Steel cord-rubber composite, tire, rubber crawler, and hose

Abstract

Provided is a steel cord-rubber composite obtained by covering, with a rubber composition, a steel cord which has one or more steel wires. The rubber composition contains a rubber component and a filler. The filler contains recycled carbon black. When the recycled carbon black is measured with a grindometer, there are not less than three lines having a length of not less than 10 mm, and of particles which result in lines having a length of not less than 10 mm, the particle size of the third-largest particles is not more than 20 μm.

Description

Steel cord-rubber composites, tires, rubber tracks, and hoses

[0001] This invention relates to steel cord-rubber composites, tires, rubber tracks, and hoses.

[0002] For rubber products requiring particularly high strength, such as automobile tires and hoses, steel cord-rubber composites are used, which consist of steel cords covered with coated rubber, to reinforce the rubber and improve its strength and durability.

[0003] Various studies have been conducted to improve the adhesion between the rubber and the steel cord, as well as durability such as crack resistance, for such steel cord-rubber composites.

[0004] For example, Patent Documents 1 to 3 each disclose a steel cord-rubber composite comprising a coated rubber in a predetermined formulation containing at least a rubber component and carbon black, and a steel cord.

[0005] Japanese Patent Publication No. 2016-041779, International Publication No. 2000 / 145274, Japanese Patent Publication No. 2023-077085

[0006] Incidentally, in recent years, from the perspective of social sustainability, there has been a demand for the use of so-called sustainable materials in businesses and products, such as materials derived from biological resources (biomass resources) and materials derived from recycled resources. Therefore, there is a demand to improve the proportion of sustainable materials (hereinafter sometimes referred to as the "sustainability rate") in the various components used in the aforementioned steel cord-rubber composite. For example, recycled carbon black is known as a material derived from recycled resources for the carbon black contained in the coating rubber.

[0007] In this case, if conventional recycled carbon black is used as a filler in the coating rubber instead of unused carbon black in order to improve the proportion of sustainable materials in the steel cord-rubber composite, there is a risk that the durability of the rubber after degradation (e.g., crack propagation resistance after thermal degradation, high-temperature tensile strength after degradation) will decrease. Such a decrease in durability after degradation may affect the steel cord-rubber composite and, consequently, the rubber articles using the composite.

[0008] Therefore, the object of the present invention is to provide a steel cord-rubber composite that contributes to improved sustainability while maintaining good durability. Furthermore, the object of the present invention is to provide a tire, rubber crawler, and hose that contribute to improved sustainability while maintaining good durability.

[0009] In other words, the gist of the present invention that solves the above problems is as follows.

[0010] [1] A steel cord-rubber composite comprising a steel cord having one or more steel wires, coated with a rubber composition, wherein the rubber composition contains a rubber component and a filler, the filler contains recycled carbon black, and the recycled carbon black is such that, when measured with a grind gauge, three or more lines with a length of 10 mm or more are confirmed, and the particle size of the third largest particle among the particles that produce the lines with a length of 10 mm or more is 20 μm or less.

[0011] [2] The steel cord-rubber composite according to [1], wherein, in the measurement of the recycled carbon black using a grind gauge, a paste of the recycled carbon black is prepared as a measurement sample in accordance with JIS K5101-1-5.

[0012] [3] The steel cord-rubber composite according to [1] or [2], wherein, in the measurement of the recycled carbon black using a grind gauge, the applied load is set to 0.4 to 0.5 kN and the rotation speed of the glass plate is set to 90 to 110 r / min in accordance with JIS K5101-1-5, and the paste of the recycled carbon black is prepared as the measurement sample.

[0013] [4] The steel cord-rubber composite according to any one of [1] to [3], wherein the recycled carbon black comprises one or more selected from the group consisting of Zn, Fe, and Cu.

[0014] [5] The steel cord-rubber composite according to [4], comprising recycled carbon black and Zn.

[0015] [6] The steel cord-rubber composite according to any one of [1] to [5], wherein the Zn content in the recycled carbon black is 1.0% by mass or less.

[0016] [7] The recycled carbon black has an ash content of 20% by mass or less, the steel cord-rubber composite according to any one of [1] to [6].

[0017] [8] The steel cord-rubber composite according to any one of [1] to [7], wherein one or more of the steel wires constituting the steel cord is a steel wire derived from recycled iron, the recycled iron derived steel wire has an N element content of 60 mass ppm or more, a C element content of 0.7 to 1.0 mass%, a Cu element content of 0.01 to 0.4 mass%, and a Cr element content of 0.05 to 0.3 mass%, and the surface of the steel cord has an N atom content of 2 atomic percent or more and 60 atomic percent or less, and a Cu / Zn ratio of 1 to 4 or less.

[0018] [9] The steel cord-rubber composite according to any one of [1] to [8], wherein the steel cord is made by twisting together a plurality of steel wires with brass plating applied to their circumferential surface, and the composition of the brass plating is 40 to 80% by mass of Cu and 20 to 60% by mass of Zn.

[0019]

[10] The steel cord-rubber composite according to any one of [1] to [9], wherein the steel cord is subjected to surface treatment with a buffer solution at pH 5.0 to 7.2 and treatment with one or more triazole compounds selected from 1,2,4-triazole, 1,2,3-triazole, 3-amino-1,2,4-triazole, 4-amino-1,2,4-triazole, benzotriazole, tolyltriazole, and 3-mercapto-1,2,4-triazole.

[0020]

[11] The steel cord-rubber composite according to [8], wherein the steel wire derived from recycled iron has a Cu element content of 0.05 to 0.4% by mass.

[0021]

[12] The steel cord-rubber composite according to [8] or

[11] , wherein the steel wire derived from recycled iron has a diameter of 0.15 mm to 0.6 mm.

[0022]

[13] The rubber composition is a metal carboxylate salt having 2 to 25 carbon atoms and the metal species being bismuth, copper, antimony, silver, niobium, or zirconium, and the following formula (A): [(RCOO) ｘ MO] ３ Z (A) [In equation (A), Z is the following equations (z-1) to (z-4): The steel cord-rubber composite according to any one of [1] to

[12] , wherein the structure is selected from the group consisting of compounds represented by ], where M is bismuth, copper, antimony, silver, niobium, or zirconium, (RCOO) is each independently a residue of an aliphatic carboxylic acid having 2 to 25 carbon atoms, and x is an integer of (valence of M - 1). The steel cord-rubber composite according to any one of [1] to

[12] , wherein the content of the rubber-metal adhesion promoter in the rubber composition is 0.01 parts by mass or more per 100 parts by mass of the rubber component.

[0023]

[14] The steel cord-rubber composite according to any one of [1] to

[13] , further comprising the rubber composition 4,4'-diphenylmethanebismaleimide.

[0024] A tire comprising the steel cord-rubber composite according to any one of

[15] [1] to

[14] .

[0025] A rubber crawler comprising the steel cord-rubber composite according to any one of

[16] [1] to

[14] .

[0026] A hose comprising the steel cord-rubber composite according to any one of

[17] [1] to

[14] .

[0027] According to the present invention, it is possible to provide a steel cord-rubber composite in which durability is maintained well while contributing to the improvement of sustainability. Further, according to the present invention, it is possible to provide a tire, a rubber crawler, and a hose in which durability is maintained well while contributing to the improvement of sustainability.

[0028] It is an explanatory diagram of an example of the measurement result by a grind gauge.

[0029] Hereinafter, the steel cord-rubber composite, tire, rubber crawler, and hose of the present invention will be illustrated and described in detail based on their embodiments.

[0030] <Definition> The compounds described in this specification may be partially or entirely derived from fossil resources, may be derived from biological resources such as plant resources, or may be derived from recycled resources such as used tires. Further, it may be derived from a mixture of any two or more of fossil resources, biological resources, and recycled resources.

[0031] <Steel cord-rubber composite> The steel cord-rubber composite according to an embodiment of the present invention (hereinafter, may be referred to as "the composite of the present embodiment") is a steel cord-rubber composite obtained by coating a steel cord having one or more steel wires with a rubber composition, The rubber composition contains a rubber component and a filler, The filler contains recycled carbon black, When measured by a grind gauge, the number of lines having a length of 10 mm or more is confirmed to be 3 or more, and among the particles that result in the lines having a length of 10 mm or more, the particle size of the third largest particle is 2 μm or less.

[0032] The composite of this embodiment not only uses recycled carbon black as a filler, but also uses, as the recycled carbon black, recycled carbon black in which, when measured by a grind gauge, the number of lines with a length of 10 mm or more is confirmed to be 3 or more, and among the particles that result in the lines with a length of 10 mm or more, the particle size of the third largest particle is 20 μm or less. Thus, by using at least recycled carbon black, the composite of this embodiment can contribute to an improvement in sustainability. Further, in the grind gauge measurement of recycled carbon black, there is a high correlation between the evaluation result and the durability of the rubber composition, particularly the performance after deterioration, and by using recycled carbon black (recycled carbon black in which the particle size of the third largest particle is 20 μm or less) determined to have good dispersibility in the grind gauge measurement, it is possible to suppress a decrease in the durability of the rubber composition, particularly the performance after deterioration. That is, by using recycled carbon black in which the particle size of the third largest particle is 20 μm or less, the adverse effect on the durability of the rubber (for example, crack growth resistance after thermal deterioration, high-temperature tensile strength after deterioration) is significantly smaller than in the case of using conventional recycled carbon black. Therefore, the composite of this embodiment contributes to an improvement in sustainability while maintaining good durability.

[0033] (Steel cord) The composite of this embodiment includes a steel cord having one or more steel wires (which may also be referred to as "steel filaments").

[0034] Preferably, one or more of the steel wires constituting the steel cord are derived from recycled iron. In this case, the recycled iron derived steel wire preferably has an N element content of 60 ppm or more by mass, a C element content of 0.7 to 1.0% by mass, a Cu element content of 0.01 to 0.4% by mass, and a Cr element content of 0.05 to 0.3% by mass. Furthermore, the surface of the steel cord preferably has an N atom content of 2 to 60 atoms and a Cu / Zn ratio of 1 to 4. Recycled iron often contains impurities, and steel cords made using steel wire (wire material) manufactured from recycled iron as a raw material contain many impurities and have an uneven surface, which may reduce adhesion to the coating rubber. However, by having an N atom content of 2 to 60 atoms and a Cu / Zn ratio of 1 to 4 on the surface of the steel cord, the reduction in adhesion to the coating rubber can be suppressed.

[0035] The recycled iron used as raw material for the aforementioned recycled iron-derived steel wire is not particularly limited as long as it is recycled, and may be derived from scrap iron, steel cords extracted from tires, etc. Furthermore, recycled iron is CO ２ From the perspective of reducing CO emissions, it is preferable that the CO is derived from an electric arc furnace (electric arc furnace steelmaking method). In the electric arc furnace steelmaking method, for example, an arc discharge is generated in an electric furnace, the raw material is melted by the heat of the discharge, impurities are removed, and iron (steel) can be obtained. On the other hand, in the blast furnace method, which is used in ordinary steelmaking, for example, iron (steel) is obtained by reducing iron ore with coke derived from coal in a blast furnace, so CO ２ This inevitably generates a large amount of CO in electric furnaces. ２ The emissions from blast furnaces are CO2 ２ Since it is about 1 / 4 of the emissions compared to other sources, using recycled iron derived from electric furnaces in steel wire reduces CO2 emissions. ２ This can significantly reduce emissions.

