Rubber compositions, rubber-metal composites, and rubber articles

Abstract

The present invention provides a rubber composition that maintains adhesion between the rubber composition and metal components while improving crack resistance. [Solution] A rubber composition comprising a rubber component, a rubber-metal adhesion promoter, and a compound represented by a predetermined general formula (I), wherein the rubber-metal adhesion promoter comprises one or more selected from a metal salt (1) of an aliphatic carboxylic acid having 2 to 25 carbon atoms and the metal species being bismuth, zinc, copper, antimony, silver, niobium, or zirconium, and a compound (2) represented by a predetermined general formula (A).

Description

[Technical Field]

[0001] The present invention relates to rubber compositions, rubber-metal composites, and rubber articles. [Background technology]

[0002] Conventionally, to improve the performance of rubber products such as hoses, conveyor belts, rubber tracks, and tires, rubber-metal composites have been used, in which metal components, such as brass-plated steel cords, are coated with a rubber composition containing natural rubber, synthetic rubber, etc. Furthermore, it is known that rubber-metal adhesion promoters are included in the rubber composition to improve the adhesion between the aforementioned metal components and the coated rubber (rubber composition). As such rubber-metal adhesion promoters, organic cobalt acid salts (e.g., cobalt stearate, cobalt versatate, cobalt naphthenate, etc.) are commonly used because they can improve the adhesion between metal components such as steel cords and the coated rubber.

[0003] However, in recent years, there has been a movement towards environmental regulations, such as the European REACH Regulation on the Registration, Evaluation, Authorization and Restriction of Chemical Substances, and organic cobalt salts, which are used as adhesion promoters as mentioned above, are also being considered as candidates for regulation under the REACH Regulation and other similar regulations. Therefore, the development of rubber-metal adhesion promoters that do not contain cobalt is desired.

[0004] In contrast, for example, Patent Document 1 discloses a technology relating to a rubber-metal adhesion promoter that can achieve high adhesive strength between rubber and metal even without containing cobalt, a rubber composition containing the rubber-metal adhesion promoter, and a tire. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2016 / 039375 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, the inventors found that when the rubber-metal adhesion promoter described in Patent Document 1 is added to a rubber composition, the resulting rubber composition exhibits high adhesion to metal members, but lacks sufficient crack resistance.

[0007] Therefore, the object of the present invention is to solve the problems of the above-mentioned prior art and to provide a rubber composition that maintains adhesion between the rubber composition and a metal member while improving crack resistance. Furthermore, a further objective of the present invention is to provide a rubber-metal composite using such a rubber composition, and even a rubber article using such a rubber-metal composite. [Means for solving the problem]

[0008] The gist of the present invention, which solves the above problems, is as follows.

[0009] [1] Rubber component, rubber-metal adhesion promoter, and general formula (I): [ka] [In formula (I), R 1 and R 2 Each of these is independently an alkyl group, a 1-propenyl group, a 2-propenyl group, an isopropenyl group, or a vinyl group. The compound represented by ] contains and The rubber-metal adhesion promoter is a metal salt (1) of an aliphatic carboxylic acid having 2 to 25 carbon atoms and the metal species being bismuth, zinc, copper, antimony, silver, niobium, or zirconium, and general formula (A): [(RCOO) x MO]3Z (A) [In formula (A), (RCOO) is a residue of an aliphatic carboxylic acid having 2 to 25 carbon atoms, x is an integer greater than or equal to 1 and (valence of M - 1), M is bismuth, zinc, copper, antimony, silver, niobium, or zirconium, and Z is as shown in formulas (z-1) to (z-4): [Chemical formula] A rubber composition comprising at least one selected from the compounds (2) having any of the structures represented by 〕.

[0010] [2] The rubber composition according to [1], wherein the rubber component contains natural rubber and the proportion of the natural rubber in the rubber component is 50% by mass or more.

[0011] [3] The rubber composition according to [1] or [2], further containing carbon black, wherein the content of the carbon black is 50 parts by mass or more based on 100 parts by mass of the rubber component.

[0012] [4] The rubber composition according to any one of [1] to [3], wherein the content of the rubber-metal adhesion promoter is 0.01 part by mass or more and 20 parts by mass or less based on 100 parts by mass of the rubber component.

[0013] [5] R 1 and R 2 are isopropenyl groups, and the rubber composition according to any one of [1] to [4].

[0014] [6] The rubber composition according to any one of [1] to [5], wherein the rubber-metal adhesion promoter contains the metal salt (1) of the aliphatic carboxylic acid, and the metal species in the metal salt (1) of the aliphatic carboxylic acid is bismuth or zinc.

[0015] [7] The rubber composition according to any one of [1] to [6], wherein the rubber-metal adhesion promoter contains the metal salt (1) of the aliphatic carboxylic acid, and the aliphatic carboxylic acid in the metal salt (1) of the aliphatic carboxylic acid is an aliphatic monocarboxylic acid or an aliphatic dicarboxylic acid.

[0016] [8] The rubber composition according to [7], wherein the aliphatic carboxylic acid in the metal salt (1) of the aliphatic carboxylic acid is a saturated aliphatic monocarboxylic acid having 2 to 20 carbon atoms.

[0017] [9] The rubber composition according to any one of [1] to [8], wherein the rubber-metal adhesion promoter comprises a compound (2) represented by the general formula (A), and M in the general formula (A) is bismuth or zinc.

[0018]

[10] The rubber composition according to any one of [1] to [9], wherein the rubber-metal adhesion promoter comprises a compound (2) represented by the general formula (A), and Z in the general formula (A) has the structure of the formula (z-1).

[0019]

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

[10] , wherein the rubber-metal adhesion promoter comprises a compound (2) represented by the general formula (A), and (RCOO) in the general formula (A) is a residue of a saturated aliphatic monocarboxylic acid having 2 to 20 carbon atoms.

[0020]

[12] The rubber composition according to [3], wherein the carbon black comprises recycled carbon black.

[0021]

[13] A rubber-metal composite comprising a rubber composition according to any one of [1] to

[12] and a metal member.

