Rubber compositions for metal coating, metal-rubber composites, and rubber articles

Abstract

The present invention provides a rubber composition for metal coatings that exhibits excellent durability (particularly in terms of crack propagation resistance and elongation at break after deterioration). [Solution] A rubber composition for metal coating, characterized in that it contains a rubber component (A), carbon black (B), and sulfur (C), wherein the rubber component (A) includes liquid isoprene-based rubber and satisfies at least one of the predetermined conditions (1) and (2).

Description

Technical Field

[0001] The present invention relates to a rubber composition for metal coating, a metal-rubber composite, and a rubber article.

Background Art

[0002] Generally, for rubber articles such as hoses, rubber crawlers, and tires that require strength, a composite of a metal member and rubber (hereinafter referred to as "metal-rubber composite") is used for the purpose of reinforcing the rubber to improve strength and durability. For example, in Patent Document 1 below, a solution containing a cobalt metal salt is attached to a zinc-plated steel wire, and then coated with a rubber composition not containing the cobalt metal salt and vulcanized and adhered to disclose a composite of a steel wire and rubber. Further, Patent Document 2 below discloses an adhesion promoter composed of a specific metal salt, a rubber composition containing such an adhesion promoter, and further a tire having a steel cord-rubber composite composed of the rubber composition and a steel cord.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] On the other hand, recently, with the high performance of rubber articles such as the above-mentioned tires, it is necessary that no failure occurs due to deterioration of the adhesion interface between the metal member and the rubber even when the rubber article is exposed to a deterioration environment during actual use. In response to such a requirement, improvement in the durability of the rubber itself is required.

[0005] In contrast, Patent Documents 1 and 2 aim to improve the adhesion between metal members and rubber, and there is room for improvement regarding the durability of the rubber itself (particularly crack propagation resistance and elongation at break after deterioration).

[0006] Therefore, the present invention aims to solve the problems of the above-mentioned prior art and provide a rubber composition for metal coatings that has excellent durability (particularly crack propagation resistance and elongation at break after deterioration). Furthermore, a further objective of the present invention is to provide a metal-rubber composite and rubber article with excellent durability using such a metal coating rubber composition. [Means for solving the problem]

[0007] The gist of the present invention's rubber composition for metal coating, metal-rubber composite, and rubber article, which solve the above problems, is as follows.

[0008] [1] A rubber composition for metal coating containing a rubber component (A), carbon black (B), and sulfur (C), The rubber component (A) includes liquid isoprene-based rubber, The following conditions (1) and (2): Condition (1) The liquid isoprene-based rubber is modified Condition (2) The rubber composition further contains peroxide (D) A rubber composition for metal coating, characterized by satisfying at least one of the following conditions.

[0009] [2] The rubber composition for metal coating according to [1], wherein the rubber component (A) further contains natural rubber, and the proportion of natural rubber in the rubber component (A) is 50% by mass or more.

[0010] [3] The metal coating rubber composition according to [1] or [2], wherein the liquid isoprene rubber is a maleic acid-modified or maleic anhydride-modified liquid isoprene rubber.

[0011] [4] The rubber composition for metal coating according to any one of [1] to [3], wherein the proportion of the liquid isoprene-based rubber in the rubber component (A) is 10% by mass or more and 50% by mass or less.

[0012] [5] The metal coating rubber composition according to any one of [1] to [4], wherein the carbon black (B) content is 50 parts by mass or more per 100 parts by mass of the rubber component (A).

[0013] [6] The peroxide (D) is contained in the above-mentioned, A rubber composition for metal coating according to any one of [1] to [5], wherein the mass ratio (C / D) of sulfur (C) to peroxide (D) is 0.5 or more and 2.5 or less.

[0014] [7] A metal coating rubber composition according to any one of [1] to [6], further comprising a metal acrylate or a derivative thereof (E).

[0015] [8] The peroxide (D) is contained in the above-mentioned, The rubber composition for metal coating according to [7], wherein the mass ratio (D / E) of the peroxide (D) to the metal acrylate or its derivative (E) is 0.5 or more.

[0016] [9] The metal coating rubber composition according to [7] or [8], wherein the metal acrylate or derivative thereof (E) is zinc diacrylate or a derivative thereof.

[0017]

[10] The metal coating rubber composition according to any one of [1] to [9], wherein the carbon black (B) comprises recycled carbon black.

