Rubber composition, rubber-metal composite, hose, conveyor belt, rubber track and tire

Abstract

The problem solved by the present invention is to provide a rubber composition having excellent adhesion to metal components. The rubber composition (being a rubber composition not containing a thiuram-based compound vulcanization accelerator) comprises a rubber component, a rubber-metal adhesion accelerator, and a vulcanization accelerator other than a thiuram-based compound, wherein the rubber component comprises EPDM in an amount of 20 parts by mass or more relative to 100 parts by mass of the rubber component, and the rubber-metal adhesion accelerator comprises aliphatic carboxylic acid / metal salt (1) and a vulcanization accelerator selected from the group consisting of: (RCOO) x MO]3Z represents one or more compounds of the compound (2), the aliphatic carboxylic acid of the metal salt (1) each has 2-25 carbon atoms, and the metal of the metal salt (1) is each Bi, Zn, Cu, Sb, Ag, Nb, or Zr. In formula (A), (RCOO) is a residue of an aliphatic carboxylic acid having 2-25 carbon atoms, M is Bi, Zn, Cu, Sb, Ag, Nb, or Zr, x is an integer from 1 to (the valence of M)-1, and Z is a structure selected from formula (z-1) to formula (z-4),

Description

Technical Field

[0001] The present invention relates to a rubber composition, a rubber-metal composite, a hose, a conveyor belt, a rubber track, and a tire. Background Art

[0002] Rubber-metal composites formed by coating reinforcing materials such as brass-plated steel cords with rubber compositions including natural rubber and synthetic rubber are conventionally used to improve the performance of rubber products such as hoses, conveyor belts, rubber tracks, and tires. Further, it is known in this regard to include an adhesion promoter in the rubber composition to improve the adhesion between the reinforcing material and the coating rubber (rubber composition). Cobalt salts of organic acids (such as cobalt stearate, cobalt versatate, and cobalt naphthenate) are generally used as adhesion promoters because they can improve the adhesion between metal components such as steel cords and the coating rubber.

[0003] However, in recent years, environmental regulations such as the EU's REACH regulation ("Registration, Evaluation, Authorization and Restriction of Chemicals") have become increasingly stringent, and thus the cobalt salts of organic acids used as adhesion promoters as described above are now listed as candidate chemicals to be regulated by the REACH regulation. Therefore, there is a demand for the development of a non-cobalt-based adhesion promoter.

[0004] In view of this, for example, PTL 1 discloses a technology of i) a cobalt-free adhesion promoter capable of achieving high adhesion between rubber and metal, and ii) a rubber composition and a tire each containing the adhesion promoter.

[0005] In the manner described above, the rubber parts of rubber products such as hoses, conveyor belts, rubber tracks, and tires are sometimes also required to have excellent weather resistance from the viewpoint of durability and / or appearance. In order to meet this requirement, it is known to use a rubber composition containing ethylene-propylene-diene rubber (EPDM) as a rubber component in the rubber parts of rubber products to improve their weather resistance.

[0006] Reference List

[0007] Patent Literature

[0008] PTL 1: WO 2016 / 039375 A1 Summary of the invention

[0009] Problem that the invention aims to solve

[0010] However, the inventors of the present invention have revealed through intensive studies that when the adhesion promoter disclosed in PTL 1 is added to a rubber composition containing ethylene-propylene-diene rubber (EPDM) as a rubber component instead of a cobalt salt of an organic acid, the resulting rubber composition cannot exhibit satisfactory adhesion to metal components.

[0011] In view of this, an object of the present invention is to solve the above-mentioned problems of the prior art and provide a rubber composition which contains ethylene-propylene-diene rubber (EPDM) and can still show excellent adhesion to metal members without necessarily containing a cobalt salt of an organic acid therein.

[0012] Furthermore, another object of the present invention is to provide i) a rubber-metal composite using the rubber composition and having excellent adhesion between rubber and metal members, and ii) a hose, a conveyor belt, a rubber crawler track, and a tire each using the rubber-metal composite and having excellent durability.

[0013] Solutions for solving problems

[0014] The main features of the present invention for achieving the above-mentioned objects are as follows.

[0015] The rubber composition of the present invention (which is a rubber composition not containing a thiuram-based vulcanization accelerator) comprises: a rubber component; a rubber-metal adhesion promoter; and a vulcanization accelerator other than a thiuram-based compound, wherein the rubber component contains 20 parts by mass or more of ethylene-propylene-diene rubber (EPDM) relative to 100 parts by mass of the rubber component, and the rubber-metal adhesion promoter contains at least one selected from the group consisting of: a metal salt (1) of an aliphatic carboxylic acid; and a vulcanization accelerator represented by the general formula (A): [(RCOO) x MO]3Z, the aliphatic carboxylic acid used in the metal salt of the aliphatic carboxylic acid (1) has 2 to 25 carbon atoms, the metal used in the metal salt of the aliphatic carboxylic acid (1) is any one of bismuth, zinc, copper, antimony, silver, niobium, and zirconium, and in the general formula (A), each "(RCOO)" represents C2-C 25 A residue of an aliphatic carboxylic acid, "M" represents bismuth, zinc, copper, antimony, silver, niobium, or zirconium, "x" represents an integer greater than or equal to {(the valence of M) - 1}, and "Z" represents a structure selected from the group consisting of formulas (z-1), (z-2), (z-3), and (z-4) shown below.

[0016]

[0017] The rubber-metal composite of the present invention is characterized by comprising the above-mentioned rubber composition and a metal member.

[0018] The hose of the present invention is characterized by comprising the above-mentioned rubber-metal composite.

[0019] The conveyor belt of the present invention is characterized by comprising the above-mentioned rubber-metal composite.

[0020] The rubber crawler of the present invention is characterized by having the above-mentioned rubber-metal composite.

[0021] The tire of the present invention is characterized by comprising the above-mentioned rubber-metal composite.

