Rubber composition and conveyor belt

Abstract

To provide a rubber composition and a conveyor belt which can adjust the vulcanization rate in an appropriate range while achieving both excellent abrasion resistance and flame retardancy and have excellent processability.SOLUTION: There are provided: a rubber composition comprising a diene-based rubber containing a natural rubber and a butadiene rubber, a flame retardant containing chlorinated paraffin and antimony trioxide, carbon black, sulfur and a vulcanization accelerator including a sulfenamide-based vulcanization accelerator and a guanidine-based vulcanization accelerator, wherein the content of natural rubber in the total amount of the diene-based rubber is 20 to 50 mass%, the content of the butadiene-based rubber is 50 to 80 mass%, the content of the chlorinated paraffin is 20 to 35 pts.mass based on 100 pts.mass of the diene-based rubber, the content of the antimony trioxide is 5 to 12 pts.mass, the mass ratio of (the total content of the sulfenamide-based vulcanization accelerator and the guanidine-based vulcanization accelerator) / (the content of the sulfur) is 1.00 or more and the mass ratio of (the content of the guanidine-based vulcanization accelerator) / (the content of the sulfenamide-based vulcanization accelerator) is 0.20 to 0.60; and a conveyor belt produced using the rubber composition.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Conventionally, a rubber composition for conveyor belts has been proposed with the aim of obtaining a conveyor belt that has excellent low loss properties while maintaining the high strength and high flame retardancy required for rubber articles (Patent Document 1). The rubber composition contains a rubber component containing natural rubber and butadiene rubber, a vulcanizing agent, a vulcanization accelerator, carbon black, chlorinated paraffin, and antimony trioxide, and the ratio of the content of the natural rubber to the content of the butadiene rubber (natural rubber content:butadiene rubber content) is 25:75 to 45:55 by mass. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2016 / 056219 Summary of the Invention [Problem to be solved by the invention]

[0004] On the other hand, rubber compositions for conveyor belts are required to have flame retardancy in the cured product obtained by curing the rubber composition, excellent processability in terms of being less susceptible to rubber scorching, a vulcanization rate in an appropriate range in terms of excellent productivity of rubber products, and excellent abrasion resistance in the cured product obtained by curing the rubber composition. The present inventors have studied the rubber composition disclosed in Patent Document 1 and have found that the rubber composition may have poor processability, poor vulcanization rate, or poor abrasion resistance or poor flame retardancy of a cured product obtained by curing the rubber composition. In this specification, the processability of a rubber composition from the viewpoint of resistance to rubber burning is also simply referred to as "processability." The vulcanization rate of a rubber composition is also simply referred to as "vulcanization rate." The abrasion resistance of a cured product obtained by curing a rubber composition is also simply referred to as "abrasion resistance." The flame retardancy of a cured product obtained by curing a rubber composition is also simply referred to as "flame retardancy."

[0005] Therefore, an object of the present invention is to provide a rubber composition which has excellent processability and can keep the vulcanization rate within an appropriate range while simultaneously achieving excellent abrasion resistance and flame retardancy. Another object of the present invention is to provide a conveyor belt. [Means for solving the problem]

[0006] As a result of intensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by a rubber composition containing a diene-based rubber containing natural rubber and butadiene rubber, a flame retardant containing chlorinated paraffin and antimony trioxide, carbon black, sulfur, and a vulcanization accelerator containing a sulfenamide-based vulcanization accelerator and a guanidine-based vulcanization accelerator, wherein the content of the natural rubber, the content of the butadiene rubber, the content of the chlorinated paraffin, and the content of the antimony trioxide are such that the mass ratio of (the total of the content of the sulfenamide-based vulcanization accelerator and the content of the guanidine-based vulcanization accelerator) / (the content of the sulfenamide-based vulcanization accelerator) and the mass ratio of (the content of the guanidine-based vulcanization accelerator) / (the content of the sulfenamide-based vulcanization accelerator) are within predetermined ranges, respectively. Specifically, the present invention solves the above problems by the following configuration.

