Rubber compositions, vulcanized products, molded articles, and transmission belts

Abstract

To provide a rubber composition with improved cold resistance after vulcanization. [Solution] A rubber composition comprising chloroprene rubber containing sulfur-modified chloroprene rubber, wherein the heat of fusion ΔH obtained by a predetermined method is 8.50 J / g or less.

Description

Technical Field

[0001] The present invention relates to a rubber composition, a vulcanizate, a molded body, and a transmission belt.

Background Art

[0002] Chloroprene rubber is excellent in mechanical strength, chemical resistance, heat resistance, cold resistance, oil resistance, etc., and is therefore used as a material for industrial transmission belts, vibration-proof rubber, hoses, wipers, seal parts, etc.

[0003] Patent Document 1 has an object of providing a chloroprene-based rubber composition capable of producing a vulcanized rubber having both low-temperature characteristics and mechanical strength. When the total amount of the rubber component is 100 parts by weight, it contains 50 parts by weight or more of chloroprene rubber and contains 5 parts by weight or more of a saturated aliphatic carboxylic acid represented by a predetermined formula and having a molecular weight of 300 or more. A rubber composition is described.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention provides a rubber composition having improved cold resistance after vulcanization.

Means for Solving the Problems

[0006] The present inventors have found that in a rubber composition containing chloroprene rubber containing sulfur-modified chloroprene rubber, the cold resistance after vulcanization of the rubber composition can be improved by setting the heat of fusion ΔH obtained by a predetermined method within a predetermined range, and completed the present invention.

[0007] In other words, the present invention provides the following rubber composition, vulcanized product, molded article, and transmission belt.

[0008] [1] Contains chloroprene rubber containing sulfur-modified chloroprene rubber, A rubber composition having a melting heat ΔH of 8.50 J / g or less, obtained by the method described below. (method) A vulcanized sheet is prepared by press vulcanizing the rubber composition under the conditions of vulcanization temperature 170°C, pressure 10 MPa, and vulcanization time 10 minutes, in accordance with JIS K 6299:2012. A test piece with a mass of 8 mg is cut from the vulcanized sheet, and differential scanning calorimetry is performed in accordance with JIS K 7122:2012. Pretreatment is performed under the conditions of heating from 25°C to 80°C at a heating rate of 10°C / min in a nitrogen atmosphere and holding for 10 minutes, cooling to 0°C at a cooling rate of 10°C / min and holding for 24 hours, and cooling to -60°C at a cooling rate of 10°C / min. Then, measurement is performed under the conditions of holding at -60°C for 5 minutes and heating to 80°C at a heating rate of 10°C / min. The heat of fusion ΔH is determined from the DSC curve obtained from the measurement. [2] The rubber composition according to [1], further comprising carbon black. [3] The rubber composition according to [2], wherein the amount of iodine adsorbed by the carbon black, as measured in accordance with JIS K 6217-1:2018, is 15 mg / g or more and 130 mg / g or less. [4] The rubber composition according to [2] or [3], wherein the carbon black content is 15 parts by mass or more and 80 parts by mass or less per 100 parts by mass of the chloroprene rubber. [5] A rubber composition according to any one of [1] to [4], further comprising an anti-aging agent. [6] The rubber composition according to [5], wherein the aforementioned antioxidant comprises an amine-based antioxidant. [7] The rubber composition according to [5] or [6], wherein the content of the antioxidant is 0.2 parts by mass or more and 8 parts by mass or less per 100 parts by mass of the chloroprene rubber. [8] A rubber composition according to any one of [1] to [7], wherein the CS obtained by the method described below is less than 51%. (method) In accordance with JIS K 6299:2012, the rubber composition is press-vulcanized under the conditions of a vulcanization temperature of 170°C, a pressure of 10 MPa, and a vulcanization time of 15 minutes to produce a large test specimen (cylindrical, diameter 29.0 ± 0.5 mm, thickness 12.5 ± 0.5 mm). Then, in accordance with JIS K 6262:2013, a compression set test is performed under the conditions of a compressibility of 25%, a test temperature of 0°C, and a test time of 72 hours to determine the compression set CS. [9] A vulcanized product of a rubber composition described in any one of [1] to [8].

