of the rubber 2 is further improved.

[0061] Among the metal acrylates or derivatives thereof (E), zinc diacrylate or derivatives thereof (E1) is preferred. When the rubber composition used for the rubber 2 contains zinc diacrylate or derivatives thereof (E1), the adhesion between the metal 1 and the rubber 2 is further improved, and the elastic modulus of the rubber 2 is also improved, thereby further improving the durability of the rubber 2. Here, examples of zinc diacrylate or its derivative (E1) include the above-mentioned zinc diacrylate and zinc dimethacrylate (ZDMA), and among these, zinc dimethacrylate is preferred.

[0062] The content of the zinc diacrylate or derivative thereof (E1) in the rubber composition is preferably 0.1 part by mass or more, more preferably 0.3 part by mass or more, and even more preferably 0.5 parts by mass or more, per 100 parts by mass of the rubber component (A), and is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 4 parts by mass or less. When the content of the zinc diacrylate or derivative thereof (E1) is 0.1 part by mass or more per 100 parts by mass of the rubber component (A), the durability of the rubber 2 is further improved. When the content of the zinc diacrylate or derivative thereof (E1) is 10 parts by mass or less per 100 parts by mass of the rubber component (A), a crosslinked rubber having sufficient elastomeric properties is obtained, and the elongation at break of the rubber 2 is further improved.

[0063] The mass ratio (D / E) of the peroxide (D) to the metal acrylate or derivative thereof (E) is preferably 0.5 or more, and more preferably 0.5 to 3. When the mass ratio (D / E) of the peroxide (D) to the metal acrylate or derivative thereof (E) is 0.5 or more, the durability of the rubber 2 is further improved. Furthermore, when the mass ratio (D / E) of the peroxide (D) to the metal acrylate or derivative thereof (E) is 0.5 to 3, the durability of the rubber 2 is further improved.

[0064] Furthermore, when the metal acrylate or derivative thereof (E) is zinc diacrylate or derivative thereof (E1), the mass ratio (D / E1) of the peroxide (D) to the zinc diacrylate or derivative thereof (E1) is preferably 0.5 or more, and more preferably 0.5 to 3. When the mass ratio (D / E1) of the peroxide (D) to the zinc diacrylate or derivative thereof (E1) is 0.5 or more, the durability of the rubber 2 is further improved. When the mass ratio (D / E1) of the peroxide (D) to the zinc diacrylate or derivative thereof (E1) is 0.5 to 3, the durability of the rubber 2 is further improved.

[0065] -others- The rubber composition used for the rubber 2 may contain the above-mentioned rubber component (A), carbon black (B), sulfur (C), peroxide (D), and metal acrylate or its derivative (E), as well as compounding agents commonly used in the rubber industry, such as fillers other than carbon black (silica, clay, talc, calcium carbonate, aluminum hydroxide, etc.), zinc oxide (zinc white), softeners, stearic acid, antioxidants, waxes, silane coupling agents, vulcanization accelerators, and retarders (vulcanization retarders), all of 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.

[0066] 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 2 to 10 parts by mass, per 100 parts by mass of the rubber component (A).

[0067] The content of the stearic acid is not particularly limited, and is preferably in the range of 0.1 to 5 parts by mass, more preferably 0.3 to 4 parts by mass, and even more preferably 0.5 to 3 parts by mass, per 100 parts by mass of the rubber component (A).

[0068] 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 0.5 to 3 parts by mass, per 100 parts by mass of the rubber component (A).

[0069] 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 3 parts by mass, per 100 parts by mass of the rubber component (A).

[0070] Examples of the retarder include N-(cyclohexylthio)phthalimide, N-phenyl-N-(trichloromethylthio)benzenesulfonamide, etc. The content of the retarder is not particularly limited, and is preferably in the range of 0.01 to 3 parts by mass, more preferably 0.1 to 2 parts by mass, per 100 parts by mass of the rubber component (A).

[0071] 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 (A), and more preferably contains no cobalt compound. Furthermore, because the addition of a cobalt compound accelerates thermal degradation of rubber 2, it is desirable that the rubber composition 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 not be compounded, at least when producing the rubber composition used for rubber 2.