[0007] [1] A rubber composition comprising a diene rubber containing natural rubber and butadiene rubber, a flame retardant containing chlorinated paraffin and antimony trioxide, carbon black, sulfur, and a vulcanization accelerator containing a sulfenamide vulcanization accelerator and a guanidine vulcanization accelerator, the content of the natural rubber is 20 to 50% by mass of the total amount of the diene rubber, the content of the butadiene rubber is 50 to 80 mass% of the total amount of the diene rubber, the content of the chlorinated paraffin is 20 to 35 parts by mass relative to 100 parts by mass of the diene rubber, the content of the antimony trioxide is 5 to 12 parts by mass per 100 parts by mass of the diene rubber, a mass ratio of (the total content of the sulfenamide vulcanization accelerator and the guanidine vulcanization accelerator) / (the sulfur content) is 1.00 or more, A rubber composition, wherein the mass ratio of (content of the guanidine vulcanization accelerator) / (content of the sulfenamide vulcanization accelerator) is 0.20 to 0.60. [2] The content of the natural rubber is 25 to 45% by mass of the total amount of the diene rubber, The rubber composition according to [1], wherein the content of the butadiene rubber is 55 to 75% by mass based on the total amount of the diene rubber. [3] The carbon black has a nitrogen adsorption specific surface area of ​​100m 2 / g or more, and the dibutyl phthalate oil absorption is 100 to 140 cm 3 The rubber composition according to [1] or [2], containing carbon black 1 in an amount of 1 / 100g. [4] The content of the chlorinated paraffin is 20 to 30 parts by mass per 100 parts by mass of the diene rubber, The rubber composition according to any one of [1] to [3], wherein the content of the antimony trioxide is 5 to 10 parts by mass per 100 parts by mass of the diene rubber. [5] The rubber composition according to any one of [1] to [4], which is for a conveyor belt. [6] A conveyor belt manufactured using the rubber composition according to any one of [1] to [5]. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a rubber composition that has excellent processability and that can keep the vulcanization rate within an appropriate range while simultaneously achieving excellent abrasion resistance and flame retardancy. The present invention also provides a conveyor belt. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view of one embodiment of the conveyor belt of the present invention. [Figure 2] FIG. 2 is a cross-sectional view of another embodiment of the conveyor belt of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described in detail below. The following description of the components may be based on a representative embodiment of the present invention, but the present invention is not limited to such an embodiment. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In the present specification, each component can be used alone or in combination of two or more kinds. In this specification, when two or more types of a certain component are used in combination, the "content" of the component means the total content of those two or more types, unless otherwise specified. In the present specification, the method for producing each component is not particularly limited unless otherwise specified, and may be, for example, a conventionally known method. In this specification, having at least one of abrasion resistance, flame retardancy, and vulcanization rate within an appropriate range, and having excellent processability, is also referred to as "having superior effects of the present invention."

[0011] [Rubber composition] The rubber composition of the present invention will be described below. The rubber composition of the present invention comprises: The rubber composition contains a diene rubber containing natural rubber and butadiene rubber, a flame retardant containing chlorinated paraffin and antimony trioxide, and a vulcanization accelerator containing carbon black, sulfur, a sulfenamide vulcanization accelerator, and a guanidine vulcanization accelerator, the content of the natural rubber is 20 to 50% by mass of the total amount of the diene rubber, the content of the butadiene rubber is 50 to 80 mass% of the total amount of the diene rubber, the content of the chlorinated paraffin is 20 to 35 parts by mass relative to 100 parts by mass of the diene rubber, the content of the antimony trioxide is 5 to 12 parts by mass per 100 parts by mass of the diene rubber, a mass ratio of (the total content of the sulfenamide vulcanization accelerator and the guanidine vulcanization accelerator) / (the sulfur content) is 1.00 or more, The rubber composition has a mass ratio of (content of the guanidine vulcanization accelerator) / (content of the sulfenamide vulcanization accelerator) of 0.20 to 0.60.

[0012] [Diene rubber] The rubber composition of the present invention contains a diene rubber including natural rubber and butadiene rubber. In the present invention, the diene rubber contained as the rubber component is a polymer formed from a monomer containing a conjugated diene compound. In the present invention, the diene rubber includes natural rubber and butadiene rubber.

[0013] [Natural rubber] In the present invention, the natural rubber (NR) contained as the diene rubber is not particularly limited, and examples thereof include conventionally known rubbers.

[0014] [Butadiene rubber] In the present invention, the butadiene rubber (BR) contained as the diene rubber is not particularly limited, and examples thereof include those known in the art. In one preferred embodiment, the BR is, for example, polybutadiene that is solid at 23° C. The BR may be unmodified or modified.

[0015] The weight average molecular weight of the BR can be set to 200,000 to 1,000,000. In this specification, the weight average molecular weight (Mw) of BR can be a value calculated as a standard polystyrene by gel permeation chromatography (GPC) measurement under the following conditions. Solvent: Tetrahydrofuran Detector: RI detector

[0016] [Natural rubber content] In the present invention, the content of the natural rubber is 20 to 50% by mass of the total amount of the diene rubber. The content of the natural rubber is preferably 25 to 45% by mass of the total amount of the diene rubber, from the viewpoint of achieving better effects of the present invention.