[10] A molded article containing the vulcanized product described in [9].

[11] A transmission belt, including the molded body described in

[10] . [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a rubber composition with improved cold resistance after vulcanization. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described below. In this specification, unless otherwise specified, "A to B" indicating a numerical range means A or greater and B or less.

[0011] (Rubber composition) The rubber composition of this embodiment contains chloroprene rubber containing sulfur-modified chloroprene rubber. The rubber composition of this embodiment has a melting heat ΔH of 8.50 J / g or less obtained by the following method.

[0012] (method) In accordance with JIS K 6299:2012, a vulcanized sheet is produced by press-vulcanizing a rubber composition under the conditions of a vulcanization temperature of 170 °C, a pressure of 10 MPa, and a vulcanization time of 10 minutes. A test piece weighing 8 mg is cut out from the vulcanized sheet, and differential scanning calorimetry is performed in accordance with JIS K 7122:2012. Under a nitrogen atmosphere, the temperature is raised from 25 °C to 80 °C at a rate of 10 °C / min and held for 10 minutes, then the temperature is lowered to 0 °C at a rate of 10 °C / min and held for 24 hours, and the pretreatment is performed under the condition that the temperature is lowered to -60 °C at a rate of 10 °C / min. Then, it is held at -60 °C for 5 minutes, and the measurement is performed under the condition that the temperature is raised to 80 °C at a rate of 10 °C / min. The heat of fusion ΔH is determined from the DSC curve obtained by the measurement.

[0013] In this embodiment, ΔH is 8.50 J / g or less, preferably 8.20 J / g or less, more preferably 8.00 J / g or less, still more preferably 7.80 J / g or less, still more preferably 7.60 J / g or less, still more preferably 7.50 J / g or less, still more preferably 7.40 J / g or less. ΔH may be 0.10 J / g or more, may be 0.50 J / g or more, may be 1.00 J / g or more, may be 2.00 J / g or more, may be 3.00 J / g or more, may be 3.50 J / g or more. That is, ΔH is 8.50 J / g or less, preferably 0.10 J / g or more and 8.20 J / g or less, more preferably 0.50 J / g or more and 8.00 J / g or less, still more preferably 1.00 J / g or more and 7.80 J / g or less, still more preferably 2.00 J / g or more and 7.60 J / g or less, still more preferably 3.00 J / g or more and 7.50 J / g or less, still more preferably 3.50 J / g or more and 7.40 J / g or less.

[0014] According to the study by the inventors, it has been clarified that by setting ΔH below the above upper limit value, the cold resistance of the rubber composition after vulcanization can be improved.

[0015] In this embodiment, by using chloroprene rubber having a relatively slow crystallization rate as the chloroprene rubber contained in the rubber composition, ΔH tends to be small.

[0016] (chloroprene rubber) The chloroprene rubber of this embodiment contains sulfur-modified chloroprene rubber. The sulfur-modified chloroprene rubber is, for example, a chloroprene rubber having a terminal group represented by the following general formula (1). -S x ~S-C(=S)-N-R2(1) In general formula (1), each R independently represents an alkyl group or an aryl group, and x represents an integer of 1 or more.

[0017] The sulfur bond possessed by the sulfur-modified chloroprene rubber has a relatively small bond energy. When the sulfur bond is broken, the viscosity of the rubber composition decreases. By containing sulfur-modified chloroprene rubber in the chloroprene rubber, the viscosity of the rubber composition is likely to decrease during kneading, and the processability of the rubber composition can be improved.

[0018] In general formula (1), each R independently represents an alkyl group or an aryl group. R preferably contains an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 15 carbon atoms. Thereby, the heat generation property after vulcanization of the rubber composition can be reduced.

[0019] The Mooney viscosity ML(1+4) 100°C of the chloroprene rubber measured in accordance with JIS K 6300-1:2013 is preferably 10 or more and 90 or less, more preferably 20 or more and 80 or less, still more preferably 30 or more and 70 or less, still more preferably 35 or more and 60 or less, still more preferably 40 or more and 55 or less. By setting the Mooney viscosity ML(1+4) 100°C of the chloroprene rubber within the above range, the processability of the rubber composition can be improved.

