Rubber composition for conveyor belt, and conveyor belt

Abstract

The purpose of the present invention is to provide: a rubber composition which gives a vulcanized rubber excellent in terms of flame retardancy, ozone resistance, bloom resistance, and power-saving properties; and a conveyor belt. The present invention provides: a rubber composition for a conveyor belt, which comprises a rubber component comprising a natural rubber and a butadiene rubber in which the mass ratio of the content of the natural rubber to the content of the butadiene rubber is 30 / 70 to 80 / 20, a flame retardant comprising a bromine-based flame retardant and antimony trioxide, a hydrocarbon-based wax (W), a filler, an antioxidant comprising an amine-based antioxidant, a vulcanization accelerator, and sulfur, in which the content of the hydrocarbon-based wax (W) is 2.5 parts by mass or less per 100 parts by mass of the rubber component, the mass ratio between the content of the bromine-based flame retardant and the content of the hydrocarbon-based wax (W) is 8.0 or higher, the hydrocarbon-based wax (W) includes a hydrocarbon-based wax (w1) having a melting point of 65°C or higher, and the content of the amine-based antioxidant is 3.0 parts by mass or higher per 100 parts by mass of the rubber component; and a conveyor belt formed using the rubber composition.

Description

Rubber composition for conveyor belt and conveyor belt

[0001] The present invention relates to a rubber composition for a conveyor belt and a conveyor belt.

[0002] It has been known that a rubber composition containing butadiene rubber or the like can be used for a conveyor belt (for example, see Patent Document 1).

[0003] International Publication No. 2017 / 141909

[0004] Vulcanized rubber obtained from a rubber composition containing butadiene rubber (BR) and wax is prone to blooming of wax and other additives. When the cover rubber layer of a conveyor belt is formed from the rubber composition, excessive blooming of wax and other additives on the surface of the cover rubber layer can cause the bloomed wax and other additives to adhere to the rollers, which in turn can cause lime powder to adhere to the cover rubber layer, resulting in a deterioration in the conveyor belt's resistance to riding over the rollers, i.e., poor conveyor belt running performance. In recent years, mining plants and steel mills that use conveyor belts have been increasingly demanding flame-retardant conveyor belts due to reduced operating rates caused by fires and safety measures. While conveyor belts have been flame-retarded by adding flame retardants, there is a need for the development of flame-retardant conveyor belts with added value, such as improved weather resistance (ozone resistance), abrasion resistance, and belt running performance. As described above, it is known that adding a flame retardant to a rubber composition can make rubber flame-retardant, but adding a flame retardant to a rubber composition can sometimes deteriorate the physical properties of the resulting vulcanized rubber (e.g., belt running performance (power saving), etc.) In this context, the present inventors evaluated rubber compositions containing butadiene rubber (BR), a flame retardant, wax, etc., and found that such rubber compositions can sometimes deteriorate the ozone resistance of the resulting vulcanized rubber.

[0005] Therefore, an object of the present invention is to provide a rubber composition that, when vulcanized, has excellent flame retardancy, ozone resistance, bloom resistance, and power saving properties. Another object of the present invention is to provide a conveyor belt.

[0006] As a result of intensive research by the present inventors to solve the above-mentioned problems, the present inventors have discovered a rubber composition comprising: a rubber component containing natural rubber and butadiene rubber, wherein the mass ratio of the content of the natural rubber to the content of the butadiene rubber is within a predetermined range; a flame retardant containing a brominated flame retardant and antimony trioxide; a hydrocarbon wax (W); a filler; an antiaging agent containing an amine-based antiaging agent; a vulcanization accelerator; and sulfur; wherein the content of the hydrocarbon wax (W), the mass ratio of the content of the brominated flame retardant to the content of the hydrocarbon wax (W), and the content of the amine-based antiaging agent are each within a specific numerical range; The present inventors have found that when the hydrocarbon wax (W) contains a hydrocarbon wax (w1) having a melting point of 65°C or higher, the resulting vulcanized rubber is imparted with flame retardancy, the vulcanized rubber is excellent in power saving, and the ozone resistance and the bloom resistance (suppression of excessive blooming of antioxidants, etc.) are balanced, thereby simultaneously improving the ozone resistance and the bloom resistance, thereby arriving at the present invention. The present invention is based on the above findings and more particularly aims to solve the above problems by the following configuration.

[0007] [1] A rubber component containing natural rubber and butadiene rubber, wherein the mass ratio of the content of the natural rubber to the content of the butadiene rubber (natural rubber / butadiene rubber) is 30 / 70 to 80 / 20; a flame retardant containing a brominated flame retardant and antimony trioxide; a hydrocarbon wax (W); a filler; an antioxidant containing an amine-based antioxidant; a vulcanization accelerator; and sulfur, wherein the content of the hydrocarbon wax (W) is 2.5 parts by mass or less per 100 parts by mass of the rubber component; the mass ratio of the content of the brominated flame retardant to the content of the hydrocarbon wax (W) (brominated flame retardant / hydrocarbon wax (W)) is 8.0 or more; and the hydrocarbon wax (W) includes a hydrocarbon wax (w1) having a melting point of 65°C or more. A rubber composition for a conveyor belt, wherein the content of the amine-based antioxidant is 3.0 parts by mass or more per 100 parts by mass of the rubber component. [2] The rubber composition for a conveyor belt according to [1], wherein the mass ratio of the content of the natural rubber to the content of the butadiene rubber is 40 / 60 to 70 / 30. [3] The rubber composition for a conveyor belt according to [1] or [2], wherein the mass ratio of the content of the brominated flame retardant to the content of the hydrocarbon wax (W) is 10 to 20. [4] The rubber composition for a conveyor belt according to any one of [1] to [3], wherein the hydrocarbon wax (w1) contains normal paraffin, and the carbon number at the peak top of the carbon number distribution of the normal paraffin is within a range of 30 to 40. [5] The rubber composition for a conveyor belt according to any one of [1] to [4], wherein the hydrocarbon wax (w1) contains normal paraffin, and the content of the normal paraffin in the hydrocarbon wax (w1) is 80 mass % or more. [6] The rubber composition for a conveyor belt according to any one of [1] to [5], wherein the amine-based antioxidant contains a p-phenylenediamine-based compound. [7] The rubber composition for a conveyor belt according to any one of [1] to [6], wherein the bromine-based flame retardant contains a compound represented by the following formula (1): In formula (1), R represents an aliphatic hydrocarbon group which may contain an unsaturated bond. [8] The rubber composition for a conveyor belt according to any one of [1] to [7], wherein the hydrocarbon wax (W) further contains a hydrocarbon wax (w2) having a melting point of less than 65°C. [9] The rubber composition for a conveyor belt according to [8], wherein the hydrocarbon wax (w2) contains normal paraffin, and the carbon number at the peak top of the carbon number distribution of the normal paraffin is within the range of 25 to 35.