[0017] [Butadiene rubber content] In the present invention, the content of the butadiene rubber is 50 to 80% by mass of the total amount of the diene rubber. From the viewpoint of achieving better effects of the present invention, the content of the butadiene rubber is preferably 55 to 75% by mass of the total amount of the diene rubber.

[0018] (Total content of natural rubber and butadiene rubber) The total content of the natural rubber and the butadiene rubber can be 70 to 100% by mass of the total amount of the diene rubber. In one preferred embodiment, the diene rubber is composed solely of natural rubber and butadiene rubber. When the total content of natural rubber and butadiene rubber is less than 100% by mass of the total amount of the diene rubber, the diene rubber may further contain, in addition to the natural rubber and butadiene rubber, no particular restrictions are placed on the diene rubber.

[0019] (Total content of diene rubber) The content of the diene rubber can be set to 30 to 80% by mass of the total amount of the rubber composition of the present invention.

[0020] [Flame retardant] The rubber composition of the present invention contains a flame retardant containing chlorinated paraffin and antimony trioxide.

[0021] [Chlorinated paraffin] In the present invention, the chlorinated paraffin contained as a flame retardant is a paraffin containing chlorine. (Percentage of chlorine in chlorinated paraffin) The proportion of chlorine in the chlorinated paraffin is not particularly limited, but from the viewpoint of achieving better effects of the present invention (particularly flame retardancy), it is preferably 40 to 90 mass % of the chlorinated paraffin, and more preferably 60 to 90 mass %.

[0022] [Chlorinated paraffin content] In the present invention, the content of the chlorinated paraffin is 20 to 35 parts by mass based on 100 parts by mass of the diene rubber. The content of the chlorinated paraffin is preferably 20 to 30 parts by mass relative to 100 parts by mass of the diene rubber, from the viewpoint of achieving better effects of the present invention.

[0023] [Antimony trioxide] In the present invention, there are no particular limitations on the antimony trioxide (Sb2O3) contained as a flame retardant.

[0024] [Antimony trioxide content] In the present invention, the content of antimony trioxide is 5 to 12 parts by mass based on 100 parts by mass of the diene rubber. From the viewpoint of achieving superior effects of the present invention, the content of antimony trioxide is preferably 5 to 10 parts by mass relative to 100 parts by mass of the diene rubber.

[0025] [Carbon black] The rubber composition of the present invention contains carbon black. The carbon black is not particularly limited, and examples thereof include ISAF grade carbon black and HAF grade carbon black.

[0026] (Carbon Black 1) From the viewpoint of achieving a more excellent effect of the present invention, the carbon black is selected from those having a nitrogen adsorption specific surface area of ​​100 m 2 / g or more, and the dibutyl phthalate oil absorption is 100 to 140 cm 3 It is preferable to use carbon black 1 having a specific surface area of ​​100g / 100g, and more preferable to use ISAF grade carbon black. The upper limit of the nitrogen adsorption specific surface area of ​​carbon black 1 is 130m 2 / g or less. The nitrogen adsorption specific surface area (N2SA) of carbon black can be measured in accordance with JIS K6217-2:2017. The dibutyl phthalate oil absorption (DBP) of carbon black can be measured in accordance with JIS K6217-4:2017.

[0027] (Carbon black content) The content of carbon black is preferably 40 to 60 parts by mass per 100 parts by mass of the diene rubber, from the viewpoint of achieving better effects of the present invention (particularly initial abrasion resistance and maintenance of physical properties after aging). When the carbon black contains the carbon black 1, the content of the carbon black 1 may be at least a part of the content of the carbon black, and the entire amount of the carbon black may be the carbon black 1.

[0028] [sulfur] The rubber composition of the present invention contains sulfur. The sulfur is not particularly limited as long as it is used in vulcanization of rubber, and examples thereof include conventionally known sulfur.

[0029] (Sulfur content) From the viewpoint of achieving superior effects of the present invention, the sulfur content is preferably 0.5 to 3.0 parts by mass, more preferably 1.1 to 1.5 parts by mass, and even more preferably 1.2 to 1.4 parts by mass, per 100 parts by mass of the diene rubber, where the sulfur content refers to the net amount of sulfur.

[0030] [Vulcanization accelerator] The rubber composition of the present invention contains a vulcanization accelerator containing a sulfenamide vulcanization accelerator and a guanidine vulcanization accelerator.