[0022] Effects of the Invention

[0023] According to the present invention, there can be provided a rubber composition which contains ethylene-propylene-diene rubber (EPDM) and is capable of exhibiting excellent adhesion to a metal member without necessarily containing a cobalt salt of an organic acid therein.

[0024] Furthermore, according to the present invention, it is possible to provide i) a rubber-metal composite having excellent adhesion between the rubber and the metal member, and ii) a hose, a conveyor belt, a rubber crawler track, and a tire each having excellent durability. DETAILED DESCRIPTION

[0025] Hereinafter, the rubber composition, the rubber-metal composite, the hose, the conveyor belt, the rubber track, and the tire of the present invention will be exemplarily described in detail based on the embodiments of the present invention.

[0026] <Rubber Composition>

[0027] The rubber composition of the present invention comprises: a rubber component; a rubber-metal adhesion promoter; and a vulcanization accelerator other than a thiuram compound, wherein the rubber component comprises 20 parts by mass or more of ethylene-propylene-diene rubber relative to 100 parts by mass of the rubber component, and the rubber-metal adhesion promoter comprises at least one selected from the group consisting of: a metal salt (1) of an aliphatic carboxylic acid; and a vulcanization accelerator represented by the general formula (A): [(RCOO) x The compound (2) represented by MO]3Z, the aliphatic carboxylic acid used in the metal salt of aliphatic carboxylic acid (1) has 2 to 25 carbon atoms, the metal used in the metal salt of aliphatic carboxylic acid (1) is any one of bismuth, zinc, copper, antimony, silver, niobium, and zirconium, and in the general formula (A), each "(RCOO)" represents C2-C 25 A residue of an aliphatic carboxylic acid, "M" represents bismuth, zinc, copper, antimony, silver, niobium, or zirconium, "x" represents an integer greater than or equal to {(the valence of M) - 1}, and "Z" represents a structure selected from the group consisting of formulas (z-1), (z-2), (z-3), and (z-4) shown below.

[0028]

[0029] It should be noted that a rubber composition containing a thiuram-based vulcanization accelerator is not included in the rubber composition of the present invention.

[0030] From the viewpoint of obtaining satisfactory weather resistance, the rubber composition of the present invention contains 20 parts by mass or more of ethylene-propylene-diene rubber relative to 100 parts by mass of the rubber component.

[0031] Further, in the rubber composition of the present invention, a rubber-metal adhesion promoter comprising at least one selected from the group consisting of: a metal salt of an aliphatic carboxylic acid (1); and a compound (2) represented by the general formula (A) contributes to improving the adhesion of the rubber composition to the metal member. However, in this regard, as described above, when the rubber composition comprises ethylene-propylene-diene rubber as in the present invention, simply including the rubber-metal adhesion promoter in the rubber composition cannot achieve satisfactory adhesion of the rubber composition to the metal member.

[0032] In order to solve this problem, the rubber composition of the present invention contains a vulcanization accelerator other than the thiuram-based compound in addition to the rubber-metal adhesion promoter, so that the rubber composition can reliably improve the adhesion of the rubber composition to the metal member in a satisfactory manner due to the synergistic effect caused by the rubber-metal adhesion promoter and the vulcanization accelerator other than the thiuram-based compound.

[0033] Therefore, the rubber composition of the present invention can achieve its excellent adhesiveness to a metal member without necessarily containing a cobalt salt of an organic acid therein.

[0034] In this regard, a rubber composition containing a thiuram-based vulcanization accelerator is not included in the rubber composition of the present invention because, in the case where the rubber composition contains ethylene-propylene-diene rubber, the presence of the thiuram-based vulcanization accelerator in the rubber composition deteriorates the adhesion of the rubber composition to a metal member even if the rubber composition additionally contains a rubber-metal adhesion promoter and a vulcanization accelerator other than the thiuram-based compound.

[0035] (Rubber component)

[0036] The rubber composition of the present invention comprises a rubber component. The rubber component comprises ethylene-propylene-diene rubber (EPDM) of more than 20 mass parts relative to 100 mass parts of the rubber component. When the rubber component comprises ethylene-propylene-diene rubber of more than 20 mass parts relative to 100 mass parts of the rubber component, the weather resistance of the rubber composition is improved.

[0037] Ethylene-propylene-diene rubber (EPDM) includes ethylene units, propylene units, and diene units. The type of diene unit is not particularly limited. Examples of monomers constituting the diene unit include ethylidene norbornene (ENB), vinyl norbornene (VNB), dicyclopentadiene (DCPD), and 1,4-hexadiene (1,4-HD), etc.

[0038] Any known EPDM can be optionally used and used as EPDM. For example, EPDM produced by emulsion / solution polymerization is commercially available for use as EPDM. The terminal of the molecular chain of EPDM may be modified or unmodified.

[0039] A single species or a combination of two or more species among these examples may be used as the EPDM.

[0040] The content of EPDM is ≥20 mass parts and preferably ≥30 mass parts relative to the rubber component of 100 mass parts. The content of EPDM can be 100 mass parts (that is, the rubber component can be all made of EPDM) relative to the rubber component of 100 mass parts. When the content of EPDM is less than 20 mass parts relative to the rubber component of 100 mass parts, the weather resistance of rubber combination can not be satisfactorily improved. On the contrary, when the content of EPDM is relative to the rubber component of 100 mass parts ≥30 mass parts, the weather resistance of rubber combination is more satisfactorily improved than other situations.

[0041] The rubber component can be made of EPDM completely, or include the rubber component other than EPDM. The example of the rubber component other than applicable EPDM includes natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), styrene-isoprene rubber (SIR), styrene-isoprene-butadiene rubber (SIBR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), and the modified rubber obtainable therefrom. The single species in these examples or the combination of two or more can be used as the rubber component other than EPDM.