[10] The rubber composition for a conveyor belt according to [8] or [9], wherein the hydrocarbon wax (w2) contains normal paraffin, and the content of the normal paraffin in the hydrocarbon wax (w2) is 80 mass% or more.

[11] A conveyor belt formed using the rubber composition for a conveyor belt according to any one of [1] to

[10] .

[12] The conveyor belt according to

[11] , which has a cover rubber formed using the rubber composition.

[0008] According to the present invention, it is possible to provide a rubber composition that, when vulcanized, has excellent flame retardancy, ozone resistance, bloom resistance, and power saving properties, and a conveyor belt formed using the rubber composition.

[0009] Fig. 1 is a cross-sectional view of an embodiment of a conveyor belt of the present invention, and Fig. 2 is a cross-sectional view of another embodiment of a conveyor belt of the present invention.

[0010] The present invention will be described in detail below. In this specification, a numerical range expressed using "to" means a range including the numerical values ​​written before and after "to". In this specification, unless otherwise specified, there are no particular limitations on the manufacturing method of each component. For example, conventionally known methods can be used. In this specification, unless otherwise specified, each component can be used alone or in combination of two or more substances corresponding to that component. When a component contains two or more substances, the content of the component means the total content of the two or more substances.

[0011] [Rubber Composition] The rubber composition for a conveyor belt of the present invention (rubber composition of the present invention) contains: a rubber component containing natural rubber and butadiene rubber, wherein the mass ratio of the content of the natural rubber to the content of the butadiene rubber (natural rubber / butadiene rubber) is 30 / 70 to 80 / 20; a flame retardant containing a brominated flame retardant and antimony trioxide; a hydrocarbon wax (W); a filler; an antioxidant containing an amine-based antioxidant; a vulcanization accelerator; and sulfur, wherein the content of the hydrocarbon wax (W) is 2.5 parts by mass or less per 100 parts by mass of the rubber component; the mass ratio of the content of the brominated flame retardant to the content of the hydrocarbon wax (W) (brominated flame retardant / hydrocarbon wax (W)) is 8.0 or more; and the hydrocarbon wax (W) includes a hydrocarbon wax (w1) having a melting point of 65°C or more. In the rubber composition for a conveyor belt, the content of the amine-based antioxidant is 3.0 parts by mass or more per 100 parts by mass of the rubber component.

[0012] The rubber composition of the present invention is believed to achieve the desired effects due to its composition. The reasons for this are unclear, but are presumed to be as follows. Typically, brominated flame retardants and antimony trioxide are not incorporated into the polymer crosslinks of the vulcanized rubber after the rubber composition is vulcanized. Therefore, similar to the addition of fillers without reinforcing properties, vulcanized rubbers containing such flame retardants suffer from deterioration in physical properties other than flame retardancy (e.g., ozone resistance, energy efficiency, etc.). The cause of this deterioration in physical properties is unclear, but possible causes include decomposition of the flame retardant during processing and excessive blooming of wax, etc. The deterioration in ozone resistance is presumed to be due to physical inhibition caused by the presence of the flame retardant as a filler, as well as consumption of the antioxidant due to flame retardant decomposition during processing and over time. Regarding the above-mentioned problem, the present invention has discovered that the ozone resistance of vulcanized rubbers containing flame retardants can be improved by using antioxidants, including amine-based antioxidants, in amounts greater than or equal to the specified amount. Regarding excessive blooming of wax, etc., in the present invention, the addition of a flame retardant as a filler suppresses (physically inhibits) the blooming of the hydrocarbon wax (W), which is believed to improve blooming resistance. Antioxidants are generally carried to the surface of the vulcanized rubber by the blooming effect of the wax and present on the surface (i.e., in a bloomed state), preventing the vulcanized rubber from deteriorating when exposed to the outside air. Therefore, the formation of a wax coating on the vulcanized rubber surface and the presence of the carried antioxidant are necessary conditions for achieving ozone resistance, and an appropriate amount of wax is required. On the other hand, adding an excessive amount of wax to a rubber composition to improve ozone resistance results in excessive blooming on the vulcanized rubber surface, which causes the transported material to adhere to the bloom, resulting in a physical deterioration of runnability (reduced power saving). As such, it has been extremely difficult to achieve high levels of both ozone resistance and blooming resistance while improving power saving. Regarding the above-mentioned problem, it has been found in the present invention that by including a hydrocarbon wax (W) containing a hydrocarbon wax (w1) in an amount not greater than a specified amount, it is possible to achieve high levels of both ozone resistance and bloom resistance and improve power saving properties.The present inventors speculate that the reason for this is that the hydrocarbon wax (W) containing the hydrocarbon wax (w1) plays a role as a processing agent to address poor dispersion of the flame retardant, filler, etc. in the rubber composition, thereby improving the processability of the rubber composition (dispersibility of the flame retardant, filler, etc.) Hereinafter, each component contained in the rubber composition of the present invention will be described in detail.

[0013] [Rubber Component] The rubber composition of the present invention contains a rubber component, which includes natural rubber and butadiene rubber. By including natural rubber and butadiene rubber as the rubber components in the rubber composition of the present invention, the vulcanized rubber obtained has excellent ozone resistance, bloom resistance, and abrasion resistance.

[0014] [Natural Rubber] In the rubber composition of the present invention, the natural rubber (NR) contained as the rubber component is not particularly limited, and examples thereof include conventionally known natural rubbers.

[0015] [Butadiene Rubber] In the rubber composition of the present invention, the butadiene rubber (BR) contained as a rubber component is not particularly limited. Examples include conventionally known butadiene rubbers. One preferred embodiment of the BR is, for example, polybutadiene, which is solid at 23°C. The BR may be unmodified or modified.

[0016] From the viewpoint of achieving better power saving and wear resistance, the weight-average molecular weight of BR is preferably 200,000 or more, and more preferably 300,000 to 1,000,000. In this specification, the weight-average molecular weight (Mw) of BR can be a standard polystyrene-equivalent value obtained by gel permeation chromatography (GPC) measurement under the following conditions: Solvent: tetrahydrofuran Detector: RI detector

[0017] [Mass Ratio of Natural Rubber Content to Butadiene Rubber Content] In the rubber composition of the present invention, the mass ratio of the natural rubber content to the butadiene rubber content (natural rubber / butadiene rubber) is 30 / 70 to 80 / 20. When the rubber composition of the present invention has this mass ratio in the above range, it has excellent ozone resistance, bloom resistance, and power saving properties.