[0031] [Sulfenamide vulcanization accelerator] The sulfenamide vulcanization accelerator is a compound that has a sulfenamide skeleton (for example, —S—NH—) and can accelerate sulfur vulcanization. Examples of the sulfenamide vulcanization accelerator include N-cyclohexylbenzothiazole sulfenamide, N-(tert-butyl)benzothiazole sulfenamide, N-oxydiethylenebenzothiazole sulfenamide, and N,N-dicyclohexylbenzothiazole sulfenamide. The sulfenamide vulcanization accelerator preferably contains N-alkyl-2-benzothiazolylsulfenamide, and more preferably N-(tert-butyl)-2-benzothiazolylsulfenamide, because these provide better effects for the present invention.

[0032] (Sulfenamide vulcanization accelerator content) The content of the sulfenamide vulcanization accelerator is preferably 1.0 to 1.5 parts by mass, more preferably 1.05 to 1.15 parts by mass, per 100 parts by mass of the diene rubber, because this provides better effects of the present invention.

[0033] [Guanidine vulcanization accelerator] The guanidine vulcanization accelerator is a compound that has a guanidine skeleton (for example, —NH—C(═NH)—NH—) and can accelerate sulfur vulcanization. Examples of the guanidine vulcanization accelerator include diphenyl guanidine and tolyl guanidine. The guanidine vulcanization accelerator preferably contains diphenylguanidine, more preferably 1,3-diphenylguanidine, because this provides better effects of the present invention.

[0034] (Guanidine vulcanization accelerator content) The content of the guanidine vulcanization accelerator is preferably 0.20 to 0.70 parts by mass, more preferably 0.35 to 0.44 parts by mass, per 100 parts by mass of the diene rubber, because this provides better effects of the present invention.

[0035] Mass ratio of [total of sulfenamide vulcanization accelerator content and guanidine vulcanization accelerator content] / (sulfur content)] In the present invention, the mass ratio of (the total content of the sulfenamide vulcanization accelerator and the guanidine vulcanization accelerator) / (the sulfur content) is 1.00 or more. The "content of the sulfenamide vulcanization accelerator" in the mass ratio above is the content of the sulfenamide vulcanization accelerator relative to 100 parts by mass of the diene rubber. The "content of the guanidine vulcanization accelerator" in the mass ratio above is the content of the guanidine vulcanization accelerator relative to 100 parts by mass of the diene rubber. The "sulfur content" in the mass ratio is the sulfur content per 100 parts by mass of the diene rubber.

[0036] From the viewpoint of achieving superior effects of the present invention, the mass ratio of (the total content of the sulfenamide-based vulcanization accelerator and the guanidine-based vulcanization accelerator) / (the sulfur content) is preferably 1.00 to 2.00, and more preferably 1.00 to 1.60.

[0037] [mass ratio of (content of guanidine vulcanization accelerator) / (content of sulfenamide vulcanization accelerator)] In the present invention, the mass ratio of (the content of the guanidine vulcanization accelerator) / (the content of the sulfenamide vulcanization accelerator) is 0.20 to 0.60. The "content of the sulfenamide vulcanization accelerator" in the mass ratio above is the content of the sulfenamide vulcanization accelerator relative to 100 parts by mass of the diene rubber. The "content of the guanidine vulcanization accelerator" in the mass ratio above is the content of the guanidine vulcanization accelerator relative to 100 parts by mass of the diene rubber.

[0038] From the viewpoint of achieving superior effects of the present invention, the mass ratio of (the content of the guanidine vulcanization accelerator) / (the content of the sulfenamide vulcanization accelerator) is preferably 0.25 to 0.55, and more preferably 0.30 to 0.40.

[0039] (Total of sulfenamide vulcanization accelerator content and guanidine vulcanization accelerator content) The total content of the sulfenamide vulcanization accelerator and the guanidine vulcanization accelerator can be set to 80 to 100% by mass of the total amount of the vulcanization accelerators.

[0040] In one preferred embodiment, the vulcanization accelerator is composed solely of a sulfenamide-based vulcanization accelerator and a guanidine-based vulcanization accelerator. When the total content of the sulfenamide-based vulcanization accelerator and the guanidine-based vulcanization accelerator is less than 100% by mass of the total amount of the vulcanization accelerator, the vulcanization accelerator may further contain other vulcanization accelerators (other vulcanization accelerators) in addition to the sulfenamide-based vulcanization accelerator and the guanidine-based vulcanization accelerator, but these vulcanization accelerators are not particularly limited. (Other vulcanization accelerators) Examples of the other vulcanization accelerators include thiuram-based vulcanization accelerators such as tetrakis(2-ethylhexyl)thiuram disulfide; and sulfide-based vulcanization accelerators such as dibenzothiazole disulfide (DM) and 4,4'-dithiomorpholine.