[0042] The rubber component of the rubber composition according to the present invention is preferably a combination of at least one of ethylene-propylene-diene rubber (EPDM) and a group consisting of natural rubber (NR), acrylonitrile-butadiene rubber (NBR), and butadiene rubber (BR). The fracture resistance (tensile properties) of the natural rubber in which strain-induced crystallization is easily generated is excellent. The oil resistance of acrylonitrile-butadiene rubber is excellent. The wear resistance of butadiene rubber is excellent. Therefore, when the rubber component includes at least one selected from the group consisting of NR, NBR, and BR in addition to EPDM, the durability of the rubber composition is improved.

[0043] From the viewpoint of durability of the rubber composition, the total content of NR, NBR, and BR is ≤ 80 parts by mass and preferably ≥ 10 parts by mass, and more preferably ≥ 20 parts by mass relative to 100 parts by mass of the rubber component.

[0044] (Rubber-Metal Adhesion Promoter)

[0045] The rubber composition of the present invention comprises a rubber-metal adhesion promoter. The rubber-metal adhesion promoter comprises at least one selected from the group consisting of: a metal salt of an aliphatic carboxylic acid (1); and a metal salt of the general formula (A): [(RCOO) x Including the metal salt of an aliphatic carboxylic acid (1) and / or the compound (2) represented by the general formula (A) as a rubber-metal adhesion promoter in the rubber composition improves the adhesion of the rubber composition to the metal member.

[0046] --Metal salts of aliphatic carboxylic acids (1)--

[0047] The aliphatic carboxylic acid used in the metal salt of aliphatic carboxylic acid (1) is C 2-25 Aliphatic carboxylic acid. Furthermore, the metal species of the metal salt (1) is selected from the group consisting of bismuth (Bi), zinc (Zn), copper (Cu), antimony (Sb), silver (Ag), niobium (Nb), and zirconium (Zr).

[0048] Using C ≥2 The aliphatic carboxylic acid improves the compatibility of the metal salt (1) of the aliphatic carboxylic acid with the rubber component, thereby improving the adhesion between the metal member and the rubber composition. ≤25 Aliphatic carboxylic acid as the aliphatic carboxylic acid allows easy synthesis of the metal salt (1) of the aliphatic carboxylic acid. It should be noted that in the present invention, the number of carbon atoms of the aliphatic carboxylic acid includes the number of carbon atoms of the carboxyl group therein.

[0049] The metal used for the metal salt of an aliphatic carboxylic acid (1) is preferably bismuth. In the case where the rubber composition contains the bismuth salt of an aliphatic carboxylic acid, the adhesion between the rubber composition and the metal member is further improved.

[0050] The aliphatic carboxylic acid used for the metal salt of an aliphatic carboxylic acid (1) is preferably an aliphatic monocarboxylic acid or an aliphatic dicarboxylic acid. In the case where the rubber composition contains the metal salt of an aliphatic monocarboxylic acid / aliphatic dicarboxylic acid, the adhesion between the rubber composition and the metal member is further improved.

[0051] Examples of the aliphatic monocarboxylic acid include saturated aliphatic monocarboxylic acid, unsaturated aliphatic monocarboxylic acid, and the like.

[0052] Examples of the saturated aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric 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, eicosanoic acid, docosanoic acid, tetracosanoic acid, and cyclohexaneic acid, and the like.

[0053] Examples of the 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 fatty acid, linseed oil fatty acid, soybean oil fatty acid, tall oil fatty acid, resin acid, rosin acid, abietic acid, neoabietic acid, palustric acid, pimaric acid, and dehydroabietic acid, and the like.

[0054] Examples of the aliphatic dicarboxylic acid include saturated aliphatic dicarboxylic acids, unsaturated aliphatic dicarboxylic acids, and the like.

[0055] Examples of the saturated aliphatic dicarboxylic acid include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid and the like.

[0056] Examples of the unsaturated aliphatic dicarboxylic acid include fumaric acid, maleic acid, and the like.

[0057] Among the above examples of aliphatic carboxylic acids, saturated aliphatic monocarboxylic acids are preferred because saturated aliphatic monocarboxylic acids hardly affect sulfur crosslinking of rubber components, thus making it possible to obtain a rubber cured product whose rubber properties are less adversely affected than otherwise, and suitable for conveyor belts, hoses, rubber tracks, tires, and the like. Among the examples of saturated aliphatic monocarboxylic acids, C 2-20 Saturated aliphatic monocarboxylic acids; more preferably 2-ethylhexanoic acid, neodecanoic acid, hexadecanoic acid and octadecanoic acid; and particularly preferably 2-ethylhexanoic acid.

[0058] The aliphatic carboxylic acid used in the metal salt of aliphatic carboxylic acid (1) is C 2-20 In the case of a saturated aliphatic monocarboxylic acid, the adhesion between the rubber composition and the metal member is further improved.

[0059] In this regard, in the case where the saturated aliphatic monocarboxylic acid is 2-ethylhexanoic acid, neodecanoic acid, hexadecanoic acid, or octadecanoic acid, the adhesion between the rubber composition and the metal member is even further improved.

[0060] Examples of the metal salt (1) of an aliphatic carboxylic acid 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 hexadecanoate, zinc hexadecanoate, copper hexadecanoate, antimony hexadecanoate, silver hexadecanoate, niobium hexadecanoate, zirconium hexadecanoate, bismuth octadecanoate, zinc octadecanoate, copper octadecanoate, antimony octadecanoate, silver octadecanoate, niobium octadecanoate, and zirconium octadecanoate. Among these examples, bismuth 2-ethylhexanoate, bismuth neodecanoate, bismuth hexadecanoate, and bismuth octadecanoate are preferred. A single species or a combination of two or more of these examples can be used as the metal salt (1) of an aliphatic carboxylic acid.

