Rubber composition, vulcanizate, molded body, and vibration-proof rubber member

Abstract

This rubber composition contains a chloroprene rubber, wherein, when the rubber composition is press-vulcanized under predetermined conditions to produce a vulcanized sheet, the elongation Eb [%] at break of a dumbbell-shaped no. 3 test piece cut out from the vulcanized sheet, as measured under the conditions of 23ºC and a tensile speed of 500 mm / min in accordance with JIS K 6251:2023, and the mass change rate Δm100 [%] of a test piece having a size of 10 mm×20 mm×2 mm and cut out from the vulcanized sheet, as measured by performing a toluene immersion test under the conditions of 23ºC and 24 hours in accordance with JIS K 6258:2016, satisfy the expression Eb>12.5×Δm100-1150.

Description

Rubber compositions, vulcanized products, molded articles, and vibration-damping rubber members

[0001] The present invention relates to rubber compositions, vulcanized products, molded articles, and vibration-damping rubber members.

[0002] Chloroprene rubber is used as a material for industrial power transmission belts, vibration damping rubber, hoses, wipers, and sealing components due to its excellent mechanical strength, chemical resistance, heat resistance, cold resistance, and oil resistance.

[0003] Patent Document 1 describes a xanthogene-modified chloroprene rubber that maintains the conventional basic properties of chloroprene rubber, has a low loss tangent (tanδ), and has high elongation at break. The invention aims to provide this xanthogene-modified chloroprene rubber, which has a structure represented by a predetermined formula at the molecular ends of the chloroprene rubber and contains sulfur in the molecule.

[0004] Japanese Patent Publication No. 2017-132945

[0005] This invention provides a rubber composition with improved vibration damping properties after vulcanization.

[0006] The present inventors have found that in a rubber composition containing chloroprene rubber, the elongation at break Eb and the rate of change in mass Δm are measured by a predetermined method. １００ We discovered that by satisfying a predetermined relation, the vibration damping properties of the rubber composition after vulcanization can be improved, thus completing the present invention.

[0007] In other words, the present invention provides the following rubber composition, vulcanized product, molded article, and vibration-damping rubber member.

[0008] [1] A rubber composition containing chloroprene rubber, when a vulcanized sheet is prepared by press vulcanizing the rubber composition in accordance with JIS K 6299:2012 under conditions of vulcanization temperature of 160°C, pressure of 10 MPa, and vulcanization time of 20 minutes or more and 25 minutes or less, the elongation at break Eb [%] measured in accordance with JIS K 6251:2023 for a dumbbell-shaped No. 3 test piece cut from the vulcanized sheet at 23°C and a tensile speed of 500 mm / min, and the rate of change in mass Δm measured by performing a toluene immersion test on a 10 mm × 20 mm × 2 mm test piece cut from the vulcanized sheet at 23°C and for 24 hours in accordance with JIS K 6258:2016. １００ [%] is given by the formula: Eb > 12.5 × Δm １００ A rubber composition satisfying -1150. [2] The rubber composition according to [1], wherein Eb is 250% or more and 750% or less. [3] Δm １００A rubber composition according to [1] or [2], wherein the amount is 115% or more and 140% or less. [4] A rubber composition according to any one of [1] to [3], wherein the chloroprene rubber comprises xanthogene-modified chloroprene rubber. [5] A rubber composition according to any one of [1] to [4], further comprising carbon black. [6] A rubber composition according to [5], wherein the average particle size of the carbon black, calculated from the mass distribution density curve of the aggregate mass distribution in accordance with JIS K 6217-6:2019, is 70 nm or more and 600 nm or less. [7] A rubber composition according to [5] or [6], wherein the carbon black content is 15 parts by mass or more and 150 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], further comprising a vulcanization accelerator. [9] A rubber composition according to [8], wherein the vulcanization accelerator comprises a thiourea-based vulcanization accelerator.

[10] The rubber composition according to [8] or [9], wherein the content of the vulcanization accelerator per 100 parts by mass of the chloroprene rubber is 0.5 parts by mass or more and 5.0 parts by mass or less.

[11] The rubber composition according to any one of [1] to

[10] , further comprising a plasticizer.

[12] The rubber composition according to

[11] , wherein the plasticizer comprises an aliphatic dibasic acid plasticizer.

[13] The rubber composition according to

[11] or

[12] , wherein the content of the plasticizer per 100 parts by mass of the chloroprene rubber is 3 parts by mass or more and 30 parts by mass or less.

[14] The rubber composition according to any one of [1] to

[13] , wherein the static-dynamic ratio α, determined by the following method, is less than 1.39. (Method) In accordance with JIS K 6299:2012, the rubber composition was press-vulcanized under the conditions of vulcanization temperature 170°C, pressure 10 MPa, and vulcanization time 15 minutes to prepare large test specimens (cylindrical, diameter 29.0 ± 0.5 mm, thickness 12.5 ± 0.5 mm), and a dynamic properties test was performed at 23°C in accordance with JIS K 6394:2007. Three test specimens were prepared. After pre-compression to 3.5 mm at 1 mm / second, compression to 3.5 mm at 0.333 mm / second was performed, and the static spring constant Ks was determined in the range of 0.5 mm to 1.5 mm in the forward stroke. The dynamic spring constant Kd was also determined under the conditions of initial compression of 1.25 mm, frequency of 100 Hz, and amplitude of 0.05 mm.The static-dynamic ratio α is determined based on the formula: α = Kd / Ks.

