Rubber composition for conveyor belt and conveyor belt

Abstract

To provide a rubber composition for conveyor belt and a conveyor belt which have processability, excellent heat resistance and abrasion resistance.SOLUTION: Provided is a rubber composition for conveyor belt contains a rubber component including ethylene-propylene-based copolymer rubber 1 in which the ethylene content is 45 mass% or more and less than 55 mass%, and ethylene-propylene-based copolymer rubber 2 in which the ethylene content is 55 mass% or more and 65 mass% or less, filler, co-cross-linking agent, organic peroxide, and antioxidant, where a mass ratio of the copolymer rubber 1 with respect to the copolymer rubber 2 is 90 / 10 to 10 / 90. Also provided is a conveyor belt fabricated by using the rubber composition for conveyor belt.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Conventionally, ethylene propylene rubber (EPM) has been used as a rubber component in rubber compositions for conveyor belts in order to impart heat resistance to the conveyor belts (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4792708 [Patent Document 2] Patent No. 5625391 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, market demand has increased for abrasion resistance in addition to heat resistance. Improved heat resistance and abrasion resistance lead to longer conveyor belt life. Improved heat resistance and abrasion resistance reduce the frequency of belt conveyor line shutdowns for replacement of end-of-life conveyor belts, improving productivity and reducing the amount of end-of-life conveyor belts that become waste.

[0005] Under these circumstances, the present inventors prepared and evaluated rubber compositions with reference to Patent Documents 1 and 2, and found that rubber obtained from a rubber composition containing EPM with a low ethylene content may have poor heat resistance or abrasion resistance (Comparative Example 1), and that rubber compositions containing EPM with a high ethylene content may have poor processability (particularly roll processability) (Comparative Example 2). Thus, in a rubber composition containing EPM, if the ethylene content in the EPM is high, the abrasion resistance and other properties improve, but the processability of the rubber composition decreases, which is a contradictory phenomenon.

[0006] Therefore, an object of the present invention is to provide a rubber composition for conveyor belts that has excellent processability, heat resistance, and abrasion resistance. Another object of the present invention is to provide a conveyor belt. [Means for solving the problem]

[0007] As a result of intensive research to solve the above problems, the present inventors have found that the desired effects can be obtained by making a rubber composition containing a rubber component containing ethylene-propylene copolymer rubbers 1 and 2 having different ethylene content ranges in a specific quantitative ratio, a filler, a co-crosslinking agent, an organic peroxide, and an antioxidant, and have arrived at the present invention. The present invention is based on the above findings and solves the above problems by specifically providing the following configurations.

[0008] [1] A rubber composition for conveyor belts, comprising a rubber component including an ethylene-propylene copolymer rubber 1 having an ethylene content of 45% by mass or more and less than 55% by mass, and an ethylene-propylene copolymer rubber 2 having an ethylene content of 55% by mass or more and 65% by mass or less, a filler, a co-crosslinking agent, an organic peroxide, and an antioxidant, wherein the mass ratio of the copolymer rubber 1 to the copolymer rubber 2 (copolymer rubber 1 / copolymer rubber 2) is 90 / 10 to 10 / 90. [2] The above filler has a nitrogen adsorption specific surface area of ​​20 to 90 m 2 / g of carbon black, and the content of the filler is 40 to 100 parts by mass per 100 parts by mass of the rubber component. [3] The rubber composition for a conveyor belt according to [1] or [2], wherein the co-crosslinking agent contains an organometallic compound, and the mass ratio of the co-crosslinking agent to the organic peroxide (co-crosslinking agent / organic peroxide) is 0.1 to 0.8. [4] The rubber composition for a conveyor belt according to any one of [1] to [3], wherein the antioxidant contains 2 to 8 parts by mass of a benzimidazole-based compound and 1 to 10 parts by mass of a styrenated diphenylamine-based compound relative to 100 parts by mass of the rubber component. [5] The rubber composition for a conveyor belt according to any one of [1] to [4], wherein the copolymer rubber 1 and the copolymer rubber 2 each independently contain an ethylene propylene rubber. [6] A conveyor belt produced using the rubber composition for a conveyor belt according to any one of [1] to [5]. [Effects of the Invention]

[0009] The rubber composition for conveyor belts of the present invention has excellent processability, heat resistance and abrasion resistance. The conveyor belt of the present invention has excellent processability, heat resistance, and abrasion resistance. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view of one embodiment of a 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

[0011] The present invention will be described in detail below. In this specification, (meth)acrylate refers to acrylate or methacrylate. Furthermore, 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 this specification, unless otherwise specified, each component may be used alone or in combination of two or more substances. When a component contains two or more substances, the content of the component means the total content of the two or more substances. In this specification, the term "the effect of the present invention is better" may be used to mean that at least one of processability, heat resistance, and abrasion resistance is better.