[0018] The mass ratio of the content of natural rubber to the content of butadiene rubber is preferably 40 / 60 to 70 / 30, and more preferably 50 / 50 to 70 / 30, from the viewpoint of achieving better ozone resistance and bloom resistance.

[0019] (Total Content of Natural Rubber and Butadiene Rubber) From the viewpoint of achieving better ozone resistance, the total content of the natural rubber and the butadiene rubber is preferably 80 to 100% by mass, and more preferably 100% by mass, of the total amount of the rubber component.

[0020] (Other Rubbers) When the total content of natural rubber and butadiene rubber is less than 100% by mass of the total amount of the rubber component, the rubber component may further contain rubbers other than natural rubber and butadiene rubber (other rubbers).

[0021] (Rubber Component Content) The rubber component (total amount) content may be 50 to 90 mass% of the total rubber composition. From the viewpoint of achieving better ozone resistance and bloom resistance, the rubber component (total amount) content is preferably 50 to 80 mass% of the total rubber composition.

[0022] [Flame Retardant] The rubber composition of the present invention contains a flame retardant, and the flame retardant contains a brominated flame retardant and antimony trioxide. By containing the flame retardant in the rubber composition of the present invention, the resulting vulcanized rubber has excellent flame retardancy and bloom resistance.

[0023] [Brominated Flame Retardant] The brominated flame retardant is a flame retardant containing bromine. In the present invention, the brominated flame retardant can also function as a filler. From the viewpoint of achieving better flame retardancy, the brominated flame retardant preferably contains a brominated flame retardant having a melting point of 300°C or higher. From the viewpoint of achieving better flame retardancy and bloom resistance, the brominated flame retardant preferably contains a compound having bromine and an aromatic hydrocarbon skeleton. Examples of the aromatic hydrocarbon skeleton include a benzene skeleton and a biphenylene skeleton. The bromine and the aromatic hydrocarbon skeleton can be directly bonded. The brominated flame retardant containing bromine and an aromatic hydrocarbon skeleton may further contain an aliphatic hydrocarbon group (a saturated aliphatic hydrocarbon group or an unsaturated aliphatic hydrocarbon group) that may contain an unsaturated bond.

[0024] From the viewpoint of achieving better flame retardancy and bloom resistance, the brominated flame retardant preferably contains a compound represented by the following formula (1), and more preferably contains bis(pentabromophenyl)ethane. In formula (1), R represents an aliphatic hydrocarbon group which may contain an unsaturated bond.

[0025] In formula (1), the aliphatic hydrocarbon group represented by R (hereinafter referred to as "R") which may contain an unsaturated bond includes a saturated aliphatic hydrocarbon group or an unsaturated aliphatic hydrocarbon group. A preferred embodiment of R is a saturated aliphatic hydrocarbon group. R may be linear, branched, cyclic, or a combination thereof, but a preferred embodiment is linear. The number of carbon atoms in R is not particularly limited. For example, it can be 1 to 10. The number of carbon atoms is preferably 2 to 8.

[0026] Examples of the saturated aliphatic hydrocarbon group include methylene, ethylene, trimethylene, propylene, butylene, pentylene, hexylene, heptylene, and octylene. Examples of the unsaturated bond that R may have include vinyl, vinylene, ethynyl, and ethynylene. When R is an unsaturated aliphatic hydrocarbon group, examples of the unsaturated aliphatic hydrocarbon group include the unsaturated bonds listed above, or combinations of the saturated aliphatic hydrocarbon group and the unsaturated bonds listed above.

[0027] An example of the compound represented by formula (1) is bis(pentabromophenyl)ethane.

[0028] [Antimony Trioxide] In the present invention, antimony trioxide (Sb ２ O ３ ) is not particularly limited. Antimony trioxide can function as a flame retardant aid for the above-mentioned bromine-based flame retardants. In the present invention, antimony trioxide is treated as a flame retardant. In the present invention, antimony trioxide can also function as a filler.

[0029] (Brominated Flame Retardant Content) From the viewpoint of achieving better flame retardancy, the brominated flame retardant content is preferably 10 to 40 parts by mass, more preferably 15 to 30 parts by mass, per 100 parts by mass of the rubber component.

[0030] (Antimony Trioxide Content) From the viewpoint of achieving better flame retardancy, the content of antimony trioxide is preferably 3 to 12 parts by mass, and more preferably 4 to 9 parts by mass, per 100 parts by mass of the rubber component.

[0031] (Total Content of Brominated Flame Retardant and Antimony Trioxide in Total Amount of Flame Retardant) From the viewpoint of achieving better flame retardant performance, the total content of the brominated flame retardant and antimony trioxide is preferably 80 to 100 mass % of the total amount of flame retardant, and more preferably 100 mass %.

[0032] (Total Content of Brominated Flame Retardant and Antimony Trioxide Per 100 Parts by Mass of Rubber Component) From the viewpoint of more excellent flame retardancy, the total content of the brominated flame retardant and antimony trioxide per 100 parts by mass of the rubber component is preferably 15 to 50 parts by mass, more preferably 20 to 40 parts by mass, and even more preferably 25 to 35 parts by mass.

[0033] (Other Flame Retardants) The flame retardant may further contain a flame retardant (other flame retardant) other than a brominated flame retardant and antimony trioxide. The other flame retardant is not particularly limited as long as it is a compound that can impart flame retardancy (however, excluding brominated flame retardants and antimony trioxide). In one preferred embodiment, the rubber composition of the present invention does not contain chlorinated paraffin.

[0034] [Hydrocarbon Wax (W)] The hydrocarbon wax (W) contained in the rubber composition of the present invention contains an aliphatic hydrocarbon compound as a main component. The hydrocarbon wax (W) is solid at room temperature (e.g., 23°C). The hydrocarbon wax (W) may be any of a linear aliphatic hydrocarbon compound (normal paraffin), a branched aliphatic hydrocarbon compound (e.g., isoparaffin), or an alicyclic aliphatic hydrocarbon compound, or a mixture thereof (e.g., commonly referred to as paraffin. The paraffin typically includes normal paraffin and isoparaffin). The aliphatic hydrocarbon compound contained in the hydrocarbon wax (W) is preferably composed only of carbon and hydrogen. Examples of the hydrocarbon wax (W) include those generally referred to as paraffin wax, microwax (microcrystalline wax), and solid wax. The above statement "The hydrocarbon wax (W) contains an aliphatic hydrocarbon compound as a main component. ... Examples include those referred to as solid waxes" also applies to the hydrocarbon waxes (w1) and (w2) described below.