[0020] (carbon black) The rubber composition of this embodiment preferably further contains carbon black. Thereby, mechanical properties such as weather resistance, abrasion resistance, and dynamic fatigue resistance after vulcanization of the rubber composition can be improved.

[0021] The amount of iodine adsorbed by carbon black, as measured in accordance with JIS K 6217-1:2018, is preferably 15 mg / g to 130 mg / g, more preferably 20 mg / g to 100 mg / g, and even more preferably 30 mg / g to 90 mg / g. By setting the amount of iodine adsorbed by carbon black within the above range, the balance of performance characteristics such as low heat generation, abrasion resistance, scorch resistance, and tensile strength of the rubber composition after vulcanization can be improved.

[0022] In accordance with JIS K 6217-6:2019, the average particle size of carbon black, calculated from the mass distribution density curve of the aggregate mass distribution, is preferably 20 nm to 60 nm, more preferably 22 nm to 56 nm, even more preferably 24 nm to 52 nm, and even more preferably 26 nm to 48 nm. By setting the average particle size of carbon black within the above range, the balance of performance characteristics such as low heat generation, abrasion resistance, scorch resistance, and tensile strength of the rubber composition after vulcanization can be improved.

[0023] The DBP (dibutyl phthalate) absorption of carbon black, measured in accordance with JIS K 6217-4:2017, is preferably 80 mL / 100g to 150 mL / 100g, more preferably 90 mL / 100g to 130 mL / 100g, and even more preferably 100 mL / 100g to 120 mL / 100g. By setting the DBP absorption of carbon black within the above range, the balance of performance characteristics such as low heat generation, abrasion resistance, and scorch resistance of the rubber composition after vulcanization can be improved.

[0024] The carbon black preferably includes at least one selected from the group consisting of FEF carbon black and HAF carbon black. This improves the mechanical properties of the rubber composition after vulcanization, such as weather resistance, abrasion resistance, and dynamic fatigue resistance. FEF carbon black refers to carbon black designated as N550 in ASTM D 1765. HAF carbon black refers to carbon black designated as N330 in ASTM D 1765.

[0025] The carbon black content per 100 parts by mass of chloroprene rubber is preferably 15 parts by mass or more and 80 parts by mass or less, more preferably 20 parts by mass or more and 70 parts by mass or less, even more preferably 25 parts by mass or more and 60 parts by mass or less, and even more preferably 30 parts by mass or more and 55 parts by mass or less. By setting the carbon black content per 100 parts by mass of chloroprene rubber within the above range, the mechanical properties of the rubber composition after vulcanization, such as weather resistance, abrasion resistance, and dynamic fatigue resistance, can be improved.

[0026] (Filler) The rubber composition of this embodiment may contain fillers other than carbon black, such as silica, clay, talc, and calcium carbonate, and may also contain silica.

[0027] (Anti-aging agent) The rubber composition of this embodiment preferably further contains an anti-aging agent. This suppresses the deterioration of the rubber composition after vulcanization.

[0028] Anti-aging agents include, for example, Amine-based antioxidants such as 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, p-(p-toluenesulfonylamide)diphenylamine, and N-isopropyl-N'-p-phenylenediamine; Phenolic antioxidants such as 2,2'-methylenebis(4-methyl-6-tert-butylphenol) and 2,2'-methylenebis(4-ethyl-6-tert-butylphenol); Sulfur-based antioxidants such as 2-mercaptobenzimidazole and 2-mercaptomethylbenzimidazole; and, It may also contain at least one selected from the group consisting of phosphorus-based anti-aging agents such as tris(nonylphenyl)phosphite.

[0029] The antioxidant preferably comprises at least one selected from the group consisting of amine-based antioxidants and sulfur-based antioxidants, more preferably comprising an amine-based antioxidant, and even more preferably comprising at least one selected from the group consisting of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, and even more preferably comprising 4,4'-bis(α,α-dimethylbenzyl)diphenylamine. This suppresses deterioration of the rubber composition after vulcanization.

[0030] Anti-aging agents do not need to contain sulfur-based anti-aging agents.