[0061] The metal salt of aliphatic carboxylic acid (1) can be obtained, for example, by (i) a "fusion method" or (ii) a "double decomposition method" as described in WO 2016 / 039375. The "fusion method" is to obtain C 2-25 A method for producing a metal salt of an aliphatic carboxylic acid by directly reacting an aliphatic carboxylic acid (a) with at least one selected from the group consisting of: an oxide (b-1) of a metal (bismuth, zinc, copper, antimony, silver, niobium, or zirconium); a hydroxide (b-2) of a metal (bismuth, zinc, copper, antimony, silver, niobium, or zirconium); and a carbonate (b-3) of a metal (bismuth, zinc, copper, antimony, silver, niobium, or zirconium), wherein the “double decomposition method” is to first react C 2-25 A method for producing a metal salt of an aliphatic carboxylic acid by reacting an aliphatic carboxylic acid (a) with NaOH in the presence of water to obtain a sodium salt of an aliphatic carboxylic acid, and then reacting the sodium salt of an aliphatic carboxylic acid thus obtained with at least one selected from the group consisting of: a sulfate of a metal (bismuth, zinc, copper, antimony, silver, niobium, or zirconium) (c-1); a chloride of a metal (bismuth, zinc, copper, antimony, silver, niobium, or zirconium) (c-2); and a nitrate of a metal (bismuth, zinc, copper, antimony, silver, niobium, or zirconium) (c-3).

[0062] --Compound (2)--

[0063] Compound (2) is represented by the general formula (A): [(RCOO) x MO]3Z indicates.

[0064] "(RCOO)" in the general formula (A) represents C 2-25 The residue of an aliphatic carboxylic acid. ≥2 The residue of the aliphatic carboxylic acid improves the compatibility of the compound (2) with the rubber component, thereby improving the adhesion between the metal member and the rubber composition. ≤25The residue of aliphatic carboxylic acid not only facilitates the synthesis of compound (2), but also improves the dispersibility of compound (2) in the rubber component and / or the adsorption of compound (2) on the surface of the metal member, thereby increasing the effect of improving the adhesion between the metal member and the rubber composition. In the present invention, the number of carbon atoms of (RCOO) means the number of carbon atoms including the carboxyl group.

[0065] The residue of aliphatic monocarboxylic acid is preferably used as C 2-25 Residue of aliphatic carboxylic acid. Preferred examples of the residue of aliphatic monocarboxylic acid include residues derived from the above-mentioned examples of aliphatic monocarboxylic acids.

[0066] Among the residues of aliphatic carboxylic acids, the residues of saturated aliphatic monocarboxylic acids are preferred because the compound (2) having a specific residue itself does not participate in the crosslinking of the rubber component, thereby promoting the dispersion of the compound (2) near the metal / the adsorption of the compound (2) on the metal surface, thereby producing an effect of promoting adhesion between the metal member and the rubber composition more significantly than in other cases. Among the residues of saturated aliphatic monocarboxylic acids, the residues of C 2-20 The residue of a saturated aliphatic monocarboxylic acid, and more preferably the residue of 2-ethylhexanoic acid, the residue of neodecanoic acid, the residue of hexadecanoic acid and the residue of octadecanoic acid.

[0067] Wherein (RCOO) in the general formula (A) is C 2-20 In the case of a residue of a saturated aliphatic monocarboxylic acid, the adhesion between the rubber composition and the metal component is further improved. In the case where the saturated aliphatic monocarboxylic acid associated with (RCOO) is 2-ethylhexanoic acid, neodecanoic acid, hexadecanoic acid, or octadecanoic acid, the adhesion between the rubber composition and the metal component is even further improved.

[0068] "M" in the general formula (A) represents a metal species, and specific examples thereof include bismuth (Bi), zinc (Zn), copper (Cu), antimony (Sb), silver (Ag), niobium (Nb), and zirconium (Zr). Among these examples of metal species, bismuth is particularly preferred as M because bismuth ensures satisfactory adhesion between the metal member and the rubber composition.

[0069] Furthermore, "x" in the general formula (A) represents an integer greater than or equal to 1 and equal to {(the valence of M) - 1}.

[0070] Furthermore, "Z" in the general formula (A) represents a structure selected from the following formulae (z-1), (z-2), (z-3) and (z-4).

[0071]

[0072] Among the structures shown above, the structure represented by formula (z-1) is preferable because the (z-1) structure further improves the adhesive force (adhesiveness) between the metal member and the rubber composition.

[0073] Examples of compound (2) include tris[(bismuth2-ethylhexanoate)oxy]boron, tris[(zinc2-ethylhexanoate)oxy]boron, tris[(copper2-ethylhexanoate)oxy]boron, tris[(antimony2-ethylhexanoate)oxy]boron, tris[(silver2-ethylhexanoate)oxy]boron, tris[(niobium2-ethylhexanoate)oxy]boron, tris[(zirconium2-ethylhexanoate)oxy]boron, tris[(bismuth2-ethylhexanoate)oxy]boron, tris[(zinc2-ethylhexanoate)oxy]boron, tris[(copper2-ethylhexanoate)oxy]boron, tris[(antimony neodecanoate)oxy]boron, tris[(silver neodecanoate)oxy]boron, tris[(niobium neodecanoate)oxy]boron, tris[(zirconium neodecanoate)oxy]boron, tris[(bismuth hexadecanoate)oxy]boron, tris[(zinc hexadecanoate)oxy]boron, tris[(copper hexadecanoate)oxy]boron, tris[(antimony hexadecanoate)oxy]boron, tris[(silver hexadecanoate)oxy]boron, tris[(niobium hexadecanoate)oxy]boron, tris[(zirconium hexadecanoate)oxy]boron, tris[(bismuth octadecanoate)oxy]boron, tris[(zinc octadecenoate)oxy]boron, tris[(copper octadecenoate)oxy]boron, tris[(antimony octadecanoate)oxy]boron, tris[(silver octadecanoate)oxy]boron, tris[(niobium octadecenoate)oxy]boron, and tris[(zirconium octadecenoate)oxy]boron. Among these examples, tris[(bismuth 2-ethylhexanoate)oxy]boron, tris[(bismuth neodecanoate)oxy]boron, tris[(bismuth hexadecanoate)oxy]boron, and tris[(bismuth octadecanoate)oxy]boron are preferred. A single species or a combination of two or more species of these examples can be used as compound (2).