[0035] [Hydrocarbon Wax (w1)] In the present invention, the hydrocarbon wax (W) includes a hydrocarbon wax (w1) having a melting point of 65°C or higher.

[0036] [Melting Point of Hydrocarbon Wax (w1)] In the present invention, the melting point of the hydrocarbon wax (w1) is 65°C or higher. By using the hydrocarbon wax (w1) at a melting point of 65°C or higher, the rubber composition of the present invention provides a vulcanized rubber with excellent ozone resistance. Furthermore, when the temperature of the environment in which the vulcanized rubber is used is high (e.g., 20°C or higher), the hydrocarbon wax (W) in the vulcanized rubber is likely to bleed to form a wax coating. Furthermore, the wax coating can be formed over a long period of time. The melting point of the hydrocarbon wax (w1) can be 100°C or lower. The melting point of the hydrocarbon wax (w1) is preferably 65 to 90°C, from the viewpoint of achieving superior effects of the present invention. In the present invention, the melting point of the hydrocarbon wax (W) can be measured in accordance with JIS K2235:2022 (Petroleum Wax).

[0037] (Normal paraffin) The hydrocarbon wax (w1) preferably contains normal paraffin, from the viewpoints that the effects of the present invention are more excellent, the wax coating formed by bleeding of the hydrocarbon wax (W) in the vulcanized rubber is more likely to be uniform, and flexibility, adhesion to the rubber, and stability are excellent.

[0038] (Carbon number distribution of normal paraffins) When the hydrocarbon wax (w1) contains normal paraffins, the carbon number distribution of the normal paraffins contained in the hydrocarbon wax (w1) may be, for example, 15 to 50 carbon atoms. In other words, the normal paraffins contained in the hydrocarbon wax (w1) may be, for example, a mixture of linear saturated aliphatic hydrocarbon compounds having 15 to 50 carbon atoms. From the viewpoints of achieving a better effect of the present invention, facilitating the formation of the wax coating in a high temperature range, and enabling the formation of the wax coating over a long period of time, the normal paraffins that can be contained in the hydrocarbon wax (w1) preferably have a carbon number at the peak top of the carbon number distribution in the range of 30 to 40, and more preferably in the range of 32 to 35.

[0039] (Normal paraffin content) When the hydrocarbon wax (w1) contains normal paraffin, the content of the normal paraffin in the hydrocarbon wax (w1) is preferably 80% by mass or more, and more preferably 85 to 95% by mass, from the viewpoints that the effects of the present invention are better, the wax coating formed by bleeding of the hydrocarbon wax (W) in the vulcanized rubber is more likely to be uniform, and flexibility, adhesion to rubber, and stability are excellent.

[0040] (Method for measuring carbon number of components contained in hydrocarbon wax (W) and content of the components) In the present invention, the carbon number distribution of components (e.g., normal paraffin) contained in the hydrocarbon wax (W) and the content of the components were analyzed under the following conditions. Analytical apparatus: Gas chromatograph <GC-17A> manufactured by Shimadzu Corporation Column: Ultra ALLOY UA1 (MS / HT) 15 m x 0.25 mm x 0.25 μm Injection port temperature, detector temperature: 420° C. Detector: FID Dilution solvent: cyclohexane Heating condition: 10° C. / min

[0041] (Hydrocarbon Wax (w2)) From the viewpoint of achieving better effects of the present invention (particularly power saving) and widening the use temperature range of the resulting vulcanized rubber to, for example, −30 to +60° C., it is preferable that the hydrocarbon wax (W) further contains a hydrocarbon wax (w2) having a melting point of less than 65° C.

[0042] (Melting Point of Hydrocarbon Wax (w2)) From the viewpoint of achieving a superior effect of the present invention and broadening the range of the working temperature of the resulting vulcanized rubber, the melting point of the hydrocarbon wax (w2) is preferably 30° C. or higher and lower than 65° C. The melting point of the hydrocarbon wax (w2) can be measured in the same manner as described above.

[0043] (Normal paraffin) The hydrocarbon wax (w2) preferably contains normal paraffin, from the viewpoints that the effects of the present invention are more excellent, the wax coating formed by bleeding of the hydrocarbon wax (W) in the vulcanized rubber is likely to be uniform not only in high temperature ranges but also in low temperature ranges (for example, below 20°C), and flexibility, adhesion to rubber, and stability are excellent.

[0044] (Carbon number distribution of normal paraffins) When the hydrocarbon wax (w2) contains normal paraffins, the carbon number distribution of the normal paraffins contained in the hydrocarbon wax (w2) may be, for example, 15 to 45 carbon atoms. That is, the normal paraffins contained in the hydrocarbon wax (w2) may be, for example, a mixture of linear saturated aliphatic hydrocarbon compounds having 15 to 45 carbon atoms. From the viewpoints of achieving a better effect of the present invention, facilitating the formation of the wax coating not only in high temperature ranges but also in low temperature ranges (for example, below 20°C), and enabling the formation of the wax coating over a long period of time, the normal paraffins that can be contained in the hydrocarbon wax (w2) preferably have a carbon number at the peak top of the carbon number distribution in the range of 25 to 35, and more preferably in the range of 27 to 30.

[0045] (Normal paraffin content) When the hydrocarbon wax (w2) contains normal paraffin, the content of the normal paraffin is preferably 80% by mass or more, and more preferably 80 to 90% by mass, of the hydrocarbon wax (w2), from the viewpoints that the effects of the present invention are better, the wax coating formed by bleeding of the hydrocarbon wax (W) in the vulcanized rubber is likely to become uniform even under low temperature conditions, and flexibility, adhesion to rubber, and stability are excellent.

[0046] [Content of Hydrocarbon Wax (W)] In the rubber composition of the present invention, the content of the hydrocarbon wax (W) is 2.5 parts by mass or less per 100 parts by mass of the rubber component. When the content of the hydrocarbon wax (W) is in the above amount, the rubber composition of the present invention provides a vulcanized rubber with excellent bloom resistance. From the viewpoint of achieving even better effects of the present invention (particularly bloom resistance), the content of the hydrocarbon wax (W) is more preferably 1.0 to 2.0 parts by mass per 100 parts by mass of the rubber component. Note that at least a part or all of the content of the hydrocarbon wax (W) can be the content of the hydrocarbon wax (w1).