[0072] -Method of manufacturing rubber composition- The method for producing the rubber composition used for the rubber 2 is not particularly limited, but it can be produced, for example, by blending various components appropriately selected as necessary with the above-mentioned rubber component (A), carbon black (B), sulfur (C), and peroxide (D), and kneading, heating, extruding, etc. Furthermore, the obtained rubber composition can be crosslinked by heating to form a crosslinked rubber.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] The crosslinking device, method, conditions, etc. are not particularly limited and can be appropriately selected depending on the purpose. Examples of devices for crosslinking include a molding vulcanizer using a mold used for crosslinking (vulcanization) of rubber compositions. The crosslinking temperature is, for example, about 100 to 190°C.

[0077] (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.

[0078] <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 includes the above-mentioned metal-rubber composite, which has excellent adhesion between the metal portion and the rubber portion and improved durability of 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.

[0079] <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, which has excellent adhesion between the metal portion and the rubber portion and improved durability of 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.

[0080] <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, which has excellent adhesion between the metal portion and the rubber portion and improved durability of 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]

[0081] 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.

[0082] <Preparation of Steel Cord 1> Steel wires whose surfaces were brass-plated (Cu: 63 mass %, Zn: 37 mass %) were twisted together to produce a steel cord 1 having a 1+6 structure.

[0083] <Preparation of Steel Cord 2> The prepared steel cord 1 was immersed in a sodium acetate aqueous solution adjusted to pH 6.4 and washed with water, then immersed in the above-mentioned amine-based rust inhibitor solution and washed with water, and then dried with hot air to prepare steel cord 2.

[0084] <Preparation of rubber sheet> According to the compounding recipe shown in Table 1, a rubber composition was prepared using a conventional Banbury mixer, and the resulting rubber composition was rolled into a rubber sheet (a) having a thickness of 2 mm.

[0085] <Production of metal-rubber composite> A rubber composition is prepared using a conventional Banbury mixer according to the compounding recipe shown in Table 1, and the resulting rubber composition is rolled into a rubber sheet (b) having a thickness of 2 mm. The steel cords (metal 1) prepared as described above are arranged in parallel at intervals of 2.5 mm, and the steel cords are covered from above with the rubber sheet (b) (rubber 2), and then crosslinked by heating at 145°C for 40 minutes to prepare a metal-rubber composite 10.

[0086] (1) Evaluation of initial adhesion The steel cord is pulled out from the metal-rubber composite 10 produced as described above, and the coverage of the rubber adhering to the steel cord is visually observed and expressed as 0 to 100%, which is used as an index of initial adhesion. The rubber coverage is shown in Table 1. A higher rubber coverage indicates better initial adhesion. The initial adhesion is evaluated / classified according to the following criteria. A: Rubber coverage is between 75% and 100% B: Rubber coverage is 50% or more but less than 75% C: Rubber coverage is 25% or more but less than 50% D: Rubber coverage is 0% or more but less than 25%

[0087] (2) Breaking elongation after degradation A 160mm x 160mm x 2mm slab plate prepared by thermally crosslinking the rubber sheet (a) was placed in a gear aging tester (gear oven) manufactured by Toyo Seiki Seisakusho, and subjected to atmospheric aging for two days at a temperature of 100°C. The aged slabs were punched into JIS No. 3 dumbbell shapes to produce rubber samples, which were then measured for breaking elongation (%) using a fully automatic tensile tester manufactured by Toyo Seiki Seisakusho Co., Ltd. The breaking elongation after aging was evaluated and classified according to the following criteria: A: Breaking elongation after degradation is 200% or more B: Breaking elongation after degradation is 150% or more and less than 200% C: Breaking elongation after degradation is less than 150%

[0088] [Table 1]

[0089] *1 Steel cord 1: A steel cord prepared as described above, the surface of which has not been treated with a solution (i) having a pH of 7 or less. *2 Steel cord 2: Steel cord prepared as described above, the surface of which has been treated with a solution (i) of pH 7 or less and an amine-based rust inhibitor (ii).

[0090] *3 Carbon black: Asahi Carbon Co., Ltd., product name "Asahi #70L" *4 Organic acid cobalt salt: Manobond, manufactured by OMG, product name "Manobond C" *5 Stearic acid: New Japan Chemical Co., Ltd., product name "Stearic Acid 50S" *6 Vulcanization accelerator 1: Ouchi Shinko Chemical Industry Co., Ltd., product name "Noccela DZ" *7 Vulcanization accelerator 2: Ouchi Shinko Chemical Industry Co., Ltd., product name "Noccela CZ-G" *8 Sulfur: Tsurumi Chemical Industry Co., Ltd., product name "Powdered sulfur" *9 Peroxide: NOF Corporation, product name "Percumyl D-40", containing dicumyl peroxide at a concentration of 40% by mass. The actual amount of peroxide is shown in the lower part. *10 Metal acrylate derivative: Zinc dimethacrylate, manufactured by Cray Valley, product name "DYMALINK 708" *11 Zinc oxide: manufactured by Hakusui Tech Co., Ltd., product name "Zinc oxide type 2" *12 Other chemicals: total amount of antioxidants and retarders