[0012] [Rubber composition for conveyor belts] The rubber composition for a conveyor belt of the present invention (rubber composition of the present invention) is The rubber composition for conveyor belts contains rubber components including ethylene-propylene copolymer rubber 1 having an ethylene content of 45% by mass or more and less than 55% by mass, and ethylene-propylene copolymer rubber 2 having an ethylene content of 55% by mass or more and 65% by mass or less, a filler, a co-crosslinking agent, an organic peroxide, and an antioxidant, and the mass ratio of the copolymer rubber 1 to the copolymer rubber 2 (copolymer rubber 1 / copolymer rubber 2) is 90 / 10 to 10 / 90. Each component contained in the rubber composition of the present invention will be described in detail below.

[0013] [Rubber component] In the present invention, the rubber component contains copolymer rubber 1 and copolymer rubber 2, which will be described later. In this specification, ethylene-propylene copolymer rubber may be referred to as "EPR," ethylene propylene (binary) rubber as "EPM," and ethylene propylene diene (ternary or higher) rubber as "EPDM." EPR is a concept that includes EPM and EPDM. It is preferable that the EPR is a solid at 23°C.

[0014] [Copolymer rubber 1] In the present invention, the copolymer rubber 1 is a copolymer rubber (EPR) formed from monomers containing at least ethylene and propylene, and the ethylene content in the copolymer rubber 1 is 45% by mass or more and less than 55% by mass.

[0015] Examples of the copolymer rubber 1 include EPM and EPDM. From the viewpoint of achieving better effects of the present invention, the copolymer rubber 1 preferably contains EPM.

[0016] [Ethylene content of copolymer rubber 1] In the present invention, the ethylene content of the copolymer rubber 1 is 45% by mass or more and less than 55% by mass in the copolymer rubber 1. When the ethylene content of the copolymer rubber 1 is in the above range, the effects of the present invention are excellent. The ethylene content of the copolymer rubber 1 is preferably 50.0% by mass or more and 52.0% by mass or less in the copolymer rubber 1, from the viewpoint of achieving better effects of the present invention.

[0017] There are no particular limitations on the compound that the EPDM as the copolymer rubber 1 can have as a third component (diene). Examples include non-conjugated dienes such as 5-ethylidene-2-norbornene, dicyclopentadiene, and 1,4-hexadiene. The content of the third component is preferably 0 to 10.0% by mass in the EPR, from the viewpoint of achieving better effects of the present invention.

[0018] In the present invention, the ethylene content of the EPR (including the copolymer rubbers 1 and 2) can be calculated based on ASTM D 3900. The ethylene content of the EPR may be a catalog value.

[0019] (Weight average molecular weight of copolymer rubber 1) The weight average molecular weight (Mw) of the copolymer rubber 1 is preferably 100,000 to 450,000, and more preferably 200,000 to 350,000, because the effects of the present invention are more excellent.

[0020] In the present invention, the Mw of EPR (including copolymer rubbers 1 and 2) is the weight-average molecular weight obtained in accordance with JIS K7252-3:2016 "Plastics - Determination of average molecular weight and molecular weight distribution of polymers by size exclusion chromatography - Part 3: Method at around room temperature." Solvent: tetrahydrofuran Detector: Differential refractive index detector (RI detector) Standard material: polystyrene

[0021] (State of copolymer rubber 1) The copolymer rubber 1 is preferably solid at 23° C., since this will result in a better effect of the present invention.

[0022] (Mooney viscosity of copolymer rubber 1) The Mooney viscosity of the copolymer rubber 1 at 125° C. is preferably 20 to 50 because the effects of the present invention are more excellent.

[0023] In the present invention, the Mooney viscosity of EPR (including copolymer rubbers 1 and 2) at 125°C is a viscosity (ML) measured in accordance with JIS K6300-1:2013 using an L-shaped rotor under the conditions of a preheating time of 1 minute, a rotor rotation time of 4 minutes, and a test temperature of 125°C. 1+4 , 125℃) (same below).

[0024] [Copolymer rubber 2] In the present invention, the copolymer rubber 2 is formed from monomers containing at least ethylene and propylene, and the ethylene content is 2 The copolymer rubber (EPR) accounts for 55% by mass or more and 65% by mass or less of the total.

