Rubber composition, vulcanizate, molded body, and transmission belt

Abstract

A rubber composition comprising chloroprene rubber, and having a tanδ(100°C), as obtained by a predetermined method, of 0.100 or less.

Description

Rubber composition, vulcanizate, molded body, and transmission belt

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

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

[0003] In Patent Document 1, with the problem 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 a rubber composition is described which 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.

[0004] Japanese Patent Application Laid-Open No. 2013-249409

[0005] The present invention provides a rubber composition with improved low heat generation after vulcanization.

[0006] The present inventors have found that in a rubber composition containing chloroprene rubber, by setting tanδ(100°C) obtained by a predetermined method within a predetermined range, the low heat generation after vulcanization of the rubber composition can be improved, and the present invention has been completed.

[0007] That is, according to the present invention, the following rubber composition, vulcanizate, molded body, and transmission belt are provided.

[0008] [1] A rubber composition comprising chloroprene rubber, wherein the tanδ (100°C) obtained by the following method is 0.100 or less. (Method) A vulcanized sheet is prepared by press vulcanizing the rubber composition in accordance with JIS K 6299:2012 under conditions of vulcanization temperature of 170°C, pressure of 10 MPa, and vulcanization time of 10 minutes. A test piece with a width of 1.5 mm, a length of 50 mm, and a thickness of 1 mm is cut from the vulcanized sheet. A thermal resistance test is performed using a forced-circulation thermal aging tester in accordance with JIS K 6257:2017 under conditions of aging temperature: 100°C and aging time: 72 hours, thereby thermal aging the test piece. [1] The rubber composition according to [1], wherein the chloroprene rubber is further comprising sulfur-modified chloroprene rubber. [2] The rubber composition according to [1], wherein the amount of iodine adsorbed by the carbon black is 15 mg / g or more and 130 mg / g or less, as measured in accordance with JIS K 6217-1:2018. [3] The rubber composition according to [1], wherein the amount of carbon black adsorbed by the carbon black is 15 mg / g or more and 130 mg / g or less. [4] The rubber composition according to [3], wherein the amount of carbon black per 100 parts by mass is 15 parts by mass or more and 80 parts by mass or less. [5] The rubber composition according to [3], wherein the amount of carbon black per 100 parts by mass of the chloroprene rubber is 15 parts by mass or more and 80 parts by mass or less. [6] The rubber composition according to any one of [1] to [5], further comprising an anti-aging agent. [7] The rubber composition according to [6], wherein the antioxidant comprises an amine-based antioxidant. [8] The rubber composition according to [6] or [7], 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 chloroprene rubber. [9] The rubber composition according to any one of [1] to [8], wherein the Δθ obtained by the following method is less than 51.0°C. (Method) In accordance with JIS K 6250:2019, the rubber composition is press-vulcanized under conditions of vulcanization temperature of 170°C, pressure of 10 MPa, and vulcanization time of 10 minutes to produce a cylindrical test piece with a diameter of 17.8 mm and a height of 25 mm. In accordance with JIS K 6265:2018, a constant strain flexometer test is performed using a Goodrich flexometer to measure the temperature rise Δθ due to internal heat generation of the test piece.The test is performed under the following conditions: test specimen temperature at the start of the test: 55°C, preheating time: 30 minutes, static compressive stress: 2 MPa, stroke: 4.45 mm, vibration speed: 1800 cycles / min, test time: 25 minutes.

[10] A vulcanized product of any one of the rubber compositions described in [1] to [9].

[11] A molded article comprising the vulcanized product described in

[10] .

[12] A transmission belt comprising the molded article described in

[11] .

[0009] According to the present invention, it is possible to provide a rubber composition with improved low heat generation after vulcanization.

[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 and has a tanδ (100°C) of 0.100 or less obtained by the following method.

[0012] (Method) In accordance with JIS K 6299:2012, a rubber composition is press-vulcanized at 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 piece measuring 1.5 mm in width, 50 mm in length, and 1 mm in thickness is cut from the vulcanized sheet. In accordance with JIS K 6257:2017, a thermal resistance test is performed using a forced-circulation thermal aging tester at an aging temperature of 100°C and an aging time of 72 hours to thermally age the test piece. After thermal aging, dynamic viscoelasticity measurements are performed on the test piece in accordance with JIS K 6394:2007 at a frequency of 10 Hz and a strain amplitude of 0.05%, and tanδ(100°C) is determined.