[0036] As described above, the steel wire derived from recycled iron can have a nitrogen (N) element content of 60 mass ppm or more, a carbon (C) element content of 0.7 to 1.0 mass%, a copper (Cu) element content of 0.01 to 0.4 mass%, and a chromium (Cr) element content of 0.05 to 0.3 mass%. Such a steel wire can be produced using general recycled iron having a nitrogen (N) element content of 60 mass ppm or more, a carbon (C) element content of 0.7 to 1.0 mass%, a copper (Cu) element content of 0.01 to 0.4 mass%, and a chromium (Cr) element content of 0.05 to 0.3 mass% as a raw material. Also, since the above general recycled iron does not require advanced refining, the manufacturing process is not complicated, the energy consumption can be reduced, and the CO ２ emissions can also be reduced, which is preferable from an environmental perspective. In addition, a steel cord using such a steel wire derived from recycled iron is preferable from an environmental perspective because it uses a steel wire that can be produced from general recycled iron. Incidentally, the steel wire derived from the recycled iron preferably has iron as the main component and an Fe (iron) element content of 98 mass% or more.

[0037] Typically, the steel wire derived from the recycled iron has a nitrogen (N) element content of 60 mass ppm or more. Generally, new iron such as iron obtained from a blast furnace has a high purity and an N element content of less than 60 mass ppm, whereas general recycled iron (i.e., recycled iron that has not been highly refined) has an N element content of 60 mass ppm or more. The steel wire derived from the recycled iron can be produced using such general recycled iron as a raw material and does not require advanced refining, so the manufacturing process is not complicated, the energy consumption can be reduced, and the CO ２Since emissions can also be reduced, this is also preferable from an environmental perspective. From a similar viewpoint, it is preferable that the N element content of the recycled iron-derived steel wire is 70 ppm by mass or more. Furthermore, from the viewpoint of durability, the N element content of the recycled iron-derived steel wire is preferably 200 ppm by mass or less, and more preferably less than 90 ppm by mass. When steel cord is used as a reinforcing material in rubber products such as tires, the steel cord is subjected to loads from various directions during the manufacturing and use of the rubber products such as tires. Therefore, the steel wire constituting the steel cord is required to have excellent resistance to twisting as one of the indicators of durability. And recycled iron-derived steel wire with an N element content of less than 90 ppm by mass has particularly excellent resistance to twisting.

[0038] The aforementioned steel wire derived from recycled iron typically has a carbon (C) content of 0.7 to 1.0 mass%, preferably 0.7 to 0.85 mass%. Recycled iron with a C content within this range does not require advanced refining and is therefore readily available, and steel wire with a C content within this range can be manufactured from general recycled iron. Furthermore, recycled iron (steel material) with a C content of 0.85 mass% or less has high ductility, and even when processed into steel wire with a small diameter, breakage can be prevented. Therefore, recycled steel wire with a C content of 0.7 to 0.85 mass% is less prone to breakage and has high durability.

[0039] The steel wire derived from recycled iron typically has a Cu (copper) content of 0.01 to 0.4 mass%, preferably 0.05 to 0.4 mass%. Recycled iron with a Cu content within this range does not require advanced refining and is therefore readily available, and steel wire with a Cu content within this range can be manufactured from general recycled iron. Furthermore, steel cords using steel wire derived from recycled iron with a Cu content of 0.05 to 0.4 mass% are also preferable from an environmental perspective because they use steel wire that can be manufactured from general recycled iron.

[0040] The steel wire derived from the aforementioned recycled iron typically has a chromium (Cr) content of 0.05 to 0.3 mass%. Generally, new iron, such as iron obtained from a blast furnace, has high purity and a Cr content of less than 0.05 mass%, whereas typical recycled iron (i.e., recycled iron that is not highly refined) has a Cr content of 0.05 mass% or more. Recycled iron with a Cr content within the aforementioned range does not require high-level refining and is therefore readily available, and steel wire with a Cr content within the aforementioned range can be manufactured from typical recycled iron.

[0041] The surface of the steel cord having at least the recycled iron-derived steel wire preferably has a nitrogen (N) atom content of 2 atomic% or more and 60 atomic% or less, and a Cu / Zn ratio of 1 or more and 4 or less by mass, as described above. Having a nitrogen atom content of 2 atomic% or more on the surface of the steel cord improves initial adhesion to the coating rubber. Having a nitrogen atom content of 60 atomic% or less on the surface of the steel cord effectively suppresses deterioration of initial adhesion to the coating rubber. Furthermore, having a Cu / Zn ratio of 1 or more on the surface of the steel cord improves initial adhesion to the coating rubber. Also, having a Cu / Zn ratio of 4 or less on the surface of the steel cord helps maintain good initial adhesion. From a similar viewpoint, the nitrogen atom content on the surface of the steel cord is more preferably 2.1 atomic% or more, and more preferably 55.0 atomic% or less. Furthermore, the Cu / Zn ratio on the surface of the steel cord is more preferably 1.1 or more, and more preferably 3.5 or less.

[0042] The adjustment of the proportion of nitrogen (N) atoms on the surface of the steel cord to 2 atomic percent or more and 60 atomic percent or less can be performed, for example, by suitably combining surface treatments such as treatment with a triazole compound (rust inhibitor), specifically contact with an aqueous solution of the triazole compound. Furthermore, the adjustment of the Cu / Zn ratio on the surface of the steel cord to 1 or more and 4 or less can be performed, for example, by suitably combining the pH of the acidic buffer solution and the concentration of the triazole aqueous solution. The lower the pH, the higher the Cu / Zn ratio of the steel cord that can be obtained.

[0043] Examples of the acidic buffer include acetate buffer, phosphate buffer, and citrate buffer with a pH of 5.0 to 7.2, with acetate buffer with a pH of 5.0 to 7.2 being preferred. If the pH is less than 5.0, it becomes difficult to keep the Cu / Zn ratio below 4, and if the pH exceeds 7.2, it becomes difficult to keep the Cu / Zn ratio above 1. The surface treatment time with this buffer can be, for example, 0.5 to 20 seconds when using acetate buffer with a pH of 5.0 to 7.2.

[0044] Furthermore, examples of the triazole aqueous solution include aqueous solutions of one or more triazole compounds selected from 1,2,4-triazole, 1,2,3-triazole, 3-amino-1,2,4-triazole, 4-amino-1,2,4-triazole, benzotriazole, tolyltriazole, and 3-mercapto-1,2,4-triazole. Among these, it is preferable to use the water-soluble forms of 1,2,4-triazole, 1,2,3-triazole, 3-amino-1,2,4-triazole, and 4-amino-1,2,4-triazole. The concentration of the triazole aqueous solution is preferably 0.01 to 20 g / L, and the treatment time can be 0.1 to 30 seconds, although this varies depending on the concentration.

[0045] Preferably, the steel cord is subjected to surface treatment with a buffer solution with a pH of 5.0 to 7.2, and treatment with one or more triazole compounds selected from 1,2,4-triazole, 1,2,3-triazole, 3-amino-1,2,4-triazole, 4-amino-1,2,4-triazole, benzotriazole, tolyltriazole, and 3-mercapto-1,2,4-triazole. A steel cord subjected to such surface treatment with a buffer solution and treatment with a triazole compound can further suppress the decrease in adhesion to the coated rubber.

[0046] In this specification, "surface" refers to the surface region of the steel wire extending to a depth of 5 nm in the radial direction. The measurement of N atoms on the surface of the steel cord and the measurement of the Cu / Zn ratio are performed after obtaining the steel cord, after cleaning and drying as necessary, and before coating with the coating rubber (rubber composition). Furthermore, in this specification, the measurement of N atoms on the surface of the steel cord refers to the measurement of N atoms on the surface of the steel cord measured by X-ray photoelectron spectroscopy (XPS), and the measurement of the Cu / Zn ratio on the surface of the steel cord refers to the measurement of the Cu / Zn ratio on the surface of the steel cord by the above photoelectron spectroscopy.

[0047] The steel cord is preferably made by twisting together multiple steel wires. Furthermore, it is preferable that the steel wires have a plating applied to their circumferential surface (i.e., have a plating layer on their surface). The plating layer can be formed by a conventional method. The plating layer is not particularly limited, but examples include a zinc plating layer, a copper plating layer, a brass plating layer, etc. Among these, a brass plating layer is preferred from the viewpoint of initial adhesion to the rubber composition and moist heat adhesion. In other words, the steel cord is preferably made by twisting together multiple steel wires that have brass plating applied to their circumferential surface. Furthermore, from the viewpoint of processability of the steel cord and adhesion to the covering rubber, the composition of the brass plating (bulk brass plating) is preferably 40 to 80% by mass of Cu (copper) and 20 to 60% by mass of Zn (zinc). Furthermore, from the same viewpoint as above, it is more preferable that the composition of the brass plating (bulk brass plating) is 55 to 70% by mass of Cu and 30 to 45% by mass of Zn. Such steel cords can further suppress the decrease in adhesion with the rubber coating.

[0048] The steel wire derived from recycled iron preferably has a diameter of 0.15 mm to 0.6 mm. When the diameter of the steel wire derived from recycled iron is 0.15 mm or more, it has excellent strength and durability, making it less likely to break during wire drawing. Furthermore, when the diameter of the steel wire derived from recycled iron is 0.6 mm or less, for example, when the steel cord is applied to rubber products such as tires, the steel wire in the steel cord can follow the deformation of the rubber products such as tires, making it less likely to break (high durability), and it also has the advantage of being lightweight. Steel cords using steel wire derived from recycled iron with a diameter of 0.15 mm to 0.6 mm have high durability.

[0049] From the viewpoint of durability, the aforementioned steel wire derived from recycled iron preferably satisfies the following equation: 4000 - 2000X ≤ Y ≤ 4500 - 2000X, where X (mm) is the diameter of the wire and Y (MPa) is the tensile strength of the wire. Here, the tensile strength of the wire is determined in accordance with the provisions of ISO 17832:2009.

[0050] From the viewpoint of fatigue resistance, the hardness of the surface layer of the recycled iron-derived steel wire is preferably 90 to 110% of the hardness of the inner layer, and particularly preferably 100%. This hardness can be measured, for example, by Vickers hardness. The surface layer of the steel wire refers to the layer from the outermost surface to a depth of 0.01 mm, and the layer inside that refers to the inner layer of the steel wire. Hardness can be measured in the region from the outermost surface to 0.005 mm for the surface layer and in the region deeper than 0.04 mm for the inner layer.

[0051] The aforementioned steel wire derived from recycled iron is manufactured from recycled iron, and the manufacturing method is not particularly limited. For example, steel wire derived from recycled iron can be manufactured by drawing steel materials derived from scrap iron or steel cords extracted from tires.

[0052] The aforementioned steel cord may or may not contain steel wires derived from non-recycled iron in addition to steel wires derived from recycled iron. That is, one or more of the steel wires constituting the steel cord may be steel wires derived from non-recycled iron. If one or more of the steel wires constituting the steel cord are steel wires derived from non-recycled iron, the decrease in the durability of the steel cord can be suppressed.

[0053] As for the non-recycled iron used as the raw material for the aforementioned non-recycled iron-derived steel wire, from the viewpoint of the durability of the steel cord, it is preferable to use non-recycled iron with few impurities, for example, iron derived from iron ore (iron derived from a blast furnace) is preferred.

[0054] The aforementioned non-recycled iron-derived steel wire preferably has a nitrogen (N) content of 20 to 40 ppm by mass, a carbon (C) content of 0.7 to 0.85% by mass, a copper (Cu) content of 0 to 0.1% by mass, and a chromium (Cr) content of 0 to 0.1% by mass. When a steel cord has a non-recycled iron-derived steel wire with such a composition, the deterioration of the steel cord's durability can be further suppressed. The aforementioned non-recycled iron-derived steel wire preferably has iron as its main component, with an iron (Fe) content of 98% by mass or more.

[0055] The diameter of the non-recycled iron-derived steel wire is not particularly limited and may be the same as or different from the diameter of the recycled iron-derived steel wire.

[0056] The composite of this embodiment is formed by coating the steel cord described above with a rubber composition. The rubber composition (hereinafter sometimes referred to as "the rubber composition of this embodiment") contains at least a rubber component and a filler, and the filler contains a predetermined recycled carbon black.

[0057] (Rubber component) The rubber composition of this embodiment contains a rubber component, which provides the composition with rubber elasticity. The sustainability rate of the rubber component is preferably 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass. Hereinafter, in this specification, "sustainability rate" refers to the total mass ratio of components derived from biological resources (biomass resources) and components derived from recycled resources in the material in question.

