Rubber composition and conveyor belt

Abstract

To provide a rubber composition which, when formed into a vulcanized rubber, has excellent flame retardant performance and can maintain the excellent power-saving performance possessed by a vulcanized rubber obtained from a rubber composition to which no flame retardant is added even if a flame retardant is added and to provide a conveyor belt.SOLUTION: There is provided a rubber composition which comprises a diene-based rubber containing a natural rubber and a butadiene rubber, carbon black having a nitrogen adsorption specific surface area of 20 to 100 m2 / g and a dibutyl phthalate oil absorption amount of 70 to 120 cm3 / 100 g, a flame retardant containing a compound represented by a specific formula and antimony trioxide, sulfur and a vulcanization accelerator, wherein the mass ratio of the natural rubber to the butadiene rubber is 40 / 60 to 80 / 20, the content of the carbon black is 20 to 50 pts.mass based on 100 pts.mass of the diene-based rubber and the total content of the compound represented by the specific formula and antimony trioxide is 15 to 50 pts.mass based on 100 pts.mass of the diene-based rubber.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to rubber compositions and conveyor belts. [Background technology]

[0002] Conventionally, it is known that rubber compositions containing natural rubber and butadiene rubber can be used in conveyor belts (for example, Patent Document 1). Furthermore, in recent years, there has been a growing demand for conveyor belts to have flame-retardant properties. Regarding flame retardancy of rubber, the general method involves adding flame retardants such as halogen-based flame retardants, phosphorus-based flame retardants, metal hydroxides, and antimony compounds to the rubber composition. However, it is known that the addition of flame retardants as described above can worsen the physical properties of rubber (e.g., Patent Document 2) and worsen the low tanδ of vulcanized rubber (e.g., Patent Document 3). Patent Document 2 indicates that it is desirable not to incorporate antimony-based flame retardants such as antimony trioxide into rubber compositions because there are concerns that this may have adverse effects on the properties of the rubber (see

[0021] and Comparative Example 1 in Patent Document 2). Patent Document 3 shows that adding a flame retardant to diene rubber increased the tanδ (under 20°C conditions) of the vulcanized rubber compared to when no flame retardant was added (comparison results between Comparative Example 3 and Comparative Examples 4-6 in Patent Document 3). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-181543 [Patent Document 2] Japanese Patent Publication No. 2021-24872 [Patent Document 3] Japanese Patent Publication No. 2012-180475 [Overview of the project] [Problems that the invention aims to solve]

[0004] Thus, conventionally, even if it was possible to impart flame retardant properties to vulcanized rubber obtained from a rubber composition containing diene rubber by adding a flame retardant, it was difficult to maintain in the vulcanized rubber the same level of power saving performance (low tanδ) as vulcanized rubber obtained from a rubber composition without flame retardant. Furthermore, if the power-saving performance (low tanδ) of vulcanized rubber obtained from a rubber composition without flame retardants is excellent under temperature conditions of -20°C, 0°C, and +20°C, it was even more difficult to maintain the same excellent power-saving performance for a rubber composition to which flame retardants have been added.

[0005] Therefore, the present invention aims to provide a rubber composition that, when vulcanized, exhibits excellent flame retardancy and maintains the excellent power-saving performance of vulcanized rubber obtained from a rubber composition without flame retardants, even when flame retardants are added. Furthermore, the present invention also aims to provide a conveyor belt. [Means for solving the problem]

[0006] As a result of diligent research to solve the above problems, the inventors of the present invention have found that a rubber composition containing a diene rubber comprising natural rubber and butadiene rubber in a specific mass ratio, carbon black having a specific range for nitrogen adsorption specific surface area and dibutyl phthalate oil absorption, a flame retardant containing two specific compounds, sulfur, and a vulcanization accelerator, wherein the carbon black content and the total content of the two specific compounds as flame retardants are within specific ranges, when the above rubber composition is made into vulcanized rubber, it exhibits excellent flame retardant performance, and even with the addition of a flame retardant, it can maintain the excellent power saving performance of vulcanized rubber obtained from a rubber composition without a flame retardant, leading to the present invention. The present invention is based on the above findings, and specifically solves the above problems with the following configuration.