[0013] In this embodiment, tanδ(100°C) is 0.100 or less, preferably 0.099 or less, more preferably 0.098 or less, even more preferably 0.097 or less, even more preferably 0.096 or less, even more preferably 0.090 or less, even more preferably 0.085 or less, and even more preferably 0.080 or less. tanδ(100°C) may be greater than 0, 0.001 or more, 0.010 or more, 0.020 or more, 0.040 or more, 0.050 or more, or 0.060 or more. That is, tanδ (100°C) is 0.100 or less, preferably greater than 0 and 0.099 or less, more preferably 0.001 or more and 0.098 or less, even more preferably 0.010 or more and 0.097 or less, even more preferably 0.020 or more and 0.096 or less, even more preferably 0.040 or more and 0.090 or less, even more preferably 0.050 or more and 0.085 or less, and even more preferably 0.060 or more and 0.080 or less.

[0014] Our investigations have revealed that by setting tanδ (100°C) to below the above upper limit, the low heat generation properties of the rubber composition after vulcanization can be improved.

[0015] Although the mechanism by which such effects are obtained is not entirely clear, our inventors' studies suggest that by setting tanδ (100°C) to below the above upper limit, energy loss due to internal friction in the vulcanized rubber composition is reduced, thereby improving its low heat generation properties.

[0016] (Chloroprene rubber) Chloroprene rubber preferably includes sulfur-modified chloroprene rubber. Sulfur-modified chloroprene rubber is, for example, chloroprene rubber having an end group represented by the following general formula (1): -S ｘ ~S-C(=S)-NR ２ (1) In general formula (1), R independently represents an alkyl group or an aryl group, and x represents an integer of 1 or more.

[0017] The sulfur bonds in sulfur-modified chloroprene rubber have relatively low bond energy, and when these sulfur bonds are broken, the viscosity of the rubber composition decreases. By including sulfur-modified chloroprene rubber in the chloroprene rubber mixture, the viscosity of the rubber composition decreases more easily during mixing, improving the processability of the rubber composition.

[0018] In general formula (1), R independently represents an alkyl group or an aryl group. Preferably, R includes an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 15 carbon atoms. This further improves the low exothermic properties of the rubber composition after vulcanization.

[0019] The Mooney viscosity ML(1+4) 100°C of chloroprene rubber, measured in accordance with JIS K 6300-1:2013, is preferably 10 to 90, more preferably 20 to 80, even more preferably 30 to 70, even more preferably 35 to 60, and even more preferably 40 to 55. By setting the Mooney viscosity ML(1+4) 100°C of 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. This improves the mechanical properties of the rubber composition after vulcanization, such as weather resistance, abrasion resistance, and dynamic fatigue resistance.

[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 still 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 amount of DBP (dibutyl phthalate) absorbed by carbon black, as measured in accordance with JIS K 6217-4:2017, is preferably 80 mL / 100 g to 150 mL / 100 g, more preferably 90 mL / 100 g to 130 mL / 100 g, and even more preferably 100 mL / 100 g to 120 mL / 100 g. By setting the DBP absorption amount of carbon black within the above range, the balance of performance 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] (Fillers) 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] The anti-aging agent may include, for example, amine-based anti-aging agents 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; phenol-based anti-aging agents such as 2,2'-methylenebis(4-methyl-6-tert-butylphenol) and 2,2'-methylenebis(4-ethyl-6-tert-butylphenol); sulfur-based anti-aging agents such as 2-mercaptobenzimidazole and 2-mercaptomethylbenzimidazole; and 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] (Vulcanizing agent and vulcanization accelerator) 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 amount of 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 amount of vulcanizing agent per 100 parts by mass of chloroprene rubber within the above range, the rubber composition can be appropriately vulcanized, and the mechanical properties of the rubber composition after vulcanization can be improved.

[0036] The rubber composition of this embodiment does not need to contain vulcanization accelerators such as thiourea-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiram-based vulcanization accelerators, and guanidine-based vulcanization accelerators. In particular, if the chloroprene rubber includes sulfur-modified chloroprene rubber, the rubber composition does not need to contain vulcanization accelerators. Since sulfur-modified chloroprene rubber crosslinks easily, the rubber composition can 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 contain an aliphatic dibasic acid-based plasticizer, and may contain at least one selected from the group consisting of dioctyl sebacate, dioctyl azelate, dioctyl adipate, diisononyl adipate, and diisodecyl adipate, and may contain dioctyl sebacate.

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

[0045] The content of the plasticizer with respect to 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 still more preferably 5 parts by mass or more and 20 parts by mass or less. By setting the content of the plasticizer with respect to 100 parts by mass of chloroprene rubber within the above range, the processability of the rubber composition and the balance of the mechanical properties after vulcanization of the rubber composition can be improved.