[0025] Examples of the copolymer rubber 2 include EPM and EPDM. From the viewpoint of achieving better effects of the present invention, the copolymer rubber 2 preferably contains EPM.

[0026] [Ethylene content of copolymer rubber 2] In the present invention, the ethylene content of the copolymer rubber 2 is 2 The ethylene content of the copolymer rubber 2 is 55 to 65% by mass. When the ethylene content of the copolymer rubber 2 is in the above range, the effects of the present invention are excellent. From the viewpoint of obtaining a more excellent effect of the present invention, the ethylene content of the copolymer rubber 2 is2 It is preferable that the content of the total amount of the cellulose is 56.0 mass % or more and less than 60.0 mass %.

[0027] The compound that the EPDM as the copolymer rubber 2 can have as the third component (diene) and the content of the third component are not particularly limited. For example, they can be the same as those of the copolymer rubber 1 above.

[0028] (Weight average molecular weight of copolymer rubber 2) The weight average molecular weight (Mw) of the copolymer rubber 2 is preferably 100,000 to 200,000 because the effects of the present invention are more excellent.

[0029] (State of copolymer rubber 2) The copolymer rubber 2 is preferably solid at 23° C., since this will result in a better effect of the present invention.

[0030] (Mooney viscosity of copolymer rubber 2) Copolymer rubber 2 The Mooney viscosity at 125° C. is preferably 20 to 50 because the effects of the present invention are more excellent.

[0031] In the combination of copolymer rubber 1 and copolymer rubber 2, it is preferable that copolymer rubber 1 and copolymer rubber 2 each independently contain ethylene propylene rubber (EPM), because this provides a better effect of the present invention.

[0032] [Mass ratio of copolymer rubber 1 / copolymer rubber 2] In the present invention, the mass ratio of copolymer rubber 1 to copolymer rubber 2 (copolymer rubber 1 / copolymer rubber 2) is 90 / 10 to 10 / 90. When the mass ratio is in the above range, the effects of the present invention are excellent. The mass ratio is preferably 75 / 25 to 25 / 75, and more preferably 70 / 30 to 30 / 70, because this provides better effects of the present invention. The mass ratio is preferably 50 / 50 to 35 / 65, and more preferably 45 / 55 to 40 / 60, because this provides better effects of the present invention (particularly heat resistance of elongation at break).

[0033] [Filler] The rubber composition of the present invention contains a filler. The rubber composition of the present invention contains a filler, which enhances the effects of the present invention. In addition, the inclusion of a filler can impart, for example, reinforcement and / or flame retardancy to the resulting rubber.

[0034] Examples of fillers include carbon black; white fillers such as calcium carbonate, clay, and silica; and metal fillers such as aluminum hydroxide, titanium hydroxide, and antimony trioxide.

[0035] (carbon black) The filler preferably contains carbon black because it provides a better effect of the present invention and the initial elongation of the resulting vulcanized rubber is excellent. The filler preferably contains carbon black and has a nitrogen adsorption specific surface area (N2SA) of 20 to 90 m 2 / g, and N2SA is 20 to 60m 2 / g of carbon black (soft carbon), and N2SA is 30 to 50 m 2 It is particularly preferred that the carbon black (soft carbon) contains 0.1g of carbon black.

[0036] The nitrogen adsorption specific surface area of ​​carbon black is the amount of nitrogen adsorbed to the carbon black surface, measured in accordance with JIS K6217-2:2017 "Carbon black for rubber use - Basic properties - Part 2: Determination of specific surface area - Nitrogen adsorption method - Single point method."

[0037] The carbon black preferably contains HAF, FEF, or GPF grade carbon black, more preferably FEF or GPF grade carbon black, and even more preferably GPF grade carbon black, because these carbon blacks provide better effects of the present invention and provide excellent initial elongation of the resulting vulcanized rubber.

[0038] (Filler content) The content of the filler is preferably 40 to 100 parts by mass, more preferably 60 to 90 parts by mass, even more preferably 65 to 80 parts by mass, and even more preferably 65 to 75 parts by mass, per 100 parts by mass of the rubber component, because this will result in better effects of the present invention and better initial elongation of the resulting vulcanized rubber.

[0039] (Combination of copolymer rubber 1, 2 and filler) When the mass ratio of copolymer rubber 1 to copolymer rubber 2 (copolymer rubber 1 / copolymer rubber 2) is 45 / 55 to 35 / 65 and the filler contains GPF carbon black, the filler content is preferably 65 to 75 parts by mass per 100 parts by mass of the rubber component, because this results in better effects of the present invention and excellent initial elongation of the resulting vulcanized rubber.