[0007] [1] Diene rubbers containing natural rubber and butadiene rubber, Nitrogen adsorption specific surface area is 20-100 m² 2 The amount is / g, and the amount of dibutyl phthalate absorbed is 70-120 cm³. 3 Carbon black is / 100g A flame retardant containing a compound represented by formula (1) described later and antimony trioxide, Sulfur, and, Contains a vulcanization accelerator, The mass ratio of the above natural rubber to the above butadiene rubber is 40 / 60 to 80 / 20. The carbon black content is 20 to 50 parts by mass per 100 parts by mass of the diene rubber. A rubber composition in which the total content of the compound represented by the above formula (1) and the above antimony trioxide is 15 to 50 parts by mass per 100 parts by mass of the diene rubber. [2] The rubber composition according to [1], wherein the content of the compound represented by formula (1) is 1 to 10 times the content of the antimony trioxide by mass. [3] A conveyor belt formed using the rubber composition described in [1] or [2]. [4] The conveyor belt according to [3], having a cover rubber formed using the above rubber composition. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a rubber composition that, when vulcanized, exhibits excellent flame retardancy and maintains the excellent power-saving performance of vulcanized rubber obtained from a rubber composition without flame retardants, even when flame retardants are added, and a conveyor belt formed using the above rubber composition. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a cross-sectional view of one embodiment of the conveyor belt of the present invention. [Figure 2] Figure 2 is a cross-sectional view of another embodiment of the conveyor belt of the present invention.

Mode for Carrying Out the Invention

[0010] The present invention will be described in detail below. In this specification, a numerical range represented by "~" means a range including the numerical values described before and after "~". In this specification, unless otherwise specified, each component is not particularly limited with respect to its production method. For example, conventionally known methods can be mentioned. In this specification, unless otherwise specified, each component can use the substances corresponding to that component alone or in combination of two or more. When the component contains two or more substances, the content of the component means the total content of the two or more substances.

[0011] [[ID=十六]] [Rubber Composition] The rubber composition of the present invention is a diene rubber containing natural rubber and butadiene rubber, carbon black having a nitrogen adsorption specific surface area of 20 to 100 m 2 / g and a dibutyl phthalate oil absorption amount of 70 to 120 cm 3 / 100 g, a flame retardant containing a compound represented by the following formula (1) and antimony trioxide, sulfur, and a vulcanization accelerator, where the mass ratio of the natural rubber to the butadiene rubber is 40 / 60 to 80 / 20, the content of the carbon black is 20 to 50 parts by mass with respect to 100 parts by mass of the diene rubber, the total content of the compound represented by the formula (1) and the antimony trioxide is 15 to 50 parts by mass with respect to 100 parts by mass of the diene rubber, and it is a rubber composition. [Chemical Formula] In formula (1), R represents an aliphatic hydrocarbon group which may contain an unsaturated bond.

[0012] It should be noted that in the above translation, for the chemical formula part, since no specific chemical formula content is provided in the original text, it is translated as "[Chemical Formula]" as it is. If there is actual chemical formula content in the original text, please provide it accurately for a more accurate translation.The reason why the above desired effects are obtained by the rubber composition of the present invention is not clear, but it is presumed to be as follows. In other words, the rubber composition of the present invention has the above configuration, and in the vulcanized rubber obtained from the rubber composition of the present invention, the compound represented by formula (1) and / or antimony trioxide as a flame retardant remain dispersed, and the flame retardant can be prevented from bleeding out of the vulcanized rubber. Therefore, it is thought that the rubber composition of the present invention can impart excellent flame retardant performance to vulcanized rubber while maintaining the excellent power saving performance of vulcanized rubber obtained from a rubber composition without a flame retardant, even when a flame retardant is added. The following describes in detail each component contained in the rubber composition of the present invention.

[0013] [Diene-based rubber] The rubber composition of the present invention contains diene rubber, and the diene rubber includes natural rubber and butadiene rubber.

[0014] [Natural rubber] In the present invention, the natural rubber (NR) included as the diene rubber is not particularly limited. Examples include conventionally known types.

[0015] [Butadiene rubber] In the present invention, the butadiene rubber (BR) included as the diene rubber is not particularly limited. Examples include conventionally known types. One preferred embodiment of BR is, for example, polybutadiene that is solid under 23°C conditions. Furthermore, BR may be unmodified or modified.