[0031] The content of the antioxidant per 100 parts by mass of chloroprene rubber is preferably 0.2 parts by mass or more and 8 parts by mass or less, more preferably 0.4 parts by mass or more and 6 parts by mass or less, even more preferably 0.6 parts by mass or more and 4 parts by mass or less, even more preferably 0.8 parts by mass or more and 3 parts by mass or less, and even more preferably 1 part by mass or more and 2 parts by mass or less. By setting the content of the antioxidant per 100 parts by mass of chloroprene rubber within the above range, it is possible to improve the mechanical properties while suppressing deterioration of the rubber composition after vulcanization.

[0032] The content of the amine-based antioxidant per 100 parts by mass of chloroprene rubber is preferably 0.2 parts by mass or more and 8 parts by mass or less, more preferably 0.4 parts by mass or more and 6 parts by mass or less, even more preferably 0.6 parts by mass or more and 4 parts by mass or less, even more preferably 0.8 parts by mass or more and 3 parts by mass or less, and even more preferably 1 part by mass or more and 2 parts by mass or less. By setting the content of the amine-based antioxidant per 100 parts by mass of chloroprene rubber within the above range, it is possible to improve the mechanical properties while suppressing deterioration of the rubber composition after vulcanization.

[0033] (Sulfurizing agents and sulfurizing accelerators) The rubber composition of this embodiment preferably further comprises a vulcanizing agent. This allows the rubber composition to be properly vulcanized.

[0034] The vulcanizing agent may, for example, contain a metal oxide, and may contain at least one selected from the group consisting of zinc oxide, magnesium oxide, lead oxide, trilead tetroxide, iron oxide, titanium dioxide, calcium oxide, and hydrotalcite, or it may contain at least one selected from the group consisting of zinc oxide and magnesium oxide.

[0035] The content of the vulcanizing agent per 100 parts by mass of chloroprene rubber is preferably 1 part by mass or more and 20 parts by mass or less, more preferably 2 parts by mass or more and 15 parts by mass or less, and even more preferably 3 parts by mass or more and 10 parts by mass or less. By setting the content of the vulcanizing agent per 100 parts by mass of chloroprene rubber within the above range, the rubber composition can be properly vulcanized, and the mechanical properties of the rubber composition after vulcanization can be improved.

[0036] The rubber composition of this embodiment does not necessarily have to contain vulcanization accelerators such as thiourea-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiram-based vulcanization accelerators, and guanidine-based vulcanization accelerators. Since sulfur-modified chloroprene rubber crosslinks easily, the rubber composition can sometimes be properly vulcanized even without the inclusion of vulcanization accelerators.

[0037] (Processing aid) The rubber composition of this embodiment preferably contains a processing aid. This improves the processability of the rubber composition.

[0038] The processing aid preferably comprises at least one selected from the group consisting of fatty acids such as stearic acid, fatty acid metal salts such as zinc stearate, and fatty acid amides such as stearic acid amide, and more preferably comprises at least one selected from the group consisting of fatty acids and fatty acid metal salts. This improves the processability of the rubber composition.

[0039] When the vulcanizing agent contains a metal oxide, the processing aid preferably contains a fatty acid, and more preferably stearic acid. This improves the processability of the rubber composition.

[0040] The content of the processing aid per 100 parts by mass of chloroprene rubber is preferably 0.1 parts by mass or more and 5 parts by mass or less, more preferably 0.2 parts by mass or more and 4 parts by mass or less, and even more preferably 0.3 parts by mass or more and 3 parts by mass or less. By setting the content of the processing aid per 100 parts by mass of chloroprene rubber within the above range, the balance between the processability of the rubber composition and the mechanical properties of the rubber composition after vulcanization can be improved.

[0041] (Plasticizer) The rubber composition of this embodiment preferably further contains a plasticizer. This improves the processability of the rubber composition.

[0042] The plasticizer may include, for example, ester-based plasticizers such as aliphatic dibasic acid-based plasticizers and epoxy-based plasticizers; and at least one selected from the group consisting of process oils such as aromatic process oils, naphthenic process oils, and paraffinic process oils.