[0041] (anti-aging agent) The rubber composition of the present invention preferably further contains an antioxidant. The antioxidant does not include the above amine-based compounds. The antioxidant is not particularly limited, but preferably contains an amine-based antioxidant, and more preferably contains N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6C). The content of the antioxidant is preferably 0.5 to 8.0 parts by mass based on 100 parts by mass of the diene rubber.

[0042] (additives) The rubber composition of the present invention may further contain additives in addition to the above-mentioned components, such as wax, zinc oxide, stearic acid, oil, and vulcanization retarders (e.g., N-cyclohexylthiophthalimide).

[0043] (Manufacturing method) The method for producing the rubber composition of the present invention is not particularly limited, and examples thereof include 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 at 90 to 180°C.

[0044] (hardening) The rubber composition of the present invention can be cured (vulcanized) under ordinary conditions, for example, at a curing temperature of 120 to 180° C. Pressure may be applied during curing.

[0045] (Application) The rubber composition of the present invention may be used, for example, as a rubber composition for conveyor belts.

[0046] (cured product) The cured product obtained by curing the rubber composition of the present invention has excellent abrasion resistance and flame retardancy, and the vulcanization rate can be set within an appropriate range, and it has excellent processability.

[0047] (Application) The cured product can be used, for example, as a conveyor belt.

[0048] [Conveyor belt] The conveyor belt of the present invention is a conveyor belt produced using the rubber composition of the present invention. The conveyor belt of the present invention is produced using the rubber composition of the present invention, and therefore has excellent processability, since the vulcanization rate can be set within an appropriate range while achieving both excellent abrasion resistance and flame retardancy.

[0049] [Rubber composition] 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 produced using the rubber composition of the present invention.

[0050] 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 can be produced using the rubber composition of the present invention.

[0051] The rubber composition of the present invention can achieve both excellent abrasion resistance and flame retardancy while maintaining a vulcanization rate within an appropriate range, and has excellent processability. Therefore, one of the preferred embodiments of the conveyor belt of the present invention has a cover rubber formed using the rubber composition of the present invention.

[0052] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of a conveyor belt according to the present invention with reference to the accompanying drawings, but the present invention is not limited to the drawings. Fig. 1 is a cross-sectional view of one embodiment of a conveyor belt of the present invention. The embodiment of the conveyor belt of the present invention shown in Fig. 1 (herein also referred to as a 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 layer, the outer periphery of which 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 a fabric layer 1 as a 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 determined appropriately depending on the intended use. The fabric layer may be, for example, canvas made of woven synthetic fibers such as nylon, vinylon, or polyester. Normally, the thicknesses T1 and T2 of the cover rubber 3 can be set to about 1.5 to 20 mm.

[0053] 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.

[0054] Next, a second embodiment of the conveyor belt of the present invention will be described with reference to FIG. 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 covered 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 made of a core material, for example, of approximately 50 to 230 parallel steel cords 5 each having a diameter of approximately 2.0 to 9.5 mm, each cord being made by twisting together a plurality of wires each having a diameter of approximately 0.2 to 0.4 mm. In general, the total thickness T of the conveyor belt 8 can be approximately 10 to 50 mm. Furthermore, adhesive rubber that can be adhered to galvanized steel cords used in known steel conveyor belts can be used as the cushion rubber 6. Specific examples of the cushion rubber that can be used include rubber compositions containing natural rubber (NR), acrylonitrile-butadiene rubber (NBR), styrene-butadiene copolymer rubber (SBR), butadiene rubber (BR), etc. as rubber components.

[0055] 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 mixture by heating and pressurizing it, for example, under conditions of about 120 to 180°C, about 0.1 to 4.9 MPa, and about 10 to 90 minutes.

[0056] The conveyor belt of the present invention can be used under temperature conditions of, for example, -30 to +60°C. [Example]

[0057] The present invention will be described in more detail below with reference to examples. The materials, amounts used, ratios, treatment details, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the following examples.

[0058] [Production of rubber composition] Each rubber composition was produced by mixing the components in the following tables in the composition (parts by mass) shown in the tables with a stirrer. Sulfur in each table * The amounts shown in the columns indicate the amounts of sulfur used as a commercially available product. Guanidine vulcanization accelerator 2 (DOPD) * Column 2: Guanidine vulcanization accelerator 2 (DOPD) * Column: Thiazole vulcanization accelerator * The same applies to the (Comparison DM) column. The values ​​shown in the column for the mass ratio of (sulfenamide + guanidine vulcanization accelerator) / sulfur in each table are calculated from the net amounts of sulfur, sulfenamide vulcanization accelerator, and guanidine vulcanization accelerator. The values ​​shown in the column for the mass ratio of sulfenamide vulcanization accelerator / guanidine vulcanization accelerator / sulfur indicate the amounts used as commercially available products. The same applies to the values ​​shown in the column for the mass ratio of sulfenamide vulcanization accelerator / guanidine vulcanization accelerator / sulfur.