[0018]

[11] A metal-rubber composite characterized in that a metal member is coated with a metal coating rubber composition described in any of [1] to

[10] .

[0019]

[12] A rubber article which is a hose, rubber crawler, or tire, characterized by comprising the metal-rubber composite described in

[11] . [Effects of the Invention]

[0020] According to the present invention, it is possible to provide a rubber composition for metal coating excellent in durability (particularly, crack growth resistance and elongation at break after deterioration). Further, according to the present invention, it is possible to provide a metal-rubber composite and a rubber article excellent in durability using such a rubber composition for metal coating.

Mode for Carrying Out the Invention

[0021] Hereinafter, the rubber composition for metal coating, the metal-rubber composite, and the rubber article of the present invention will be specifically illustrated and described based on their embodiments.

[0022] <Definition> The compounds described in this specification may be partially or entirely derived from fossil resources, may be derived from biological resources such as plant resources, or may be derived from recycled resources such as used tires. Further, it may be derived from a mixture of any two or more of fossil resources, biological resources, and recycled resources.

[0023] <Rubber Composition for Metal Coating> The rubber composition for metal coating according to an embodiment of the present invention (hereinafter sometimes referred to as "the rubber composition of the present embodiment") is a rubber composition used for coating a metal, and contains a rubber component (A), carbon black (B), and sulfur (C). And, in the rubber composition of the present embodiment, the rubber component (A) includes a liquid isoprene rubber, the following conditions (1) and condition (2): Condition (1) The liquid isoprene rubber is modified (that is, it is a modified liquid isoprene rubber) Condition (2) The rubber composition further contains a peroxide (D) satisfies at least any one of the above, and is characterized in that.

[0024] The rubber composition of this embodiment contains carbon black (B), which improves the reinforcing properties of the rubber composition and contributes to improving its durability. Furthermore, the rubber composition of this embodiment contains sulfur (C) as a crosslinking agent, and sulfur crosslinks are formed in the rubber composition after crosslinking. Furthermore, in the rubber composition of this embodiment, when condition (1) is met, the molecular chains of rubber component (A) form a structure in which they are directly linked to each other through the modifying groups of the modified liquid isoprene rubber, thus the modified liquid isoprene rubber contributes to further improvement in durability. In other words, the coexistence of sulfur crosslinking and crosslinking caused by the modified liquid isoprene rubber can synergistically or dramatically improve the durability of the rubber composition. Furthermore, when condition (2) is met, the rubber composition of this embodiment contains sulfur (C) and peroxide (D) as crosslinking agents, and after crosslinking, the rubber composition will have both sulfur crosslinking structures and crosslinking structures (such as CC bonds) caused by the peroxide. In particular, peroxide (D) forms a crosslinking structure that directly links the molecular chains of rubber component (A), thus contributing to a further improvement in durability. In other words, the coexistence of sulfur crosslinking and crosslinking caused by the peroxide can synergistically or dramatically improve the durability of the rubber composition. Furthermore, since the rubber composition of this embodiment contains a liquid isoprene-based rubber (i.e., an isoprene-based rubber with a relatively small molecular weight) as rubber component (A), the low molecular weight component of the liquid isoprene-based rubber efficiently contributes to crosslinking. Therefore, the effect of improving durability based on the coexistence of the sulfur crosslinking described above, crosslinking caused by peroxides and / or crosslinking caused by the modified liquid isoprene-based rubber, and in particular the effect of improving the elongation at break after deterioration, can be exhibited even more effectively. Therefore, the rubber composition of this embodiment exhibits excellent durability, particularly in crack propagation resistance and elongation at break after deterioration.

[0025] The rubber composition of this embodiment may satisfy only condition (1), only condition (2), or both of the two conditions (1 and 2).

[0026] (Rubber component (A)) The rubber composition of this embodiment contains a rubber component (A), which provides the composition with rubber elasticity.

[0027] The rubber component (A) of the rubber composition of this embodiment includes liquid isoprene rubber. Isoprene rubber is rubber whose main backbone is isoprene units, and specific examples include natural rubber (NR) and synthetic isoprene rubber (IR). Liquid isoprene rubber is a type of isoprene rubber that is liquid at 25°C. Liquid isoprene rubber may be used alone or in combination of two or more types.