[0046] (Physical properties of the rubber composition) Δθ obtained by the following method may be less than 51.0 °C, may be 20.0 °C or more and 50.5 °C or less, may be 30.0 °C or more and 50.0 °C or less, may be 35.0 °C or more and 49.5 °C or less, or may be 38.0 °C or more and 49.0 °C or less.

[0047] (Method) In accordance with JIS K 6250:2019, 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 cylindrical test piece with a diameter of 17.8 mm and a height of 25 mm. In accordance with JIS K 6265:2018, a constant strain flexometer test is performed using a Goodrich flexometer, and the temperature rise Δθ due to internal heat generation of the test piece is measured. The test is performed under the conditions of a test piece temperature at the start of the test: 55 °C, a preheating time: 30 minutes, a static compression stress: 2 MPa, a stroke: 4.45 mm, a vibration speed: 1800 times / minute, and a test time: 25 minutes.

[0048] (Use of the rubber composition) The rubber composition of this embodiment is preferably used for a transmission belt.

[0049] (Method for producing the rubber composition) The rubber composition of this embodiment can be obtained 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 tanδ (100°C).

[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] (Vulcanized product) 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 or more and 220°C or less, or 150°C or more and 180°C or less. The pressure during vulcanization may be 3.5 MPa or more and 20 MPa or 5 MPa or more and 15 MPa or less. The vulcanization time may be 1 minute or more and 60 minutes or 3 minutes or more and 30 minutes or less.

[0055] (Molded body and transmission belt) 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.

[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 1-5 and Comparative Example 1) Using a 1.7 L Banbury mixer (MS-1.7 Internal Mixer, manufactured by Minami Senju Seisakusho Co., Ltd.), chloroprene rubber was kneaded for 1 minute under water cooling conditions of 30°C and 50 rpm. Then, each raw material 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 in each example and comparative example is shown in Table 1. Next, using an 8-inch open roll, the mixture was kneaded under water cooling conditions of 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] (Comparative Example 2) A rubber composition was prepared in the same manner as in Example 1, except that the mixing conditions were changed. Specifically, all raw materials were mixed for 1 minute at 30°C and 50 rpm under water cooling using a 1.7 L Banbury mixer (MS-1.7 Internal Mixer, manufactured by Minami Senju Seisakusho Co., Ltd.). The discharge temperature of the mixed material is shown in Table 1. Next, the mixture was kneaded at 30°C under water cooling using an 8-inch open roll and cut 6 times (3 times on each side) to obtain the rubber composition. The amount of each raw material used is shown in Table 1.

[0060] Details of each ingredient are shown below.

[0061] (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 51, moderate crystallization rate Sulfur-modified CR4: Mooney viscosity 43, slow crystallization rate Mercaptan-modified CR: Mooney viscosity 48, very slow crystallization rate

[0062] Mooney viscosity is defined as Mooney viscosity ML(1+4) at 100°C, measured in accordance with JIS K 6300-1:2013.

[0063] 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.

[0064] (Other raw materials) FEF carbon black: Asahi Carbon Co., Ltd. "Asahi #60UG", average particle size 43 nm, iodine adsorption capacity 40 mg / g, DBP absorption capacity 110 mL / 100 g HAF carbon black: Asahi Carbon Co., Ltd. "Asahi #70G", average particle size 28 nm, iodine adsorption capacity 80 mg / g, DBP absorption capacity 101 mL / 100 g Anti-aging agent: 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, Ouchi Shinko Chemical Industry Co., Ltd. "Nocrac CD" Aromatic process oil: Fuji Kosan Co., Ltd. "Aromax 3" Naphthenic process oil: Idemitsu Kosan Co., Ltd. "Diana Process Oil NP-24" Dioctyl sebacate (DOS): Shin Nippon Rika Co., Ltd. "Sensor DOS" Zinc oxide: Sakai Chemical Industry Co., Ltd. "Zinc Oxide Type 2" Magnesium oxide: Kyowa Chemical Industry Co., Ltd. "Kyowa Mag 150" Stearic acid: Kao Corporation "Lunaq S-70V" Thiourea-based vulcanization accelerator: Ethylene thiourea, Kawaguchi Chemical Industry Co., Ltd. "Accel 22-S" Thiazole-based vulcanization accelerator: N-cyclohexylbenzothiazole-2-sulfenamide, Ouchi Shinko Chemical Industry Co., Ltd. "Noxellar CZ"

[0065] 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.