[0047] (Mass ratio of hydrocarbon wax (w1) to hydrocarbon wax (w2)) When the hydrocarbon wax (W) further contains a hydrocarbon wax (w2), the content of the hydrocarbon wax (w1) is preferably 50 to 90 mass%, and more preferably 55 to 70 mass%, of the total amount of the hydrocarbon wax (W), from the viewpoint of achieving better effects of the present invention (particularly, ozone resistance, bloom resistance, and power saving). When the hydrocarbon wax (W) further contains a hydrocarbon wax (w2), the content of the hydrocarbon wax (w2) can be the amount remaining after subtracting the above-mentioned content of the hydrocarbon wax (w1) from the total amount of the hydrocarbon wax (W).

[0048] [Mass Ratio of Brominated Flame Retardant Content to Hydrocarbon Wax (W)] In the rubber composition of the present invention, the mass ratio of the brominated flame retardant content to the hydrocarbon wax (W) content (brominated flame retardant / hydrocarbon wax (W)) is 8.0 or more. When the mass ratio is as described above, the rubber composition of the present invention provides a vulcanized rubber having excellent ozone resistance, power saving properties, and bloom resistance. Furthermore, when the mass ratio is as described above, even when the amount of brominated flame retardant is varied, the hydrocarbon wax (W) can compensate for the disadvantages of adding a brominated flame retardant.

[0049] The mass ratio (brominated flame retardant / hydrocarbon wax (W)) is preferably 10 or more and 20 or less, from the viewpoint of obtaining a vulcanized rubber with better bloom resistance.

[0050] [Filler] The rubber composition of the present invention contains a filler. However, the filler does not include brominated flame retardants and antimony trioxide as the flame retardants. By including a filler in the rubber composition of the present invention, the vulcanized rubber obtained has excellent ozone resistance, bloom resistance, flame retardancy, and power saving properties. Examples of the filler include white fillers such as carbon black and silica. From the viewpoint of further improving the power saving properties and improving the mechanical strength of the vulcanized rubber obtained, it is preferable that the filler contains carbon black and / or silica.

[0051] (Carbon Black) When the rubber composition of the present invention contains carbon black (CB) as a filler, the carbon black has a nitrogen adsorption specific surface area of ​​20 to 100 m ２ / g and / or dibutyl phthalate oil absorption of 70 to 120 cm ３ It is preferable that the carbon black has a nitrogen adsorption specific surface area of ​​20 to 100 m / 100 g. ２ / g, and the dibutyl phthalate oil absorption is 70 to 120 cm ３ It is preferable that the composition contains carbon black having a density of 100 g / 100 g.

[0052] (Nitrogen adsorption specific surface area of ​​CB) N of CB ２ SA is set to 20 to 100 m from the viewpoint that the power saving of the obtained vulcanized rubber is more excellent. ２ / g, and 30 to 70m ２ / g. The nitrogen adsorption specific surface area (N ２ SA) can be measured in accordance with JIS K6217-2:2017.

[0053] (Dibutyl phthalate oil absorption of CB) From the viewpoint of obtaining a vulcanized rubber with better power saving properties, the DBP of CB is 70 to 120 cm ３ / 100g, and 70 to 90cm ３ The dibutyl phthalate oil absorption (DBP) of carbon black can be measured in accordance with JIS K6217-4:2017.

[0054] (Silica) When the rubber composition of the present invention contains silica as a filler, the silica is not particularly limited. For example, conventionally known silica can be used. Specific examples include wet silica, dry silica, and fumed silica.

[0055] (Filler Content) The filler content is preferably 20 to 50 parts by mass, and more preferably 20 to 40 parts by mass, per 100 parts by mass of the rubber component, from the viewpoint of achieving better power saving properties and mechanical strength of the resulting vulcanized rubber.

[0056] [Antiaging Agent] The rubber composition of the present invention contains an antioxidant, and the antioxidant includes an amine-based antioxidant. By containing the amine-based antioxidant, the vulcanized rubber obtained from the rubber composition of the present invention has excellent ozone resistance.

[0057] [Amine-Based Antiaging Agent] The amine-based antiaging agent contained as an antiaging agent in the rubber composition of the present invention has an amino group (—NH ２ ) or an imino group (—NH—). Examples of the amine-based antioxidant include diamine-based compounds such as p-phenylenediamine-based compounds and monoamine-based compounds such as p,p′-dioctyldiphenylamine.

[0058] (p-Phenylenediamine Compound) From the viewpoint of obtaining a vulcanized rubber with superior ozone resistance, the amine antioxidant preferably contains a diamine compound, and more preferably contains a p-phenylenediamine compound. The p-phenylenediamine compound is a compound having a p-phenylenediamine skeleton. The two nitrogen atoms in the p-phenylenediamine skeleton can each independently form an amino group or an imino group, and it is preferable that at least one of the nitrogen atoms is an imino group, and more preferably that both are imino groups. Examples of p-phenylenediamine compounds include N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), N,N'-dinaphthyl-p-phenylenediamine (DNPD), and N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD). The p-phenylenediamine compound preferably contains N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, from the viewpoint that the resulting vulcanized rubber has better ozone resistance.

[0059] [Content of Amine-Based Antiaging Agent] In the rubber composition of the present invention, the content of the amine-based antiaging agent is 3.0 parts by mass or more per 100 parts by mass of the rubber component. When the content of the amine-based antiaging agent is in the above amount, the vulcanized rubber obtained from the rubber composition of the present invention has excellent ozone resistance. From the viewpoint of achieving even better ozone resistance and bloom resistance, the content of the amine-based antiaging agent is preferably 3.0 to 5.0 parts by mass, more preferably 3.0 to 4.0 parts by mass, per 100 parts by mass of the rubber component.

[0060] [Vulcanization Accelerator] The rubber composition of the present invention contains a vulcanization accelerator. The vulcanization accelerator is not particularly limited as long as it is one that is used in rubber vulcanization. Examples of vulcanization accelerators include sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazolylsulfenamide (CZ) and N-tert-butyl-2-benzothiazolylsulfenamide (NS); thiuram-based vulcanization accelerators such as tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); and guanidine-based vulcanization accelerators such as diphenylguanidine (DPG). From the viewpoint of achieving superior flame retardancy and power saving, the vulcanization accelerator preferably contains a sulfenamide-based vulcanization accelerator. From the viewpoint of achieving superior flame retardancy and power saving, the content of the vulcanization accelerator is preferably 0.5 to 8.0 parts by mass per 100 parts by mass of the rubber component.