[0022] A rubber article characterized by using the rubber-metal composite described in

[14]

[13] . [Effects of the Invention]

[0023] According to the present invention, it is possible to provide a rubber composition that maintains adhesion between the rubber composition and a metal member while improving crack resistance. Furthermore, according to the present invention, it is possible to provide a rubber-metal composite using such a rubber composition, and even a rubber article using such a rubber-metal composite. [Modes for carrying out the invention]

[0024] The rubber compositions, rubber-metal composites, and rubber articles of the present invention will be described in detail below, based on their embodiments. The compounds described herein may be derived in part or in whole from fossil resources, from biological resources such as plant resources, or from recycled resources such as used tires. They may also be derived from a mixture of two or more of fossil resources, biological resources, or recycled resources.

[0025] In this specification, "number of carbon atoms in an aliphatic carboxylic acid" refers to the number of carbon atoms including the carboxyl group. Furthermore, in this specification, "(RCOO) carbon number" refers to the number of carbon atoms including the carboxyl group.

[0026] <Rubber composition> A rubber composition according to one embodiment of the present invention (hereinafter sometimes referred to as "the rubber composition of this embodiment") comprises a rubber component, a rubber-metal adhesion promoter, and a general formula (I): [ka] [In formula (I), R 1 and R 2 Each of these is independently an alkyl group, a 1-propenyl group, a 2-propenyl group, an isopropenyl group, or a vinyl group. The compound represented by ] contains and The rubber-metal adhesion promoter is a metal salt (1) of an aliphatic carboxylic acid having 2 to 25 carbon atoms and the metal species being bismuth, zinc, copper, antimony, silver, niobium, or zirconium, and general formula (A): [(RCOO) x MO]3Z (A) [In formula (A), (RCOO) is a residue of an aliphatic carboxylic acid having 2 to 25 carbon atoms, x is an integer greater than or equal to 1 and (valence of M - 1), M is bismuth, zinc, copper, antimony, silver, niobium, or zirconium, and Z is as shown in formulas (z-1) to (z-4): [ka] It is characterized by containing one or more compounds selected from the compounds represented by (2) ], which have any of the structures of ].

[0027] As a result of the inventors' diligent research, it was found that when a cobalt-free rubber-metal adhesion promoter is applied to a rubber composition, the molecular chains of rubber components such as natural rubber are more easily cleaved. It was also found that when molecular chains are cleaved, radicals are generated, and these radicals cause further molecular chain cleavage, which can result in poor crack resistance. As a result of further diligent research by the inventors, it was found that by including a compound represented by general formula (I) in the rubber composition, these radicals can be trapped, and crack resistance can be improved. Furthermore, the inventors have surprisingly discovered that even when the compound represented by general formula (I) is included in the rubber composition, the adhesion between the rubber composition and the metal component is maintained. The reason why the adhesion between the rubber composition and the metal component is maintained is not clear, but it is thought to be due to the interaction between the two substituents on the benzene ring of the compound represented by general formula (I) and the rubber component. Therefore, according to the present invention, it is possible to provide a rubber composition with improved crack resistance while maintaining adhesion between the rubber composition and a metal member.

[0028] -Rubber components- Examples of rubber components used in the rubber composition of this embodiment include diene-based rubbers. Examples of diene-based rubbers include natural rubber (NR) and diene-based synthetic rubbers. Examples of diene-based synthetic rubbers include isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), styrene-isoprene-butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR). The rubber components may be used individually or in combination of two or more. In particular, it is preferable that the rubber components include natural rubber, which is easily stretched and crystallized and has excellent fracture properties, and it is preferable that the proportion of natural rubber in the rubber components is 50% by mass or more.

[0029] -Rubber-metal bonding promoter- The rubber-metal adhesion promoter used in the rubber composition of this embodiment includes one or more selected from the aliphatic carboxylic acid metal salt (1) and the compound represented by the general formula (A) (2). By including the aliphatic carboxylic acid metal salt (1) and / or the compound represented by the general formula (A) (2) as a rubber-metal adhesion promoter in the rubber composition, the adhesion between the rubber composition and the metal member can be improved.

[0030] As mentioned above, the metal salts (1) of aliphatic carboxylic acids have 2 to 25 carbon atoms, and the metal species is bismuth (Bi), zinc (Zn), copper (Cu), antimony (Sb), silver (Ag), niobium (Nb), or zirconium (Zr).

[0031] From the viewpoint of sufficiently improving the adhesion between the rubber composition and the metal member, it is preferable that the metal salt (1) of the aliphatic carboxylic acid is bismuth or zinc.

[0032] Regarding the above aliphatic carboxylic acid metal salt (1), when an aliphatic carboxylic acid having 2 or more carbon atoms is used as the aliphatic carboxylic acid, the compatibility of the aliphatic carboxylic acid metal salt (1) with the rubber component is improved, and as a result, the adhesion between the rubber composition and the metal component is improved. Furthermore, when an aliphatic carboxylic acid having 25 or fewer carbon atoms is used as the aliphatic carboxylic acid, the synthesis of the aliphatic carboxylic acid metal salt (1) is easy. From the viewpoint of sufficiently improving the adhesion between the rubber composition and the metal member, the aliphatic carboxylic acid in the metal salt (1) of the aliphatic carboxylic acid is preferably an aliphatic monocarboxylic acid or an aliphatic dicarboxylic acid.

[0033] Examples of aliphatic monocarboxylic acids include saturated aliphatic monocarboxylic acids and unsaturated aliphatic monocarboxylic acids. Examples of saturated aliphatic monocarboxylic acids include ethaneic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, 2-ethylhexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, isononanoic acid, decanoic acid, neodecanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid (stearic acid), eicosanoic acid, docosanoic acid, tetracosanoic acid, and naphthenic acid.

[0034] Examples of unsaturated aliphatic monocarboxylic acids include 9-hexadecenoic acid, cis-9-octadecenoic acid, 11-octadecenoic acid, cis,cis-9,12-octadecadienoic acid, 9,12,15-octadecatrienoic acid, 6,9,12-octadecatrienoic acid, 9,11,13-octadecatrienoic acid, eicosanoic acid, 8,11-eicosadienoic acid, 5,8,11-eicosatrienoic acid, 5,8,11,14-eicosatetraenoic acid, tung oil acid, linseed oil acid, soybean oil acid, resin acid, tall oil fatty acid, rosinic acid, abietic acid, neoabietic acid, parastric acid, pimaric acid, and dehydroabietic acid.