[0074] The compound (2) represented by the general formula (A) can be prepared, for example, by the method disclosed in WO 2016 / 039375, which comprises: (i) mixing and heating the following: C 2-25 Aliphatic carboxylic acid (a); C 1-5 Borate esters of lower alcohols (d-1), C 1-5 Borate esters of lower alcohols (d-2), C 1-5 Phosphate esters of lower alcohols (d-3), and C 1-5 Any of the phosphites of lower alcohols (d-4); capable of reacting with the C 1-5 The lower alcohol residue forms an acid of a volatile ester (e); and a metal compound M as a metal source (f), and (ii) removing the resulting volatile ester.

[0075] The content of the rubber-metal adhesion promoter is not particularly limited, but is preferably ≥ 0.1 parts by mass, more preferably ≥ 0.5 parts by mass, and particularly preferably ≥ 1.0 parts by mass relative to 100 parts by mass of the rubber component from the viewpoint of obtaining even better adhesion to metal members than otherwise. On the other hand, from the viewpoint of suppressing degradation of the rubber composition, the content of the rubber-metal adhesion promoter is preferably ≤ 20 parts by mass, more preferably ≤ 15 parts by mass, and particularly preferably ≤ 10 parts by mass relative to 100 parts by mass of the rubber component.

[0076] Further, the content of the rubber-metal adhesion promoter in terms of the metal element therein is preferably ≥0.01 parts by mass, more preferably ≥0.1 parts by mass, and preferably ≤5 parts by mass, more preferably ≤3 parts by mass relative to 100 parts by mass of the rubber component. In the case where the content of the rubber-metal adhesion promoter in terms of the metal element therein is ≥0.01 parts by mass, the adhesion between the rubber composition and the metal member is further improved. In the case where the content of the rubber-metal adhesion promoter in terms of the metal element therein is ≤5 parts by mass, the rubber-metal adhesion promoter has a relatively small effect on the crosslinking reaction of the rubber component, thereby having a relatively small deterioration effect on the rubber composition.

[0077] The total content of the metal salt of aliphatic carboxylic acid (1) and the compound (2) represented by the general formula (A) in the rubber-metal adhesion promoter is preferably ≥50% by mass, more preferably ≥80% by mass, and may be 100% by mass. The unreacted residual raw materials (such as the above-mentioned "C 2-25 Aliphatic carboxylic acids (a)" etc.) may remain in the rubber-metal adhesion promoter.

[0078] (Vulcanization accelerators other than thiuram compounds)

[0079] The rubber composition of the present invention contains a vulcanization accelerator other than a thiuram compound. Including a vulcanization accelerator other than a thiuram compound in the rubber composition improves the adhesion of the rubber composition to a metal member.

[0080] It should be noted in this regard that a rubber composition containing a thiuram-based vulcanization accelerator is not included in the rubber composition of the present invention because the presence of the thiuram-based vulcanization accelerator in the rubber composition (which offsets this advantage and therefore) deteriorates the adhesion of the rubber composition to the metal member.

[0081] Examples of the vulcanization accelerator other than the thiuram-based compound include a sulfenamide-based vulcanization accelerator, a thiazole-based vulcanization accelerator, a guanidine-based vulcanization accelerator, and the like.

[0082] In the rubber composition of the present invention, the vulcanization accelerator other than the thiuram-based compound is preferably at least one selected from the group consisting of sulfenamide-based vulcanization accelerators and thiazole-based vulcanization accelerators. Including the sulfenamide-based vulcanization accelerator and / or the thiazole-based vulcanization accelerator in the rubber composition further improves the adhesion of the rubber composition to the metal member.

[0083] Examples of sulfenamide-based vulcanization accelerators include N-cyclohexyl-2-benzothiazole sulfenamide (CZ, CBS), N-tert-butyl-2-benzothiazole sulfenamide (NS, BBS), N-oxydiethyl-2-benzothiazole sulfenamide (OBS), N,N-diisopropyl-2-benzothiazole sulfenamide (DPBS), and N,N-dicyclohexyl-2-benzothiazole sulfenamide (DZ, DCBS), etc.

[0084] Examples of the thiazole-based vulcanization accelerator include 2-mercaptobenzothiazole (MBT) and the like.

[0085] A single species or a combination of two or more species among these examples may be used as a vulcanization accelerator other than the thiuram-based compound.

[0086] The content of the vulcanization accelerator other than the thiuram-based compound is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, even more preferably 0.2 parts by mass or more, particularly preferably 0.3 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 3 parts by mass or less, particularly preferably 1 part by mass or less, relative to 100 parts by mass of the rubber component.

[0087] (Other components)

[0088] In addition to the above-mentioned rubber component, rubber-metal adhesion promoter and vulcanization accelerators other than thiuram compounds, known additives usually blended with rubber composition can be optionally added to the rubber composition of the present invention. The example of additive includes filler, vulcanizing agent (crosslinking agent), vulcanization aid, oil, vulcanization retarder, antioxidant, reinforcing agent, colorant, flame retardant, lubricant, foaming agent, plasticizer, processing aid, antioxidant, scorch retarder, ultraviolet protection agent, antistatic agent and coloring prevention agent etc. Single species or a combination of two or more in these examples can be used as additive.