[0016] The weight-average molecular weight of BR is preferably 200,000 or more, and more preferably 300,000 to 1,000,000, from the viewpoint of having better power-saving performance and superior wear resistance. In this specification, the weight-average molecular weight (Mw) of BR can be expressed as the 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 to butadiene rubber] In this invention, the mass ratio of natural rubber to butadiene rubber (NR / BR) is 40 / 60 to 80 / 20. The above mass ratio (NR / BR) is preferably 50 / 50 to 80 / 20, and more preferably 60 / 40 to 75 / 25, from the viewpoint of having better power saving performance and better rubber properties (e.g., tensile strength: TB, elongation: EB).

[0018] (Total content of natural rubber and butadiene rubber) The total content of natural rubber and butadiene rubber is preferably 80 to 100% by mass of the total amount of diene rubber, and more preferably 100% by mass, from the viewpoint of having better power saving performance and superior rubber properties.

[0019] (Other diene-based rubbers) The diene rubber may further include diene rubbers other than natural rubber and butadiene rubber (other diene rubbers). Other diene rubbers are not particularly limited, for example, polymers formed from monomers containing conjugated diene monomers (except for natural rubber and butadiene rubber).

[0020] [Carbon Black] The rubber composition of the present invention has a nitrogen adsorption specific surface area of ​​20 to 100 m². 2 The amount is / g, and the amount of dibutyl phthalate absorbed is 70-120 cm³. 3 It contains carbon black at a concentration of 100g. In this specification, the specific surface area for nitrogen adsorption is 20 to 100 m². 2 The amount is / g, and the amount of dibutyl phthalate absorbed is 70-120 cm³. 3 Carbon black that is 100g is sometimes referred to as "specific carbon black" or "specific CB".

[0021] [Specific surface area for nitrogen adsorption] In the present invention, the nitrogen adsorption specific surface area (N2SA) of the specific CB is 20 to 100 m 2 / g. From the viewpoint of more excellent power saving performance and excellent flex fatigue resistance, the N2SA of the specific CB is preferably 30 to 70 m 2 / g, and more preferably 30 to 50 m 2 / g. The nitrogen adsorption specific surface area (N2SA) of carbon black can be measured in accordance with JIS K6217-2:2017.

[0022] [Oil absorption of dibutyl phthalate] In the present invention, the oil absorption of dibutyl phthalate (DBP) of the specific CB is 70 to 120 cm 3 / 100 g. From the viewpoint of more excellent power saving performance and excellent flex fatigue resistance, the DBP of the specific CB is preferably 70 to 90 cm 3 / 100 g. The oil absorption of dibutyl phthalate (DBP) of carbon black can be measured in accordance with JIS K6217-4:2017.

[0023] [Content of specific carbon black] In the present invention, the content of the specific carbon black is 2 to 5 parts by mass with respect to 100 parts by mass of the above-described diene rubber. From the viewpoint of more excellent power saving performance and excellent rubber physical properties, the content of the specific carbon black is preferably 2 to 3.5 parts by mass with respect to 100 parts by mass of the above-described diene rubber.

[0024] (Silica)<00叭75>The rubber composition of the present invention may further contain silica. When the rubber composition of the present invention further contains silica, the obtained vulcanized rubber has more excellent power saving performance and excellent rubber physical properties. The silica that may be further contained in the rubber composition of the present invention is not particularly limited. For example, conventionally known ones can be mentioned. Specifically, for example, wet silica, dry silica, and fumed silica can be mentioned. From the viewpoint of having better power-saving performance and superior rubber properties, the silica content is preferably 0 to 50 parts by mass, and more preferably 5 to 30 parts by mass, per 100 parts by mass of the diene-based rubber mentioned above.

[0025] [Flame retardant] The rubber composition of the present invention contains a flame retardant, the flame retardant comprising a compound represented by formula (1) described later and antimony trioxide.

[0026] [Compound represented by formula (1)] In the present invention, the flame retardant includes a compound represented by the following formula (1). [ka] In formula (1), R represents an aliphatic hydrocarbon group which may contain an unsaturated bond. In this specification, the compound represented by formula (1) is also referred to as the "specific compound." In the present invention, the specific compound can function as a flame retardant.