[0035] Examples of aliphatic dicarboxylic acids include saturated aliphatic dicarboxylic acids and unsaturated aliphatic dicarboxylic acids. Examples of saturated aliphatic dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, and adipic acid. Examples of unsaturated aliphatic dicarboxylic acids include fumaric acid and maleic acid.

[0036] Among these aliphatic carboxylic acids, saturated aliphatic monocarboxylic acids having 2 to 20 carbon atoms are preferred. In this case, the metal salt (1) of the aliphatic carboxylic acid is less likely to affect the sulfur crosslinking of the rubber component, and as a result, a rubber cured product suitable for use in rubber articles can be obtained with less adverse effect on the rubber properties, and the adhesion between the rubber composition and the metal member is further improved. From a similar viewpoint, 2-ethylhexanoic acid, neodecanoic acid, hexadecanoic acid and octadecanoic acid are more preferred as aliphatic carboxylic acids, and 2-ethylhexanoic acid and neodecanoic acid are even more preferred.

[0037] As the metal salt of the aliphatic carboxylic acid (1), commercially available salts can be used, but examples include bismuth 2-ethylhexanoate, zinc 2-ethylhexanoate, copper 2-ethylhexanoate, antimony 2-ethylhexanoate, silver 2-ethylhexanoate, niobium 2-ethylhexanoate, zirconium 2-ethylhexanoate, bismuth neodecanoate, zinc neodecanoate, copper neodecanoate, antimony neodecanoate, silver neodecanoate, niobium neodecanoate, zirconium neodecanoate, bismuth hexadecanate, zinc hexadecanate, copper hexadecanate, antimony hexadecanate, silver hexadecanate, niobium hexadecanate, zirconium hexadecanate, bismuth octadecanoate, zinc octadecanoate, copper octadecanoate, antimony octadecanoate, silver octadecanoate, niobium octadecanoate, zirconium octadecanoate, etc. Among these, bismuth 2-ethylhexanoate, bismuth neodecanoate, bismuth hexadecanate, bismuth octadecanoate, zinc 2-ethylhexanoate, zinc neodecanoate, zinc hexadecanate, and zinc octadecanoate are preferred.

[0038] The metal salt (1) of the aliphatic carboxylic acid may be used alone or in combination of two or more types.

[0039] The metal salt (1) of an aliphatic carboxylic acid can be produced, for example, by a direct method of directly reacting an aliphatic carboxylic acid (a) having 2 to 25 carbon atoms with one or more selected from oxides (b-1) of metals (bismuth, zinc, copper, antimony, silver, niobium, zirconium), hydroxides (b-2) of metals (bismuth, zinc, copper, antimony, silver, niobium, zirconium), and carbonates (b-3) of metals (bismuth, zinc, copper, antimony, silver, niobium, zirconium) as described in International Publication No. 2016 / 039375; after reacting an aliphatic carboxylic acid (a) having 2 to 25 carbon atoms with sodium hydroxide in the presence of water to obtain a sodium salt of the aliphatic carboxylic acid, and then reacting the sodium salt of the aliphatic carboxylic acid with one or more selected from sulfates (c-1) of metals (bismuth, zinc, copper, antimony, silver, niobium, zirconium), chlorides (c-2) of metals (bismuth, zinc, copper, antimony, silver, niobium, zirconium), and nitrates (c-3) of metals (bismuth, zinc, copper, antimony, silver, niobium, zirconium) (double decomposition method).

[0040] As described above, the compound (2) has the general formula (A): [(RCOO) x MO]3Z (A) In the general formula (A), (RCOO) is a residue of an aliphatic carboxylic acid having 2 to 25 carbon atoms, x is an integer of 1 or more and (valence of M - 1), M is a metal species, specifically, bismuth (Bi), zinc (Zn), copper (Cu), antimony (Sb), silver (Ag), niobium (Nb), or zirconium (Zr), and Z has any one of the structures of the following formulas (z-1) to (z-4):

Chemical formula

[0041]

[0042] ​In general formula (A), Z preferably has the structure of formula (z-1) above, from the viewpoint of sufficiently improving the adhesion between the rubber composition and the metal member.

[0043] In general formula (A), (RCOO) is an aliphatic carboxylic acid residue having 2 to 25 carbon atoms. When the residue is an aliphatic carboxylic acid with 2 or more carbon atoms, the compatibility of compound (2) with the rubber component is improved, and as a result, the adhesion between the rubber composition and the metal component is significantly improved. Furthermore, when the residue is an aliphatic carboxylic acid with 25 or fewer carbon atoms, in addition to the ease of synthesis of compound (2), the dispersibility of compound (2) in the rubber composition and the adsorption of compound (2) to the metal surface are improved, resulting in a greater effect of significantly improving the adhesion between the rubber composition and the metal component.

[0044] As the aliphatic carboxylic acid residue having 2 to 25 carbon atoms, for example, residues of aliphatic monocarboxylic acids are preferred, and in particular, residues derived from the aliphatic monocarboxylic acids described above can be preferred examples.

[0045] Among these aliphatic carboxylic acid residues, saturated aliphatic monocarboxylic acid residues are preferred because compound (2) does not crosslink the rubber component, and more effectively promotes the dispersion of compound (2) near the metal member or the adsorption of compound (2) onto the surface of the metal member, thereby enhancing the adhesion between the rubber composition and the metal member. From a similar viewpoint, among saturated aliphatic monocarboxylic acid residues, residues of saturated aliphatic monocarboxylic acids having 2 to 20 carbon atoms are preferred, and residues of 2-ethylhexanoic acid, neodecanoic acid, hexadecanoic acid, and octadecanoic acid are more preferred.