[0058] In this specification, the term "biomass resources" refers to carbon-neutral organic resources of biological origin, excluding fossil resources (such as petroleum, coal, and natural gas). These biological resources may be edible or inedible, but are preferably inedible, as they do not compete with food resources and are considered to be resources that can be used effectively.

[0059] In this specification, the term "recycled resources" refers to resources obtained by recycling products that have been used, collected without being used, or discarded. For example, recycled resources include resources obtained by recycling used rubber products such as used tires.

[0060] The rubber component is preferably derived from biological resources and recycled resources. Here, the proportion of the monomer component derived from biological resources in 100 mol% of the monomer component constituting the rubber derived from biological resources is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may also be 100 mol%. Similarly, the proportion of the monomer component derived from recycled resources in 100 mol% of the monomer component constituting the rubber derived from recycled resources is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may also be 100 mol%.

[0061] The aforementioned rubber component is a component that contributes to crosslinking, and typically has a weight-average molecular weight (Mw) of 10,000 or more, preferably 50,000 or more, more preferably 150,000 or more, even more preferably 200,000 or more, and also preferably 5,000,000 or less, more preferably 2,000,000 or less, and even more preferably 1,500,000 or less. In this specification, the weight-average molecular weight (Mw) of the rubber component can be determined, for example, by converting it to standard polystyrene based on measurements obtained by gel permeation chromatography (GPC).

[0062] The rubber component is preferably a diene-based rubber, and among the diene-based rubbers, isoprene-based rubber and butadiene-based rubber are preferred.

[0063] Examples of isoprene-based rubbers include natural rubber and synthetic isoprene rubber. The origin of natural rubber is not particularly limited; for example, it may be derived from the Para rubber tree, guayule, or Russian dandelion. Natural rubber may be modified or altered, and synthetic isoprene rubber may also be altered. These isoprene-based rubbers may be used individually or in combination of two or more. Natural rubber is preferred as the isoprene-based rubber.

[0064] Examples of the butadiene-based rubber include butadiene rubber and styrene-butadiene rubber. Here, it is preferable that the butadiene used as a raw material for the butadiene-based rubber is derived from biological resources or recycled resources.

[0065] Examples of the styrene-butadiene rubber include emulsion-polymerized styrene-butadiene rubber and solution-polymerized styrene-butadiene rubber.

[0066] The isoprene-based rubber and the butadiene-based rubber preferably have a sustainability rate of 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass.

[0067] Furthermore, in order to keep the overall sustainability rate of the rubber component within the aforementioned range, it is preferable to use natural rubber as the rubber component, or to use polymers synthesized using monomer components derived from biological resources or recycled resources. It is also possible to use mass balance certified synthetic rubber to keep the sustainability rate within the aforementioned range.

[0068] The ratio of each monomer unit (for example, units derived from isoprene, units derived from butadiene, and units derived from aromatic vinyl compounds) in the entire rubber component can be appropriately adjusted depending on the member to which it is applied. The ratio of each monomer unit in the entire rubber component can be adjusted, for example, by appropriately combining the isoprene-based rubber and butadiene-based rubber mentioned above. The ratio of cis-bonded units in the butadiene-derived units can also be appropriately adjusted depending on the member to which it is applied. In this specification, "monomer unit" means a constituent unit of a polymer, "unit derived from isoprene" means a constituent unit in a polymer composed of isoprene, which is a monomer (including isoprene units in natural rubber), "unit derived from butadiene" means a constituent unit in a polymer composed of butadiene, which is a monomer, and "unit derived from aromatic vinyl compounds" means a constituent unit in a polymer composed of aromatic vinyl compounds, which are monomers. In this specification, the ratio of each monomer unit is measured by NMR.

[0069] In addition to the isoprene-based rubber, butadiene rubber, and styrene-butadiene copolymer rubber mentioned above, the rubber component may also include diene-based rubbers such as acrylonitrile-butadiene rubber, chloroprene rubber, butyl rubber, and styrene-isoprene-butadiene copolymer rubber. These rubber components may be used individually or in combination of two or more.

[0070] The rubber component may have functional groups that interact with fillers such as carbon black and silica introduced through modification. Examples of such functional groups include amino groups, amide groups, isocyanate groups, imino groups, imidazole groups, urea groups, ammonium groups, imide groups, hydrazo groups, azo groups, diazo groups, carboxyl groups, nitrile groups, pyridyl groups, alkoxy groups, hydroxyl groups, oxy groups, epoxy groups, ether groups, carbonyl groups, oxycarbonyl groups, silyl groups, alkoxysilyl groups, mercapto groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, and thiocarbonyl groups. These functional groups may also have substituents. These functional groups may be introduced into the rubber component individually or in combination of two or more. Among these, amino groups, alkoxy groups, and alkoxysilyl groups are preferred, and substituted amino groups in which the hydrogen atoms of the amino group are replaced by alkyl groups having 1 to 6 carbon atoms, alkoxy groups having 1 to 6 carbon atoms, and alkoxysilyl groups having 1 to 6 carbon atoms are even more preferred.

[0071] The functional group can be introduced, for example, by reacting a compound having the functional group (modifier) ​​with the rubber component. The compound having the functional group (modifier) ​​is a modifying functional group that interacts with fillers such as silica and carbon black, and can be a nitrogen-containing functional group, a silicon-containing functional group, or an oxygen-containing functional group. Examples of nitrogen-containing functional groups include amino group-containing compounds, examples of silicon-containing functional groups include silicon halides and hydrocarbyloxysilane compounds, and examples of oxygen-containing functional groups include alkoxy group-containing compounds, alkylene oxide group-containing compounds, and trialkylsilyloxy group-containing compounds. More specifically, examples include compounds described in WO2016 / 194316 and WO2019 / 117256. These modifiers may be used individually or in combination of two or more.

[0072] The aforementioned rubber derived from sustainable materials (materials derived from biological resources or materials derived from recycled resources) can be manufactured, for example, using monomer components derived from biological resources or monomer components derived from recycled resources, and, if necessary, monomer components derived from fossil resources, in the same manner as conventional methods for manufacturing synthetic rubber derived from fossil resources.

[0073] For example, the method described in Japanese Patent Publication No. 2022-179158 can be used to prepare rubber derived from biological resources.

[0074] As the butadiene obtained from the aforementioned biological resources, butadiene derived from alkyl alcohols (preferably ethanol and butanol, more preferably butanol), butadiene derived from alkenes (preferably ethylene), and butadiene derived from unsaturated carboxylic acids (preferably tigric acid) can be suitably used.

[0075] In one embodiment, the rubber component preferably includes natural rubber having a fatty acid content of 1.60% by mass or less. Natural rubber contains fatty acids such as stearic acid as a non-rubber component, but by using natural rubber with a fatty acid content of 1.60% by mass or less, the initial adhesion and heat-resistant adhesion between the coated rubber and the steel cord can be improved. From a similar viewpoint, the fatty acid content in the natural rubber used is more preferably 1.45% by mass or less, even more preferably 1.30% by mass or less, and even more preferably 1.20% by mass or less. On the other hand, the fatty acid content in the natural rubber used may be 0% by mass, but from the viewpoint of promoting the crosslinking reaction, it is preferably 0.3% by mass or more, more preferably 0.6% by mass or more, and even more preferably 0.80% by mass or more.

[0076] The fatty acid content in natural rubber refers to the total amount of all fatty acids contained in the natural rubber. The fatty acids contained in natural rubber may be saturated or unsaturated fatty acids, and may include one or more selected from the group consisting of stearic acid, palmitic acid, oleic acid, and linoleic acid.

[0077] The fatty acid content in natural rubber can be measured by titration. The reagents used in the titration are not particularly limited; commercially available alkaline reagents and indicators can be used. The apparatus and measurement conditions used in the titration are also not particularly limited; those skilled in the art can use commercially available equipment as appropriate.

[0078] Commercially available natural rubber with a fatty acid content of 1.60% by mass or less can be used. Furthermore, by washing the natural rubber, the fatty acid content can be reduced, allowing for the acquisition of natural rubber with a desired fatty acid content.

[0079] (Filler) The rubber composition of this embodiment contains a filler. The inclusion of a filler improves the reinforcing properties of the rubber composition. Examples of fillers include carbon black, silica, talc, clay, aluminum hydroxide, and titanium oxide.

[0080] -Carbon Black- Carbon black can reinforce rubber compositions and improve their abrasion resistance. Examples of carbon black include plant-derived carbon black and carbon black obtained through recycling (also referred to as "recycled carbon black" or "regenerated carbon black").

[0081] From the viewpoint of further improving the wear resistance of the rubber composition and rubber articles such as tires to which it is applied, the carbon black content in the rubber composition is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, from the viewpoint of the workability of the rubber composition, the carbon black content in the rubber composition is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 70 parts by mass or less, per 100 parts by mass of the rubber component.

[0082] --Recycled Carbon Black-- As stated above, the rubber composition of this embodiment requires that the filler contain recycled carbon black. In this specification, "recycled carbon black" refers to carbon black obtained by recovering from raw materials that are waste materials that have been recycled. Examples of such waste materials include waste rubber, used tires, and waste oil. Waste rubber is not limited to that generated from rubber products, but refers to all discarded rubber, including unwanted scraps generated during the production or repair of rubber products. Examples of scraps include buffing powder and peeling rubber. Buffing powder is, for example, fine rubber generated in the buffing process that removes the tread portion remaining on the base tire during tire retreading. Peeling rubber is, for example, long pieces of rubber, 1 to 2 cm wide, that are peeled off from the surface of rubber products such as tires. Peeling rubber is generated by using a U-shaped or V-shaped knife like a peeler to scrape the surface of rubber products such as tires. Furthermore, waste rubber is not limited to cross-linked rubber, but also includes unvulcanized rubber. Rubber products include, for example, finished products such as tires and rubber hoses, as well as rubber parts or components used in the manufacturing process of these finished products. Used tires may be retreaded, or they may be tires discarded for any reason, such as tires resulting from tire replacement or vehicle scrapping, or End-of-Life Tires (ELTs) that have reached the end of their lifespan as tires. Waste oil is not limited to that generated when plastics and rubber are decomposed, but also includes used oils discharged from industry, such as animal and vegetable oils, lubricating oils, insulating oils, and cutting oils. Among these, waste oils that do not contain any non-organic composition, such as those derived from silicone rubber or polyvinyl chloride, are desirable. Furthermore, waste oils that contain carbon black or rubber containing carbon black are desirable. "Recycled carbon black" is different from carbon black that is directly manufactured using hydrocarbons such as petroleum, natural gas, and coal as raw materials, i.e., carbon black that is not recycled. Note that "used" here includes not only those that have been discarded after being actually used, but also those that were manufactured but discarded without actually being used.

[0083] Furthermore, it is preferable that the recycled carbon black used in this embodiment is obtained by the thermal decomposition of a vulcanized rubber product containing carbon black. In this case, recycled carbon black is readily available. Moreover, it is preferable that the recycled carbon black used in this embodiment is obtained from the solid residue generated by the thermal decomposition of the above-mentioned vulcanized rubber product containing carbon black. When a rubber product containing carbon black is thermally decomposed, solid residue and volatile components (oil) are obtained, and recycled carbon black can be recovered from either. When recovering carbon black from volatile components, it is possible to recover oil with a specific gravity suitable for producing carbon black and use it to produce carbon black using an existing carbon black production method (for example, Japanese Patent Publication No. 2015-520259). In this case, unlike carbon black recovered from solid residue, there are advantages such as the absence of impurities and the absence of mixtures of different grades. Furthermore, in the production of environmentally friendly carbon black, there are various options other than using oil obtained by recovering volatile components obtained from the aforementioned rubber thermal decomposition, such as using vegetable oil or oil derived from waste plastics. However, edible resources such as vegetable oils 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. Furthermore, oils derived from waste plastics are used in other applications such as horizontal recycling of plastics, so supply issues are also likely. On the other hand, when using volatile components (oils) produced by the thermal decomposition of vulcanized rubber products, particularly tires, the tire industry has a system in place to continue using existing materials, making it possible to continue using existing materials and reduce the consumption of new materials in new tire manufacturing, thereby contributing to reducing the environmental burden on the industry. The grades of carbon black mentioned above are not particularly limited, but include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, N762, etc.