[0043] The plasticizer may include an aliphatic dibasic acid plasticizer, and may include at least one selected from the group consisting of dioctyl sebacate, dioctyl azelaate, dioctyl adipicate, diisononyl adipicate, and diisodecyl adipicate, and may also include dioctyl sebacate.

[0044] The plasticizer may include process oils, and may include at least one selected from the group consisting of aromatic process oils and naphthenic process oils.

[0045] The content of plasticizer per 100 parts by mass of chloroprene rubber is preferably 3 parts by mass or more and 30 parts by mass or less, more preferably 4 parts by mass or more and 25 parts by mass or less, and even more preferably 5 parts by mass or more and 20 parts by mass or less. By setting the content of plasticizer per 100 parts by mass of chloroprene rubber within the above range, the balance between the processability of the rubber composition and the mechanical properties of the rubber composition after vulcanization can be improved.

[0046] (Physical properties of rubber compositions) The CS obtained by the following method may be less than 51%, 10% to 50%, 15% to 45%, 20% to 40%, or 25% to 35%.

[0047] (method) In accordance with JIS K 6299:2012, the rubber composition was press-vulcanized under the conditions of a vulcanization temperature of 170°C, a pressure of 10 MPa, and a vulcanization time of 15 minutes to produce a large test specimen (cylindrical, diameter 29.0 ± 0.5 mm, thickness 12.5 ± 0.5 mm). Then, in accordance with JIS K 6262:2013, a compression set test was performed under the conditions of a compression ratio of 25%, a test temperature of 0°C, and a test time of 72 hours to determine the compression set CS.

[0048] (Uses of rubber compositions) The rubber composition of this embodiment is preferably used in a power transmission belt.

[0049] (Method for manufacturing rubber composition) The rubber composition of this embodiment can be obtained, for example, by kneading the above-mentioned components using a kneading device such as a Banbury mixer.

[0050] According to the inventors' studies, the following mixing conditions make it easier to obtain a rubber composition with a small ΔH.

[0051] The method for producing the rubber composition of this embodiment preferably includes a first kneading step of kneading chloroprene rubber, and a second kneading step of kneading the kneaded chloroprene rubber with raw materials other than chloroprene rubber.

[0052] In the first kneading step, it is preferable to use a Banbury mixer as the kneading device. The kneading temperature in the first kneading step is preferably 30°C to 120°C, more preferably 40°C to 100°C, and even more preferably 50°C to 90°C. The kneading speed in the first kneading step is preferably 40 rpm to 60 rpm, more preferably 45 rpm to 55 rpm. The kneading time in the first kneading step is preferably 30 seconds to 120 seconds, more preferably 45 seconds to 90 seconds.

[0053] In the second kneading step, it is preferable to use a Banbury mixer as the kneading device. The kneading temperature in the second kneading step is preferably 80°C to 160°C, more preferably 90°C to 140°C, and even more preferably 100°C to 130°C. The kneading speed in the second kneading step is preferably 40 rpm to 60 rpm, more preferably 45 rpm to 55 rpm. The kneading time in the second kneading step is preferably 120 seconds to 420 seconds, more preferably 180 seconds to 300 seconds.

[0054] (vulcanizate) The vulcanized product of this embodiment is a vulcanized product of the rubber composition of this embodiment. The vulcanized product of this embodiment is obtained by vulcanizing the rubber composition of this embodiment. The vulcanization temperature may be 140°C to 220°C, or 150°C to 180°C. The pressure during vulcanization may be 3.5 MPa to 20 MPa, or 5 MPa to 15 MPa. The vulcanization time may be 1 minute to 60 minutes, or 3 minutes to 30 minutes.

[0055] (Molded bodies and transmission belts) The molded body of this embodiment includes the vulcanized product of this embodiment. The transmission belt of this embodiment includes the molded body of this embodiment.

[0056] Although embodiments of the present invention have been described above, these are merely examples, and various other configurations can be adopted. Furthermore, the present invention is not limited to the embodiments described above, and modifications, improvements, etc., within the scope that can achieve the objectives of the present invention are included in the present invention. [Examples]

[0057] The present invention will be described in detail below with reference to the examples. However, the present invention is not limited in any way to the descriptions in these examples.