[0046] Examples of compound (2) include bismuth boron-2-ethylhexanoate, zinc boron-2-ethylhexanoate, copper boron-2-ethylhexanoate, antimony boron-2-ethylhexanoate, silver boron-2-ethylhexanoate, niobium boron-2-ethylhexanoate, zirconium boron-2-ethylhexanoate, bismuth boron-neodecanate, zinc boron-neodecanate, copper boron-neodecanate, antimony boron-neodecanate, silver boron-neodecanate, niobium boron-neodecanate, and boron-neodecanate. Examples include zirconium decanoate, bismuth boron hexadecanate, zinc boron hexadecanate, copper boron hexadecanate, antimony boron hexadecanate, silver boron hexadecanate, niobium boron hexadecanate, zirconium boron hexadecanate, bismuth boron octadecanoate, zinc boron octadecanoate, copper boron octadecanoate, antimony boron octadecanoate, silver boron octadecanoate, niobium boron octadecanoate, and zirconium boron octadecanoate. Among these, bismuth boron-2-ethylhexanoate, bismuth boron-neodecanate, bismuth boron-hexadecanate, bismuth boron-octadecanoate, zinc boron-2-ethylhexanoate, zinc boron-neodecanate, zinc boron-hexadecanate, and zinc boron-octadecanoate are preferred.

[0047] Compound (2) may be used alone or in combination of two or more compounds.

[0048] Compound (2) can be produced, for example, by mixing and heating an aliphatic carboxylic acid (a) having 2 to 25 carbon atoms, as described in International Publication No. 2016 / 039375, an acid (e) capable of producing volatile esters with a lower alcohol residue having 1 to 5 carbon atoms present in the esters (d-1) to (d-4), a borate ester (d-1) of a lower alcohol having 1 to 5 carbon atoms, a metaborate ester (d-2) of a lower alcohol having 1 to 5 carbon atoms, a phosphoric acid ester (d-3) of a lower alcohol having 1 to 5 carbon atoms, and a metal-containing compound (f) that is a source of metal (bismuth, zinc, copper, antimony, silver, niobium, zirconium), and removing the resulting volatile ester.

[0049] The content of the rubber-metal adhesion promoter in the rubber composition is not particularly limited, but from the viewpoint of sufficiently improving the adhesion between the rubber composition and the metal member, it is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, even more preferably 0.5 parts by mass or more, and particularly preferably 1.0 part by mass or more, per 100 parts by mass of the rubber component. Furthermore, from the viewpoint of suppressing deterioration of the rubber composition, the content of the rubber-metal adhesion promoter is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and particularly preferably 10 parts by mass or less, per 100 parts by mass of the rubber component.

[0050] The content of the rubber-metal adhesion promoter in the rubber composition is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, more preferably 5 parts by mass or less, and more preferably 3 parts by mass or less, based on the metal elements of bismuth, zinc, copper, antimony, silver, niobium, and zirconium, per 100 parts by mass of the rubber component. When the content of the rubber-metal adhesion promoter is 0.01 parts by mass or more in terms of metal elements, the adhesion between the rubber composition and the metal member is sufficiently improved, and when it is 5 parts by mass or less, the effect on the crosslinking reaction of the rubber component is small, and the rubber composition is less likely to deteriorate.

[0051] - Compounds represented by general formula (I) - The rubber composition of this embodiment is of general formula (I): [ka] It contains the compound represented by (hereinafter sometimes referred to as "Compound (I)").

[0052] In general formula (I), R 1 and R 2 Each of these is independently an alkyl group, a 1-propenyl group, a 2-propenyl group, an isopropenyl group, or a vinyl group.

[0053] R 1 and R 2 The alkyl group in this expression may be linear or branched. The alkyl group is not particularly limited and examples include C1-C4 alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, and tert-butyl groups.

[0054] From the perspective of reliably obtaining the effect of improving crack resistance, R 1 and R 2 The group is preferably a 1-propenyl group, a 2-propenyl group, an isopropenyl group, or a vinyl group, and more preferably an isopropenyl group.

[0055] General formula (I) is preferably general formula (II) shown below. In this case, crack resistance can be further improved.

[0056] [ka] In general formula (II), R 1 and R 2 This is R in general formula (I). 1 and R 2 The same things can be cited.

[0057] The content of compound (I) in the rubber composition is preferably 0.1 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the rubber component. By having a compound (I) content of 0.5 parts by mass or more, crack resistance can be more reliably improved. From a similar viewpoint, the content of compound (I) is more preferably 1 part by mass or more, and even more preferably 3 parts by mass or more. Furthermore, by having a compound (I) content of 10 parts by mass or less, the effect of maintaining adhesion between the rubber composition and the metal member can be reliably obtained. From a similar viewpoint, the content of compound (I) is more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less.

[0058] -Carbon Black- The rubber composition of this embodiment preferably further contains carbon black. The carbon black is not particularly limited, and examples include SAF, ISAF, HAF, and FEF grade carbon blacks. One type of carbon black may be used alone, or two or more types may be used in combination. The carbon black content in the rubber composition is not particularly limited, but from the viewpoint of improving the abrasion resistance of the rubber composition and the rubber articles to which it is applied, it is preferably 20 parts by mass or more, and more preferably 50 parts by mass or more, per 100 parts by mass of rubber components. Furthermore, from the viewpoint of maintaining good workability, the carbon black content in the rubber composition is preferably 100 parts by mass or less, and more preferably 80 parts by mass or less.

[0059] Furthermore, from the perspective of contributing to improved sustainability, it is preferable that the carbon black includes recycled carbon black.

[0060] --Recycled Carbon Black-- In this specification, "recycled carbon black" refers to carbon black obtained by recovering from raw materials that are waste materials submitted for recycling. Examples of waste materials include waste rubber, used tires, and waste oil. Waste rubber refers to all discarded rubber, including not only that generated from rubber products, but also unwanted scraps generated during the production or repair of rubber products. Examples of scraps include buffing powder and peeling rubber. Buffing powder is fine rubber generated, for example, in the buffing process of retreading tires, where the tread portion remaining on the base tire is scraped off. 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 scraping the surface of rubber products such as tires using a U-shaped or V-shaped knife like a peeler. Furthermore, waste rubber includes not only cross-linked rubber, but also unvulcanized rubber. Rubber products include, for example, final products such as tires and rubber hoses, and rubber parts or components at the manufacturing stage of final products. Used tires may include, for example, tires that have been retreaded, tires generated from tire replacement or vehicle scrapping, and End-of-Life Tires (ELTs) that have reached the end of their lifespan, or any other type of tire that has been discarded for any reason. Waste oil is not limited to that generated when plastics and rubber are broken down, but also includes used oils discharged from industry, such as animal and vegetable oils, lubricating oils, insulating oils, and cutting oils. Among these, waste oil that does not contain any non-organic components, such as those derived from silicone rubber or polyvinyl chloride, is preferable. Furthermore, waste oil that contains carbon black or rubber containing carbon black is 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.