[0040] [Co-crosslinking agent] The rubber composition of the present invention contains a co-crosslinking agent. The co-crosslinking agent refers to a monomer having multiple functional groups. The rubber composition of the present invention can co-crosslink the copolymer rubbers 1 and 2 by containing a co-crosslinking agent together with an organic peroxide described below.

[0041] Examples of the co-crosslinking agent include organometallic compounds and organic compounds (excluding those containing metals). Examples of organometallic compounds include di(meth)acrylate metal salts such as magnesium di(meth)acrylate and zinc dimethacrylate. Examples of organic compounds (excluding those containing metals) include (meth)acrylate compounds such as trimethylolpropane triacrylate, ethylene glycol dimethacrylate, and polyethylene glycol dimethacrylate, quinone dioxime compounds, and diallyl compounds.

[0042] The co-crosslinking agent preferably contains an organometallic compound, more preferably contains a di(meth)acrylate metal salt, and even more preferably contains magnesium di(meth)acrylate, because these provide better effects of the present invention.

[0043] (Co-crosslinking agent content) The content of the co-crosslinking agent is preferably 0.5 to 5.0 parts by mass, more preferably 1.5 to 2.5 parts by mass, per 100 parts by mass of the rubber component, because this provides better effects of the present invention (e.g., heat resistance of elongation at break) and better initial elongation of the resulting vulcanized rubber.

[0044] [Organic peroxide] The rubber composition of the present invention contains an organic peroxide. The rubber composition of the present invention contains an organic peroxide as a crosslinking agent together with the above-mentioned co-crosslinking agent, so that the copolymer rubbers 1 and 2 can be co-crosslinked.

[0045] The organic peroxide is not particularly limited as long as it is an organic substance having an -OO- bond. Specific examples include dicumyl peroxide, di-t-butyl peroxide, 1,3-bis(t-butylperoxyisopropyl)benzene (trade name "Perkadox 14-40", manufactured by Kayaku Akzo Co., Ltd.), n-butyl 4,4'-di(t-butylperoxy)valerate, and 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane. The organic peroxide may be a mixture of an organic substance having an -OO- bond and calcium carbonate.

[0046] (Organic peroxide content) The content of the organic peroxide (when the organic peroxide is a mixture of an organic substance having an -OO- bond and calcium carbonate, the total amount of these) is preferably 1.0 to 8.0 parts by mass, more preferably 4.0 to 6.0 parts by mass, per 100 parts by mass of the rubber component, because this provides better effects of the present invention. When the organic peroxide is a mixture of an organic substance having an —OO— bond and calcium carbonate, the content of calcium carbonate contained in the organic peroxide is not included in the content of the filler described below.

[0047] (mass ratio of co-crosslinking agent / organic peroxide) The mass ratio of the co-crosslinking agent to the organic peroxide (co-crosslinking agent / organic peroxide) is preferably 0.1 to 0.8, more preferably 0.3 to 0.6, and even more preferably 0.35 to 0.45, because this provides better effects of the present invention (for example, heat resistance of elongation at break) and better initial elongation of the resulting vulcanized rubber.

[0048] [Anti-aging agent] The rubber composition of the present invention contains an antioxidant. Examples of the antioxidant include benzimidazole compounds and amine compounds such as styrenated diphenylamine compounds.

[0049] (Anti-aging agent content) The content of the antioxidant is preferably 3.0 to 10.0 parts by mass, more preferably 4.0 to 9.0 parts by mass, and even more preferably 5.5 to 7.5 parts by mass, per 100 parts by mass of the rubber component, because the effects of the present invention (e.g., heat resistance of elongation at break) are superior and the initial elongation of the resulting vulcanized rubber is superior. When two or more antioxidants are used, the total content of the two or more antioxidants is the same as the content of the antioxidants described above.

[0050] The antioxidant preferably contains a benzimidazole-based compound and / or a styrenated diphenylamine-based compound, and more preferably contains a benzimidazole-based compound and a styrenated diphenylamine-based compound, because the effects of the present invention are more excellent.

[0051] (benzimidazole compounds) Examples of benzimidazole compounds include 2-mercaptobenzimidazole, 2-mercaptomethylbenzimidazole, zinc salt of 2-mercaptobenzimidazole, zinc salt of 2-mercaptomethylbenzimidazole, etc. Among them, it is preferable that the benzimidazole compound contains 2-mercaptobenzimidazole and / or 2-mercaptomethylbenzimidazole, because the effects of the present invention are more excellent.