[0027] In formula (1), the aliphatic hydrocarbon group R, which may contain an unsaturated bond, may be linear, branched, cyclic, or a combination thereof, but a linear configuration is preferred. The number of carbon atoms in the above aliphatic hydrocarbon group is not particularly limited. For example, it can be 1 to 10. The number of carbon atoms is preferably 2 to 8.

[0028] Furthermore, the aliphatic hydrocarbon group which may contain an unsaturated bond may be either a saturated aliphatic hydrocarbon group which does not contain an unsaturated bond or an unsaturated aliphatic hydrocarbon group which contains an unsaturated bond, but a saturated aliphatic hydrocarbon group is preferred as an example of the embodiment. Examples of the saturated aliphatic hydrocarbon groups mentioned above include methylene, ethylene, trimethylene, propylene, butylene, pentylene, hexylene, heptylene, and octylene groups. Examples of unsaturated bonds that the above-mentioned aliphatic hydrocarbon group may have include vinyl, vinylene, ethynyl, and ethynylene groups. When an aliphatic hydrocarbon group that may contain an unsaturated bond is an unsaturated aliphatic hydrocarbon group, examples of the unsaturated aliphatic hydrocarbon group include the above-mentioned combination of a saturated aliphatic hydrocarbon group and the above-mentioned unsaturated bond.

[0029] Examples of the specified compounds mentioned above include bis(pentabromophenyl)ethane. From the viewpoint of having superior flame retardant properties and energy-saving properties, the above-mentioned specific compound preferably contains bis(pentabromophenyl)ethane.

[0030] [Antimony trioxide] In the present invention, the antimony trioxide (Sb2O3) included as a flame retardant is not particularly limited. Antimony trioxide can function as a flame retardant additive for the compound represented by formula (1) above. For this reason, antimony trioxide is treated as a flame retardant in this invention.

[0031] [Total content of the compound represented by formula (1) and antimony trioxide] In the present invention, the total content of the compound represented by formula (1) (specific compound) and antimony trioxide is 15 to 50 parts by mass per 100 parts by mass of the diene rubber described above. From the viewpoint of having superior flame retardant properties and power saving properties, the total content is preferably 20 to 40 parts by mass, and more preferably 25 to 35 parts by mass, per 100 parts by mass of diene rubber.

[0032] (Content of the compound represented by formula (1)) The content of the compound represented by formula (1) (specific compound) is preferably 1 to 10 times, and more preferably 2.0 to 4.0 times, by mass, the content of antimony trioxide, from the viewpoint of having superior flame retardant performance and power saving performance.

[0033] (Total content of the compound represented by formula (1) and antimony trioxide in the total amount of rubber composition) Furthermore, the total content of the compound represented by formula (1) and antimony trioxide is preferably 5 to 25% by mass of the total rubber composition, from the viewpoint of having superior flame retardant and power-saving performance.

[0034] (Total content of the compound represented by formula (1) and antimony trioxide in the total amount of flame retardant) Furthermore, the total content of the compound represented by formula (1) (specific compound) and antimony trioxide is preferably 80 to 100% by mass of the total amount of flame retardant, and more preferably 100% by mass, from the viewpoint of having superior flame retardant performance and power saving performance.

[0035] (Other flame retardants) The flame retardant may further include flame retardants other than the compound represented by formula (1) and antimony trioxide (other flame retardants). The other flame retardants are not particularly limited as long as they are compounds that can impart flame retardant properties (except for the compound represented by formula (1) and antimony trioxide). In addition, one preferred embodiment of the rubber composition of the present invention is that it does not contain chlorinated paraffin.

[0036] [sulfur] The rubber composition of the present invention contains sulfur. The sulfur used is not particularly limited as long as it is used for vulcanization of diene rubbers. Examples include conventionally known sulfurs. From the viewpoint of having superior flame retardant and / or power-saving performance and superior rubber properties, the sulfur content is preferably 0.5 to 5.0 parts by mass per 100 parts by mass of the above-mentioned diene-based rubber.