[0061] Furthermore, it is preferable that the recycled carbon black is obtained by the thermal decomposition of vulcanized rubber products containing carbon black. Recycled carbon black obtained by the thermal decomposition of vulcanized rubber products containing carbon black is readily available because large quantities of vulcanized rubber products containing carbon black exist and it can be easily obtained by thermal decomposition. Moreover, it is preferable that the recycled carbon black is obtained from the solid residue generated by the thermal decomposition of vulcanized rubber products containing carbon black. When rubber products containing carbon black are thermally decomposed, solid residue and volatile components (oil) are obtained, and recycled carbon black can be recovered from both. Furthermore, when recovering carbon black from volatile components, it is possible to recover oil with a specific gravity suitable for carbon black production and use it to produce carbon black using existing carbon black production methods (for example, Japanese Patent Publication No. 2015-520259). In this case, unlike carbon black recovered from solid residues, there are advantages such as the absence of impurities and the absence of mixtures of different grades. In addition, in the production of low-environmental-impact carbon black, there are various options other than using oil obtained by recovering volatile components from the aforementioned rubber pyrolysis, such as using vegetable oil or oil derived from waste plastics. However, edible resources such as vegetable oil present challenges in securing sufficient quantities due to other uses such as food, and the environmental impact associated with the expansion of cultivated land must also be considered. Similarly, oil derived from waste plastics is also used for other purposes such as horizontal recycling of plastics, so supply issues are also likely to arise. On the other hand, when using vulcanized rubber products, particularly volatile components (oils) produced by the thermal decomposition of tires, the tire industry has a system in place to continue using existing materials. This allows for the continued use of existing materials, reducing the consumption of new materials in new tire manufacturing and contributing to a reduction in the industry's environmental impact. There are no particular limitations on the grade of carbon black, but examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762.

[0062] The solid residue obtained by thermally decomposing waste materials such as used rubber and used tires contains ash in addition to carbon black. The ash originates from non-volatile components contained in rubber and tires. Therefore, recycled carbon black obtained from this solid residue has a relatively low carbon black content. On the other hand, considering the various physical properties required for tires manufactured using recycled carbon black, a higher carbon content in recycled carbon black is preferable. In recycled carbon black, the carbon content is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 87% by mass or more, and particularly preferably 89% by mass or more. Furthermore, the carbon content in recycled carbon black is preferably 97% by mass or less. Note that the carbon content does not include adsorbed water.

[0063] Ash content specifically includes zinc oxide, zinc sulfide, silica, iron compounds (iron oxide), calcium oxide, aluminum oxide, magnesium oxide, etc. In the case of recycled carbon black produced from solid residue obtained by thermal decomposition of waste, a certain amount of ash remains even after various processes to remove it. In this embodiment, the presence of ash in recycled carbon black is permitted. In one embodiment, the lower limit of the ash content of recycled carbon black may be 0.5% by mass.

[0064] Furthermore, recycled carbon black can be obtained from the pyrolysis process of used pneumatic tires. For example, European Patent Application Publication No. 3427975, which refers to "Rubber Chemistry and Technology," Vol. 85, No. 3, pp. 408-449 (2012), particularly pp. 438, 440, and 442, states that it can be obtained by the pyrolysis of organic materials at 550-800°C in the absence of oxygen, or by vacuum pyrolysis at relatively low temperatures (paragraph

[0027] ). Carbon black obtained from such pyrolysis processes usually lacks functional groups on its surface, as referred to in paragraph

[0004] of Patent Publication No. 6856781 (Comparison of Surface Morphology and Chemistry of Pyrolysis Carbon Black and Commercial Carbon Black, Powder Technology 160 (2005) 190-193).

[0065] Recycled carbon black may lack functional groups on its surface, or it may have been treated to contain functional groups on its surface. Treatment to contain functional groups on the surface of recycled carbon black can be carried out by conventional methods. For example, in European Patent Application Publication No. 3173251, carbon black obtained from a thermal decomposition process is treated with potassium permanganate under acidic conditions to obtain carbon black containing hydroxyl groups and / or carboxyl groups on its surface. In addition, in Japanese Patent Publication No. 6856781, carbon black obtained from a thermal decomposition process is treated with an amino acid compound containing at least one thiol group or disulfide group to obtain carbon black with an activated surface. The recycled carbon black according to this embodiment also includes carbon black that has been treated to contain functional groups on its surface.

[0066] Furthermore, for the thermal decomposition of cross-linked rubber products (vulcanized rubber products) such as used tires, one example is a thermal decomposition method at a temperature of 650°C or higher.

[0067] The cross-linked rubber products used for decomposition may be grouped by the type of rubber component they contain beforehand, and the decomposition process may be carried out separately for each group. Alternatively, they may be grouped by the type of filler they contain beforehand (for example, the type of carbon black, the type of silica, the mixing ratio of carbon black and silica, etc.), and the decomposition process may be carried out separately for each group. Furthermore, they may be grouped by both the type of rubber component and the type of filler, and the decomposition process may be carried out separately for each group. When the decomposition process is carried out separately for each group in this way, recycled carbon black with more uniform physical properties can be obtained, and when it is again incorporated into the rubber component, a rubber composition with better performance can be obtained.