[0084] 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, the 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 the recycled carbon black used in this embodiment, 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 still more preferably 89% by mass or more. In the recycled carbon black used in this embodiment, the carbon content is preferably 97% by mass or less. Note that the above carbon content does not include adsorbed water.

[0085] The aforementioned ash content specifically includes zinc oxide, zinc sulfide, silica, iron compounds (iron oxide), calcium oxide, aluminum oxide, magnesium oxide, and the like. 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. The lower limit of the ash content of the recycled carbon black used in this embodiment may be 0.5% by mass.

[0086] Furthermore, recycled carbon black can be obtained from the pyrolysis process of used pneumatic tires. For example, European Patent Application Publication No. 3427975, "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 (

[0027] ). Carbon black obtained from such pyrolysis processes typically lacks functional groups on its surface, as mentioned in

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

[0087] Recycled carbon black may lack functional groups on its surface, or it may be 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 and / or carboxyl groups on its surface. In addition, in Japanese Patent 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.

[0088] 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.

[0089] Furthermore, the recycled carbon black used in this embodiment must, when measured with a grind gauge, show at least three lines with a length of 10 mm or more, and the particle size of the third largest particle among those particles that produce such lines of 10 mm or more is 20 μm or less.

[0090] The measurement using the grind gauge described above is for evaluating the dispersibility of carbon black and can be performed in accordance with the descriptions in JIS K5101-1-5 (especially regarding the preparation of paste) and JIS K5400 (especially regarding the method of evaluation by the manner in which linear traces are generated).

[0091] The range of the grind gauge used is preferably 0 to 25 μm, from the viewpoint of accurately measuring particle size and from the viewpoint of ease of measurement. However, a grind gauge with an upper limit of 20 μm is also usable, as it can determine whether the particle size of the third largest particle is 20 μm or less.

[0092] JIS K5101-1-5 describes a method for preparing a paste of recycled carbon black as a measurement sample in grind gauge measurements. The paste of recycled carbon black can be prepared in accordance with JIS K5101-1-5 as a measurement sample for grind gauge measurements. By preparing the paste of recycled carbon black in accordance with JIS K5101-1-5, the accuracy of grind gauge measurements can be further improved.

[0093] In one embodiment, the accuracy of grind gauge measurement can be further improved by appropriately adjusting the viscosity of the paste. In one embodiment, it is preferable to prepare a paste (measurement sample) containing recycled carbon black by blending recycled carbon black and zinc oxide with epoxidized soybean oil. Here, the blending ratio of the paste is not particularly limited, but it is preferable to use about 8 to 12 g of recycled carbon black and about 160 to 200 g of zinc oxide per 100 mL of epoxidized soybean oil.

[0094] Furthermore, in the measurement of recycled carbon black using a grind gauge, the paste of recycled carbon black can be prepared as a measurement sample by setting the applied load to 0.4 to 0.5 kN and the rotation speed of the glass plate to 90 to 110 r / min, in accordance with JIS K5101-1-5. In this case, the accuracy of the grind gauge measurement can be further improved.

[0095] When the recycled carbon black is measured with a grind gauge, three or more lines with a length of 10 mm or more can be observed. If the number of lines with a length of 10 mm or more is less than three, it is considered that the recycled carbon black being measured is too minute, and therefore cannot be sufficiently detected. In addition, while several lines caused by particles in the sample are observed when measuring with a grind gauge, in this embodiment, in accordance with JIS standards, lines with a length of 10 mm or more are not considered, and lines with a length of 10 mm or more are considered.

[0096] Furthermore, in this embodiment, in accordance with JIS standards, among the lines with a length of 10 mm or more, the line caused by the largest particle and the line caused by the second largest particle are judged to be abnormal values, and from the viewpoint of improving measurement accuracy, attention is paid to the line caused by the third largest particle and its particle size is confirmed. Here, the smaller the particle size of the third largest particle in the recycled carbon black, the better the dispersibility of the recycled carbon black in the rubber composition when the recycled carbon black is blended into the rubber composition, and the more likely it is that the durability of the rubber composition will improve. As described above, in the case of the recycled carbon black, if the particle size of the third largest particle among the particles that cause the line with a length of 10 mm or more is 20 μm or less, the dispersibility of the recycled carbon black in the rubber composition is improved, and the durability of the rubber composition can be effectively improved.

[0097] Figure 1 shows an explanatory diagram of an example of measurement results using a grind gauge. In the measurement using grind gauge 1, several lines attributable to particles in the sample are observed. In this embodiment, in accordance with JIS standards, lines 2 with a length of less than 10 mm are not considered, and lines 3 with a length of 10 mm or more are considered. Furthermore, among the lines 3 with a length of 10 mm or more, line 31 attributable to the largest particle and line 32 attributable to the second largest particle are judged to be abnormal values. In this embodiment, from the viewpoint of improving measurement accuracy, attention is paid to line 33 attributable to the third largest particle. The scale 4 at the location where line 33 attributable to the third largest particle appears is read, and this reading is taken as the particle size of the third largest particle. In this specification, the measurement of recycled carbon black using a grind gauge is performed by the method described in the examples.

[0098] The recycled carbon black in which the third largest particle size is 20 μm or less can be manufactured by various methods. For example, recycled carbon black in which the third largest particle size is 20 μm or less can be manufactured by further grinding the recycled carbon black produced by a general method from recycled waste by extending the grinding process for a longer time or increasing the grinding intensity.

[0099] The recycled carbon black preferably has an ash content of 25% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less, even more preferably 10% by mass, and particularly preferably 6.0% 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 the recycled carbon black is determined according to ASTM D8474 / D1506.

[0100] The recycled carbon black preferably contains one or more elements selected from the group consisting of Zn (zinc), Fe (iron), and Cu (copper). Such recycled carbon black can maintain the physical properties of the rubber composition while retaining components that may affect the deterioration of the rubber composition's properties, thus simplifying processing steps such as purification to completely remove components that may affect the deterioration of the rubber composition's properties.

[0101] Furthermore, the recycled carbon black may contain Zn (zinc). The Zn in the recycled carbon black originates from, for example, zinc oxide used as a vulcanization aid. If the Zn content in the recycled carbon black exceeds a certain amount, the physical properties of the rubber composition will deteriorate, but if it is below a certain amount, the deterioration of the physical properties of the rubber composition can be suppressed. However, the recycled carbon black may also not contain Zn.

[0102] If the recycled carbon black contains Zn, the Zn content in the recycled carbon black is preferably 2.5% by mass or less. A lower Zn content in the carbon black is preferable, but if the Zn content is 2.5% by mass or less, the deterioration of the physical properties of the rubber composition can be suppressed. From the viewpoint of suppressing the deterioration of the physical properties of the rubber composition, the Zn content in the recycled carbon black is more preferably 2.0% by mass or less, even more preferably 1.5% by mass or less, even more preferably 1.0% by mass or less, even more preferably 0.5% by mass or less, even more preferably 0.4% by mass or less, even more preferably 0.3% by mass or less, particularly preferably 0.2% by mass or less, and most preferably 0.1% by mass or less. Furthermore, the Zn content in the recycled carbon black may be 0.01% by mass or more, or 0.05% by mass or more. The above upper and lower limits can be combined as appropriate.

[0103] Methods to keep the Zn content in recycled carbon black within the above range include, for example, acid treatment and analyzing the amount of Zn contained in the raw rubber to be recycled in advance, and using some or all of the raw rubber with a low Zn content.

[0104] The recycled carbon black may contain Fe (iron). The Fe is derived, for example, from steel cords in tires. If the Fe content in the recycled carbon black exceeds a certain amount, the physical properties of the rubber composition will deteriorate, but if it is below a certain amount, the deterioration of the physical properties of the rubber composition can be suppressed.

[0105] The Fe content in the recycled carbon black is preferably 0% by mass or more and 0.1% by mass or less. A lower Fe content in the recycled carbon black is preferable, but if the Fe content is 0.1% by mass or less, the deterioration of the physical properties of the rubber composition can be suppressed. From the viewpoint of suppressing the deterioration of the physical properties of the rubber composition, the Fe content in the recycled carbon black is more preferably 0.09% by mass or less, even more preferably 0.08% by mass or less, even more preferably 0.07% by mass or less, even more preferably 0.06% by mass or less, even more preferably 0.05% by mass or less, particularly preferably 0.04% by mass or less, and most preferably 0.03% by mass or less. Furthermore, the Fe content in the recycled carbon black may be 0.01% by mass or more, or 0.02% by mass or more. The above upper and lower limits can be combined as appropriate.

[0106] Methods for adjusting the Fe content in the recycled carbon black to within the above range include, for example, performing acid treatment and analyzing the amount of Fe contained in the raw rubber to be recycled in advance, and using some or all of the raw rubber with a low Fe content.

[0107] The recycled carbon black may contain Cu (copper). The Cu may originate from plating such as steel cord.

[0108] The Cu content in the recycled carbon black is preferably 0% by mass or more and 0.05% by mass or less. A lower Cu content in the recycled carbon black is preferable, but a Cu content of 0.05% by mass or less can suppress a decrease in the physical properties of the rubber composition. From the viewpoint of suppressing a decrease in the physical properties of the rubber composition, the Cu content in the recycled carbon black is more preferably 0.04% by mass or less, even more preferably 0.03% by mass or less, even more preferably 0.02% by mass or less, and even more preferably 0.01% by mass or less. Furthermore, the Cu content in the recycled carbon black may be 0.01% by mass or more, or 0.02% by mass or more. The above upper and lower limits can be combined as appropriate.

[0109] Methods for adjusting the Cu content of the recycled carbon black to within the above range include, for example, performing acid treatment and analyzing the amount of Cu contained in the raw rubber to be recycled in advance, and using some or all of the raw rubber with a low Cu content.

[0110] The recycled carbon black may contain components other than Zn, Fe, and Cu as described above. "Components other than Zn, Fe, and Cu" refers to components other than Zn, Fe, and Cu in the ash. Examples of components other than Zn, Fe, and Cu in the ash include Si (silicon), S (sulfur), Ca (calcium), K (potassium), Br (bromine), Mg (magnesium), Cl (chlorine), P (phosphorus), Co (cobalt), Na (sodium), and Al (aluminum).

[0111] The recycled carbon black may contain silicon (Si). Preferably, the Si content in the recycled carbon black is 0% by mass or more and 1.0% by mass or less. A Si content of 1.0% by mass or less suppresses a decrease in the physical properties of the rubber composition. From a similar viewpoint, the Si content in the recycled carbon black is more preferably 0.5% by mass or less, and even more preferably 0.3% by mass or less. Furthermore, it is also preferable that the Si content in the recycled carbon black is 0% by mass, i.e., the recycled carbon black is substantially Si-free. On the other hand, the Si content in the recycled carbon black may be 0.01% by mass or more, or 0.05% by mass or more. The above upper and lower limits can be combined as appropriate.

[0112] Methods for adjusting the Si content in the recycled carbon black to the above range include, for example, hydrofluoric acid treatment and base treatment.

[0113] The recycled carbon black may contain sulfur (S). The S content in the recycled carbon black is preferably 0.4% by mass or more, and more preferably 0.5% by mass or more. Furthermore, the S content in the recycled carbon black is preferably 2.0% by mass or less, more preferably 1.8% by mass or less, and even more preferably 1.0% by mass or less. The above upper and lower limits can be combined as appropriate.

[0114] Methods for adjusting the sulfur content in the recycled carbon black to the above range include, for example, acid treatment.