[0037] [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 used for vulcanizing diene rubbers. Examples of vulcanization accelerators include sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazolyl sulfenamide (CZ) and N-tert-butyl-2-benzothiazolyl sulfenamide (NS); thiram-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 having superior flame retardant properties and / or power saving properties, it is preferable that the vulcanization accelerator includes a sulfenamide-based vulcanization accelerator. From the viewpoint of having superior flame retardant performance and / or power saving performance, the content of the vulcanization accelerator is preferably 0.5 to 8.0 parts by mass per 100 parts by mass of the above-mentioned diene rubber.

[0038] (Additives) The rubber composition of the present invention may further contain additives in addition to the components described above. Examples of additives include vulcanization aids such as zinc oxide and stearic acid, vulcanization retarders, anti-aging agents, antioxidants, and plasticizers. Furthermore, one preferred embodiment of the rubber composition of the present invention is that it does not contain molybdate metal compounds as described in Patent Document 2.

[0039] (Manufacturing method) The method for producing the rubber composition of the present invention is not particularly limited. For example, one method is to mix the above-mentioned essential components and any additional additives that may be used as needed in a Banbury mixer or the like.

[0040] (vulcanization) The rubber composition of the present invention can be vulcanized under conventional conditions. The vulcanization temperature can be, for example, 120 to 180°C. Pressurization may be performed during vulcanization.

[0041] (Application) Examples of applications for the rubber composition of the present invention include conveyor belts.

[0042] [Conveyor belt] The conveyor belt of the present invention is a conveyor belt formed using the rubber composition of the present invention.

[0043] 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. There are no particular limitations on which component of the conveyor belt of the present invention the rubber composition of the present invention may be applied to. All or part of the rubber constituting the conveyor belt of the present invention can be formed from the rubber composition of the present invention.

[0044] The vulcanized rubber obtained from the rubber composition of the present invention has excellent flame retardancy and maintains the excellent power-saving performance of vulcanized rubber obtained from a rubber composition that does not contain flame retardants. Therefore, one preferred embodiment of the conveyor belt of the present invention is one in which it has a cover rubber formed using the rubber composition of the present invention.

[0045] Embodiments of the conveyor belt of the present invention will be described below with reference to the attached drawings. However, the present invention is not limited to the attached drawings. Figure 1 is a cross-sectional view of one embodiment of the conveyor belt of the present invention. The embodiment of the conveyor belt of the present invention shown in Figure 1 (hereinafter also referred to as the first embodiment of the conveyor belt of the present invention) is a conveyor belt 4 in which a fabric layer 1 is covered with a coating rubber (adhesive rubber) 2 to form a core material layer, and its outer circumference is covered with a cover rubber 3. The cover rubber 3 is preferably formed from the rubber composition of the present invention. In Figure 1, the conveyor belt 4 has a fabric layer 1 as its core material, and the number of layers of fabric 1, the thickness of the cover rubber 3, the belt width, etc., can be appropriately determined according to the purpose of use. Examples of fabric layers include canvas made from woven synthetic fibers such as nylon, vinylon, and polyester. The thicknesses T1 and T2 of the cover rubber 3 can typically be around 1.5 to 20 mm, respectively.

[0046] Furthermore, the coating rubber 2 can be a coating rubber known to be used in conveyor belts. As the coating rubber, 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), etc. as rubber components can be used.

[0047] Next, a second embodiment of the conveyor belt of the present invention will be described with reference to Figure 2. Figure 2 is a cross-sectional view of another embodiment of the conveyor belt of the present invention. As shown in Figure 2, a second embodiment of the conveyor belt of the present invention is a conveyor belt 8 in which a steel cord 5 is covered with cushion rubber (adhesive rubber) 6 to form a core material layer, and its outer circumference is covered with cover rubber 7. The cover rubber 7 is preferably formed from the rubber composition of the present invention. The conveyor belt 8 can be constructed using, for example, 50 to 230 steel cords 5 with a diameter of approximately 2.0 to 9.5 mm, each made by twisting together multiple strands of wire with a diameter of approximately 0.2 to 0.4 mm, as the core material. 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 adhere to galvanized steel cords used in known steel conveyor belts. Specifically, as the cushion rubber, a rubber composition containing natural rubber (NR), acrylonitrile-butadiene rubber (NBR), styrene-butadiene copolymer rubber (SBR), butadiene rubber (BR), etc. as rubber components can be used.