[0068] Furthermore, if the cross-linked rubber product used for decomposition is derived from tires, it may be grouped beforehand by tire type (for example, passenger car tires, truck and bus tires, heavy off-road vehicle tires, aircraft tires, agricultural vehicle tires, etc.) and then the decomposition process may be carried out for each group. Alternatively, it may be grouped beforehand by tire component (for example, tread rubber, sidewall rubber, bead rubber, steel cord coated rubber, organic fiber coated rubber, pad rubber, cushion rubber, etc.) and then the decomposition process may be carried out for each group. In addition, it may be possible to group by tire type and by tire component and then carry out the decomposition process for each group. When the decomposition process is carried out for each group in this way, recycled carbon black with more uniform physical properties can be obtained, and when it is again blended into rubber components, a rubber composition with better performance can be obtained.

[0069] Recycled carbon black has a nitrogen adsorption specific surface area of ​​40-100 m² as measured by the BET method. 2 It is preferable that the amount be / g, and 50-90m 2 It is more preferable that the amount be / g, which is 55-75m 2 It is particularly preferable that the value be / g. Herein, in this specification, the nitrogen adsorption specific surface area of ​​recycled carbon black by the BET method is the statistical thickness specific surface area (STSA), which is determined according to ASTM D6556.

[0070] The recycled carbon black preferably has a pH of 4 to 12, more preferably 5 to 11, and particularly preferably 6 to 10. Herein, in this specification, the pH of recycled carbon black is determined according to ASTM D1512.

[0071] The recycled carbon black preferably has a toluene color transmission rate of 60% or more, more preferably 70% or more, and particularly preferably 80% or more. Herein, in this specification, the toluene staining transmittance of recycled carbon black is determined according to ASTM D1618.

[0072] The recycled carbon black preferably has a heating loss of 3% by mass or less at 125°C, more preferably 2.5% by mass or less, and particularly preferably 2% by mass or less. Herein, in this specification, the heating loss of recycled carbon black at 125°C is determined according to ASTM D1509.

[0073] The recycled carbon black preferably has a sulfur content of 5% by mass or less, more preferably 3.5% by mass or less, and particularly preferably 3% by mass or less.

[0074] The recycled carbon black preferably has a residue of 20 ppm by mass or less after sieving with a 35 mesh, more preferably 15 ppm by mass or less, and particularly preferably 10 ppm by mass or less. Herein, in this specification, the 35-mesh sieve residue of recycled carbon black is determined according to ASTM D1514.

[0075] The recycled carbon black preferably has a residue of 1000 ppm by mass or less after sieving with a 325 mesh (44 μm) sieve, more preferably 700 ppm by mass or less, and particularly preferably 300 ppm by mass or less. Herein, in this specification, the 325-mesh (44 μm) sieve residue of recycled carbon black is determined according to ASTM D1514.

[0076] The recycled carbon black preferably has a pellet hardness of 100 cN or less, more preferably 90 cN or less, and particularly preferably 80 cN or less. Herein, in this specification, the pellet hardness of recycled carbon black is determined according to ASTM D5230.

[0077] The recycled carbon black preferably has a pellet fine powder content of 10% by mass or less, more preferably 7% by mass or less, and particularly preferably 5% by mass or less. Herein, in this specification, the amount of recycled carbon black pellets is determined according to ASTM D1508.

[0078] The recycled carbon black preferably has a particle size (D97) of 25 μm or less, more preferably 15 μm or less, and particularly preferably 10 μm or less. In this specification, the particle size (D97) of recycled carbon black is determined using a laser diffraction particle size analyzer, with a refractive index of 1.33 for water and 1.75 for the filler.

[0079] The recycled carbon black preferably contains 50% or more by volume of particles 5 μm or smaller, more preferably 70% or more by volume, and particularly preferably 80% or more by volume.

[0080] The recycled carbon black preferably has an ash content of 25% by mass or less, more preferably 20% by mass or less, and particularly preferably 15% by mass or less. When the ash content of the recycled carbon black is 25% by mass or less, the various physical properties of rubber products to which the rubber composition is applied can be improved. Herein, in this specification, the ash content of recycled carbon black is determined according to ASTM D8474·D1506.

[0081] Recycled carbon black preferably has a dibutyl phthalate (DBP) absorption rate of 70-120 mL / 100g, more preferably 75-110 mL / 100g, and particularly preferably 80-100 mL / 100g. Herein, in this specification, the DBP absorption amount of recycled carbon black is determined according to ASTM D2414.

[0082] The recycled carbon black preferably has a compressed dibutyl phthalate (24M4DBP) absorption capacity of 50-110 mL / 100 g, more preferably 60-100 mL / 100 g, and particularly preferably 70-90 mL / 100 g. Herein, in this specification, the 24M4DBP absorption amount of recycled carbon black is determined according to ASTM D3493.

[0083] Commercially available recycled carbon black can be used. Examples of such commercially available products include "PB365" manufactured by Enrestec. PB365 is recycled carbon black produced through the thermal decomposition of used tires, and its nitrogen adsorption specific surface area by the BET method is 73.6 m². 2 It is [value] / g and also contains approximately 17% by mass of ash.

[0084] The recycled carbon black content in the rubber composition is preferably 1 to 100 parts by mass, more preferably 5 to 80 parts by mass, even more preferably 5 to 50 parts by mass, even more preferably 5 to 30 parts by mass, and particularly preferably 5 to 20 parts by mass, per 100 parts by mass of rubber components. When the recycled carbon black content is 5 parts by mass or more per 100 parts by mass of rubber components, it has a significant effect on improving the proportion of sustainable materials in the rubber product to which the rubber composition is applied, and when it is 50 parts by mass or less, the fracture resistance of the rubber composition can be maintained more reliably.

[0085] -Other ingredients- The rubber composition in the composite of this embodiment may appropriately contain other components besides those described above, such as fillers such as silica, filler modifiers such as silane coupling agents, vulcanizing agents such as sulfur, vulcanization accelerators, vulcanization accelerators such as zinc oxide, softeners such as oil, antioxidants, anti-scorch agents, processing aids, lubricants, tackifiers, colorants, etc., depending on the purpose.

[0086] The rubber composition of this embodiment may contain silica as a filler. The silica is not particularly limited and examples include wet silica (hydrated silica), dry silica (anhydrous silica), calcium silicate, and aluminum silicate. Silica may be used alone or in combination of two or more types.