[0115] The recycled carbon black may contain Ca (calcium). The Ca content in the recycled carbon black is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.5% by mass or more, even more preferably 0.7% by mass or more, and even more preferably 0.8% by mass or more. Furthermore, the Ca content in the recycled carbon black is preferably 1.5% by mass or less, more preferably 1.2% by mass or less, and even more preferably 1.1% by mass or less. The above upper and lower limits can be combined as appropriate.

[0116] Methods for adjusting the Ca content in the recycled carbon black to the above range include, for example, acid treatment.

[0117] The recycled carbon black may contain components selected from K, Br, Mg, Cl, P, Co, Na, and Al. Preferably, the content of K, Br, Mg, Cl, P, Co, Na, and Al in the recycled carbon black is 0% by mass or more and 0.2% by mass or less, respectively. More preferably, the content of P, Co, Na, and Al in the recycled carbon black is 0% by mass, i.e., the recycled carbon black is substantially free of P, Co, Na, and Al.

[0118] The recycled carbon black used in this embodiment has a nitrogen adsorption specific surface area (N) determined by the BET method. ２ SA) 40-100m ２ It is preferable that the amount be / g, and 50 to 90 m ２ It is more preferable that the amount be / g, and 55 to 75 m ２ It is particularly preferable that the amount is 1 / g. Furthermore, it is preferable that the oil (OAN) absorption amount is 70 to 120 mL / 100 g, more preferably 75 to 110 mL / 100 g, and particularly preferably 80 to 100 mL / 100 g. In this specification, the specific surface area (N) of nitrogen adsorption of carbon black by the BET method is used. ２SA) is the statistical thickness specific surface area (STSA), which is determined according to ASTM D6556. In this specification, the OAN absorption of carbon black is determined according to ASTM D2414.

[0119] The recycled carbon black preferably has a pH of 4 to 12, more preferably 5 to 11, and particularly preferably 6 to 10. Herein, the pH of the recycled carbon black is determined according to ASTM D1512.

[0120] The recycled carbon black preferably has a toluene staining transmittance 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.

[0121] 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. Hereinafter, the heating loss of the recycled carbon black at 125°C is determined according to ASTM D1509.

[0122] The recycled carbon black preferably has a 35-mesh sieve residue of 20 ppm by mass or less, more preferably 15 ppm by mass or less, and particularly preferably 10 ppm by mass or less. Here, in this specification, the 35-mesh sieve residue of the recycled carbon black is determined according to ASTM D1514.

[0123] The recycled carbon black preferably has a 325-mesh (44 μm) sieve residue of 1,000 ppm by mass or less, more preferably 700 ppm by mass or less, and particularly preferably 300 ppm by mass or less. Here, in this specification, the 325-mesh (44 μm) sieve residue of the recycled carbon black is determined according to ASTM D1514.

[0124] 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. Hereinafter, the pellet hardness of the recycled carbon black is determined according to ASTM D5230.

[0125] 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. Hereinafter, the pellet fine powder content of the recycled carbon black is determined according to ASTM D1508.

[0126] 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. Hereinafter, the particle size (D97) of the recycled carbon black is determined using a laser diffraction particle size analyzer, with the refractive index of water being 1.33 and the refractive index of the filler being 1.75.

[0127] 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.

[0128] The recycled carbon black preferably has an oil (COAN) absorption rate of 50 to 110 mL / 100 g of the compressed sample, more preferably 60 to 100 mL / 100 g, and particularly preferably 70 to 90 mL / 100 g. Hereinafter, the COAN absorption rate of the recycled carbon black is determined according to ASTM D3493.

[0129] The recycled carbon black content in the rubber composition is preferably 1 to 100 parts by mass per 100 parts by mass of the rubber component. When the recycled carbon black content is 1 part by mass or more per 100 parts by mass of the rubber component, it has a great effect in improving the ratio of sustainable materials in the rubber product to which the rubber composition is applied, and when it is 100 parts by mass or less, the fracture resistance of the rubber composition can be maintained more reliably. From a similar viewpoint, the recycled carbon black content per 100 parts by mass of the rubber component is more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more. Furthermore, the recycled carbon black content per 100 parts by mass of the rubber component is more preferably 80 parts by mass or less, even more preferably 70 parts by mass or less, even more preferably 60 parts by mass or less, even more preferably 50 parts by mass or less, even more preferably 40 parts by mass or less, even more preferably 30 parts by mass or less, and particularly preferably 20 parts by mass or less.

[0130] --Carbon Black Other Than Recycled Carbon Black-- The rubber composition of this embodiment may further contain, in addition to the recycled carbon black described above, carbon black other than recycled carbon black (virgin carbon black) as a filler. Examples of carbon black other than recycled carbon black include plant-derived carbon black, such as that derived from castor oil and pine resin oil. The grade of the carbon black is not particularly limited, and examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, N762, etc. Commercially available carbon black can be used, and examples of commercially available carbon black include products from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Nippon Steel Carbon Co., Ltd., Birla Carbon, etc. These carbon blacks may be used individually or in combination of two or more types.

[0131] The content of carbon black other than the recycled carbon black is not particularly limited, but is preferably 1 part by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, the content of carbon black other than the recycled carbon black is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, even more preferably 100 parts by mass or less, and even more preferably 90 parts by mass or less, per 100 parts by mass of the rubber component.

[0132] The proportion of recycled carbon black in the total amount of recycled carbon black and other carbon black (i.e., the total amount of carbon black) is preferably 1 to 99% by mass. When the proportion of recycled carbon black in the total amount of carbon black is 1% by mass or more, it has a significant effect on improving the ratio of sustainable materials in the rubber composition and the side rubber using it, and when the proportion of recycled carbon black in the total amount of carbon black is 99% by mass or less, the crack propagation resistance of the rubber composition can be further improved. From a similar viewpoint, the proportion of recycled carbon black in the total amount of carbon black is more preferably 5% by mass or more, even more preferably 10% by mass or more, even more preferably 90% by mass or less, and even more preferably 80% by mass or less.

[0133] -Silica- The filler may contain silica. The type of silica is not particularly limited. Examples include wet silica, colloidal silica, calcium silicate, aluminum silicate, etc. Among the above, wet silica is preferred, and precipitated silica is more preferred. These silicas may be used individually or in combination of two or more types.

[0134] From the viewpoint of reducing environmental impact, silica derived from silicate plants is preferred. These silicate plants include, for example, mosses, ferns, horsetails, plants of the Cucurbitaceae family, Urticaceae family, and grasses. Among these plants, grasses are preferred. Among grasses, silica derived from rice husks (hereinafter also referred to as "rice husk silica") is particularly preferred from the viewpoint of availability. Further examples of silica include silicon wafer scraps used as raw materials for semiconductors, silica recycled from glass bottles, etc., and used in manufacturing.

[0135] The silica has a nitrogen adsorption specific surface area (N ２ SA) is 50m ２ It is preferable that it be 100m or more per gram. ２ It is more preferable that the amount is 150m or more per gram. ２ It is even more preferable that it be 350m or more ２ It is preferable that the amount is less than or equal to 250m ２ It is more preferable that it be less than or equal to 230m ２ It is even more preferable that it be less than or equal to 200m ２ It is even more preferable that it be less than or equal to / g. In this specification, the specific surface area of ​​silica for nitrogen adsorption (N ２ SA) is a value measured by the BET method in accordance with ASTM D3037-93.

[0136] The silica content in the rubber composition can be appropriately adjusted depending on, for example, the category of rubber articles such as tires to which it is applied, the components in the rubber articles such as tires, the target performance, etc. For example, the silica content in the rubber composition is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, more preferably 30 parts by mass or more, more preferably 50 parts by mass or more, more preferably 70 parts by mass or more, even more preferably 80 parts by mass or more, even more preferably 100 parts by mass or more, particularly preferably 110 parts by mass or more, and also preferably 300 parts by mass or less, more preferably 200 parts by mass or less, even more preferably 180 parts by mass or less, and particularly preferably 150 parts by mass or less.

[0137] (Silane coupling agent) When the filler contains silica, it is preferable that the rubber composition contains a silane coupling agent in order to improve the effect of the silica. Examples of the silane coupling agent include bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide, 3-triethoxysilylpropyl- Examples include N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis(3-diethoxymethylsilylpropyl) tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, and dimethoxymethylsilylpropylbenzothiazolyl tetrasulfide. These silane coupling agents may be used individually or in combination of two or more.

[0138] Furthermore, bioethanol can also be used as a raw material for silane coupling agents.

[0139] (Resin components) The rubber composition of this embodiment may contain resin components. Examples of such resin components include terpene resins, phenolic resins, coumarone-indene resins, xylene resins, rosin-based resins, aromatic hydrocarbon resins, aliphatic hydrocarbon resins, alicyclic hydrocarbon resins, polyurethane resins, and acrylic resins. Furthermore, the above resin components can be those described in Japanese Patent Application Publication No. 2022-132289 or WO2019116656. These resin components may be used individually or in combination of two or more.

[0140] The resin component preferably has a softening point of 30°C or higher, more preferably 60°C or higher, more preferably 90°C or higher, more preferably higher than 110°C, and more preferably 120°C or higher. Furthermore, the resin component preferably has a softening point of 160°C or lower, more preferably 150°C or lower, more preferably 145°C or lower, and more preferably 140°C or lower. The softening point of the resin is measured in accordance with JIS-K2207-1996 (ring-sphere method).

[0141] The content of the resin component is not particularly limited, but for example, it is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and preferably 100 parts by mass or less, and more preferably 60 parts by mass or less, per 100 parts by mass of the rubber component.

[0142] (Fatty Acids) The rubber composition of this embodiment may contain fatty acids. To distinguish them from fatty acids in natural rubber, fatty acids blended in the preparation of the rubber composition are referred to as "blended fatty acids." Blended fatty acids primarily function as crosslinking aids for the rubber composition. Examples of blended fatty acids include stearic acid, palmitic acid, and oleic acid, with stearic acid being preferred.

[0143] The content of the blended fatty acid in the rubber composition is preferably 1.0 part by mass or less, and more preferably 0.8 parts by mass or less, per 100 parts by mass of the rubber component. Furthermore, the content of stearic acid as a blended fatty acid in the rubber composition is preferably 0.8 parts by mass or less per 100 parts by mass of the rubber component. In these cases, the initial adhesion and heat-resistant adhesion between the coated rubber and the steel cord can be further improved. The content of the blended fatty acid in the rubber composition may be 0 parts by mass per 100 parts by mass of the rubber component, but it is preferably 0.3 parts by mass or more.

[0144] (Liquid Softener) The rubber composition of this embodiment may further contain a liquid softener. Here, "liquid softener" refers to a compounding agent that is liquid at 25°C (room temperature) and has the effect of softening the rubber composition. The liquid softener is not particularly limited and includes oils, liquid polymers, etc., and among these, oil is preferred. These liquid softeners may be used individually or in combination of two or more.

[0145] The aforementioned oils refer to the drawstring oils contained in rubber components and the liquid oils added as compounding agents to rubber compositions. Examples include vegetable oils, process oils, oils obtained by recycling vegetable oils or process oils, or mixtures thereof. From the viewpoint of reducing environmental impact, vegetable oils and recycled oils are preferred as oils. Examples of vegetable oils include palm oil, castor oil, cottonseed oil, soybean oil, linseed oil, rapeseed oil, coconut oil, peanut oil, pine oil, pine tar, tall oil, corn oil, rice oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, tung oil, coconut oil, seed oils, cereal oils, potato oils, bean oils, and vegetable oils. Examples of process oils include paraffinic process oils, aromatic process oils, and naphthenic process oils. Commercially available oils can be used as the aforementioned oils. Examples of commercially available oils that can be used include those from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., ENEOS Corporation, Orisoy Co., Ltd., H&R Co., Ltd., Toyokuni Oil Co., Ltd., Nisshin Oillio Group Ltd., etc. These oils may be used individually or in combination of two or more types.