[0028] In the rubber composition of this embodiment, the liquid isoprene rubber is preferably modified (condition 1). By modifying the liquid isoprene rubber (i.e., being a modified liquid isoprene rubber), durability can be further improved. Modified liquid isoprene rubber can be obtained by modifying liquid isoprene rubber with a modifying agent. In particular, the liquid isoprene rubber is preferably maleic acid modified or maleic anhydride modified. In this case, durability can be improved more effectively.

[0029] The proportion of liquid isoprene-based rubber in rubber component (A) is preferably 10% by mass or more and 50% by mass or less. By keeping the above proportion within the above range, durability can be more effectively improved. From a similar viewpoint, the proportion of liquid isoprene-based rubber in rubber component (A) is more preferably 15% by mass or more, even more preferably 20% by mass or more, and preferably 40% by mass or less, and more preferably 30% by mass or less.

[0030] The rubber component (A) of the rubber composition of this embodiment may include rubber components other than the liquid isoprene-based rubber described above. Preferably, such rubber components are diene-based rubbers, and examples of such diene-based rubbers include isoprene-based rubbers that are not liquid at 25°C (natural rubber (NR), synthetic isoprene rubber (IR), etc.), 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.), ethylene-propylene rubber (EPR, EPDM), etc. Furthermore, the rubber component (A) may or may not include non-diene-based rubbers, and examples of such non-diene-based rubbers include fluororubber, silicone rubber, and urethane rubber. These rubber components other than liquid isoprene-based rubber may be used individually or in combination of two or more types.

[0031] The rubber component (A) of the rubber composition of this embodiment preferably contains natural rubber (i.e., natural rubber that is not liquid at 25°C) in addition to the liquid isoprene-based rubber described above. Rubber compositions containing natural rubber have excellent adhesion to metal members and are suitable for use as rubber coatings for metals. Furthermore, the inclusion of natural rubber in rubber component (A) can also improve the strength of the rubber composition. The proportion of natural rubber in rubber component (A) is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more.

[0032] (Carbon Black (B)) The rubber composition of this embodiment contains carbon black (B). The inclusion of carbon black (B) in the rubber composition improves its reinforcing properties and thus its durability.

[0033] Examples of the carbon black (B) include GPF, FEF, HAF, ISAF, and SAF grade carbon blacks. These carbon blacks (B) may be used individually or in combination of two or more types.

[0034] Carbon black (B) preferably includes recycled carbon black from the viewpoint of contributing to improved sustainability. In this specification, "recycled carbon black" refers to carbon black obtained by recovering from raw materials that are waste materials that have been recycled. Examples of waste materials include waste rubber, used tires, and waste oil. Waste rubber is not limited to that generated from rubber products, but includes all discarded rubber, including unwanted scraps generated during the production or repair of rubber products. Examples of scraps include buffing powder and peeling rubber. Buffing powder is, for example, fine rubber generated in the buffing process that removes the tread portion remaining on the base tire during tire retreading. Peeling rubber is long pieces of rubber, for example, 1 to 2 cm wide, that are peeled off from the surface of rubber products such as tires. Peeling rubber is generated by using a U-shaped or V-shaped knife like a peeler to scrape the surface of rubber products such as tires. Furthermore, waste rubber is not limited to cross-linked rubber, but also includes unvulcanized rubber. Rubber products include, for example, finished products such as tires and rubber hoses, as well as rubber parts or components used in the manufacturing process of these finished products. Used tires may be retreaded, or they may be tires discarded for any reason, such as tires resulting from tire replacement or vehicle scrapping, or End-of-Life Tires (ELTs) that have reached the end of their lifespan. Waste oil is not limited to that generated when plastics and rubber are decomposed, but also includes used oils discharged from industry, such as animal and vegetable oils, lubricating oils, insulating oils, and cutting oils. Among these, waste oils that do not contain any non-organic components, such as those derived from silicone rubber or polyvinyl chloride, are preferable. Furthermore, waste oils that contain carbon black or rubber containing carbon black are preferable. "Recycled carbon black" is different from carbon black that is not recycled, which is manufactured directly using hydrocarbons such as petroleum, natural gas, and coal as raw materials. Furthermore, "used" here includes not only carbon black that has been discarded after actual use, but also carbon black that was manufactured but discarded without actually being used.