[0089] Examples of the filler include carbon black, silica, aluminum hydroxide, clay, aluminum oxide, talc, mica, kaolin, glass spheres, glass beads, calcium carbonate, magnesium carbonate, magnesium hydroxide, magnesium oxide, titanium oxide, potassium titanate, and barium sulfate, etc. Among these examples, as the filler, carbon black and silica are preferred, and carbon black is particularly preferred from the viewpoint of satisfactorily reinforcing the rubber composition.

[0090] The type of carbon black is not particularly limited. For example, any hard carbon produced by an oil furnace method can be used. Specifically, for example, at least one of GPF, FEF, SRF, HAF, ISAF, IISAF, SAF grades can be used as carbon black, without being particularly limited thereto.

[0091] The kind of silica is not particularly limited, and examples thereof include wet silica (hydrated silica), dry silica (anhydrous silica), calcium silicate, aluminum silicate, and the like.

[0092] The content of the filler is not particularly limited, and the content is preferably ≥20 parts by mass, more preferably ≥30 parts by mass, even more preferably ≥40 parts by mass, particularly preferably ≥50 parts by mass, relative to 100 parts by mass of the rubber component, and preferably ≤200 parts by mass, more preferably ≤175 parts by mass, even more preferably ≤150 parts by mass, particularly preferably ≤125 parts by mass. The content of the filler ≥20 parts by mass relative to 100 parts by mass of the rubber component further improves the reinforcement of the rubber composition. The content of the filler ≤200 parts by mass relative to 100 parts by mass of the rubber component ensures good processability of the rubber composition in the mixing process.

[0093] Sulfur is preferred as the vulcanizing (crosslinking) agent. The type of sulfur is not particularly limited, and examples thereof include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and oil-treated sulfur, etc. The content of the vulcanizing (crosslinking) agent is preferably ≥0.1 parts by mass, more preferably ≥0.2 parts by mass, even more preferably ≥0.3 parts by mass, particularly preferably ≥0.5 parts by mass, and preferably ≤10 parts by mass, more preferably ≤8 parts by mass, even more preferably ≤6 parts by mass, particularly preferably ≤4 parts by mass, relative to 100 parts by mass of the rubber component.

[0094] Zinc white (zinc oxide) is preferred as a vulcanization aid. The content of the vulcanization aid is preferably ≥1 part by mass, more preferably ≥2 parts by mass, even more preferably ≥3 parts by mass, particularly preferably ≥4 parts by mass, and is preferably ≤20 parts by mass, more preferably ≤17.5 parts by mass, even more preferably ≤15 parts by mass, particularly preferably ≤12.5 parts by mass, relative to 100 parts by mass of the rubber component.

[0095] From the viewpoint of actively responding to relevant environmental regulations, the rubber composition of the present invention preferably does not contain cobalt added thereto. Specifically, the content of the cobalt compound in the rubber composition is preferably ≤0.01 parts by mass and more preferably 0 parts by mass relative to 100 parts by mass of the rubber component (except for a very small amount of cobalt as an unavoidable impurity).

[0096] (Method for producing rubber composition)

[0097] The method for producing the rubber composition of the present invention is not particularly limited, and any known related method may be employed.

[0098] For example, the rubber composition of the present invention can be obtained by blending the rubber component, the rubber-metal adhesion promoter, the vulcanization accelerator other than the thiuram-based compound, and any optional components simultaneously or in any desired order; and kneading them by using a kneading device such as a Banbury mixer, a roll or an internal mixer.

[0099] (Application of rubber composition)

[0100] The use of the rubber composition according to the present invention is not particularly limited. The rubber composition of the present invention can be applied to, for example, any rubber product such as a hose, a conveyor belt, a rubber track, a tire, an electric wire, and a vibration-proof material.

[0101] <Rubber-Metal Composite>

[0102] The rubber-metal composite of the present invention is characterized by comprising the rubber composition of the present invention and a metal member. The rubber-metal composite of the present invention has excellent adhesion between the rubber (rubber composition) and the metal member.

[0103] In the rubber-metal composite of the present invention, it is sufficient that the rubber composition of the present invention is in contact only with the metal member. Examples of acceptable embodiments of the rubber-metal composite include an embodiment in which at least a portion of a metal wire as a metal member is coated with the rubber composition, and an embodiment in which a rubber layer made of the rubber composition is laminated on at least one surface side of a layer made of the metal wire.

[0104] “Metal member” means a member made of metal, and may have various forms such as a metal wire, a metal cord formed by twisting a plurality of metal wires (steel wires), a metal cord composed of a single metal wire, a metal spring, a metal plate, and a metal ring.

[0105] The metal type of the metal member is not particularly limited, and can be arbitrarily selected from steel, iron, copper, gold, and the like according to the application.

[0106] The metal member may be plated or non-plated. The type of plating is not particularly limited, and any known plating such as brass plating, zinc plating, chrome plating, or nickel plating may be optionally adopted.

[0107] In this regard, in the case where the metal member is a metal wire, the metal member is preferably provided with at least one plating selected from the group consisting of brass plating and zinc plating.

[0108] The method for producing the rubber-metal composite of the present invention is not particularly limited, and any known optional method may be adopted. For example, in the case of a rubber-metal composite in which a metal wire is coated with a rubber composition, the composite can be obtained by coating the metal wire with a rubber composition and vulcanizing the rubber composition thus provided on the wire. Further, in the case of a rubber-metal composite in which a rubber layer made of a rubber composition is laminated on at least one surface side of a layer made of a metal wire, the composite can be obtained by, for example, the method for producing a laminate disclosed in WO 2017 / 056414 A1.

[0109] <Hose>

[0110] The hose of the present invention is characterized in that it has the above-mentioned rubber-metal composite. The hose of the present invention has excellent durability because its adhesiveness between rubber and metal is equal to or better than the corresponding adhesiveness exhibited by a hose using a rubber composition containing a cobalt salt.

[0111] The hose of the present invention is not particularly limited except that the above-mentioned rubber-metal composite is used, and any known hose structure and manufacturing method may be optionally adopted.