[0087] The rubber composition of this embodiment may contain sulfur as a vulcanizing agent. The sulfur is not particularly limited and examples include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and oil-treated sulfur. The sulfur content is not particularly limited, but it is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and preferably 10 parts by mass or less, and more preferably 8 parts by mass or less, per 100 parts by mass of the rubber component.

[0088] When using the above-mentioned vulcanizing agent, the rubber composition of this embodiment may further contain a vulcanization accelerator. The vulcanization accelerator is not particularly limited and examples include compounds such as guanidine, aldehyde-amine, aldehyde-ammonia, thiazole, sulfenamide, thiourea, thiuram, dithiocarbamate, and xantate compounds.

[0089] Furthermore, from the viewpoint of complying with environmental regulations, the rubber composition in this embodiment preferably contains 0.01 parts by mass or less of cobalt-containing compounds per 100 parts by mass of the rubber component, and more preferably contains substantially no cobalt-containing compounds.

[0090] <Method for manufacturing rubber composition> The method for producing the rubber composition of this embodiment is not particularly limited, and for example, the rubber composition can be prepared by compounding and kneading the above-mentioned components according to a conventional method. When compounding and kneading, all components may be compounded and kneaded at once, or each component may be compounded and kneaded in two or three stages. When kneading, a kneader such as a Banbury mixer or kneader can be used. Furthermore, when molding the rubber composition into a sheet or strip, known molding machines such as an extruder or press can be used.

[0091] <Applications of rubber compositions> The rubber composition of this embodiment is suitable for use in any rubber article, such as tires, hoses, conveyor belts, and crawlers.

[0092] <Rubber-metal composite> A rubber-metal composite according to one embodiment of the present invention (hereinafter sometimes referred to as "the rubber-metal composite of this embodiment") is characterized by comprising the rubber composition of this embodiment and a metal member. The rubber-metal composite of this embodiment comprises the rubber composition of this embodiment, and therefore maintains the adhesion between the rubber composition and the metal member while improving crack resistance.

[0093] In this embodiment, the rubber-metal composite typically has the rubber composition of the present invention described above in contact with a metal member. For example, a part or all of a metal wire, which is a metal member, may be covered with the rubber composition, or a rubber layer made of the rubber composition may be laminated on at least one side of a layer made of metal wire.

[0094] Metal components refer to parts made of metal, and can take various forms, such as metal wires, metal cords made by twisting together multiple metal wires (metal steel wires), metal cords made from a single strand of metal wire, metal springs, metal plates, metal rings, etc. Furthermore, there are no particular limitations on the type of metal used for the metal components; steel, iron, copper, gold, etc., can be appropriately selected depending on the application.

[0095] Metal components may or may not be plated. The type of plating is not particularly limited, and known platings such as brass plating, zinc plating, chromium plating, and nickel plating can be used as appropriate. If the metal component is a metal wire, it is preferable that it is plated with one or more types of plating selected from the group consisting of brass plating and zinc plating.

[0096] <Method for manufacturing rubber-metal composites> The method for manufacturing the rubber-metal composite in this embodiment is not particularly limited, and known methods can be used as appropriate. For example, in a composite in which a metal wire is coated with a rubber composition, the composite can be obtained by vulcanizing the rubber composition while the metal wire is coated with the rubber composition. Also, for example, in a composite in which a rubber layer made of a rubber composition is laminated on at least one side of a layer made of a metal wire, the composite can be obtained, for example, by the method for manufacturing a laminate described in International Publication No. 2017 / 056414.

[0097] <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 characterized by using the rubber-metal composite of this embodiment. Because the rubber article of this embodiment uses the rubber-metal composite of this embodiment, it has high durability.

[0098] Examples of rubber articles in this embodiment include tires, hoses, conveyor belts, crawlers, and the like.

[0099] -tire- The tire of one embodiment of the present invention is not particularly limited except that it uses the rubber-metal composite of this embodiment, and may employ known tire configurations and manufacturing methods.

[0100] There are no particular limitations on the application parts of the rubber-metal composite of this embodiment in a tire, and they can be appropriately selected according to the purpose. Examples include the carcass, belt, bead core, etc.

[0101] Conventional methods can be used to manufacture the above-mentioned tires. For example, components commonly used in tire manufacturing, such as a carcass and belt (rubber-metal 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 conventional methods to produce the desired tire (for example, a pneumatic tire).

[0102] -hose- The hose of one embodiment of the present invention is not particularly limited except that it uses the rubber-metal composite of this embodiment, and can employ known hose configurations and manufacturing methods. In one embodiment, the hose comprises at least an inner rubber layer located radially inward, a reinforcing layer made of steel cord or the like located outside the inner rubber layer, and an outer rubber layer located outside the reinforcing layer. If there are multiple reinforcing layers, it also comprises an intermediate rubber layer located between the reinforcing layers. In the hose of this embodiment, the rubber-metal composite of this embodiment can be preferably applied to the combination of the inner rubber layer and the reinforcing layer, and / or the combination of the outer rubber layer and the reinforcing layer, and / or the combination of the intermediate rubber layer and the reinforcing layer.

[0103] -Conveyor belt- The conveyor belt of one embodiment of the present invention is not particularly limited except for the use of the above-mentioned rubber-metal composite, and may employ known conveyor belt configurations and manufacturing methods. In one embodiment, the conveyor belt comprises at least an inner surface rubber layer (bottom cover rubber) that contacts the drive pulley, etc., below the reinforcing layer made of steel cord or the like and its covering rubber, and an outer surface rubber layer (top cover rubber) that contacts the transported goods, above the reinforcing layer. In the conveyor belt of this embodiment, the rubber-metal composite of this embodiment can be applied as the reinforcing layer.

[0104] -Crawler- The crawler of one embodiment of the present invention is not particularly limited except that it uses the rubber-metal composite of this embodiment, and can employ known rubber crawler configurations and manufacturing methods. In one embodiment, the crawler has a structure in which a steel cord coated with a protective rubber material is embedded inside an endless strip-shaped elastic rubber body, and numerous protruding rubber pieces (lug rubbers) are formed on its outer surface. In the crawler of this embodiment, the rubber-metal composite of this embodiment can be preferably applied to the above combination of protective rubber and steel cord. [Examples]

[0105] 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.