[0035] The carbon black (B) content in the rubber composition is preferably 10 parts by mass or more per 100 parts by mass of the rubber component (A). In this case, the reinforcing properties of the rubber composition are further improved, and the durability is further enhanced. From a similar viewpoint, the carbon black (B) content per 100 parts by mass of the rubber component (A) is more preferably 30 parts by mass or more, and even more preferably 50 parts by mass or more. Furthermore, the carbon black (B) content in the rubber composition is preferably 120 parts by mass or less per 100 parts by mass of the rubber component (A). In this case, the workability in kneading the rubber composition is further improved. From a similar viewpoint, the carbon black (B) content per 100 parts by mass of the rubber component (A) is more preferably 100 parts by mass or less, and even more preferably 80 parts by mass or less.

[0036] (Sulfur (C)) The rubber composition of this embodiment contains sulfur(C). The presence of sulfur(C) in the rubber composition results in the presence of sulfur crosslinks in the crosslinked rubber composition (also referred to as the "crosslinked rubber composition" or "crosslinked rubber"), thereby improving the durability of the rubber composition.

[0037] There are no particular restrictions on the sulfur (C) mentioned above; various types of sulfur can be used, such as ordinary sulfur (soluble sulfur (powdered sulfur), etc.) and insoluble sulfur, and oil-treated sulfur can also be used. Here, insoluble sulfur is sulfur that is insoluble in carbon disulfide (amorphous polymeric sulfur), and soluble sulfur (powdered sulfur) is sulfur that is soluble in carbon disulfide.

[0038] The sulfur (C) content in the rubber composition is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, even more preferably 1 part by mass or more, 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 sulfur (C) content is 0.1 parts by mass or more per 100 parts by mass of the rubber component (A), the mesh density due to sulfur is improved, and the durability of the rubber composition is further improved. Furthermore, when the sulfur (C) content 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 composition is improved. Furthermore, when the sulfur (C) content is 4 parts by mass or less per 100 parts by mass of the rubber component (A), the elongation at break after deterioration of the rubber composition is further improved.

[0039] (Peroxide (D)) The rubber composition of this embodiment further contains peroxide (D) (Condition 2) / preferably contains peroxide (D). The presence of peroxide (D) in the rubber composition results in the presence of crosslinked structures (such as CC bonds) caused by peroxide (D) in the crosslinked rubber composition, thereby improving the durability of the rubber composition.

[0040] The peroxide (D) may be an organic peroxide or an inorganic peroxide, but an organic peroxide is preferred. Here, the organic peroxide is not particularly limited, but includes tert-butyl hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, cumene hydroperoxide, p-menthane hydroperoxide, diisopropylbenzene hydroperoxide, dicumyl peroxide, di-tert-butyl peroxide, di-tert-hexyl peroxide, diisopropylbenzene hydroperoxide, tert-butylcumyl peroxide, di(2-tert-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, perbenzoic acid, benzoyl peroxide, 1,1-bis(1,1-dimethylethylperoxy)cyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, Examples 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-butylperoxylaurate, tert-butylperoxy-2-ethylhexanate, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, tert-hexylperoxy-2-ethylhexanoate, tert-butylperoxy-2-ethylhexanoate, tert-butylperoxyacetate, cyclohexanone peroxide, acetylacetone peroxide, diisopropylperoxydicarbonate, and di(4-tert-butylcyclohexyl)peroxydicarbonate. Examples of inorganic peroxides include hydrogen peroxide, sodium persulfate, potassium persulfate, and ammonium persulfate. These peroxides (D) may be used individually or in combination of two or more.

[0041] When the rubber composition of this embodiment contains peroxide (D), the content of peroxide (D) in the rubber composition is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, even more preferably 1 part by mass or more, 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 peroxide (D) is 0.1 parts by mass or more per 100 parts by mass of the rubber component (A), the network density of the crosslinked structure caused by the peroxide (D) is improved, and the durability of the rubber composition is further improved. Furthermore, when the content of peroxide (D) 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 composition is further improved.

[0042] When the rubber composition of this embodiment contains peroxide (D), the mass ratio (C / D) of sulfur (C) to peroxide (D) is preferably 0.5 or more and 2.5 or less. When the above mass ratio (C / D) is 0.5 or more, the crack propagation resistance of the rubber composition is improved, and when it is 2.5 or less, the elongation at break after deterioration of the rubber composition can be further improved. By having a mass ratio (C / D) of sulfur (C) to peroxide (D) of 0.5 to 2.5, it is possible to achieve a high degree of balance between crack propagation resistance and elongation at break after deterioration, which are indicators of durability. From a similar viewpoint, the mass ratio (C / D) of sulfur (C) to peroxide (D) is more preferably less than 2.0, even more preferably 1.99 or less, even more preferably 1.98 or less, even more preferably 1.97 or less, even more preferably 1.96 or less, and particularly preferably 1.95 or less.