[0058] (1) Preparation of rubber composition (Examples 1-4 and Comparative Example 1) Using a 1.7L Banbury mixer (MS-1.7 Internal Mixer, manufactured by Minami-Senju Seisakusho Co., Ltd.), chloroprene rubber was kneaded for 1 minute under water-cooled conditions at 30°C and 50 rpm. Then, each of the raw materials other than chloroprene rubber was added and kneaded for 3 minutes. After that, the tank was cleaned and kneaded for 1 minute. The discharge temperature of the kneaded material for each example and comparative example is shown in Table 1. Next, using an 8-inch open roll, the mixture was kneaded under water-cooled conditions at 30°C and cut 6 times (3 times on each side) to obtain the rubber composition. The amount of each raw material added is shown in Table 1.

[0059] Details of each ingredient are shown below.

[0060] (Chloroprene rubber (CR)) Sulfur-modified CR1: Mooney viscosity 45, slow crystallization rate. Sulfur-modified CR2: Mooney viscosity 52, slow crystallization rate. Sulfur-modified CR3: Mooney viscosity 43, slow crystallization rate. Sulfur-modified CR4: Mooney viscosity 51, moderate crystallization rate.

[0061] Mooney viscosity is measured in accordance with JIS K 6300-1:2013 as Mooney viscosity ML(1+4) at 100°C.

[0062] Furthermore, the crystallization rate of chloroprene rubber was evaluated as follows. First, the polymer density of chloroprene rubber was measured in accordance with Method A specified in JIS K 6268:1998 to identify the crystalline and amorphous regions. Then, the ratio of the mass of the crystalline region to the total mass of the chloroprene rubber was determined as the degree of crystallinity (%) of the chloroprene rubber. Next, based on the obtained degree of crystallinity value, the crystallization rate was evaluated in four stages: "fast," "moderate," "slow," and "very slow." It should be noted that there is a correlation between the degree of crystallinity and the crystallization rate; the higher the degree of crystallinity, the faster the crystallization rate.

[0063] (Other ingredients) FEF Carbon Black: Asahi Carbon Co., Ltd. "Asahi #60UG", average particle size 43nm, iodine adsorption capacity 40mg / g, DBP absorption capacity 110mL / 100g HAF carbon black: Asahi Carbon Co., Ltd. "Asahi #70G", average particle size 28nm, iodine adsorption capacity 80mg / g, DBP absorption capacity 101mL / 100g Anti-aging agent: 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, manufactured by Ouchi Shinko Chemical Industry Co., Ltd. in "Nocrac CD" Aromatic process oil: "Aromax 3" manufactured by Fuji Kogyo Co., Ltd. Naphthenic process oil: "Diana Process Oil NP-24" manufactured by Idemitsu Kosan Co., Ltd. Dioctyl sebacate (DOS): "Sensor DOS" manufactured by Shin Nippon Rika Co., Ltd. Zinc oxide: "Zinc Oxide Type 2" manufactured by Sakai Chemical Industry Co., Ltd. Magnesium oxide: "Kyowa Mag 150" manufactured by Kyowa Chemical Industry Co., Ltd. Stearic acid: Kao Corporation's "Lunaq S-70V"

[0064] The average particle size of carbon black is calculated from the mass distribution density curve of the aggregate mass distribution in accordance with JIS K 6217-6:2019. The amount of iodine adsorbed by carbon black is measured in accordance with JIS K 6217-1:2018. The amount of DBP absorbed by carbon black is measured in accordance with JIS K 6217-4:2017.