[0052] (Benzimidazole compound content) When the antioxidant contains a benzimidazole-based compound, the content of the benzimidazole-based compound is preferably 2 to 8 parts by mass, more preferably 3.0 to 5.0 parts by mass, per 100 parts by mass of the rubber component, because this provides better effects of the present invention (e.g., heat resistance of elongation at break) and the resulting vulcanized rubber has better initial elongation.

[0053] (Styrenated diphenylamine compounds) Examples of styrenated diphenylamine compounds include compounds represented by the following formulas (I) to (VIII).

[0054] [ka]

[0055] [ka]

[0056] [ka]

[0057] [ka]

[0058] From the viewpoint of achieving better effects of the present invention, the styrenated diphenylamine compound preferably contains a compound represented by the above formula (I) and a compound represented by the above formula (II).

[0059] (Styrenated diphenylamine compound content) When the antioxidant contains a styrenated diphenylamine compound, the content of the styrenated diphenylamine compound is preferably 1.0 to 10 parts by mass, more preferably 1.0 to 3.5 parts by mass, and even more preferably 2.0 to 3.0 parts by mass, per 100 parts by mass of the rubber component, because the effects of the present invention (for example, heat resistance of elongation at break) are more excellent and the initial elongation of the resulting vulcanized rubber is excellent.

[0060] (Mass ratio of benzimidazole compound / styrenated diphenylamine compound) When the antioxidant contains a benzimidazole compound and a styrenated diphenylamine compound, the mass ratio of the content of the benzimidazole compound to the styrenated diphenylamine compound (benzimidazole compound / styrenated diphenylamine compound) is preferably more than 1.0 and not more than 2.0, because the effects of the present invention are more excellent.

[0061] (Combination of copolymer rubbers 1 and 2 with antioxidant) When the mass ratio of copolymer rubber 1 to copolymer rubber 2 (copolymer rubber 1 / copolymer rubber 2) is 45 / 55 to 35 / 65 and the antioxidant contains a benzimidazole-based compound and a styrenated diphenylamine-based compound, the total content of the antioxidants (total content of the benzimidazole-based compound and the styrenated diphenylamine-based compound) is preferably 4.0 to 9.0 parts by mass, and more preferably 5.5 to 7.5 parts by mass, per 100 parts by mass of the rubber component, because the effects of the present invention (for example, heat resistance of elongation at break) are more excellent and the initial elongation of the obtained vulcanized rubber is excellent.

[0062] (optional ingredient) In addition to the above components, the rubber composition of the present invention may further contain additives such as zinc oxide, stearic acid, and oils such as paraffin oil, within the range not impairing the object of the present invention. The type and content of each additive may be appropriately determined within the range not impairing the object of the present invention.

[0063] In one preferred embodiment, the rubber composition of the present invention is substantially free of sulfur. "Substantially free of sulfur" means that the sulfur content is 0 to 1.0% by mass of the total amount of the rubber composition of the present invention.

[0064] The rubber composition of the present invention can be produced under known conditions and by known methods. For example, the rubber composition of the present invention can be produced by mixing the above-mentioned components using a Banbury mixer, a kneader, a roll, or the like.

[0065] The rubber composition of the present invention can be used as a rubber composition for conveyor belts.

[0066] [Conveyor belt] Next, the conveyor belt of the present invention will be described. The conveyor belt of the present invention is a conveyor belt produced using the rubber composition of the present invention, and its shape, production method, etc. are the same as those of known conveyor belts.

[0067] 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, as long as all or a part of the rubber constituting the conveyor belt of the present invention is formed from the rubber composition of the present invention. Since the rubber composition of the present invention has excellent processability, heat resistance, and abrasion resistance as described above, it is preferable that the cover rubber (upper cover rubber and / or lower cover rubber) of the conveyor belt of the present invention is made of the rubber composition of the present invention, and it is more preferable that at least the upper cover rubber is made of the rubber composition of the present invention.

[0068] Specific configurations of the conveyor belt of the present invention include, for example, the following: Note that the conveyor belt of the present invention is not limited to the attached drawings.

[0069] A first embodiment of the conveyor belt of the present invention will be described with reference to FIG. Figure 1 is a cross-sectional view of one embodiment of a conveyor belt of the present invention. As shown in Figure 1, 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 layer, and the outer periphery of the core layer is covered with a cover rubber 3. The cover rubber 3 is preferably made of the rubber composition of the present invention, and it is more preferable that at least the upper cover rubber is made of the rubber composition of the present invention. The conveyor belt 4 in FIG. 1 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. The thicknesses T1 and T2 of the cover rubber 3 can usually be set to about 1.5 to 20 mm.