[0043] (Metal acrylates or their derivatives (E)) The rubber composition of this embodiment preferably further contains a metal acrylate or its derivative (E). The inclusion of a metal acrylate or its derivative (E) in the rubber composition improves the elastic modulus and further enhances the durability of the rubber composition. Here, metal acrylate refers to a metal salt of acrylic acid. A derivative of metal acrylate is a compound in which a hydrogen atom in the metal salt of acrylic acid is replaced by a substituent, and examples of such substituents include alkyl groups such as methyl groups. Examples of metal acrylate derivatives include metal salts of methacrylic acid.

[0044] Examples of metals constituting the metal acrylate or its derivative (E) include zinc, magnesium, and calcium. Regarding the metal ions in the metal acrylate or its derivative (E), the valency of the ions is not particularly limited and can be any valency possible for each element, but it is preferably valency 2 or higher.

[0045] Examples of the metal acrylate or its derivative (E) include zinc diacrylate, magnesium diacrylate, calcium diacrylate, zinc dimethacrylate, magnesium dimethacrylate, calcium dimethacrylate, and the like. These metal acrylates or their derivatives (E) may be used individually or in combination of two or more.

[0046] The content of the metal acrylate or its derivative (E) in the rubber composition is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, even more preferably 0.5 parts by mass or more, 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 its derivative (E) is 0.1 parts by mass or more per 100 parts by mass of the rubber component (A), the durability of the rubber composition is further improved. Furthermore, when the content of the metal acrylate or its derivative (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 elongation at break of the rubber composition is further improved.

[0047] Among the metal acrylates or their derivatives (E), zinc diacrylate or its derivatives are preferred. The durability of the rubber composition can be further improved by using zinc diacrylate or its derivatives as the metal acrylate or its derivative (E). Here, examples of zinc diacrylate or its derivatives include the aforementioned zinc diacrylate, zinc dimethacrylate (ZDMA), etc., and among these, zinc dimethacrylate is preferred.

[0048] When the rubber composition of this embodiment contains peroxide (D), the mass ratio (D / E) of peroxide (D) to metal acrylate or its derivative (E) is preferably 0.5 or higher, and more preferably 0.5 to 3. A rubber composition with a mass ratio (D / E) of peroxide (D) to metal acrylate or its derivative (E) of 0.5 or higher exhibits an improved balance between crack propagation resistance and elongation at break after degradation. Furthermore, a rubber composition with a mass ratio (D / E) of peroxide (D) to metal acrylate or its derivative (E) of 0.5 to 3 exhibits an even further improved balance between crack propagation resistance and elongation at break after degradation.

[0049] (others) In addition to the rubber component (A), carbon black (B), sulfur (C), peroxide (D), metal acrylate or its derivative (E) described above, the rubber composition of this embodiment may also contain 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 oxide), softeners, stearic acid, antioxidants, waxes, silane coupling agents, vulcanization accelerators, retarders (vulcanization retarders), etc., selected as appropriate within a range that does not impair the purpose of the present invention. Commercially available products can be suitably used as these compounding agents.

[0050] The content of zinc oxide (zinc oxide) is not particularly limited, but 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).

[0051] The stearic acid content is not particularly limited, but 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).

[0052] Examples of the aforementioned antioxidants 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 individually or in combination of two or more. There are no particular restrictions on the content of the antioxidant, but it is preferably in the range of 0.1 to 5 parts by mass, and more preferably 0.5 to 3 parts by mass, per 100 parts by mass of the rubber component (A).

[0053] Examples of the vulcanization accelerator include sulfenamide-based vulcanization accelerators, guanidine-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiram-based vulcanization accelerators, and dithiocarbamate-based vulcanization accelerators. These vulcanization accelerators may be used individually or in combination of two or more. There are no particular restrictions on the content of the vulcanization accelerator, but it is preferably in the range of 0.1 to 5 parts by mass, and more preferably in the range of 0.2 to 3 parts by mass, per 100 parts by mass of the rubber component (A).