[0146] The liquid polymer is preferably a liquid diene polymer. Examples of liquid diene polymers include liquid styrene-butadiene copolymer (liquid SBR), liquid polybutadiene (liquid BR), liquid polyisoprene (liquid IR), liquid styrene-isoprene copolymer (liquid SIR), liquid styrene-butadiene-styrene block copolymer (liquid SBS block polymer), liquid styrene-isoprene-styrene block copolymer (liquid SIS block polymer), liquid polyfarnesene, liquid farnesene-butadiene copolymer, and the like. These liquid polymers may be hydrogenated, or their ends or main chains may be modified with functional groups (polar groups). These liquid polymers may be used individually or in combination of two or more. The above liquid polymers are not included in the definition of "rubber components."

[0147] The content of the liquid softener is not particularly limited and can be adjusted as appropriate depending on, for example, the category of rubber articles such as tires to which it is applied, the components of the rubber articles such as tires, the target performance, etc. For example, the content of the liquid softener is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, even more preferably 10 parts by mass or more, and also preferably 100 parts by mass or less, more preferably 70 parts by mass or less, even more preferably 50 parts by mass or less, and even more preferably 30 parts by mass or less, per 100 parts by mass of the rubber component.

[0148] (Rubber-Metal Adhesion Promoter) The rubber composition of this embodiment contains a carboxylate metal salt (hereinafter sometimes referred to as "carboxylate metal salt (1)") having 2 to 25 carbon atoms and the metal species being bismuth, copper, antimony, silver, niobium, or zirconium, and the following formula (A): [(RCOO) ｘ MO] ３ Z (A) [In equation (A), Z is the following equations (z-1) to (z-4): The structure is selected from the following, where M is bismuth, copper, antimony, silver, niobium, or zirconium, (RCOO) is each independently a residue of an aliphatic carboxylic acid having 2 to 25 carbon atoms, and x is an integer of (valence of M - 1). Preferably, the mixture further contains a rubber-metal adhesion promoter selected from the group consisting of compounds represented by [ ] (hereinafter sometimes referred to as "compound (2)" ). In this case, the durability of the rubber after vulcanization and the thermal degradation adhesion of the steel cord-rubber composite can be improved. These rubber-metal adhesion promoters may be used individually or in combination of two or more types.

[0149] The carboxylate metal salt (1) is a metal salt of a carboxylic acid having 2 to 25 carbon atoms, and more particularly, a metal salt of an aliphatic carboxylic acid having 2 to 25 carbon atoms. Here, the metal species is bismuth, copper, antimony, silver, niobium, or zirconium. Among these metal species, bismuth, copper, antimony, or silver are preferred, and bismuth or copper are more preferred, because they act as adhesion promoters that provide good adhesion between the steel cord and rubber even under humid heat conditions. If the number of carbon atoms in the carboxylate metal salt (1) is less than 2, the compatibility between the carboxylate metal salt (1) and the rubber component is low, and high adhesion between the rubber and the steel cord after vulcanization cannot be obtained. Furthermore, carboxylate metal salts (1) with more than 25 carbon atoms are difficult to synthesize.

[0150] Examples of aliphatic carboxylic acids having 2 to 25 carbon atoms include aliphatic monocarboxylic acids and aliphatic dicarboxylic acids. The carbon number of an aliphatic carboxylic acid refers to the total number of carbon atoms including the carboxyl group.

[0151] Examples of aliphatic monocarboxylic acids having 2 to 25 carbon atoms include saturated aliphatic monocarboxylic acids and unsaturated aliphatic monocarboxylic acids.

[0152] Examples of the 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, eicosanoic acid, docosanoic acid, tetracosanoic acid, naphthenic acid, and the like. Examples of the aforementioned 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.

[0153] Examples of aliphatic dicarboxylic acids having 2 to 25 carbon atoms include saturated aliphatic dicarboxylic acids and unsaturated aliphatic dicarboxylic acids.

[0154] 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.

[0155] As the aliphatic carboxylic acid having 2 to 25 carbon atoms, aliphatic monocarboxylic acids or aliphatic dicarboxylic acids are preferred, aliphatic monocarboxylic acids are more preferred, and saturated aliphatic monocarboxylic acids are even more preferred. By using saturated aliphatic monocarboxylic acids, the sulfur crosslinking of rubber is less likely to be affected, and the deterioration of rubber properties after vulcanization can be suppressed. Among the saturated fatty acids, saturated aliphatic monocarboxylic acids having 2 to 20 carbon atoms are preferred, and 2-ethylhexanoic acid, neodecanoic acid, hexadecanoic acid, or octadecanoic acid are more preferred.

[0156] The metal carboxylate salt (1) can be obtained, for example, by the method shown below. Method 1: A direct reaction (direct method) of an aliphatic carboxylic acid (a) having 2 to 25 carbon atoms with one or more selected from oxides (b-1) of metals (bismuth, copper, antimony, silver, niobium, zirconium), hydroxides (b-2) of metals (bismuth, copper, antimony, silver, niobium, zirconium), and carbonates (b-3) of metals (bismuth, copper, antimony, silver, niobium, zirconium). Method 2: A method of production (double decomposition method) in which an aliphatic carboxylic acid having 2 to 25 carbon atoms (a) is reacted with sodium hydroxide in the presence of water or an organic solvent to obtain a sodium salt of the aliphatic carboxylic acid, and then the sodium salt of the aliphatic carboxylic acid is reacted with one or more selected from metal (metal salts of bismuth, copper, antimony, silver, niobium, and zirconium) sulfates (c-1), metal (bismuth, copper, antimony, silver, niobium, and zirconium) chlorides (c-2), and metal (bismuth, copper, antimony, silver, niobium, and zirconium) nitrates (c-3).

[0157] Examples of metal oxides (b-1) of metals (bismuth, copper, antimony, silver, niobium, zirconium) include bismuth(III) oxide, copper(I) oxide, copper(II) oxide, antimony(III) oxide, antimony(V) oxide, silver(I) oxide, silver(II) oxide, silver(III) oxide, niobium(IV) oxide, niobium(V) oxide, and zirconium oxide. Examples of metal hydroxides (b-2) of metals (bismuth, copper, antimony, silver, niobium, zirconium) include copper(II) hydroxide and zirconium hydroxide. Examples of metal carbonates (b-3) of metals (bismuth, copper, antimony, silver, niobium, zirconium) include bismuth(III) carbonate, bismuth(III) carbonate oxide, and copper(II) carbonate. Examples of metal sulfates (c-1) of metals (bismuth, copper, antimony, silver, niobium, zirconium) include copper(II) sulfate and zirconium sulfate. Examples of chlorides (C-2) of metals (bismuth, copper, antimony, silver, niobium, zirconium) include bismuth(III) chloride, copper(I) chloride, copper(II) chloride, antimony(III) chloride, antimony(V) chloride, silver(I) chloride, and niobium(V) chloride. Examples of nitrates (C-3) of metals (bismuth, copper, antimony, silver, niobium, zirconium) include bismuth(III) nitrate, bismuth(III) subnitrate, and silver(I) nitrate.

[0158] In method 1, the reaction temperature when reacting the aliphatic carboxylic acid (a) having 2 to 25 carbon atoms with compounds (b-1) to (b-3) is usually 50 to 150°C. The reaction time is usually 1 to 20 hours.

[0159] In method 2, the reaction temperature when reacting an aliphatic carboxylic acid (a) having 2 to 25 carbon atoms with sodium hydroxide in the presence of water or an organic solvent is usually 20 to 100°C. The reaction time is usually 1 to 5 hours. In method 2, the reaction temperature when reacting the sodium salt of the aliphatic carboxylic acid with compounds (c-1) to (c-3) is usually 20 to 100°C. The reaction time is usually 1 to 5 hours. In method 2, after reacting the sodium salt of the aliphatic carboxylic acid with compounds (c-1) to (c-3), the aqueous layer in the reaction system is separated. Subsequently, the solvent present in the oil layer is removed by vacuum distillation to obtain the carboxylic acid metal salt (1).

[0160] In compound (2) represented by formula (A), (RCOO) is an aliphatic carboxylic acid residue having 2 to 25 carbon atoms. If the number of carbon atoms in the aliphatic carboxylic acid residue is less than 2, the compatibility between the rubber component and compound (2) is poor, resulting in a decrease in the adhesive strength between the vulcanized rubber and the steel cord. Furthermore, if the number of carbon atoms in the aliphatic carboxylic acid residue is greater than 25, compound (2) is difficult to synthesize. Also, if the number of carbon atoms in the aliphatic carboxylic acid residue is greater than 25, compound (2) is difficult to disperse in the rubber component, or the vulcanized rubber is difficult to adsorb onto the steel cord surface, resulting in a decrease in the adhesive strength between the vulcanized rubber and the steel cord.

[0161] Examples of aliphatic monocarboxylic acid residues having 2 to 25 carbon atoms include aliphatic monocarboxylic acid residues, and the residues derived from aliphatic monocarboxylic acids described in the explanation of carboxylic acid metal salt (1) are preferably exemplified. Among aliphatic carboxylic acid residues, saturated aliphatic monocarboxylic acid residues are preferred. By using saturated aliphatic monocarboxylic acid residues, compound (2) becomes easier to disperse near the steel cord, or the rubber after vulcanization becomes easier to adsorb onto the steel cord surface. 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, or octadecanoic acid are more preferred.

[0162] In compound (2) represented by formula (A), M is a metal species, specifically bismuth, copper, antimony, silver, niobium, or zirconium. Among these metal species, bismuth, copper, antimony, or silver are preferred, and bismuth or copper is more preferred, because they act as adhesion promoters that provide good adhesion between steel cord and rubber even under humid heat conditions.

[0163] In compound (2) represented by formula (A), Z is a structure selected from formulas (z-1) to (z-4) described above. Among these, Z is preferably the structure represented by formula (z-1) because it is easier to obtain an adhesion promoter that exhibits high adhesion between the vulcanized rubber and the steel cord.

[0164] Compound (2) represented by formula (A) can be produced, for example, by mixing an aliphatic carboxylic acid (a) having 2 to 25 carbon atoms, an inorganic acid ester (d), an acid (e), and a metal compound M (f), heating the mixture, and then removing the volatile ester (g) obtained from the mixture.

[0165] Examples of aliphatic carboxylic acids (a) having 2 to 25 carbon atoms include the aliphatic monocarboxylic acids having 2 to 25 carbon atoms as described above.

[0166] Examples of the inorganic acid ester (d) include borate esters of lower alcohols having 1 to 5 carbon atoms (d-1), metaborate esters of lower alcohols having 1 to 5 carbon atoms (d-2), phosphate esters of lower alcohols having 1 to 5 carbon atoms (d-3), and phosphorous acid esters of lower alcohols having 1 to 5 carbon atoms (d-4). Examples of borate esters of lower alcohols (d-1) include trimethyl borate, triethyl borate, tripropyl borate, and tributyl borate. Examples of metaborate esters of lower alcohols (d-2) include trimethyl metaborate, triethyl metaborate, tripropyl metaborate, and tributyl metaborate. Examples of phosphate esters of lower alcohols (d-3) include methyl phosphate, ethyl phosphate, propyl phosphate, and butyl phosphate. Examples of phosphorous acid esters of lower alcohols (d-4) include methyl phosphate, ethyl phosphate, propyl phosphate, and butyl phosphate. Among these, the lower alcohol metaboric acid ester (d-2) is preferred as the inorganic acid ester (d) from the viewpoint of suppressing metal corrosion after treatment.

[0167] The acid (e) is an acid capable of forming a volatile ester (g) with a lower alcohol residue having 1 to 5 carbon atoms present in the inorganic acid ester (d). Specific examples of the acid (e) include ethaneic acid, propanoic acid, and butanoic acid.