[0070] Furthermore, a coating rubber used in known conveyor belts can be used as the coating rubber 2. Examples of the coating rubber that can be used include rubber compositions 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.

[0071] 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 steel cords 5 are 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 made of the rubber composition of the present invention, and it is more preferable that at least the upper cover rubber is made of 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. Generally, the 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.

[0072] The conveyor belt of the present invention can be easily produced, for example, by placing a core fabric layer, steel cords, or a core layer between unvulcanized rubber sheets of the rubber composition of the present invention and vulcanizing the resulting mixture under heat and pressure in accordance with a conventional method. The vulcanization conditions are typically, for example, about 120 to 180°C, about 0.1 to 4.9 MPa, and about 10 to 90 minutes.

[0073] The conveyor belt of the present invention is produced using the rubber composition of the present invention described above, and therefore has excellent processability, heat resistance, and abrasion resistance. [Example]

[0074] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0075] <Production of Rubber Composition> Each rubber composition was produced by mixing the components shown in Table 1 in the proportions (parts by mass) shown in the table with a mixer. Specifically, each rubber composition was produced by first mixing the components shown in Table 1 with a Banbury mixer at 140°C.

[0076] <Evaluation> The rubber compositions produced as described above were subjected to the following evaluations, and the results are shown in Table 1.

[0077] (Processability: Roll processability) In the present invention, the processability was evaluated by roll processability. In the above <Production of Rubber Composition>, the state of the rubber sheet wrapping around the roll during mixing in the kneading roll machine was visually observed, and the processability (roll processability) was evaluated according to the following criteria.

[0078] Evaluation criteria ⊚: The rubber sheet is wrapped around the roll without any lift, allowing for good kneading and excellent processability. ○: The rubber sheet is wrapped around the roll with some floating, but mixing can be performed without any problems, and the processability is very good. △: The rubber sheet is wrapped around the roll with some floating, but it can be kneaded and the processability is somewhat excellent. ×: The rubber sheet floats above the roll and is not wound around, making it impossible to perform kneading processing, and processability is poor.

[0079] <Preparation of samples for tensile property evaluation> -Sample for initial tensile property evaluation Each rubber composition prepared as described above was vulcanized for 45 minutes under a pressure of 3.0 MPa using a press molding machine at 160°C to produce a vulcanized sheet with a thickness of 2 mm. JIS No. 3 dumbbell-shaped test pieces were punched out from this sheet to obtain samples for evaluating initial tensile properties.

[0080] -Sample for evaluating tensile properties after aging (180℃ x 168 hours) An aging test was carried out on each of the initial samples for evaluating tensile properties obtained as described above, in which the samples were placed at 180° C. for 168 hours. The samples obtained after the aging test are referred to as "samples for evaluating tensile properties after aging."

[0081] <Tensile test> For each of the initial samples for evaluating tensile properties and each of the samples for evaluating tensile properties after aging obtained as described above, a tensile test was performed at 23°C and a pulling rate of 500 mm / min in accordance with JIS K6251:2017, and the breaking strength (TB) and elongation at break (EB, unit: %) of each of the samples were measured.

[0082] (Initial elongation) The results of the elongation at break of each sample for evaluating initial tensile properties are shown in the "Initial Elongation" column in Table 1. The elongation at break (initial EB) of the sample for evaluating initial tensile properties was evaluated according to the following criteria. ⊚: When the initial EB is more than 495%, the initial elongation at break is particularly excellent. ◯: When the initial EB is more than 450% and 495% or less, the initial elongation at break is very excellent. Δ: When the initial EB is more than 330% and 450% or less, the initial elongation at break is slightly excellent. ×: When the initial EB is 330% or less, the initial elongation at break is poor.

[0083] [Heat resistance evaluation] In the present invention, heat resistance was evaluated comprehensively based on the evaluation results of heat resistance 1 (ΔTB), heat resistance 2 (ΔEB), and heat resistance 3 (wear resistance after aging) described below, according to the following criteria. When heat resistance 1 to heat resistance 3 were all △ or higher, the heat resistance was deemed excellent. When there were more ◎ ratings in the evaluations of heat resistance 1 to heat resistance 3, the heat resistance was deemed more excellent, and when both the evaluations of heat resistance 1 and 2 were ◎ and ΔEB of heat resistance 2 was −10% or higher, the heat resistance was deemed even more excellent. On the other hand, if any of heat resistance 1 to heat resistance 3 was x, the heat resistance was evaluated as poor.