[0054] The rubber composition preferably contains 0.01 parts by mass or less of cobalt compound per 100 parts by mass of rubber component (A), and more preferably contains no cobalt compound at all. Adding cobalt compound accelerates thermal degradation of the rubber composition, so from the viewpoint of degradation resistance, it is desirable not to include cobalt compound. Although cobalt compound (or cobalt metal or cobalt ions derived from cobalt compound) may migrate from the outside to the application site of the rubber composition, it is preferable not to include cobalt compound at least when manufacturing the rubber composition.

[0055] (Method for manufacturing rubber composition) The method for producing the rubber composition is not particularly limited, but for example, it can be produced by mixing the aforementioned rubber component (A), carbon black (B), and sulfur (C) with various components, including a peroxide (D) as needed, and then kneading, heating, extruding, etc. Furthermore, the obtained rubber composition can be crosslinked by heating and crosslinking to produce crosslinked rubber.

[0056] There are no particular restrictions on the mixing conditions, and various conditions such as the input volume of the mixing device, the rotation speed of the rotor, the ram pressure, as well as the mixing temperature, mixing time, and the type of mixing device can be appropriately selected according to the purpose. Examples of mixing devices include Banbury mixers, intermixes, kneaders, and rolls, which are commonly used for mixing rubber compositions.

[0057] There are no particular restrictions on the heat treatment conditions, and various conditions such as heat treatment temperature, heat treatment time, and heat treatment equipment can be appropriately selected according to the purpose. Examples of such heat treatment equipment include heat treatment roll machines commonly used for heat treatment of rubber compositions.

[0058] There are no particular restrictions on the extrusion conditions, and various conditions such as extrusion time, extrusion speed, extrusion equipment, and extrusion temperature can be appropriately selected according to the purpose. Examples of extrusion equipment include extruders typically used for extruding rubber compositions. The extrusion temperature can be determined as appropriate.

[0059] There are no particular restrictions on the apparatus, method, and conditions for performing the aforementioned crosslinking, and they can be appropriately selected according to the purpose. Examples of apparatus for performing crosslinking include molding vulcanizers using molds, which are typically used for crosslinking (vulcanizing) rubber compositions. As for the conditions for crosslinking, the temperature is, for example, around 100 to 190°C.

[0060] <Metal-rubber composite> A metal-rubber composite according to one embodiment of the present invention (hereinafter sometimes referred to as "the composite of this embodiment") is characterized in that a metal member is coated with the metal coating rubber composition of this embodiment described above. The composite of this embodiment has excellent durability because it uses the rubber composition of this embodiment described above, which has excellent durability.

[0061] The metal component is not particularly limited and can take on various shapes. In one embodiment, the metal is a metal cord. Preferably, the metal cord is made by twisting together multiple metal wires (metal steel wires) or by using a single metal wire. The metal wire is not particularly limited, but examples include wires made of iron, steel (stainless steel), lead, aluminum, copper, brass, bronze, Monel metal alloy, nickel, zinc, etc. Steel cord is preferred as the metal. Steel cord is easily deformed into the desired shape and offers excellent productivity for the composite of this embodiment.

[0062] Preferably, the metal member has a plating applied to its surface. Here, the plating is not particularly limited, but from the viewpoint of adhesion between the metal member and the rubber composition for metal coating, examples include zinc plating, copper plating, brass plating, etc., and among these, brass plating is preferred. When the metal member is brass plated, the adhesion between the metal member and the rubber composition for metal coating is further improved.

[0063] The composite material of this embodiment can be suitably used in various rubber articles, specifically in tires, hoses, rubber tracks, and the like.

[0064] <Rubber Products> A rubber article according to one embodiment of the present invention (hereinafter sometimes referred to as "the rubber article of this embodiment") is a hose, rubber crawler, or tire characterized by comprising the composite material of this embodiment described above. The rubber article of this embodiment is highly durable because it comprises the composite material of this embodiment described above, which is highly durable.

[0065] (hose) When the rubber article of this embodiment is a hose, there are no particular restrictions on the application area of ​​the composite (rubber composition of this embodiment) in the hose, and it can be appropriately selected according to the purpose. In one embodiment, the hose comprises an inner rubber layer (inner tube rubber) located radially inward, an outer rubber layer located radially outward, and a metal reinforcing layer (metal member) located between the inner rubber layer and the outer rubber layer. In one embodiment, the rubber composition of this embodiment described above can be used in at least one of the inner rubber layer and the outer rubber layer.