[0112] In one embodiment, the hose has an inner rubber layer (inner tube rubber) located on the radial inner side thereof, an outer rubber layer located on the radial outer side thereof, and a metal reinforcement layer (metal member) located between the inner rubber layer and the outer rubber layer. In one embodiment, the rubber composition can be used for at least one of the inner rubber layer and the outer rubber layer. A rubber composition containing EPDM and having excellent weather resistance can be suitably applied to the outer rubber layer.

[0113] <Conveyor Belt>

[0114] The conveyor belt of the present invention is characterized in that it has the above-mentioned rubber-metal composite. The conveyor belt of the present invention has excellent durability because its adhesion between rubber and metal is equal to or better than the corresponding adhesion exhibited by a conveyor belt using a rubber composition containing a cobalt salt.

[0115] The conveyor belt of the present invention is not particularly limited except that the above-mentioned rubber-metal composite is used, and any known structure and manufacturing method of conveyor belts may be optionally adopted.

[0116] In one embodiment, the rubber-metal composite of the present invention can be used at least for the surface rubber (lower surface covering rubber) on the inner peripheral side of the lower side of the metal reinforcement (metal member) made of steel cords etc. of a conveyor belt, which is in contact with a drive pulley, a driven pulley, and a shape retaining rotor etc. Further, the rubber-metal composite can also be used for the surface rubber (upper surface covering rubber) on the outer peripheral side of the upper side of the metal reinforcement of a conveyor belt, which is in contact with an article to be conveyed.

[0117] A specific example of the method for manufacturing the above-mentioned conveyor belt includes: inserting a metal reinforcement material between rubber sheets made of the above-mentioned rubber composition; then press-attaching the rubber sheets under heating to bond the metal reinforcement material and the rubber to each other, and bonding the metal reinforcement material with the rubber coating by vulcanization.

[0118] <Rubber Tracks>

[0119] The rubber crawler of the present invention is characterized in that it has the above-mentioned rubber-metal composite body. The rubber crawler of the present invention has excellent durability because its adhesion between rubber and metal is equal to or better than the corresponding adhesion exhibited by a rubber crawler using a rubber composition containing a cobalt salt.

[0120] The rubber crawler of the present invention is not particularly limited except that the above-mentioned rubber-metal composite is required to be used, and any known structure and manufacturing method of rubber crawlers may be optionally adopted.

[0121] In one embodiment, the rubber track has: a steel cord (metal member); an intermediate rubber layer that coats the steel cord so that the steel cord is coated with an intermediate rubber; a metal rod (metal member) disposed on the intermediate rubber layer; and a main body rubber layer in which the intermediate rubber layer and the metal rod are embedded, wherein a plurality of lugs are formed on a side of the main body rubber layer that contacts the ground. The rubber composition described above can be used in any part of the rubber track.

[0122] <Tires>

[0123] The tire of the present invention is characterized in that it has the above-mentioned rubber-metal composite. The tire of the present invention has excellent durability because its adhesion between rubber and metal is equal to or better than the corresponding adhesion exhibited by a tire using a rubber composition containing a cobalt salt.

[0124] The tire of the present invention is not particularly limited except that the above-mentioned rubber-metal composite is required to be used, and any known tire structure and manufacturing method may be optionally adopted.

[0125] The tire part to which the rubber-metal composite of the present invention can be applied is not particularly limited, and the tire part can be appropriately selected as required. Examples of such tire parts include carcasses, belts, bead cores, and the like.

[0126] As a method for manufacturing the tire of the present invention, a conventional tire manufacturing method can be adopted.

[0127] For example, a desired tire (e.g., a pneumatic tire) can be manufactured by: sequentially stacking components commonly used in tire manufacturing, such as a carcass and a belt (rubber-metal composite) made of a rubber composition in an unvulcanized state and metal cords, and a tread made of an unvulcanized rubber composition, on a tire forming drum; removing the drum to obtain a green tire; and heating and vulcanizing the green tire in accordance with conventional methods.

[0128] Example

[0129] The present invention will be further described in detail below by way of examples. The examples do not limit the present invention in any way. Unless otherwise specified, in the examples, the contents of the components are expressed as "parts by weight".

[0130] (Examples 1 to 4, Comparative Examples 1 to 6)

[0131] Each unvulcanized rubber composition of Examples 1 to 4 and Comparative Examples 1 to 6 was obtained by: preparing the relevant components (except sulfur and a vulcanization accelerator) according to the blending formula shown in Table 1; mixing the components by using an internal mixer until the temperature thereof reaches 160° C.; cooling the mixture until the temperature thereof drops below 40° C.; and then adding sulfur and a vulcanization accelerator to the mixture.

[0132] (1) Preparation of samples for rubber-metal adhesion test

[0133] Two test samples were obtained from each unvulcanized rubber composition thus formed by the following steps: two sheets (150 mm×150 mm, thickness: 2 mm) were prepared from the unvulcanized rubber composition by rolling; 7 metal wires were placed without gaps on each of the two sheets; and each sheet was vulcanized at 150° C. for 60 minutes, thereby obtaining two test samples of a rubber-metal composite including a vulcanized rubber (derived from the unvulcanized rubber composition).

[0134] (2) Rubber-metal adhesion test

[0135] Two test samples of the rubber-metal composite including the above-mentioned vulcanized rubber were subjected to a rubber-metal adhesion test by the following steps: for one of the samples, five metal wires except the two metal wires at the two ends were pulled together with a constant force using a pair of pliers; the coverage rate (%) of the surface of the metal wires thus pulled by the vulcanized rubber was measured; and the same test procedure was repeated for the other test sample. The results are shown in Table 1. A higher coverage rate indicates better adhesion between rubber and metal. In Table 1, the value on the left side of the symbol " / " indicates the result of the first test, and the value on the right side of the symbol " / " indicates the result of the second test.