[0059] [evaluation] The rubber compositions produced as described above were subjected to the following evaluations, and the results are shown in Table 1. [Mooney scouring time @ 125℃] (Measurement of Mooney scorch time) In accordance with the Mooney scorch test method of JIS K6300-1:2013 "Unvulcanized rubber - Physical properties - Part 1: Determination of viscosity and scorch time using a Mooney viscometer," the Mooney minimum viscosity (MIN torque) and Mooney scorch time at 125°C were measured for each rubber composition (unvulcanized) produced as described above using a Mooney viscometer (L-type rotor). The Mooney scorch time was measured as the time required for the torque to increase by 5 Mooney torque from the MIN torque (ML-5up, unit: minutes), and is shown in the Mooney scorch time (min) @ 125°C column in each table.

[0060] (Evaluation criteria for workability) In the present invention, when the Mooney scorch time measured as described above was 25.0 to 35.0 minutes, the processability was evaluated as excellent. When the Mooney scorch time is within the above range, rubber burning is unlikely to occur, which is preferable. When the Mooney scorch time is 25.0 to 35.0 minutes, a longer Mooney scorch time is more preferable from the viewpoint that rubber scorching is less likely to occur.

[0061] [Vulcanization time] (Measurement of each vulcanization time T) Each rubber composition (unvulcanized) produced as described above was subjected to torque measurement at 148°C using a rotorless vulcanization tester as a rheometer in accordance with JIS K6300-2:2001 "Unvulcanized rubber - Physical properties - Part 2: Determination of vulcanization characteristics using a vibration vulcanization tester." A vulcanization curve was created with the torque obtained as described above on the vertical axis and the vulcanization time (minutes) on the horizontal axis, and the maximum torque value MH and minimum torque value ML were obtained from the vulcanization curve. The difference between the maximum value MH and the minimum value ML obtained as described above is defined as ME. The time when the torque reaches ML+ME×0.05 (the time (minutes) from the start of vulcanization until the torque measured by the vibration vulcanization tester reaches 5% of ME, the difference between the maximum torque MH and the minimum torque ML in the vulcanization curve) is defined as T5. The time when the torque reaches ML+ME×0.30 is defined as T30 (the time (minutes) from the start of vulcanization until the torque measured by the vibration vulcanization tester reaches 30% of ME, the difference between the maximum torque MH and the minimum torque ML in the vulcanization curve). The time when the torque reaches ML+ME×0.70 is defined as T70 (the time (minutes) from the start of vulcanization until the torque measured by the vibration vulcanization tester reaches 70% of ME, the difference between the maximum torque MH and the minimum torque ML in the vulcanization curve). The time when the torque reaches ML+ME×0.95 is defined as T95 (the time (minutes) from the start of vulcanization until the torque measured by the vibration vulcanization tester reaches 95% of ME, the difference between the maximum torque MH and the minimum torque ML on the vulcanization curve).

[0062] (T70-T30) The T70 and T30 obtained as above are applied to "T70-T30". (T95-T5) The T95 and T5 obtained as above are applied to "T95-T5".

[0063] (Evaluation criteria for vulcanization speed) In the present invention, when the T70-T30 value obtained as described above satisfies the formula (1): 3.0≦(T70-T30)≦3.5, and the T95-T5 value obtained as described above satisfies the formula (2): 15.0≦(T95-T5)≦18.0, the vulcanization rate was evaluated to be within an appropriate range. When the vulcanization rate is within an appropriate range, the productivity of the obtained rubber product is excellent, which is preferable. The vulcanization rate was evaluated as being more appropriate the closer the T70-T30 value was to 3.0 and / or the closer the T95-T5 value was to 15.0.

[0064] [Wear resistance] (Preparation of vulcanized test specimens) Each rubber composition produced 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 vulcanized test specimens having a diameter of 16 mm and a thickness of 6 mm. (DIN abrasion test) Using each vulcanized test specimen prepared as described above, a DIN abrasion test (Method A: non-rotating type where the test specimen is not rotated) was carried out at 23°C using a DIN abrasion tester in accordance with JIS K6264-2:2005, with the drum rotation speed of the DIN abrasion tester at 40 rpm and a load of 9.8 N. The abrasion loss [mm 3 ] was measured. The wear measured as above was 40 mm 3 Cases where the result was as follows were marked with "◎". The wear measured as above was 40 mm 3 Over 70mm 3 If the result was as follows, it was marked as "○". When the wear amount measured as above exceeded 70 mm, it was marked as "X."