[0084] [Heat resistance 1 (ΔTB)] TB change rate (%) The initial and post-aging TB values ​​measured as described above were applied to the following formula to determine the rate of change in TB (ΔTB), and ΔTB was evaluated according to the following criteria. ΔTB(%)=(Initial TB-Aging TB) / Initial TB×100 ⊚: When ΔTB was greater than −50% (greater than −50%), the heat resistance 1 was particularly excellent. ◯: When ΔTB is more than −53% and not more than −50%, the heat resistance 1 is very excellent. △: When ΔTB is more than −55% and −53% or less, heat resistance 1 is slightly excellent. ×: When ΔTB is −55% or less, the heat resistance 1 is poor. In the present invention, when the evaluation of ΔTB is Δ or higher, heat resistance 1 is deemed to be excellent.

[0085] [Heat resistance 2 (ΔEB)] EB change rate (%) The initial and post-aging EB values ​​measured as described above were applied to the following formula to determine the rate of change in EB (ΔEB), and ΔEB was evaluated according to the following criteria. ΔEB(%)=(Initial EB - Post-aging EB) / Initial EB×100 ⊚: When ΔEB was more than −21%, the heat resistance 2 was particularly excellent. ◯: When ΔEB is more than −22% or less and −21% or less, the heat resistance 2 is very excellent. △: When ΔEB is more than −28% and not more than −22%, heat resistance 2 is slightly excellent. ×: When ΔEB is −28% or less, the heat resistance 2 is poor. In the present invention, when the evaluation of ΔEB is Δ or higher, the heat resistance 2 is deemed to be excellent.

[0086] (wear resistance) Preparation of samples for wear resistance evaluation Each rubber composition (unvulcanized) produced as described above was vulcanized for 45 minutes using a press molding machine at 160°C under a surface pressure of 3.0 MPa to prepare an initial sample (diameter 16 mm, thickness 6 mm).

[0087] Aging sample (180℃ x 336 hours) The initial sample obtained as described above was subjected to an aging test in which it was left for 168 hours under the condition of 180° C. The sample for evaluating abrasion resistance obtained after the aging test is referred to as the "post-aging sample."

[0088] Wear test Using the initial sample and the aged sample obtained as described above, a DIN abrasion test (method A) was carried out at 23°C in accordance with JIS-K6264-2:2005, and the initial abrasion loss and the abrasion loss after aging (mm 3 ) was measured.

[0089] -Abrasion resistance evaluation criteria ◎: Initial wear amount is 120mm 3 If it is below this, the abrasion resistance is particularly excellent. ○: Initial wear amount is 120mm 3 Super 130mm 3 If it is below this, the abrasion resistance is very excellent. △: Initial wear amount is 130mm 3 Super 150mm 3 If it is less than 100%, the abrasion resistance is slightly better. ×: Initial wear amount is 150mm 3 If it is more than this, the wear resistance is poor. In the present invention, when the initial wear amount is evaluated as fair or higher, the wear resistance is deemed to be excellent.

[0090] [Heat resistance 3 (wear resistance after aging)] Based on the wear amount after aging measured as described above, heat resistance 3 was evaluated according to the following criteria. ◎: Wear amount after aging is 155mm 3 If it is below 3, the heat resistance is particularly excellent. ○: Wear amount after aging is 155 mm 3 Super 170mm 3 If it is below 3, the heat resistance is excellent. △: Wear amount after aging is 170 mm 3 Super 180mm 3 If it is less than 3, the heat resistance is slightly better. ×: Wear amount after aging is 180mm 3 If it is more than this, the heat resistance is 3, which is poor. In the present invention, when the evaluation of the wear amount after aging is Δ or higher, the heat resistance is considered to be excellent (3).

[0091] [Table 1]

[0092] [Table 2]

[0093] [Table 3]

[0094] The details of each component shown in Table 1 are as follows: (Copolymer rubber 1) EPR1-1: Ethylene-propylene copolymer rubber (EPM) having an ethylene content of 51.5% by mass, a Mooney viscosity at 125°C of 26, and a weight-average molecular weight of 310,000. Product name: "KEP-110" (manufactured by Kumho Polychem). Solid at 23°C. EPR1-1 corresponds to Copolymer Rubber 1 in the present invention.

[0095] (Copolymer rubber 2) EPR2-1: Ethylene-propylene copolymer rubber (EPM) having an ethylene content of 59.0% by mass and a Mooney viscosity at 125°C of 30. Product name: "Dutral CO 054" (manufactured by Lotte Versalis). Solid at 23°C. EPR2-1 corresponds to copolymer rubber 2 in the present invention.