[0066] (Rubber tracks) When the rubber article of this embodiment is a rubber crawler, there are no particular restrictions on the application area of ​​the composite (rubber composition of this embodiment) on the rubber crawler, and it can be appropriately selected according to the purpose. In one embodiment, the rubber crawler comprises a steel cord (metal member), an intermediate rubber layer covering the steel cord, a core metal (metal member) placed on the intermediate rubber layer, and a main rubber layer surrounding the intermediate rubber layer and the core metal, and further comprises a plurality of lugs on the contact surface side of the main rubber layer. In one embodiment, the rubber composition of this embodiment described above can be used on any part of the rubber crawler.

[0067] (tire) When the rubber article of this embodiment is a tire, there are no particular restrictions on the application area of ​​the composite of this embodiment in the tire, and it can be appropriately selected according to the purpose. Examples include the carcass, belt, bead core, etc.

[0068] Conventional methods can be used to manufacture the aforementioned tire. For example, components commonly used in tire manufacturing, such as a carcass and belt (metal-rubber composite) made of an unvulcanized rubber composition and metal cords, and a tread made of an unvulcanized rubber composition, are sequentially layered on a tire molding drum, and the drum is removed to obtain a green tire. Then, the green tire is heated and vulcanized according to a conventional method to produce a desired tire (for example, a pneumatic tire). [Examples]

[0069] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to the following examples.

[0070] <Manufacturing and evaluation of rubber compositions> Rubber compositions were manufactured using a standard Banbury mixer with the formulations shown in Table 1. The crack propagation resistance and elongation at break after degradation were measured and evaluated for the obtained rubber compositions using the methods described below. The results are shown in Table 1.

[0071] (1) Crack propagation resistance For Comparative Example 1 and Examples 2-4, rectangular test specimens were prepared from the rubber composition by heat crosslinking and drilling a hole in the center. The number of fracture cycles in a DC / DN test (conducted using a Shimadzu Servopulsa at a frequency of 5 Hz and 80°C, with a constant stress test (1.7 MPa)) was measured. A higher number of cycles before fracture indicates a lower crack propagation rate and superior durability (crack propagation resistance). The measured value for Comparative Example 1 was set to 100, and the measured values ​​for each example were indexed.

[0072] For Example 1, a rectangular test specimen was prepared from the rubber composition by heat crosslinking and drilling a hole in the center. The number of fractures in a DC / DN test (using a Shimadzu Servopulsa at a frequency of 5 Hz and 80°C, performing a constant stress test (1.7 MPa)) was measured. A higher number of fractures indicates a lower crack propagation rate and superior durability (crack propagation resistance). The measured value in Comparative Example 1 was set to 100, and the measured value in Example 1 was indexed accordingly.

[0073] (2) Elongation at break after deterioration For Comparative Example 1 and Examples 2-4, 160mm x 160mm x 2mm slab plates, prepared by heat crosslinking of the rubber composition, were placed in a gear aging tester (gear oven) manufactured by Toyo Seiki Seisakusho and subjected to two days of atmospheric degradation at an internal temperature of 100°C. After degradation, rubber samples were prepared by punching out the slab plates into a JIS-3 dumbbell shape and measured using a fully automatic tensile testing machine manufactured by Toyo Seiki Seisakusho to determine the elongation at break (%) after degradation. A higher measured value indicates better elongation at break after degradation. The measured value for Comparative Example 1 was set to 100, and the measured values ​​for each example were indexed accordingly.

[0074] For Example 1, a 160mm x 160mm x 2mm slab plate, prepared by heat crosslinking a rubber composition, was placed in a gear aging tester (gear oven) manufactured by Toyo Seiki Seisakusho Co., Ltd., and subjected to atmospheric degradation at an internal temperature of 100°C for two days. After degradation, the slab plate was punched into a JIS-3 dumbbell shape to prepare a rubber sample, which was then measured using a fully automatic tensile testing machine manufactured by Toyo Seiki Seisakusho Co., Ltd. to determine the elongation at break (%) after degradation. A higher measured value indicates better elongation at break after degradation. The measured value in Comparative Example 1 was set to 100, and the measured values ​​in each example were indexed accordingly.