[0065] (Evaluation criteria for abrasion resistance) In the present invention, the amount of wear measured as described above is 70 mm 3 When the value was equal to or less than this, the abrasion resistance was evaluated as excellent. The above wear amount is 70 mm 3 The smaller the value, the better the abrasion resistance.

[0066] [Flame retardant] (Preparation of test specimens) Using each rubber composition produced 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 performance conveyor belts - Grades and test methods" for fabric-layer conveyor rubber. The test specimens were vulcanized under normal vulcanization conditions using a press molding machine at 148°C under a surface pressure of 3.0 MPa for 30 minutes.

[0067] (Flame retardancy evaluation method) The flame duration (unit: seconds) of the test specimens prepared as described above was measured in accordance with JIS K6324:2013 "Flame retardant performance conveyor belts - Grades and test methods." (Flame retardancy evaluation criteria) In the present invention, when the above test piece satisfies the JIS Class 3 flame retardancy test standard [flame duration of 1 minute or less (flame duration is the average value of 3 test pieces), no re-burning], the flame retardancy is evaluated as excellent, and this is indicated by "Good". If the test piece did not meet the JIS Class 3 flame retardancy test standard, it was evaluated as having poor flame retardancy and marked with "X".

[0068] [Table 1]

[0069] [Table 2]

[0070] [Table 3]

[0071] [Table 4]

[0072] Details of each component shown in Tables 1 to 4 are as follows. (Diene 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.)

[0073] (carbon black) CB (ISAF): Show Black N220, manufactured by Cabot Japan. N2SA: 111m 2 / g, DBP:115cm 3 / 100g CB (HAF): Product name: Seast N, manufactured by Shin-Nichika Carbon Co., Ltd. N2SA: 74m 2 / g, DBP: 101 cm 3 / 100g

[0074] (Flame retardant) Chlorinated paraffin: CHLORINATED PARAFFIN 70 (trade name) manufactured by NEIMENGGU XIHE CHEMICAL CO., LTD. Average chlorine content: 70% by mass. Antimony trioxide: PATOX-M (product name) manufactured by Nihon Seiko Co., Ltd.

[0075] Antioxidant (6C): Amine-based antioxidant. N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (structure shown below). Trade name: Ozonone 6C (manufactured by Seiko Chemical Co., Ltd.). [ka] Wax: Paraffin wax. Product name: OZOACE-0037 (manufactured by Nippon Seiro Co., Ltd.) Zinc oxide: Product name: "Zinc oxide type 3" (manufactured by Seido Chemical Industry Co., Ltd.). Stearic acid: Product name "Stearic Acid 50S" (manufactured by Nisshin Rika Co., Ltd.)

[0076] (sulfur) ·sulfur * : Oil-treated sulfur. Manufactured by Hosoi Chemical Industry Co., Ltd. Sulfur concentration: 95.24% by mass.

[0077] (Sulfenamide vulcanization accelerator) Sulfenamide vulcanization accelerator 1 (CZ): N-cyclohexyl-2-benzothiazolyl sulfenamide (structure shown below) (trade name: Noccela CZ, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) [ka] Sulfenamide vulcanization accelerator 2 (NS): N-(tert-butyl)-2-benzothiazole sulfenamide (structure shown below) (trade name: Suncerer NS-G, manufactured by Sanshin Chemical Industry Co., Ltd.) [ka]

[0078] (Guanidine vulcanization accelerator) Guanidine vulcanization accelerator 1 (DPG): diphenylguanidine (structure shown below) (trade name: Soxinol DG, manufactured by Sumitomo Chemical Co., Ltd.) [ka] Guanidine vulcanization accelerator 2 (DOPG) * 1,3-di-o-tolylguanidine (structure below) (trade name: Soxinol DT-O, manufactured by Sumitomo Chemical Co., Ltd.) 1,3-di-o-tolylguanidine concentration of 95% by mass or more. When calculating the net amount of 1,3-di-o-tolylguanidine contained in the above commercially available product, the concentration of 1,3-di-o-tolylguanidine in the above commercially available product was set to 95% by mass. [ka]

[0079] Thiuram vulcanization accelerator (comparison: TMTM): Tetramethylthiuram monosulfide (trade name: Noccela TS, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) Thiazole vulcanization accelerator * (Comparative example: DM): Dibenzothiazole disulfide (trade name: Noccela DM-PO, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) with a dibenzothiazole disulfide concentration of 95% by mass or more. When calculating the net amount of dibenzothiazole disulfide in the above commercially available product, the dibenzothiazole disulfide concentration in the above commercially available product was assumed to be 95% by mass.