[0168] The metal compound M(f) is a metal source for compound (2), and for example, oxides (b-1), hydroxides (b-2), carbonates (b-3), etc., as described in the method for producing the metal carboxylic acid salt (1), can be used. The proportion of the metal compound M(f) used as the metal source is, for example, 20 to 100 parts by mass per 100 parts by mass of aliphatic carboxylic acid (a) having 2 to 25 carbon atoms.

[0169] The proportion of the inorganic acid ester (d) used is, for example, 10 to 50 parts by mass per 100 parts by mass of aliphatic carboxylic acid (a) having 2 to 25 carbon atoms. The proportion of the acid (e) used is, for example, 10 to 50 parts by mass per 100 parts by mass of aliphatic carboxylic acid (a) having 2 to 25 carbon atoms.

[0170] The mixing of an aliphatic carboxylic acid having 2 to 25 carbon atoms (a), an inorganic acid ester (d), an acid (e), and a metal compound M (f) may be carried out in one step or in multiple steps.

[0171] As an example of a method for mixing various components in multiple steps, a manufacturing method including the following first and second steps can be cited. The first step is to mix an aliphatic carboxylic acid (a) having 2 to 25 carbon atoms, an acid (e), and a metal compound M (f), and heat the mixture to obtain a reactant (h). The second step is to remove water from the reaction system containing the reactant (h) obtained in the first step, then add an inorganic acid ester (d) to the reaction system from which the water has been removed, and react the reactant (h) with the inorganic acid ester (d). By manufacturing compound (2) in the above two steps, it is possible to prevent the inorganic acid ester (d) from being hydrolyzed by the water generated in the first step, and to efficiently manufacture compound (2).

[0172] In the above-described multi-step manufacturing method, the temperature at which the aliphatic carboxylic acid (a) having 2 to 25 carbon atoms, the inorganic acid ester (d), the acid (e), and the metal compound M (f) are reacted is, for example, 100 to 250°C, preferably 150 to 220°C. The reaction time is, for example, 1 to 20 hours, preferably 1 to 5 hours.

[0173] From the viewpoint of improving the adhesion between the rubber and steel cord after vulcanization and improving the durability of the steel cord-rubber composite and rubber articles such as tires, the content of the rubber-metal adhesion promoter in the rubber composition is preferably 0.01 parts by mass or more per 100 parts by mass of the rubber component. Furthermore, the content of the rubber-metal adhesion promoter in the rubber composition is preferably less than 1.0 part by mass per 100 parts by mass of the rubber component. From a similar viewpoint, the content of the rubber-metal adhesion promoter in the rubber composition is more preferably 0.02 parts by mass or more, more preferably 0.9 parts by mass or less, even more preferably 0.8 parts by mass or less, and even more preferably 0.7 parts by mass or less per 100 parts by mass of the rubber component.

[0174] (4,4'-diphenylmethanebismaleimide) The rubber composition of this embodiment preferably further contains 4,4'-diphenylmethanebismaleimide. In particular, the rubber composition of this embodiment preferably further contains 4,4'-diphenylmethanebismaleimide when it contains the rubber-metal adhesion promoter described above. In this case, the durability of the rubber after vulcanization and the thermal degradation adhesion of the steel cord-rubber composite can be further improved.

[0175] The content of 4,4'-diphenylmethanebismaleimide in the rubber composition is preferably 0.05 parts by mass or more per 100 parts by mass of rubber component, from the viewpoint of improving the adhesion between the rubber and steel cord after vulcanization and improving the durability of steel cord-rubber composites and rubber articles such as tires. Furthermore, the content of 4,4'-diphenylmethanebismaleimide in the rubber composition is preferably 10 parts by mass or less per 100 parts by mass of rubber component.

[0176] (Boron-containing compound) The rubber composition may also contain a boron-containing compound from the viewpoint of further improving the adhesive durability between the steel cord and the coated rubber and from the viewpoint of fully exhibiting a rust-preventive effect. The boron-containing compound is not particularly limited as long as it contains boron, but examples include boric acid, ammonium borate, zinc borate, tetrafluoroboric acid, etc. These boron-containing compounds may be used individually or in combination of two or more. Among these, boric acid is preferred as the boron-containing compound from the viewpoint of availability and low cost. Note that those rubber-metal adhesion promoters that contain boron as described above are not included in the definition of "boron-containing compound".

[0177] Specifically, the content of the boron-containing compound in the rubber composition is preferably 0.005 to 0.08 parts by mass of the boron-containing compound per 100 parts by mass of the rubber component. If the content is 0.005 parts by mass or more, the adhesive durability between the steel cord and the coated rubber can be sufficiently improved, and if it is 0.08 parts by mass or less, the decrease in the initial vulcanization rate of the rubber can be suppressed, and the initial adhesion rate between the steel cord and the coated rubber can be well maintained. From a similar viewpoint, the content of the boron-containing compound per 100 parts by mass of the rubber component is more preferably 0.01 parts by mass or more, even more preferably 0.02 parts by mass or more, even more preferably 0.06 parts by mass or less, and even more preferably 0.055 parts by mass or less, in terms of the boron content of the boron-containing compound.

[0178] (Cobalt-containing compounds) The rubber composition of this embodiment may or may not contain cobalt-containing compounds. Examples of cobalt-containing compounds include cobalt fatty acid salts and cobalt metal complexes. Examples of cobalt fatty acid salts include cobalt naphthenate, cobalt stearate, cobalt neodecanoate, cobalt rosinate, cobalt versatate, cobalt tol oilate, cobalt oleate, cobalt linoleate, cobalt linolenate, and cobalt palmitate. Examples of cobalt metal complexes include cobalt acetylacetonate.

[0179] Preferably, the content of the cobalt-containing compound in the rubber composition is 1 part by mass or less per 100 parts by mass of the rubber component. This means that the rubber composition is substantially free of cobalt-containing compounds. This is to reduce the burden on the environment and comply with various regulations. From a similar viewpoint, it is preferable that the content of the cobalt-containing compound (especially cobalt fatty acid salt) in the rubber composition is 0 parts by mass per 100 parts by mass of the rubber component, i.e., the rubber composition does not contain cobalt-containing compounds (is cobalt-free).

[0180] (Other components) In addition to the components described above, the rubber composition of this embodiment may further contain various additives used in rubber products, particularly tires, such as antioxidants, zinc oxide, sulfur, vulcanization accelerators, waxes, bismaleimide compounds, organic peroxides, cellulose nanofibers, cellulose particles, solid fine particles such as eggshells, rice husks, and walnut powder, and rubber powder obtained by crushing used rubber products.

[0181] (Method for manufacturing the steel cord-rubber composite) The method for manufacturing the composite of this embodiment is not particularly limited, and can be obtained by coating the steel cord described above with the rubber composition of this embodiment.

[0182] The method for preparing the rubber composition of this embodiment is not particularly limited, and known methods can be used. For example, it can be obtained by mixing a predetermined rubber component, a filler such as carbon black, and other components using a mixer such as a Banbury mixer, roll mixer, or internal mixer. Alternatively, components other than the crosslinking accelerator and crosslinking agent may be mixed in a non-production (non-pro) stage, and the crosslinking accelerator and crosslinking agent may be added to the mixture and mixed in a production (pro) stage to prepare the rubber composition.

[0183] The method for coating the steel cords with the rubber composition is not particularly limited. For example, such a method may include the steps of: arranging a predetermined number of steel cords in parallel at predetermined intervals; coating these steel cords from both the top and bottom with an unvulcanized rubber sheet made of the rubber composition and approximately 0.5 mm thick; and then performing a vulcanization treatment. By this method, the steel cord-rubber composite of this embodiment can be obtained. The vulcanization treatment can be carried out, for example, at a temperature of approximately 160°C for approximately 20 minutes.

[0184] <Tire> A tire according to one embodiment of the present invention (hereinafter sometimes referred to as "the tire of this embodiment") comprises the steel cord-rubber composite described above. Because the tire of this embodiment comprises the steel cord-rubber composite described above, it contributes to improved sustainability while maintaining good durability.

[0185] The application area of ​​the steel cord-rubber composite of this embodiment in a tire is not particularly limited and can be appropriately selected depending on the purpose. Examples include the carcass, belt, bead core, etc.

[0186] The method for manufacturing the tire in this embodiment is not particularly limited and can be manufactured using conventional methods. Generally, a rubber composition containing various components is processed into each component at an unvulcanized stage, and then bonded and molded on a tire molding machine using conventional methods to form a green tire. This green tire is then heated and pressurized in a vulcanizing machine to produce a tire. For example, a tire can be obtained by kneading a rubber composition, using the resulting rubber composition to rubberize steel cords, laminating an unvulcanized belt, an unvulcanized carcass, and other unvulcanized components, and then vulcanizing the unvulcanized laminate.

[0187] <Rubber Crawler> A rubber crawler according to one embodiment of the present invention comprises the steel cord-rubber composite described above. Because such a rubber crawler comprises the steel cord-rubber composite described above, it contributes to improved sustainability while maintaining good durability.

[0188] In one embodiment, the rubber crawler comprises a steel cord, an intermediate rubber layer covering the steel cord, a core metal positioned on the intermediate rubber layer, and a main rubber layer surrounding the intermediate rubber layer and the core metal, and further comprises a plurality of lugs on the contact surface side of the main rubber layer. In one embodiment, the above-described rubber composition can be applied to any part of the rubber crawler.

[0189] <Hose> A hose according to one embodiment of the present invention comprises the steel cord-rubber composite described above. Because such a hose comprises the steel cord-rubber composite described above, it contributes to improved sustainability while maintaining good durability.

[0190] In one embodiment, the hose comprises an inner rubber layer (inner tube rubber) located radially inward, an outer rubber layer located radially outward, and a steel cord reinforcing layer (metal 1) located between the inner rubber layer and the outer rubber layer. In one embodiment, the above-described rubber composition can be used in at least one of the inner rubber layer and the outer rubber layer.

[0191] The present invention will be described in more detail below with reference to examples, but these examples are for illustrative purposes only and do not limit the present invention in any way.

[0192] <Evaluation 1> Two types of rubber compositions having the compound compositions shown in Table 1 were prepared, and these rubber compositions were vulcanized at 145°C for 33 minutes to obtain vulcanized rubber test pieces.

[0193] (Sustainable Material Ratio) For each rubber composition prepared, the sustainable material ratio was evaluated by calculating the total mass ratio of components derived from biological resources (biomass resources) and components derived from recycled resources. The results are shown in Table 1.

[0194] (Breaking Strength (Crack Resistance)) The obtained vulcanized rubber test pieces were punched into JIS-3 dumbbells, and the resulting samples were subjected to tensile tests at room temperature according to JIS K 6251:2004. The breaking strength (TB) before thermal degradation (initial) and after thermal degradation (100°C × 24 hours) was measured. The results are shown in Table 1. A higher value indicates better fracture resistance, i.e., better crack resistance.

[0195]

[0196] *1 Butadiene rubber: Manufactured by UBE Elastomers, product name "BR150L" *2 Virgin carbon black: Manufactured by Asahi Carbon, product name "N550", nitrogen adsorption specific surface area (N ２ SA) = 40m ２ / g, OAN oil absorption = 121 mL / 100 g *3 Recycled carbon black: Enrestec, product name "PB365", ash content = 17% by mass *4 Anti-aging agent A: Ouchi Shinko Chemical Industry Co., Ltd., product name "Nocrac 6C" *5 Anti-aging agent B: Ouchi Shinko Chemical Industry Co., Ltd., product name "Nocrac 224" *6 Oil: ENEOS, product name "A / Omix" *7 Fatty acid: Miyoshi Oil & Fat Co., Ltd., product name "MXST" *8 Other chemicals: Total amount of sulfur, vulcanization accelerator, resin, and wax, same ratio in each rubber composition

[0197] Table 1 shows that replacing carbon black (virgin carbon black) with recycled carbon black among the various materials contained in the rubber composition contributes to improved sustainability, but it also reduces the tensile strength before and after thermal degradation, meaning there is room for improvement in crack resistance.