[0061] [Sulfur] The rubber composition of the present invention contains sulfur. There are no particular limitations on the sulfur as long as it is used in vulcanizing rubber. For example, conventionally known sulfur can be used. From the viewpoint of achieving better flame retardancy and power saving properties, as well as excellent rubber physical properties, the sulfur content is preferably 0.5 to 5.0 parts by mass per 100 parts by mass of the rubber component.

[0062] (Additives) The rubber composition of the present invention may further contain additives in addition to the above-mentioned components, such as zinc oxide, stearic acid, and a vulcanization retarder.

[0063] (Production Method) The method for producing the rubber composition of the present invention is not particularly limited, and may be, for example, a method in which the above-mentioned essential components and any additives that may be further used as needed are mixed in a Banbury mixer or the like.

[0064] (Vulcanization) The rubber composition of the present invention can be vulcanized under ordinary conditions. The vulcanization temperature can be, for example, 120 to 180° C. Pressure may be applied during vulcanization.

[0065] (Applications) Applications of the rubber composition of the present invention include, for example, conveyor belts.

[0066] [Conveyor Belt] The conveyor belt of the present invention is a conveyor belt formed using the rubber composition of the present invention.

[0067] The rubber composition used in the conveyor belt of the present invention is not particularly limited as long as it is the rubber composition of the present invention. The conveyor belt of the present invention is not particularly limited except that it is formed using the rubber composition of the present invention. Since the conveyor belt of the present invention is formed using the above-mentioned rubber composition of the present invention, it has excellent flame retardancy, ozone resistance, bloom resistance, and power saving properties.

[0068] There is no particular limitation on which component of the conveyor belt of the present invention the rubber composition of the present invention is applied to, and all or a part of the rubber constituting the conveyor belt of the present invention may be formed from the rubber composition of the present invention.

[0069] The vulcanized rubber obtained from the rubber composition of the present invention has excellent ozone resistance, bloom resistance, flame retardancy, and power saving properties, and therefore, one of the preferred embodiments of the conveyor belt of the present invention is one in which the cover rubber is formed using the rubber composition of the present invention.

[0070] An embodiment of a conveyor belt according to the present invention will be described below with reference to the accompanying drawings. However, the present invention is not limited to the accompanying drawings. FIG. 1 is a cross-sectional view of an embodiment of a conveyor belt according to the present invention. The embodiment of the conveyor belt according to the present invention shown in FIG. 1 (herein also referred to as a first embodiment of the conveyor belt according to the present invention) is a conveyor belt 4 in which a fabric layer 1 is coated with a coating rubber (bonded rubber) 2 to form a core layer, and the outer periphery of the core layer is covered with a cover rubber 3. The cover rubber 3 is preferably formed using the rubber composition of the present invention. In FIG. 1, the conveyor belt 4 has the fabric layer 1 as the core material, and the number of layers of the fabric layer 1, the thickness of the cover rubber 3, the belt width, etc. can be appropriately determined depending on the intended use. Examples of the fabric layer include canvas made of a woven fabric of synthetic fibers such as nylon, vinylon, and polyester. The thickness T of the cover rubber 3 is 1 / 2 mm. １ , T ２ In normal cases, each of these can be set to about 1.5 to 20 mm.

[0071] Furthermore, a coating rubber used in known conveyor belts can be used as the coating rubber 2. For example, a rubber composition containing natural rubber (NR), acrylonitrile-butadiene rubber (NBR), styrene-butadiene copolymer rubber (SBR), butadiene rubber (BR), ethylene-propylene rubber (EPT), ethylene-propylene-diene rubber (EPDM), or the like as a rubber component can be used as the coating rubber.

[0072] Next, a second embodiment of the conveyor belt of the present invention will be described with reference to FIG. 2. FIG. 2 is a cross-sectional view of another embodiment of the conveyor belt of the present invention. As shown in FIG. 2, the second embodiment of the conveyor belt of the present invention is a conveyor belt 8 in which a steel cord 5 is coated with cushion rubber (adhesive rubber) 6 to form a core layer, and the outer periphery of the core layer is covered with cover rubber 7. The cover rubber 7 is preferably formed using the rubber composition of the present invention. The conveyor belt 8 can be formed, for example, by arranging approximately 50 to 230 steel cords 5, each having a diameter of approximately 2.0 to 9.5 mm, in parallel, each of which is formed by twisting together a plurality of wires having a diameter of approximately 0.2 to 0.4 mm. Generally, the total thickness T of the conveyor belt 8 can be approximately 10 to 50 mm. Furthermore, the cushion rubber 6 can be, for example, an adhesive rubber that can be bonded to galvanized steel cords used in known steel conveyor belts. As the cushion rubber, specifically, for example, a rubber composition containing natural rubber (NR), acrylonitrile-butadiene rubber (NBR), styrene-butadiene copolymer rubber (SBR), butadiene rubber (BR), or the like as a rubber component can be used.

[0073] The conveyor belt of the present invention can be produced, for example, by interposing a fabric layer, steel cords, or a core layer, etc., which will serve as a core material, between unvulcanized rubber sheets formed from the rubber composition of the present invention, and vulcanizing the resulting mixture by heating and pressurizing it, for example, at about 120 to 180°C, at about 0.1 to 4.9 MPa, and for about 10 to 90 minutes.

[0074] The conveyor belt of the present invention can be used under temperature conditions of, for example, -30 to +60°C.

[0075] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0076] <Production of Rubber Compositions> Each component in Table 1 below was used in the composition (parts by mass) shown in the table and mixed in a Banbury mixer to produce each rubber composition (unvulcanized).

[0077] (Preparation of vulcanized rubber sheets) Each rubber composition (unvulcanized) prepared as described above was vulcanized for 30 minutes using a press molding machine at 148°C under a surface pressure of 3.0 MPa to prepare a vulcanized rubber sheet measuring 150 mm in length, 150 mm in width and 2 mm in thickness.

[0078] <Evaluation> The vulcanized rubber sheets prepared as described above were subjected to the following evaluations. The results are shown in Table 1.