[0096] Liquid EPM: An ethylene-propylene copolymer that is liquid at 23°C. Product name: "Lucant HC-3000X" (manufactured by Mitsui Chemicals). An ethylene-propylene copolymer with an ethylene content of 73 mol% (64 mass%), a propylene content of 27 mol%, and a weight-average molecular weight of 14,000. It is liquid at 23°C. Since liquid EPR has an ethylene content of 64 mass%, it is the copolymer rubber of the present invention. 2 This applies to:

[0097] (filler) Carbon Black 1: HAF grade carbon black. Nitrogen adsorption specific surface area 78m 2 / g Product name: "Vulcan 3D" (manufactured by Cabot Japan) Carbon Black 2: FEF grade carbon black. Nitrogen adsorption specific surface area 40m 2 / g Product name: "Seast F" (manufactured by Tokai Carbon Co., Ltd.) Carbon Black 3: GPF grade carbon black. Nitrogen adsorption specific surface area 35m 2 / g Product name: Niteron #GN (manufactured by Nippon Steel Carbon Co., Ltd.)

[0098] (anti-aging agent) Anti-aging agent 1 (benzimidazole compound): 2-mercaptomethylbenzimidazole. Product name: Nocrac MMB (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) Antioxidant 2: Styrenated diphenylamine compound. Product name: Nonflex LAS-P (Seiko Chemical Co., Ltd.). A mixture of compounds with the following structure: [ka]

[0099] (co-crosslinking agent) Co-crosslinking agent: Magnesium dimethacrylate, product name "High Cross GT" (Seiko Chemical Co., Ltd.)

[0100] (organic peroxide) Organic peroxide: Trade name "Perkadox 14-40" (manufactured by Kayaku Akzo Co., Ltd.). A mixture of bis(tert-butyldioxyisopropyl)benzene (content 37.5-42.5%) and calcium carbonate (content 57.5-62.5%).

[0101] Oil: Paraffin oil. Product name: SUNPAR2280 (manufactured by Japan Sun Oil Co., Ltd.)

[0102] As is clear from the results shown in Table 1, Comparative Example 1, which did not contain copolymer rubber 2, was poor in heat resistance and abrasion resistance. Comparative Example 2, which did not contain the copolymer rubber 1, had poor processability. Comparative Example 3, which did not contain copolymer rubber 1 but instead contained liquid EPM with an ethylene content of 55% by mass or more, had poor processability.

[0103] In contrast, the rubber composition of the present invention is excellent in processability, heat resistance and abrasion resistance. As described above, the rubber composition of the present invention has excellent processability, heat resistance, and abrasion resistance, and therefore, it is believed that a conveyor belt made using the rubber composition of the present invention has excellent productivity, long life, and excellent toughness. [Explanation of symbols]

[0104] 1: Cloth layer 2:Coated rubber 3, 7: Cover rubber 4, 8: Conveyor belt 5: Steel cord 6: Cushion rubber

Claims

1. A rubber composition for a conveyor belt comprising a rubber component containing only an ethylene-propylene-based copolymer rubber 1 having an ethylene content of 45% by mass or more and less than 55% by mass, and a copolymer rubber 2, a filler, a co-crosslinking agent, an organic peroxide, and an antioxidant, wherein the content of the rubber component is 49.8 to 56.2% by mass of the total amount of the rubber composition for a conveyor belt, a mass ratio of the copolymer rubber 1 to the copolymer rubber 2 (copolymer rubber 1 / copolymer rubber 2) is 90 / 10 to 30 / 70, and the copolymer rubber 2 is an ethylene propylene rubber having an ethylene content of 55% by mass or more and less than 60.0% by mass and being solid at 23°C.

2. The filler has a nitrogen adsorption specific surface area of ​​20 to 90 m 2 / g of carbon black, and the content of the filler is 40 to 100 parts by mass per 100 parts by mass of the rubber component.

3. 3. The rubber composition for a conveyor belt according to claim 1, wherein the co-crosslinking agent comprises an organometallic compound, and a mass ratio of the co-crosslinking agent to the organic peroxide (co-crosslinking agent / organic peroxide) is 0.1 to 0.

8.

4. 4. The rubber composition for a conveyor belt according to claim 1, wherein the antioxidant comprises 2 to 8 parts by mass of a benzimidazole-based compound and 1 to 10 parts by mass of a styrenated diphenylamine-based compound relative to 100 parts by mass of the rubber component.

5. The rubber composition for a conveyor belt according to any one of claims 1 to 4, wherein the copolymer rubber 1 contains an ethylene propylene rubber.

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

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