[0198] <Evaluation 2> Recycled carbon black 1 and recycled carbon black 2 were prepared as test recycled carbon blacks.

[0199] Next, 3.75 g of zinc oxide, 0.20 g of the recycled carbon black under test, and 2.00 mL of epoxidized soybean oil were mixed to obtain a mixture. The obtained mixture was kneaded for 5 to 10 minutes to form a paste, and the sample paste was prepared. In accordance with JIS K5101-1-5, the paste was prepared using a Toyo Seiki Huber Mahler (model: H3) under conditions of a load of 0.4536 kN and a glass plate rotation speed of 100 r / min. In accordance with JIS K5400, each sample paste was placed on a grind gauge and stretched with a scraper. The grind gauge used had a range of 0 to 25 μm. It was confirmed that three or more continuous lines of 10 mm or more appeared, and the scale reading at the location where the line caused by the third largest particle among the particles that produced the continuous lines of 10 mm or more appeared was read, and this reading was taken as the particle size of the third largest particle. The same procedure was performed a total of four times, and the average particle size of the third largest particle from the four measurements was calculated. The results are shown in Table 2.

[0200] Furthermore, for recycled carbon black 1 and recycled carbon black 2, the nitrogen adsorption specific surface area (N) was determined according to ASTM D6556. ２ SA was measured. The results are shown in Table 2.

[0201] Furthermore, the Zn, Fe, and Cu content of recycled carbon black 1 and recycled carbon black 2 was measured by X-ray fluorescence analysis (XRF). The results are shown in Table 2.

[0202] Furthermore, the ash content of recycled carbon black 1 and recycled carbon black 2 was measured according to ASTM D8474 / D1506. The results are shown in Table 2.

[0203]

[0204] (Preparation of Rubber Compositions) Using recycled carbon black 1 or recycled carbon black 2 as described above, rubber compositions were prepared according to the formulations shown in Table 3. Other chemicals included antioxidants, oils, fatty acids, sulfur, and vulcanization accelerators, and the same types and amounts were added in the reference comparative example and reference example. Commercially available chemicals commonly used in the preparation of rubber compositions were used. The amounts added were the amounts commonly used in the preparation of rubber compositions. For each rubber composition prepared, the sustainable material ratio was evaluated by calculating the total mass ratio of components derived from biological resources (biomass resources) and components derived from recycled resources (recycled resources). Furthermore, the durability of the obtained rubber compositions was evaluated as high-temperature tensile strength after degradation and crack propagation resistance after thermal degradation using the following methods. The results are shown in Table 3.

[0205] (Evaluation of high-temperature tensile strength after degradation) Each rubber composition was vulcanized at 145°C for 33 minutes to obtain vulcanized rubber. The obtained vulcanized rubber was subjected to thermal degradation at 100°C for 48 hours in an air atmosphere. A tensile test was performed at 100°C in accordance with JIS K6251:2017, and the tensile strength was measured. The high-temperature tensile strength (fracture resistance) after degradation was expressed as an index using the following formula, with the tensile strength of the test piece of Reference Example 1 set to 100. High-temperature tensile strength index after degradation = (Tensile strength of the test piece / Tensile strength of the test piece of Reference Example 1) × 100 A higher high-temperature tensile strength index after degradation indicates that the vulcanized rubber is less prone to fracture and has superior performance (fracture resistance) after degradation.

[0206] (Evaluation of crack propagation resistance after thermal degradation) The rubber composition to be tested was pre-treated by thermal degradation at 100°C for 24 hours in an air atmosphere. A strip-shaped test piece was prepared from the rubber composition with a 0.5 mm hole drilled in the lengthwise direction in the center. Using this test piece, a dc / dn test (using Shimadzu Corporation's "ServoPulsa") was performed, applying repeated fatigue at a frequency of 5 Hz and 80°C with a strain of 30-100%, and the tear energy [J / m] at 1950 cycles was measured. ２The crack propagation rate was calculated when the common logarithm of [ ] was 3.9. In the crack propagation rate obtained by the above process, the formulation data of Reference Example 1 was used as a control (index value 100), and the formula data of each example was normalized by the reciprocal of the formula data. A larger index value indicates a lower crack propagation rate and superior crack propagation resistance.

[0207]

[0208] *11 Natural rubber: RSS #3 *12 Butadiene rubber: Manufactured by UBE Elastomers, product name "BR150L" *13 Virgin carbon black: Manufactured by Asahi Carbon, N550, new carbon black

[0209] Tables 2 and 3 show that the reference example using recycled carbon black with a particle size of 20 μm or less for the third largest particle size exhibits better high-temperature tensile strength after degradation compared to the reference comparative example using recycled carbon black with a particle size of more than 20 μm for the third largest particle size. Furthermore, the reference example also showed better crack propagation resistance after thermal degradation compared to the reference comparative example.

[0210] Based on these evaluations, it can be seen that using recycled carbon black in which the third largest particle size measured with a grind gauge is 20 μm or less contributes to improved sustainability while maintaining good durability after degradation (crack propagation resistance after thermal degradation, and high-temperature tensile strength after degradation).

[0211] <Evaluation 3 (Relationship between Zn content in carbon black and rubber properties)> Carbon black (CB) and styrene-butadiene rubber with different ash, Zn, and sulfur content were kneaded according to the formulations shown in Table 4 to prepare rubber compositions for each example.

[0212] Furthermore, the Zn and S content of the carbon black used was measured by X-ray fluorescence analysis. The results are shown in Table 4.

[0213] Furthermore, the ash content of the carbon black used was measured by thermogravimetric analysis (TGA, RIGAKU Corporation) using the following procedure. The sample was heated from room temperature to 550°C under a nitrogen atmosphere, and then heated to maintain 550°C under an air atmosphere, and the loss on heating was measured. The loss on heating (mass%) when the sample was heated from room temperature to 550°C under a nitrogen atmosphere was defined as "Loss on heating 1," and the loss on heating (mass%) when heated to maintain 550°C under an air atmosphere was defined as "Loss on heating 2." The ash content was calculated using the following formula. The results are shown in Table 4. Ash content (mass%) = 100 - Loss on heating 1 - Loss on heating 2

[0214] For each example of rubber composition, vulcanized rubber was obtained by vulcanization at 145°C for 33 minutes. Tensile strength was measured for each vulcanized rubber by performing a tensile test at room temperature in accordance with JIS K6301-1995. The tensile strength of the test specimen of the standard rubber composition was set to 100, and the index was expressed using the following formula. The results are shown in Table 4. Tensile strength index = (Tensile strength of test specimen other than the standard rubber composition / Tensile strength of test specimen of the standard rubber composition) × 100 A larger index indicates that the vulcanized rubber is less prone to fracture and has superior tensile strength.

[0215] For each example of rubber composition, a viscoelasticity test was performed using TA Instruments' "ARES-G2" under the conditions of a frequency of 15 Hz, shear strain of 10%, and temperature of 50°C, and the storage modulus (G') was measured. The evaluation results were indexed with the standard rubber composition as the control (index value 100). The results (viscoelasticity) are shown in Table 4. A higher index indicates a higher G', and a better rubber property for application in products such as tires.

[0216]

[0217] *21 SBR: Styrene-butadiene rubber, product name "#1500" *22 CB1: Carbon black, recycled carbon black equivalent to N330 *23 CB2: Carbon black, recycled carbon black equivalent to N330 *24 CB3: Carbon black, recycled carbon black equivalent to N330 *25 CB5: Carbon black, virgin (new) carbon black equivalent to N330

[0218] Table 4 shows that when carbon black with reduced Zn content is applied to a rubber composition, the deterioration of the rubber composition's physical properties is suppressed.

[0219] According to the present invention, it is possible to provide a steel cord-rubber composite that contributes to improved sustainability while maintaining good durability. Furthermore, according to the present invention, it is possible to provide tires, rubber tracks, and hoses that contribute to improved sustainability while maintaining good durability.

[0220] 1: Grind gauge 2: Line less than 10 mm in length 3: Line 10 mm or longer 31: Line caused by the largest particle 32: Line caused by the second largest particle 33: Line caused by the third largest particle 4: Scale mark at the location where the line caused by the third largest particle appeared

Claims

1. A steel cord-rubber composite comprising a steel cord having one or more steel wires, coated with a rubber composition, wherein the rubber composition contains a rubber component and a filler, the filler contains recycled carbon black, and the recycled carbon black is characterized in that, when measured with a grind gauge, three or more lines with a length of 10 mm or more are confirmed, and the particle size of the third largest particle among the particles that produce the lines with a length of 10 mm or more is 20 μm or less.

2. The steel cord-rubber composite according to claim 1, wherein, in the measurement of the recycled carbon black using a grind gauge, a paste of the recycled carbon black is prepared as the measurement sample in accordance with JIS K5101-1-5.

3. The steel cord-rubber composite according to claim 1, wherein, in the measurement of the recycled carbon black using a grind gauge, the applied load is set to 0.4 to 0.5 kN and the rotation speed of the glass plate is set to 90 to 110 r / min in accordance with JIS K5101-1-5, and the paste of the recycled carbon black is prepared as the measurement sample.

4. The steel cord-rubber composite according to claim 1, wherein the recycled carbon black comprises one or more selected from the group consisting of Zn, Fe, and Cu.

5. The steel cord-rubber composite according to claim 4, wherein the recycled carbon black contains Zn.

6. The steel cord-rubber composite according to claim 5, wherein the Zn content in the recycled carbon black is 1.0% by mass or less.

7. The steel cord-rubber composite according to claim 1, wherein the recycled carbon black has an ash content of 20% by mass or less.

8. The steel cord-rubber composite according to claim 1, wherein one or more of the steel wires constituting the steel cord are steel wires derived from recycled iron, the recycled iron-derived steel wires have an N element content of 60 ppm by mass or more, a C element content of 0.7 to 1.0% by mass, a Cu element content of 0.01 to 0.4% by mass, and a Cr element content of 0.05 to 0.3% by mass, and the surface of the steel cord has an N atom content of 2 atomic% or more and 60 atomic% or less, and a Cu / Zn ratio of 1 to 4 or less.

9. The steel cord-rubber composite according to claim 1, wherein the steel cord is made by twisting together a plurality of steel wires with brass plating applied to their circumferential surfaces, and the composition of the brass plating is 40 to 80% by mass of Cu and 20 to 60% by mass of Zn.

10. The steel cord-rubber composite according to claim 1, wherein the steel cord is subjected to surface treatment with a buffer solution at pH 5.0 to 7.2 and treatment with one or more triazole compounds selected from 1,2,4-triazole, 1,2,3-triazole, 3-amino-1,2,4-triazole, 4-amino-1,2,4-triazole, benzotriazole, tolyltriazole, and 3-mercapto-1,2,4-triazole.

11. The steel cord-rubber composite according to claim 8, wherein the steel wire derived from recycled iron has a Cu element content of 0.05 to 0.4% by mass.

12. The steel cord-rubber composite according to claim 8, wherein the steel wire derived from recycled iron has a diameter of 0.15 mm to 0.6 mm.

13. The rubber composition is a carboxylate metal salt having 2 to 25 carbon atoms and the metal species being bismuth, copper, antimony, silver, niobium, or zirconium, and the following formula (A): [(RCOO) ｘ MO] ３ Z (A) [In equation (A), Z is the following equations (z-1) to (z-4): The steel cord-rubber composite according to claim 1, further comprising a rubber-metal adhesion promoter selected from the group consisting of compounds represented by [ ], wherein the rubber composition contains 0.01 parts by mass or more per 100 parts by mass of the rubber component.

14. The steel cord-rubber composite according to claim 13, further comprising 4,4'-diphenylmethanebismaleimide in the rubber composition.

15. A tire characterized by comprising a steel cord-rubber composite according to any one of claims 1 to 14.

16. A rubber crawler characterized by comprising a steel cord-rubber composite according to any one of claims 1 to 14.

17. A hose comprising a steel cord-rubber composite as described in any one of claims 1 to 14.

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