[0079] (Ozone Resistance) In accordance with JIS K6259-1:2015, each vulcanized rubber sheet prepared as described above was placed in an ozone tank (40°C, 50 pphm) and left at 20% elongation for 96, 168, 336, and 504 hours to undergo an ozone resistance test (accelerated test). After the ozone resistance test, the surface of the vulcanized rubber sheet was visually observed. If the vulcanized rubber sheet did not show any cracks after the ozone resistance test at each time point, this was indicated as "N.C.". - Evaluation Criteria for Ozone Resistance In the present invention, if the vulcanized rubber sheet did not show any cracks after the ozone resistance test at 504 hours, the resulting vulcanized rubber was evaluated as having excellent ozone resistance. If cracks occurred in the vulcanized rubber sheet after the ozone resistance test after 504 hours but no cracks occurred in the vulcanized rubber sheet after the ozone resistance test after 336 hours, the ozone resistance of the resulting vulcanized rubber was evaluated as being somewhat excellent. In the present invention, if there were no cracks in the vulcanized rubber sheet after the ozone resistance test after at least 336 hours, the ozone resistance of the resulting vulcanized rubber was evaluated as being excellent. On the other hand, if cracks occurred in the vulcanized rubber sheet after the ozone resistance test after 336 hours, the ozone resistance of the resulting vulcanized rubber was evaluated as being poor. If cracks occurred in the vulcanized rubber sheet after the ozone resistance test after 336 hours, the level of the cracks was evaluated in accordance with JIS K6259-1:2015 and indicated by a combination of letters and numbers, such as the above level "C2." In the present invention, if cracks occurred in the vulcanized rubber sheet after the ozone resistance test even when the elapsed time in the ozone resistance test was the same, levels "B" and "C" were considered to have worse ozone resistance than level "A." Furthermore, when the alphabet of the level is the same, the larger the number after the alphabet, the worse the ozone resistance.

[0080] (Bloom Resistance) A bloom test was conducted in which each vulcanized rubber sheet prepared as described above was placed at 23±2°C for 5 weeks. After the bloom test, the vulcanized rubber sheet was visually observed. - Evaluation Criteria for Bloom Resistance In the present invention, if no or almost no bloom (whitening of the surface of the vulcanized rubber sheet) was visually observed on the vulcanized rubber sheet after the bloom test, the bloom resistance of the obtained vulcanized rubber was evaluated as very excellent and given a rating of "1." If some bloom was observed on the vulcanized rubber sheet after the bloom test, the bloom resistance of the obtained vulcanized rubber was evaluated as somewhat excellent and given a rating of "2." As described above, excellent bloom resistance indicates that the vulcanized rubber sheet has an excellent appearance and that excessive blooming has been suppressed. Furthermore, when the ozone resistance and bloom resistance are both evaluated as excellent, even if no bloom is observed visually, this is considered to indicate that the hydrocarbon wax (W) has bled invisibly together with the antioxidant to form a wax film on the surface of the vulcanized rubber. On the other hand, when bloom is clearly observed on the vulcanized rubber sheet after the bloom test, the bloom resistance of the obtained vulcanized rubber is evaluated as poor, and this is indicated by a rating of "3."

[0081] (Power Saving RRF) - Preparation of Vulcanized Rubber Sheets Each rubber composition produced as described above was heated and vulcanized at 148°C for 30 minutes to prepare a vulcanized rubber sheet measuring 40 mm in length, 5 mm in width, and 2 mm in thickness. - Measurement of Dynamic Viscoelasticity Using the vulcanized rubber sheet, dynamic viscoelasticity was measured using a viscoelasticity spectrometer (manufactured by Toyo Seiki Seisaku-sho, Ltd.) under the measurement conditions of a chuck distance of 10 mm, a dynamic strain of 2%, and a frequency of 20 Hz. The loss tangent (tan δ) and dynamic modulus of elasticity E' (N / mm) were measured at 0°C and 20°C, and the obtained loss tangent (tan δ) and dynamic modulus of elasticity E' were applied to the following equation to determine the rolling resistance factor (RRF). In the present invention, the power saving performance was evaluated by the RRF. The RRF results were expressed as an index, with the RRF of Example 4 being set to 100.

[0082] Evaluation Criteria for Power Savings In the present invention, when the RRF indexes at both 0°C and 20°C were 100 or less, the power saving was evaluated as excellent. The smaller the RRF index, the better the power saving. On the other hand, when at least one of the indexes at 0°C and 20°C exceeded 100, the power saving was evaluated as poor.

[0083] (Flame retardancy) - Preparation of test specimens Using each rubber composition produced as described above, test specimens (three for each test specimen) were prepared in accordance with JIS K6324:2013 "Flame retardancy conveyor belts - Grades and test methods" Section 7.2.1 for fabric layer conveyor rubber.

[0084] Evaluation method: The flame duration (unit: seconds) was measured in accordance with JIS K6324:2013 "Flame retardant performance conveyor belts - Grades and test methods."

[0085] Evaluation criteria: If the JIS Class 3 flame retardancy test standard (flame duration of less than 60 seconds (flame duration is the average value of three test pieces), no re-burning) was met, the flame retardancy performance was evaluated as excellent and marked with "◯". On the other hand, if the JIS Class 3 flame retardancy test standard was not met, the flame retardancy performance was evaluated as poor and marked with "X".

[0086]

[0087]

[0088]

[0089]

[0090] Details of each component shown in Table 1 are as follows: (Rubber components) NR: Natural rubber, RSS#3 BR: Butadiene rubber, trade name Nipol BR1220 (weight average molecular weight: 460,000, manufactured by Nippon Zeon Co., Ltd.) SBR: Styrene butadiene rubber, trade name Nipol 1502, manufactured by Nippon Zeon Co., Ltd.

[0091] (Flame retardants) Brominated flame retardant: bis(pentabromophenyl)ethane, trade name "SAYTEX 8010" (manufactured by ALBEMARLE CORPORATION). Melting point of 300°C or higher. Chlorinated paraffin (for comparison): Enpara 70S (trade name) manufactured by Dover Chemical Co., Ltd., chlorine content 68 to 72% by mass. Antimony trioxide: PATOX-M (trade name) manufactured by Nippon Seiko Co., Ltd.

[0092] (Hydrocarbon wax (W)) Hydrocarbon wax (w1): solid paraffin. Product name: OZOACE-0015 (Nippon Seiro Co., Ltd.). A mixture containing at least normal paraffin and isoparaffin. The carbon number of the top peak in the carbon number distribution of the normal paraffin is in the range of 32 to 35. The content of the normal paraffin is 89 mass% of the total amount of the solid paraffin. Melting point: 68°C Hydrocarbon wax (w2): solid paraffin. Product name: OZOACE-0037 (Nippon Seiro Co., Ltd.). A mixture containing at least normal paraffin and isoparaffin. The carbon number of the top peak in the carbon number distribution of the normal paraffin is in the range of 27 to 30. The content of the normal paraffin is 81 mass% of the total amount of the solid paraffin. Melting point: 61°C

[0093] (Anti-aging agent) Amine-based anti-aging agent (Anti-aging agent 6C): N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, trade name Ozonone 6C (manufactured by Seiko Chemical Co., Ltd.)