[0066] (2) Evaluation of the rubber composition (Dynamic viscoelasticity measurement after thermal aging test) In accordance with JIS K 6299:2012, 70 g of the rubber composition was press-vulcanized using a heating and cooling press molding machine (KMI Co., Ltd. "100 TON 500 square 3-stage compression molding machine") at a vulcanization temperature of 170°C, a pressure of 10 MPa, and a vulcanization time of 10 minutes to produce a vulcanized sheet. Test pieces with a width of 1.5 mm, a length of 50 mm, and a thickness of 1 mm were cut from the vulcanized sheet. In accordance with JIS K 6257:2017, a thermal resistance test was performed using a forced-circulation thermal aging test machine (Suga Test Machine Co., Ltd. "Gear Aging Test Machine TG100", vertical air type) at an aging temperature of 100°C, an aging time of 72 hours, and an air exchange rate of 3 to 10 times / hour, and the test pieces were thermally aged. Dynamic viscoelasticity measurements were performed on the heat-aged specimens using a viscoelasticity measuring device (RSA-G2, manufactured by T.A. Instruments Co., Ltd.) in accordance with JIS K 6394:2007, under the conditions of frequency: 10 Hz, strain amplitude: 0.05%, and test temperature: 30°C to 150°C, and tanδ(100°C) at 100°C was determined.

[0067] (Flexometer Test) In accordance with JIS K 6250:2019, the rubber composition was press-vulcanized under conditions of vulcanization temperature of 170°C, pressure of 10 MPa, and vulcanization time of 10 minutes to prepare cylindrical test specimens with a diameter of 17.8 mm and a height of 25 mm. In accordance with JIS K 6265:2018, a constant-strain flexometer test was performed using a Goodrich flexometer, and the temperature rise Δθ due to internal heat generation of the test specimen was measured. The test was conducted under the following conditions: test specimen temperature at the start of the test: 55°C, preheating time: 30 minutes, static compressive stress: 2 MPa, stroke: 4.45 mm, vibration speed: 1800 cycles / min, and test time: 25 minutes.

[0068] Table 1 shows the evaluation results of the rubber compositions in each example and comparative example.

[0069]

[0070] This application claims priority based on Japanese Patent Application No. 2025-017432, filed on 5 February 2025, and incorporates all of its disclosures herein.

Claims

Contains chloroprene rubber, A rubber composition having a tanδ (100°C) of 0.100 or less obtained by the method described below. (method) In accordance with JIS K 6299:2012, the rubber composition is press-vulcanized at 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 piece measuring 1.5 mm in width, 50 mm in length, and 1 mm in thickness is cut from the vulcanized sheet. In accordance with JIS K 6257:2017, a thermal resistance test is performed using a forced-circulation thermal aging tester at an aging temperature of 100°C and an aging time of 72 hours to thermally age the test piece. Dynamic viscoelasticity measurements were performed on the aforementioned test specimens after thermal aging, in accordance with JIS K 6394:2007, under conditions of frequency: 10 Hz and strain amplitude: 0.05%, to determine tanδ(100°C). 　 The rubber composition according to claim 1, wherein the chloroprene rubber includes sulfur-modified chloroprene rubber. 　 The rubber composition according to claim 1 or 2, further comprising carbon black. The rubber composition according to claim 3, wherein the iodine adsorption amount of 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. 　 The rubber composition according to claim 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. 　 The rubber composition according to claim 1 or 2, further comprising an anti-aging agent. 　 The rubber composition according to claim 6, wherein the anti-aging agent comprises an amine-based anti-aging agent. 　 The rubber composition according to claim 6, 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. 　 The rubber composition according to claim 1 or 2, wherein the Δθ obtained by the method described below is less than 51.0°C. (method) In accordance with JIS K 6250:2019, a 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 cylindrical test specimen with a diameter of 17.8 mm and a height of 25 mm. In accordance with JIS K 6265:2018, a constant-strain flexometer test is performed using a Goodrich flexometer to measure the temperature rise Δθ due to internal heat generation in the test specimen. The test is conducted under the following conditions: test specimen temperature at the start of the test: 55°C, preheating time: 30 minutes, static compressive stress: 2 MPa, stroke: 4.45 mm, vibration speed: 1800 cycles / min, and test time: 25 minutes. 　 A vulcanized product of the rubber composition according to claim 1 or 2. 　 A molded article comprising the vulcanized product described in claim 10. 　 A transmission belt comprising the molded body described in claim 11.

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