[0091] Example 1 in Table 1 shows that a metal-rubber composite using a steel cord whose surface was treated with solution (i) having a pH of 7 or less, while using a rubber composition containing both sulfur and peroxide as crosslinking agents in the rubber portion and no organic acid cobalt salt, exhibited excellent initial adhesion between the metal and rubber. On the other hand, Comparative Example 2 shows that a metal-rubber composite using a rubber composition that does not contain an organic acid cobalt salt in the rubber portion has poor initial adhesion between the metal and rubber. Also, Comparative Example 3 shows that a metal-rubber composite using a rubber composition that does not contain an organic acid cobalt salt, has a reduced sulfur content, and is blended with peroxide in the rubber portion has significantly poor initial adhesion between the metal and rubber. Furthermore, a comparison between Comparative Example 3 and Comparative Example 4 shows that using a rubber composition containing a metal acrylate derivative in the rubber portion can suppress a decrease in the initial adhesion between the metal and the rubber. However, a comparison between Comparative Example 4 and Example 1 shows that when a rubber composition not containing an organic acid cobalt salt is used in the rubber portion, the decrease in the initial adhesion between the metal and the rubber cannot be sufficiently suppressed unless the surface of the steel cord is treated with solution (i) having a pH of 7 or less.

[0092] Furthermore, it can be seen from Example 1, Comparative Example 3, and Comparative Example 4 that rubbers made from rubber compositions that do not contain organic acid cobalt salts and contain both sulfur and peroxide as crosslinking agents have large breaking elongation after aging and excellent durability. On the other hand, Comparative Example 1 shows that the rubber made from the rubber composition containing the organic acid cobalt salt has a low breaking elongation after aging and poor durability. Also, Comparative Example 2 shows that the rubber made from the rubber composition containing no peroxide and a high sulfur content also has a low breaking elongation after aging and poor durability. [Industrial Applicability]

[0093] The metal-rubber composite of the present invention can be used for hoses, rubber crawlers, tires, etc.

[0094] [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]

[0095] 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 is made of a rubber composition containing a rubber component (A), carbon black (B), sulfur (C), and a peroxide (D), A metal-rubber composite, characterized in that the surface of the metal is treated with a solution (i) having a pH of 7 or less.

2. 2. The metal-rubber composite according to claim 1, wherein the surface of the metal is treated with an organic acid (i-1).

3. 2. The metal-rubber composite according to claim 1, wherein the surface of the metal is further treated with an amine-based rust inhibitor (ii).

4. 2. The metal-rubber composite according to claim 1, wherein the content of the sulfur (C) in the rubber composition is 4 parts by mass or less per 100 parts by mass of the rubber component (A).

5. 2. The metal-rubber composite according to claim 1, wherein the mass ratio (C / D) of the sulfur (C) to the peroxide (D) in the rubber composition is 0.5 to 2.

5.

6. The metal-rubber composite according to claim 1, wherein the rubber composition further comprises a metal acrylate or a derivative thereof (E).

7. The metal-rubber composite according to claim 1, wherein the rubber composition further comprises zinc diacrylate or a derivative thereof (E1).

8. The metal-rubber composite according to claim 6, wherein the mass ratio (D / E) of the peroxide (D) to the metal acrylate or its derivative (E) in the rubber composition is 0.5 or more.

9. The metal-rubber composite according to claim 7, wherein the mass ratio (D / E1) of the peroxide (D) to the zinc diacrylate or its derivative (E1) in the rubber composition is 0.5 or more.

10. The metal-rubber composite according to claim 1, wherein the mass ratio (C / D) of the sulfur (C) to the peroxide (D) in the rubber composition is 0.5 or more and less than 2.

0.

11. The metal-rubber composite according to claim 6, wherein the mass ratio (D / E) of the peroxide (D) to the metal acrylate or its derivative (E) in the rubber composition is 0.5 to 3.

12. The metal-rubber composite according to claim 7, wherein the mass ratio (D / E1) of the peroxide (D) to the zinc diacrylate or its derivative (E1) in the rubber composition is 0.5 to 3.

13. The metal-rubber composite according to claim 1, wherein the rubber component (A) contains an isoprene skeleton rubber (A1).

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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