[0106] (Example 1, Comparative Example 1) Samples of rubber compositions were prepared by compounding and kneading according to the formulations shown in Table 1 using conventional methods.

[0107] (1) Preparation of test samples The obtained rubber composition (unvulcanized) was rolled into a sheet measuring 150 mm in length, 150 mm in width, and 2 mm in thickness. Seven metal wires were then placed without gaps on each sheet, and the sheet was vulcanized at 150°C for 60 minutes to obtain a test sample of a rubber-metal composite containing vulcanized rubber. For the metal wire used, a brass-plated (Cu: 63% by mass, Zn: 37% by mass, plating amount 4g / kg) steel wire with a diameter of 0.30 mm and a length of 100 mm was used.

[0108] (2) Adhesion between the rubber composition and the metal component For the above test sample, five of the metal wires, excluding the two at both ends, were pulled together with a constant force using pliers. The percentage of vulcanized rubber coating on the surface of the metal wires after pulling was then measured. The results are shown in Table 1. A higher coating percentage indicates better adhesion between the rubber composition and the metal component.

[0109] (3) Crack resistance Strip-shaped test specimens with a hole in the center were prepared from the rubber composition, and the number of fractures was measured in a DC / DN test using these specimens (constant stress test (1.7 MPa) performed at a frequency of 5 Hz and 80°C using a Shimadzu "Servopulsa"). Number of fractures An index was taken, and the index for the number of fractures in Comparative Example 1 was set to 100. The results are shown in Table 1. If the index for Example 1 is greater than 100, it indicates that the rubber composition of Example 1 has improved crack resistance compared to the rubber composition of Comparative Example 1.

[0110] [Table 1]

[0111] *1 Natural rubber: RSS3 *2 IR: Isoprene rubber, manufactured by ENEOS Material, "IR2200" *3 Carbon black: Manufactured by Tokai Carbon Co., Ltd., "Seast 300" *4 Bismuth neodecanoate: Equivalent to a metal salt of an aliphatic carboxylic acid (1), metal element content = 27% by mass *5 1,3-Diisopropenylbenzene: Corresponds to compound (I) *6 Others: This is the total amount of stearic acid, vulcanization accelerator, sulfur, zinc oxide, etc., and the same amount of each component was used in Comparative Example 1 and Example 1.

[0112] Table 1 shows that the rubber composition of Example 1, which contains 1,3-diisopropenylbenzene corresponding to compound (I), exhibits improved crack resistance while maintaining adhesion between the rubber composition and the metal. [Industrial applicability]

[0113] According to the present invention, it is possible to provide a rubber composition that maintains adhesion between the rubber composition and a metal member while improving crack resistance. Furthermore, according to the present invention, it is possible to provide a rubber-metal composite using such a rubber composition, and even a rubber article using such a rubber-metal composite.

[0114] [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. Rubber component, rubber-metal adhesion promoter, and general formula (I): 【Chemistry 1】 [In formula (I), R １ and R ２ Each of these is independently an alkyl group, a 1-propenyl group, a 2-propenyl group, an isopropenyl group, or a vinyl group. The compound represented by ] contains and The rubber-metal adhesion promoter is a metal salt (1) of an aliphatic carboxylic acid having 2 to 25 carbon atoms and the metal species being bismuth, zinc, copper, antimony, silver, niobium, or zirconium, and general formula (A): (RCOO) ｘ MO] ３ Z (A) [In formula (A), (RCOO) is a residue of an aliphatic carboxylic acid having 2 to 25 carbon atoms, x is an integer of 1 or more and (valence of M - 1), M is bismuth, zinc, copper, antimony, silver, niobium, or zirconium, and Z is the following formulas (z-1) to (z-4): 【Chemistry 2】 A rubber composition characterized by comprising one or more compounds selected from the compounds represented by (2) ], which have any of the structures of ].

2. The rubber composition according to claim 1, wherein the rubber component includes natural rubber, and the proportion of natural rubber in the rubber component is 50% by mass or more.

3. The rubber composition according to claim 1, further containing carbon black, wherein the carbon black content is 50 parts by mass or more per 100 parts by mass of the rubber component.

4. The rubber composition according to claim 1, wherein the content of the rubber-metal adhesion promoter is 0.01 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the rubber component.

5. R １ and R ２ The rubber composition according to claim 1, wherein is an isopropenyl group.

6. The rubber composition according to claim 1, wherein the rubber-metal adhesion promoter comprises a metal salt (1) of the aliphatic carboxylic acid, and the metal species in the metal salt (1) of the aliphatic carboxylic acid is bismuth or zinc.

7. The rubber composition according to claim 1, wherein the rubber-metal adhesion promoter comprises a metal salt (1) of the aliphatic carboxylic acid, and the aliphatic carboxylic acid in the metal salt (1) of the aliphatic carboxylic acid is an aliphatic monocarboxylic acid or an aliphatic dicarboxylic acid.

8. The rubber composition according to claim 7, wherein the aliphatic carboxylic acid in the metal salt (1) of the aliphatic carboxylic acid is a saturated aliphatic monocarboxylic acid having 2 to 20 carbon atoms.

9. The rubber composition according to claim 1, wherein the rubber-metal adhesion promoter comprises a compound (2) represented by the general formula (A), and M in the general formula (A) is bismuth or zinc.

10. The rubber composition according to claim 1, wherein the rubber-metal adhesion promoter comprises compound (2) represented by the general formula (A), and Z in the general formula (A) has the structure of formula (z-1).

11. The rubber composition according to claim 1, wherein the rubber-metal adhesion promoter comprises compound (2) represented by the general formula (A), and (RCOO) in the general formula (A) is a residue of a saturated aliphatic monocarboxylic acid having 2 to 20 carbon atoms.

12. The rubber composition according to claim 3, wherein the carbon black includes recycled carbon black.

13. A rubber-metal composite comprising the rubber composition described in claim 1 and a metal member.

14. A rubber article characterized by using the rubber-metal composite described in claim 13.

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