[0075] [Table 1]

[0076] *1 Natural rubber: Not liquid at 25°C *2 Isoprene rubber: Not liquid at 25°C *3 Liquid isoprene rubber: Kuraray Co., Ltd., "LIR-30", unmodified synthetic isoprene rubber *4 Modified liquid isoprene rubber A: Kuraray Co., Ltd., "LIR-410", maleic acid modified synthetic isoprene rubber *5 Modified liquid isoprene rubber B: Kuraray Co., Ltd., "LIR-403", maleic anhydride modified synthetic isoprene rubber *6 Carbon Black: Manufactured by Asahi Carbon Co., Ltd., product name "Asahi #70L" *7 Stearic acid: Manufactured by Shin Nippon Rika Co., Ltd., product name "Stearic Acid 50S" *8 Vulcanization accelerator: Manufactured by Ouchi Shinko Chemical Industry Co., Ltd., product name "Noxellar CZ-G" *9 Sulfur: Manufactured by Tsurumi Chemical Industries, Ltd., product name "Powdered Sulfur" *10 Peroxide: Manufactured by NOF Corporation, product name "Parkmyl D-40", contains dicumyl peroxide at a concentration of 40% by mass, the actual amount of peroxide is shown below. *11 Metal acrylate derivative: Zinc dimethacrylate, manufactured by Cray Valley, trade name "DYMALINK 708" *12 Zinc oxide: Manufactured by Hakusui Tech Co., Ltd., product name "Zinc Oxide Type 2" *13 Other chemicals: The total amount of two anti-aging agents and retarder, blended in the same ratio in all examples and comparative examples.

[0077] Table 1 shows that the rubber compositions of the embodiments according to the present invention have crack propagation resistance values ​​equivalent to or higher than those of Comparative Example 1, and also have significantly higher values ​​of elongation at break after degradation, thus demonstrating superior durability. [Industrial applicability]

[0078] According to the present invention, it is possible to provide a rubber composition for metal coatings that has excellent durability (particularly crack propagation resistance and elongation at break after deterioration). Furthermore, according to the present invention, it is possible to provide a metal-rubber composite and rubber articles with excellent durability using such a metal coating rubber composition.

[0079] [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 considered to be a technology that can contribute to "No. 12: Responsible Consumption and Production" and "No. 13: Climate Action," among others.

Claims

1. A rubber composition for metal coating containing a rubber component (A), carbon black (B), and sulfur (C), The rubber component (A) includes liquid isoprene-based rubber, The following conditions (1) and (2): Condition (1) The liquid isoprene-based rubber is modified Condition (2) The rubber composition further contains peroxide (D) A rubber composition for metal coating, characterized by satisfying at least one of the following conditions.

2. The rubber composition for metal coating according to claim 1, wherein the rubber component (A) further contains natural rubber, and the proportion of natural rubber in the rubber component (A) is 50% by mass or more.

3. The metal coating rubber composition according to claim 1, wherein the liquid isoprene rubber is a maleic acid-modified or maleic anhydride-modified liquid isoprene rubber.

4. The rubber composition for metal coating according to claim 1, wherein the proportion of the liquid isoprene-based rubber in the rubber component (A) is 10% by mass or more and 50% by mass or less.

5. The metal coating rubber composition according to claim 1, wherein the carbon black (B) content is 50 parts by mass or more per 100 parts by mass of the rubber component (A).

6. The above peroxide (D) is contained, The rubber composition for metal coating according to claim 1, wherein the mass ratio (C / D) of sulfur (C) to peroxide (D) is 0.5 or more and 2.5 or less.

7. The metal coating rubber composition according to claim 1, further containing a metal acrylate or a derivative thereof (E).

8. The above peroxide (D) is contained, The metal coating rubber composition according to claim 7, wherein the mass ratio (D / E) of the peroxide (D) to the metal acrylate or its derivative (E) is 0.5 or more.

9. The metal coating rubber composition according to claim 7, wherein the metal acrylate or its derivative (E) is zinc diacrylate or its derivative.

10. The metal coating rubber composition according to claim 1, wherein the carbon black (B) includes recycled carbon black.

11. A metal-rubber composite characterized in that a metal member is coated with the metal coating rubber composition described in claim 1.

12. A rubber article that is a hose, rubber crawler, or tire, characterized by comprising the metal-rubber composite described in claim 11.

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