[0065] (2) Evaluation of rubber composition (Differential scanning calorimetry) In accordance with JIS K 6299:2012, 70g of rubber composition was press-vulcanized using a heating and cooling press molding machine (KMI Co., Ltd. "100TON 500mm square 3-stage compression molding machine") under the conditions of vulcanization temperature 170°C, pressure 10MPa, and vulcanization time 10 minutes to produce a vulcanized sheet. An 8mg test piece was cut from the vulcanized sheet, and differential scanning calorimetry was performed using a differential scanning calorimetry device (PerkinElmer "Diamond DSC") in accordance with JIS K 7122:2012. Pretreatment was performed under the conditions of heating from 25°C to 80°C at a heating rate of 10°C / min in a nitrogen atmosphere and holding for 10 minutes, cooling to 0°C at a cooling rate of 10°C / min and holding for 24 hours, and then cooling to -60°C at a cooling rate of 10°C / min. Next, measurements were taken under conditions where the sample was held at -60°C for 5 minutes and then heated to 80°C at a heating rate of 10°C / min. The heat of fusion ΔH was determined from the DSC curve obtained from the measurements.

[0066] (Compression set test) In accordance with JIS K 6299:2012, 14g of rubber composition was press-vulcanized using a heating and cooling press molding machine (KMI Co., Ltd. "100-ton 500mm square 3-stage compression molding machine") under the conditions of vulcanization temperature of 170°C, pressure of 10 MPa, and vulcanization time of 15 minutes to produce a large test specimen (cylindrical, diameter 29.0 ± 0.5 mm, thickness 12.5 ± 0.5 mm). Next, in accordance with JIS K 6262:2013, a compression set test was performed under the conditions of compression ratio: 25%, test temperature: 0°C, and test time: 72 hours, and the compression set CS was determined. The compression set is an indicator of cold resistance.

[0067] Table 1 shows the evaluation results of the rubber compositions in each example and comparative example.

[0068] [Table 1]

Claims

1. Contains chloroprene rubber containing sulfur-modified chloroprene rubber, A rubber composition having a melting heat ΔH of 8.50 J / g or less, obtained by the method described below. (method) In accordance with JIS K 6299:2012, the rubber composition is press-vulcanized under the conditions of a vulcanization temperature of 170°C, a pressure of 10 MPa, and a vulcanization time of 10 minutes to produce a vulcanized sheet. A test specimen with a mass of 8 mg is cut from the vulcanized sheet, and differential scanning calorimetry is performed in accordance with JIS K 7122:2012. Pretreatment is performed under the following conditions: heating from 25°C to 80°C at a heating rate of 10°C / min in a nitrogen atmosphere and holding for 10 minutes, cooling to 0°C at a cooling rate of 10°C / min and holding for 24 hours, and then cooling to -60°C at a cooling rate of 10°C / min. Next, the measurement is performed under the conditions of holding at -60°C for 5 minutes and heating up to 80°C at a heating rate of 10°C / min. The heat of fusion ΔH is determined from the DSC curve obtained from the above measurement.

2. The rubber composition according to claim 1, further comprising carbon black.

3. The rubber composition according to claim 2, wherein the amount of iodine adsorbed by the carbon black, as measured in accordance with JIS K 6217-1:2018, is 15 mg / g or more and 130 mg / g or less.

4. The rubber composition according to claim 2 or 3, wherein the carbon black content is 15 parts by mass or more and 80 parts by mass or less per 100 parts by mass of chloroprene rubber.

5. A rubber composition according to any one of claims 1 to 3, further comprising an anti-aging agent.

6. The rubber composition according to claim 5, wherein the anti-aging agent comprises an amine-based anti-aging agent.

7. The rubber composition according to claim 5, wherein the content of the anti-aging agent is 0.2 parts by mass or more and 8 parts by mass or less per 100 parts by mass of the chloroprene rubber.

8. The rubber composition according to any one of claims 1 to 3, wherein the CS obtained by the method described below is less than 51%. (method) In accordance with JIS K 6299:2012, the rubber composition is press-vulcanized under the conditions of a vulcanization temperature of 170°C, a pressure of 10 MPa, and a vulcanization time of 15 minutes to produce a large test specimen (cylindrical, diameter 29.0 ± 0.5 mm, thickness 12.5 ± 0.5 mm). Then, in accordance with JIS K 6262:2013, a compression set test is performed under the conditions of a compressibility of 25%, a test temperature of 0°C, and a test time of 72 hours to determine the compression set CS.

9. A vulcanized product of a rubber composition according to any one of claims 1 to 3.

10. A molded article comprising the vulcanized product described in claim 9.

11. A transmission belt comprising the molded body described in claim 10.

Images