[0048] The conveyor belt of the present invention can be manufactured, for example, by interposing a core material fabric layer, steel cord, or core material layer between unvulcanized rubber sheets molded from the rubber composition of the present invention, according to a conventional method, and then vulcanizing by heating and pressurizing. The vulcanization conditions can be, for example, approximately 120 to 180°C, 0.1 to 4.9 MPa, and for approximately 10 to 90 minutes.

[0049] Since the conveyor belt of the present invention is formed using the rubber composition of the present invention described above, it has excellent flame retardancy and can maintain the excellent power-saving performance of vulcanized rubber (conveyor belt) obtained from a rubber composition that does not contain flame retardants. [Examples]

[0050] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these examples.

[0051] <Manufacturing of rubber compositions> Each component in Table 1 below was used in the composition (parts by mass) shown in the same table, and these were mixed in a Banbury mixer to produce each rubber composition (unvulcanized).

[0052] <Rating> (Power saving performance) • Production of vulcanized sheets Each rubber composition (unvulcanized) manufactured as described above was vulcanized for 30 minutes at a pressure of 3.0 MPa using a press molding machine at 148°C to produce vulcanized sheets measuring 150 mm in length, 150 mm in width, and 2 mm in thickness. Test specimens were then prepared by punching out the vulcanized sheets to a size of 40 mm in length, 5 mm in width, and 2 mm in thickness.

[0053] • Evaluation method Using each vulcanized sheet prepared as described above, dynamic viscoelasticity measurements were performed using a viscoelastic spectrometer (manufactured by Toyo Seiki Seisakusho Co., Ltd.) under the following measurement conditions: chuck distance of 10 mm, dynamic strain of 2%, and frequency of 20 Hz. The loss tangent (tanδ) was measured at -20°C, 0°C, and +20°C. The results are shown in the "tanδ" column of Table 1. Furthermore, the tanδ at each temperature is expressed as an exponent. For tanδ at -20°C, the value of tanδ at -20°C, "0.3950", is expressed as an exponent of "100". For tanδ at 0°C, the value of tanδ at 0°C, "0.1835", is expressed as an exponent of "100". For tanδ at +20°C, the value of tanδ at +20°C, "0.1660", is expressed as an exponent of "100". If the tanδ (exponent) at each temperature was 100 or less, it is indicated as "○", and if the tanδ (exponent) at each temperature was greater than 100, it is indicated as "×". The results are shown in the "tanδ (exponent)" column of Table 1.

[0054] • Evaluation criteria First, in the present invention, if the tanδ (index) of the vulcanized rubber obtained from a rubber composition without added flame retardants is 100 or less at -20°C, 0°C, and +20°C, then the vulcanized rubber obtained from a rubber composition without added flame retardants is considered to have excellent power-saving performance. Next, if the tanδ (index) at -20°C, 0°C, and +20°C for vulcanized rubber obtained from a rubber composition without added flame retardant, and the tanδ (index) at -20°C, 0°C, and +20°C for vulcanized rubber obtained from the rubber composition with added flame retardant, were all 100 or less, it was evaluated that the power-saving performance of the vulcanized rubber obtained from the rubber composition with added flame retardant was maintained at the same level as the excellent power-saving performance of the vulcanized rubber obtained from the rubber composition without added flame retardant. The smaller the exponent of tanδ at each temperature, the better the power saving performance.

[0055] On the other hand, even if the tanδ (index) of vulcanized rubber obtained from a rubber composition without flame retardants is 100 or less at -20°C, 0°C, and +20°C, if the tanδ (index) of vulcanized rubber obtained from a rubber composition with flame retardants added to the above rubber composition exceeds 100, it was evaluated that the power-saving performance of the vulcanized rubber obtained from the rubber composition with flame retardants could not be maintained at the same level as the excellent power-saving performance of the vulcanized rubber obtained from the rubber composition without flame retardants.

[0056] Furthermore, if the tanδ (index) of vulcanized rubber obtained from a rubber composition without added flame retardants exceeded 100 at -20°C, 0°C, or +20°C, the power-saving performance of the vulcanized rubber was evaluated as poor.