[0094] (Fillers) GPF-grade CB: GPF-grade carbon black, trade name Niteron #GN, manufactured by Shin-Nichika Carbon Co., Ltd. Silica: trade name "Nipsil AQ" (manufactured by Tosoh Silica Corporation)

[0095] (Additives) Zinc oxide: Trade name "Zinc Oxide Type 3" (manufactured by Seido Chemical Industry Co., Ltd.) Stearic acid: Trade name "Stearic Acid 50S" (manufactured by Chiba Fatty Acid Co., Ltd.)

[0096] (Vulcanization accelerator) Vulcanization accelerator NS: N-tert-butyl-2-benzothiazolylsulfenamide (trade name: Noccela NS, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)

[0097] (Sulfur) Insoluble sulfur: Shikoku Chemicals Corporation (product name) Myucron OT-20

[0098] From the results shown in Table 1, Comparative Examples 1 to 3, which did not contain a flame retardant and did not contain the required amount of amine-based antioxidant, had poor flame retardancy. Comparative Example 1 also had poor bloom resistance. Comparative Example 4, which did not contain butadiene rubber but instead contained SBR and did not contain the required amount of amine-based antioxidant, had poor ozone resistance and power saving properties. As such, it can be seen that depending on the type of rubber component, ozone resistance and other properties can be poor even when a hydrocarbon wax (W) is contained. Comparative Example 5, which did not contain a brominated flame retardant but instead contained chlorinated paraffin, had poor bloom resistance and power saving properties. Comparative Example 6, which did not contain the required amount of amine-based antioxidant, had poor ozone resistance. Comparative Example 7, which did not contain the required amount of hydrocarbon wax (W) and the required mass ratio of brominated flame retardant to hydrocarbon wax (W), had poor bloom resistance. Comparative Examples 8 and 9, in which the mass ratio of natural rubber to butadiene rubber was outside the specified range, exhibited poor ozone resistance, bloom resistance, and / or power saving properties. Comparative Example 10, which did not contain the hydrocarbon wax (W) and in which the content of the amine-based antioxidant did not satisfy the specified amount, exhibited poor ozone resistance and power saving properties. Comparative Examples 11 to 13, in which the content of the amine-based antioxidant did not satisfy the specified amount, exhibited poor ozone resistance. Note that Comparative Example 13 also did not contain the hydrocarbon wax (w1). Comparative Example 14, in which the mass ratio of the bromine-based flame retardant to the hydrocarbon wax (W) did not satisfy the specified value, exhibited poor bloom resistance. Comparative Example 15, in which the content of the hydrocarbon wax (W) did not satisfy the specified value, exhibited poor bloom resistance. Comparative Example 16, in which the content of the hydrocarbon wax (W) and the amine-based antioxidant did not satisfy the specified amount, exhibited poor ozone resistance and bloom resistance. Comparative Examples 17 and 18, which did not contain the hydrocarbon wax (w1) but instead contained the hydrocarbon wax (w2), had poor ozone resistance.

[0099] In contrast, the rubber composition of the present invention, when vulcanized, has excellent flame retardancy, ozone resistance and bloom resistance.

[0100] 1: Fabric layer 2: Coating rubber 3, 7: Cover rubber 4, 8: Conveyor belt 5: Steel cord 6: Cushion rubber

Claims

1. a rubber component containing natural rubber and butadiene rubber, wherein the mass ratio of the content of the natural rubber to the content of the butadiene rubber (natural rubber / butadiene rubber) is 30 / 70 to 80 / 20; a flame retardant containing a brominated flame retardant and antimony trioxide; A hydrocarbon wax (W), A filler; an antioxidant including an amine-based antioxidant; a vulcanization accelerator; containing sulfur, the content of the hydrocarbon wax (W) is 2.5 parts by mass or less based on 100 parts by mass of the rubber component, a mass ratio of the content of the brominated flame retardant to the content of the hydrocarbon wax (W) (brominated flame retardant / hydrocarbon wax (W)) of 8.0 or more; The hydrocarbon wax (W) includes a hydrocarbon wax (w1) having a melting point of 65°C or higher, The rubber composition for a conveyor belt, wherein the content of the amine-based antioxidant is 3.0 parts by mass or more per 100 parts by mass of the rubber component.

2. 2. The rubber composition for a conveyor belt according to claim 1, wherein a mass ratio of the content of the natural rubber to the content of the butadiene rubber is 40 / 60 to 70 / 30.

3. 2. The rubber composition for a conveyor belt according to claim 1, wherein a mass ratio of a content of the brominated flame retardant to a content of the hydrocarbon wax (W) is 10 or more and 20 or less.

4. 2. The rubber composition for a conveyor belt according to claim 1, wherein the hydrocarbon wax (w1) contains normal paraffin, and the carbon number at the peak top of the carbon number distribution of the normal paraffin is in the range of 30 to 40.

5. 2. The rubber composition for a conveyor belt according to claim 1, wherein the hydrocarbon wax (w1) contains normal paraffin, and the content of the normal paraffin in the hydrocarbon wax (w1) is 80% by mass or more.

6. 2. The rubber composition for a conveyor belt according to claim 1, wherein the amine-based antioxidant comprises a p-phenylenediamine-based compound.

7. The rubber composition for a conveyor belt according to claim 1, wherein the brominated flame retardant comprises a compound represented by the following formula (1): 【Chemical 1】 In formula (1), R represents an aliphatic hydrocarbon group which may contain an unsaturated bond.

8. The rubber composition for a conveyor belt according to claim 1, wherein the hydrocarbon wax (W) further comprises a hydrocarbon wax (w2) having a melting point of less than 65°C.

9. 9. The rubber composition for a conveyor belt according to claim 8, wherein the hydrocarbon wax (w2) contains normal paraffin, and the carbon number at the peak top of the carbon number distribution of the normal paraffin is in the range of 25 to 35.

10. 9. The rubber composition for a conveyor belt according to claim 8, wherein the hydrocarbon wax (w2) contains normal paraffin, and the content of the normal paraffin in the hydrocarbon wax (w2) is 80 mass % or more.

11. A conveyor belt formed using the rubber composition for a conveyor belt according to any one of claims 1 to 10.

12. The conveyor belt according to claim 11, comprising a cover rubber formed using the rubber composition.

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