[0080] From the results in Tables 1 to 4, it was confirmed that the rubber composition of the present invention exhibits the desired effects.

[0081] On the other hand, Comparative Examples 1 and 9, in which the mass ratio of (content of guanidine vulcanization accelerator) / (content of sulfenamide vulcanization accelerator) was smaller than the predetermined range, had poor processability. Also, Comparative Example 9 did not achieve an appropriate vulcanization rate. In Comparative Examples 2 and 10 to 12, in which the mass ratio of (total of the sulfenamide vulcanization accelerator content and the guanidine vulcanization accelerator content) / (sulfur content) was less than 1.00, the vulcanization rate was not within an appropriate range. Comparative Examples 2 and 11 also had poor processability. Comparative Example 3, which did not contain a guanidine vulcanization accelerator but instead contained a thiuram vulcanization accelerator, Comparative Example 4, which did not contain a guanidine vulcanization accelerator but instead contained a thiazole vulcanization accelerator, and Comparative Example 5, which did not contain a guanidine vulcanization accelerator, did not at least achieve a vulcanization rate within an appropriate range.Comparative Examples 4 and 5 also had poor processability. In Comparative Examples 6 and 7, in which the contents of natural rubber and butadiene rubber were outside the prescribed ranges, at least the vulcanization rate did not fall within the appropriate range. Comparative Example 8, in which the content of chlorinated paraffin was outside the specified range, had poor processability and abrasion resistance, and the vulcanization rate did not fall within the appropriate range. In Comparative Example 13, in which the mass ratio of (total of the content of sulfenamide-based vulcanization accelerator and the content of guanidine-based vulcanization accelerator) / (content of sulfur) was less than 1.00 and the mass ratio of (content of guanidine-based vulcanization accelerator) / (content of sulfenamide-based vulcanization accelerator) was outside the predetermined range, the vulcanization rate did not fall within an appropriate range. In Comparative Example 14, in which the mass ratio of (content of guanidine vulcanization accelerator) / (content of sulfenamide vulcanization accelerator) was greater than the predetermined range, the vulcanization rate did not fall within the appropriate range. [Explanation of symbols]

[0082] 1: Cloth layer 2:Coated rubber 3, 7: Cover rubber 4, 8: Conveyor belt 5: Steel cord 6: Cushion rubber

Claims

1. The rubber composition contains a diene rubber containing natural rubber and butadiene rubber, a flame retardant containing chlorinated paraffin and antimony trioxide, and a vulcanization accelerator containing carbon black, sulfur, a sulfenamide vulcanization accelerator, and a guanidine vulcanization accelerator, the content of the natural rubber is 20 to 50% by mass of the total amount of the diene rubber, the content of the butadiene rubber is 50 to 80% by mass of the total amount of the diene rubber, the content of the chlorinated paraffin is 20 to 35 parts by mass based on 100 parts by mass of the diene rubber, the content of the antimony trioxide is 5 to 12 parts by mass per 100 parts by mass of the diene rubber, a mass ratio of (the total content of the sulfenamide-based vulcanization accelerator and the guanidine-based vulcanization accelerator) / (the content of the sulfur) is 1.00 or more, A rubber composition, wherein the mass ratio of (the content of the guanidine vulcanization accelerator) / (the content of the sulfenamide vulcanization accelerator) is 0.20 to 0.

60.

2. the content of the natural rubber is 25 to 45% by mass of the total amount of the diene rubber, 2. The rubber composition according to claim 1, wherein the content of the butadiene rubber is 55 to 75 mass % of the total amount of the diene rubber.

3. The carbon black has a nitrogen adsorption specific surface area of ​​100 m ２ / g or more, and the dibutyl phthalate oil absorption is 100 to 140 cm ３ 2. The rubber composition according to claim 1, further comprising carbon black 1 in an amount of 100g / 100g.

4. the content of the chlorinated paraffin is 20 to 30 parts by mass based on 100 parts by mass of the diene rubber, 2. The rubber composition according to claim 1, wherein the content of the antimony trioxide is 5 to 10 parts by mass per 100 parts by mass of the diene rubber.

5. The rubber composition according to claim 1, which is used for a conveyor belt.

6. A conveyor belt manufactured using the rubber composition according to any one of claims 1 to 5.

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