[0057] (Flame retardant properties) • Preparation of test specimens Using each rubber composition manufactured as described above, test specimens (three for each test specimen) were prepared in accordance with Section 7.2.1 of JIS K6324:2013 "Flame-retardant conveyor belts - Grades and test methods" for fabric-layered conveyor rubber.

[0058] • Evaluation method The duration of the flame (in seconds) was measured in accordance with JIS K6324:2013 "Flame-retardant conveyor belts - Grades and test methods".

[0059] • Evaluation criteria If the material meets the JIS Class 3 flame retardancy test standards [flame duration must be less than 60 seconds (the flame duration is the average of three test pieces), and there must be no re-ignition], it is evaluated as having excellent flame retardancy and is marked with "〇". On the other hand, if the product did not meet the JIS Class 3 flame retardancy test standards, it was evaluated as having poor flame retardancy and was marked with an "×". The results are shown in Table 1.

[0060] [Table 1]

[0061] [Table 2]

[0062] [Table 3]

[0063] The details of each component shown in Table 1 are as follows: (Diene-based rubber) • NR: Natural rubber. RSS#3 • BR: Butadiene rubber. Product name: Nipol BR1220 (Weight-average molecular weight: 460,000, manufactured by Nippon Zeon Co., Ltd.) • SBR (comparative): Styrene-butadiene rubber. Product name: Nipol 1502, manufactured by Nippon Zeon Co., Ltd.

[0064] (Carbon Black) The table shows the N2SA values ​​(unit: m) for each carbon black (CB). 2 / g), DBP (unit: cm) 3 This indicates (per 100g). • SAF-class CB (comparative): Product name Show Black S118, Cabot Japan Co., Ltd. • ISAF Class CB (Comparative): Product name: Showblack N220, Cabot Japan Co., Ltd. The above SAF class CB and ISAF class CB have N2SA at 100m 2 Since it exceeds the limit per gram, it does not fall under the category of specified carbon black. • HAF class CB: Product name: Seast N, Tokai Carbon Co., Ltd. • FEF grade CB: Product name: Nitelon #10N, Shin-Nippon Carbon Co., Ltd. GPF Class CB: Product name: Nitelon #GN, Shin-Nippon Carbon Co., Ltd. The above-mentioned HAF-grade CB, FEF-grade CB, and GPF-grade CB fall under the category of specified carbon blacks.

[0065] (Vulcanization accelerator) • Vulcanization accelerator NS: N-tert-butyl-2-benzothiazolyl sulfenamide (product name Noxellar NS, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)

[0066] • Vulcanization retarder PVI:N-cyclohexylthiophthalimide. Product name: Retarder CTP, manufactured by Toray Fine Chemicals Co., Ltd.

[0067] (sulfur) • Insoluble sulfur: Shikoku Chemicals Co., Ltd. (product name) Mucron OT-20

[0068] (Flame retardant) • Antimony trioxide: Manufactured by Nippon Seikou Co., Ltd. (product name) PATOX-M Compound 1 represented by formula (1): Bis(pentabromophenyl)ethane. Trade name "SAYTEX8010" (manufactured by ALBEMARLE CORPORATION) • Chlorinated paraffin (for comparison): Dover Chemical Co., Ltd. (product name) Enpara 70S • Aluminum hydroxide (for comparison): Manufactured by Nippon Light Metal Co., Ltd., (product name) Aluminum hydroxide BF013

[0069] As shown in Table 1, Comparative Example 1, which did not contain a flame retardant, had excellent power-saving performance but poor flame retardancy. Comparative Examples 2 and 3, which contained only antimony trioxide or a compound represented by formula (1) as a flame retardant, exhibited poor flame retardancy and worse energy-saving performance compared to Comparative Example 1. Comparative Examples 4 and 5, which did not contain the compound represented by formula (1) as a flame retardant and instead contained chlorinated paraffin or aluminum hydroxide, showed worse power saving performance than Comparative Example 1.