[0136] [Table 1]

[0137]

[0138] *1NR: Natural rubber, RSS3

[0139] *2NBR: Acrylonitrile butadiene rubber, trade name "N250S" manufactured by JSR Corporation

[0140] *3EPDM: Ethylene-propylene-diene rubber, trade name "EP33" manufactured by JSR Corporation

[0141] *4 Carbon black: Trade name "Asahi #50" manufactured by Asahi Carbon Co., Ltd.

[0142] *5 Oil: Trade name "SUNTHENE 4240" manufactured by Japan Sun Oil Company, Ltd.

[0143] *6 Bismuth neodecanoate: metal salt corresponding to aliphatic carboxylic acid (1), bismuth content = 27 mass%

[0144] *7 Cobalt stearate: Trade name "Co-STEARATE" manufactured by DIC Corporation, cobalt content = 9.5 mass%

[0145] *8 Sulfur: Trade name manufactured by Tsurumi Chemical Industry Co., Ltd.

[0146] *9 Vulcanization accelerator TS: Thiuram-based vulcanization accelerator (tetramethylthiuram monosulfide), manufactured by SANSHINCHEMICAL INDUSTRY CO., LTD. under the trade name “Sanceler TS”

[0147] *10 Vulcanization accelerator M: Thiazole vulcanization accelerator (2-mercaptobenzothiazole), trade name "ACCEL M" manufactured by Kawaguchi Chemical Industry Co., LTD.

[0148] *11 Vulcanization accelerator CZ: Sulfenamide-based vulcanization accelerator (N-cyclohexyl-2-benzothiazolesulfenamide), trade name "Sanceler CM-G" manufactured by SANSHIN CHEMICAL INDUSTRY CO., LTD.

[0149] *12 Zinc White: Trade name manufactured by Toho Zinc Co., Ltd.

[0150] *13 Metal wire 1: Steel wire with a diameter of 0.30 mm and a length of 100 mm and plated with brass (Cu: 63 mass%, Zn: 37 mass%, coating weight: 4 g / kg)

[0151] *14 Metal wire 2: Steel wire with a diameter of 0.38 mm and a length of 100 mm and plated with brass (Cu: 63 mass%, Zn: 37 mass%, coating weight: 4 g / kg)

[0152] It is understood from the results of the examples shown in Table 1 that each rubber composition of the examples containing EPDM as a rubber component significantly improves its adhesion to metal members by including a rubber-metal adhesion promoter, a vulcanization accelerator other than a thiuram-based compound, and excluding a thiuram-based vulcanization accelerator therein, so that the rubber composition can obtain adhesion between rubber and metal that is equivalent to or better than the corresponding adhesion exhibited by the rubber composition containing a cobalt salt of an organic acid (Comparative Example 1).

[0153] In contrast, it is understood from the results of Comparative Examples 2 and 3 that the adhesion of the EPDM-containing rubber composition to the metal member is significantly deteriorated when the rubber composition does not contain the rubber-metal adhesion promoter.

[0154] Furthermore, it is understood from the results of Comparative Examples 4 to 6 that when the rubber composition sufficiently containing the rubber-metal adhesion promoter and the vulcanization accelerator other than the thiuram-based compound further contains the thiuram-based vulcanization accelerator therein, the adhesion of the EPDM-containing rubber composition to the metal member is deteriorated.

[0155] Industrial Applicability

[0156] The rubber composition of the present invention can be applied to a rubber-metal composite. Furthermore, the rubber-metal composite of the present invention can be applied to a hose, a conveyor belt, a rubber track, a tire, and the like.

Claims

1. A rubber composition comprising: Rubber component; Rubber-metal adhesion promoter; and Vulcanization accelerators other than thiuram compounds, wherein the rubber component contains 20 parts by mass or more of ethylene-propylene-diene rubber relative to 100 parts by mass of the rubber component, The rubber-metal adhesion promoter comprises a metal salt of an aliphatic carboxylic acid (1); The aliphatic carboxylic acid used in the metal salt of aliphatic carboxylic acid (1) has 2 to 25 carbon atoms. The metal used in the metal salt (1) of the aliphatic carboxylic acid is any one of bismuth, copper, antimony, silver, and niobium. The rubber composition does not contain a thiuram-based vulcanization accelerator, The rubber component is a combination of ethylene-propylene-diene rubber and at least one selected from the group consisting of natural rubber, acrylonitrile-butadiene rubber, and butadiene rubber, and The content of the vulcanization accelerator other than the thiuram compound is 0.01 parts by mass or more and less than 1 part by mass based on 100 parts by mass of the rubber component, The vulcanization accelerator other than the thiuram-based compound is a thiazole-based vulcanization accelerator. 2 . The rubber composition according to claim 1 , wherein the rubber-metal adhesion promoter comprises the metal salt (1) of the aliphatic carboxylic acid, and the metal for the metal salt (1) of the aliphatic carboxylic acid is bismuth.

3. The rubber composition according to claim 1, wherein the aliphatic carboxylic acid used in the metal salt of aliphatic carboxylic acid (1) is C 2-20 Saturated aliphatic monocarboxylic acid. 4 . The rubber composition according to claim 3 , wherein the saturated aliphatic monocarboxylic acid is 2-ethylhexanoic acid, neodecanoic acid, hexadecanoic acid, or octadecanoic acid. 5 . The rubber composition according to claim 1 , wherein the content of the thiazole-based vulcanization accelerator is 0.01 parts by mass or more and 0.4 parts by mass or less relative to 100 parts by mass of the rubber component. 6 . A rubber-metal composite comprising the rubber composition according to claim 1 and a metal member.

7. A hose comprising the rubber-metal composite according to claim 6.

8. A conveyor belt comprising the rubber-metal composite according to claim 6.

9. A rubber crawler having the rubber-metal composite according to claim 6.

10. A tire comprising the rubber-metal composite according to claim 6.

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