[0070] Comparative Example 19, which contained carbon black with N2SA outside the specified range and did not contain a flame retardant, inherently had poor power saving and flame retardant performance. Furthermore, Comparative Example 6, which was identical to Comparative Example 19 except for containing the compound represented by formula (1) and antimony trioxide as flame retardants, had even worse power saving performance than Comparative Example 19. Comparative Example 20, which contained carbon black with N2SA outside the specified range and did not contain a flame retardant, had poor power saving and flame retardant performance to begin with. Furthermore, Comparative Example 7, which was the same as Comparative Example 20 except for containing the compound represented by formula (1) and antimony trioxide as flame retardants, had even worse power saving performance than Comparative Example 20. Comparative Example 8, which contained SBR instead of BR and did not include a flame retardant, had poor power saving and flame retardant performance to begin with. Furthermore, Comparative Example 9, which was the same as Comparative Example 8 except for containing the compound represented by formula (1) and antimony trioxide as flame retardants, had even worse power saving performance than Comparative Example 8. Comparative Example 10, which did not contain NR but instead contained SBR and did not contain a flame retardant, had poor power saving and flame retardant performance to begin with. Furthermore, Comparative Example 11, which was the same as Comparative Example 10 except for containing the compound represented by formula (1) and antimony trioxide as flame retardants, had even worse power saving performance than Comparative Example 10. Comparative Examples 12 and 13, in which the mass ratio of natural rubber / butadiene rubber fell outside the specified range and did not contain flame retardants, inherently had poor power saving and flame retardancy performance. Comparative Examples 14 and 15, which contained specific carbon black outside the specified range and did not include flame retardants, inherently had poor power saving and flame retardancy.

[0071] On the other hand, when Examples 1 to 3 were made into vulcanized rubber, they exhibited superior flame retardancy compared to Comparative Example 1, and even when they contained the compound represented by formula (1) and antimony trioxide as flame retardants, they maintained the same excellent power saving performance as Comparative Example 1. Example 4, when used as vulcanized rubber, exhibited superior flame retardancy compared to Comparative Example 16 (which was the same as Example 4 except for not containing a flame retardant). Even when containing the compound represented by formula (1) and antimony trioxide as flame retardants, it maintained the same excellent power-saving performance as Comparative Example 16. Similar results were obtained in the comparison between Example 5 and Comparative Example 17, and between Example 6 and Comparative Example 18.

[0072] Thus, the rubber composition of the present invention, when made into vulcanized rubber, exhibits excellent flame retardancy, and even with the addition of a flame retardant, it maintains the excellent power-saving performance of vulcanized rubber obtained from a rubber composition without a flame retardant. As described above, the rubber composition of the present invention was able to achieve both flame retardancy and energy saving performance. Furthermore, the rubber composition of the present invention exhibits excellent power-saving performance under temperature conditions of -20°C, 0°C, and +20°C. [Explanation of Symbols]

[0073] 1: Cloth layer 2: Coated rubber 3, 7: Cover rubber 4, 8: Conveyor belt 5: Steel cord 6: Cushion rubber

Claims

1. Diene rubbers containing natural rubber and butadiene rubber, Nitrogen adsorption specific surface area is 20 to 100 m² ２ The amount is / g, and the amount of dibutyl phthalate absorbed is 70-120 cm³. ３ Carbon black, which is 100g A flame retardant comprising a compound represented by the following formula (1) and antimony trioxide, Sulfur, and, Contains a vulcanization accelerator, The mass ratio of the natural rubber to the butadiene rubber is 50 / 50 to 80 / 20. The carbon black content is 20 to 50 parts by mass per 100 parts by mass of the diene rubber. A rubber composition in which the total content of the compound represented by formula (1) and the antimony trioxide is 15 to 50 parts by mass per 100 parts by mass of the diene rubber. 【Chemistry 1】 In formula (1), R represents an aliphatic hydrocarbon group which may contain an unsaturated bond.

2. The rubber composition according to claim 1, wherein the content of the compound represented by formula (1) is 1 to 10 times the content of the antimony trioxide by mass.

3. The rubber composition according to claim 1, wherein the total content of the compound represented by formula (1) and the antimony trioxide is 25 to 35 parts by mass per 100 parts by mass of the diene rubber, and the content of the compound represented by formula (1) is 2.0 to 4.0 times by mass the content of the antimony trioxide.

4. A conveyor belt formed using the rubber composition described in any one of claims 1 to 3.

5. The conveyor belt according to claim 4, having a cover rubber formed using the rubber composition.

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