[15] A vulcanized rubber composition according to any one of [1] to

[14] .

[16] A molded article containing the vulcanized article according to

[15] .

[17] A vibration-damping rubber member containing the molded article according to

[16] .

[0009] According to the present invention, it is possible to provide a rubber composition with improved vibration damping properties after vulcanization.

[0010] In each example and comparative example, Δm １００ This is a graph showing the relationship between and Eb.

[0011] 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.

[0012] (Rubber Composition) The rubber composition of this embodiment contains chloroprene rubber. In this embodiment, a vulcanized sheet is prepared by press vulcanizing the rubber composition in accordance with JIS K 6299:2012, under conditions of vulcanization temperature of 160°C, pressure of 10 MPa, and vulcanization time of 20 minutes to 25 minutes. In accordance with JIS K 6251:2023, the elongation at break Eb [%] is measured on a dumbbell-shaped No. 3 test piece cut from the vulcanized sheet at 23°C and a tensile speed of 500 mm / min, and in accordance with JIS K 6258:2016, the rate of change in mass Δm is measured by performing a toluene immersion test on a 10 mm × 20 mm × 2 mm test piece cut from the vulcanized sheet at 23°C and for 24 hours. １００ [%] is given by the formula: Eb > 12.5 × Δm １００ It satisfies -1150.

[0013] According to the rubber composition of this embodiment, the vibration damping properties of the rubber composition after vulcanization can be improved by satisfying the above formula. Although the mechanism is not entirely clear, the inventors' investigations suggest the following: When the vulcanized rubber composition is immersed in toluene, the toluene is retained in the crosslinked network structure of the chloroprene rubber, causing the vulcanized rubber composition to swell. Therefore, the mass change rate Δm １００The size is considered to be an index representing the crosslinked structure of chloroprene rubber. The crosslinked structure of chloroprene rubber is considered to affect the physical properties of the vulcanizate of the rubber composition. On the other hand, the size of the elongation at break Eb is considered to be an index representing the flexibility of the vulcanizate of the rubber composition. Thus, the elongation at break Eb and the mass change rate Δm １００ are indices representing the physical properties of the vulcanizate of the rubber composition, and it is considered that the vibration damping characteristics after vulcanization of the rubber composition can be improved by satisfying the above formula.

[0014] From the viewpoint of further improving the vibration damping characteristics after vulcanization of the rubber composition, Eb is preferably 250% or more, more preferably 300% or more, still more preferably 320% or more, still more preferably 340% or more, still more preferably 350% or more, still more preferably 360% or more, still more preferably 365% or more. From the viewpoint of further improving the vibration damping characteristics after vulcanization of the rubber composition, Eb is preferably 750% or less, more preferably 700% or less, still more preferably 650% or less, still more preferably 600% or less, still more preferably 580% or less, still more preferably 560% or less, still more preferably 550% or less. Eb may be 250% or more and 750% or less, may be 300% or more and 700% or less, may be 320% or more and 650% or less, may be 340% or more and 600% or less, may be 350% or more and 580% or less, may be 360% or more and 560% or less, may be 365% or more and 550% or less.

[0015] From the viewpoint of further improving the vibration damping characteristics after vulcanization of the rubber composition, Δm １００ is preferably 115% or more, more preferably 116% or more, still more preferably 117% or more, still more preferably 118% or more, still more preferably 119% or more, still more preferably 120% or more. From the viewpoint of further improving the vibration damping characteristics after vulcanization of the rubber composition, Δm １００ is preferably 140% or less, more preferably 138% or less, still more preferably 136% or less, still more preferably 134% or less, still more preferably 132% or less, still more preferably 130% or less. Δm １００It may be 115% or more and 140% or less, 116% or more and 138% or less, 117% or more and 136% or less, 118% or more and 134% or less, 119% or more and 132% or less, or 120% or more and 130% or less.

[0016] (Chloroprene rubber) Chloroprene rubber preferably includes xanthogene-modified chloroprene rubber. Xanthogene-modified chloroprene rubber is, for example, chloroprene rubber having a terminal group represented by the following general formula (1): -S-C(=S)-O-R (1) In general formula (1), R represents an alkyl group.

[0017] Because the end groups represented by general formula (1) are highly reactive, the inclusion of xanthogene-modified chloroprene rubber in the chloroprene rubber results in a network structure. Therefore, the mechanical properties of the rubber composition after vulcanization can be improved.

[0018] In general formula (1), R represents an alkyl group. R may include an alkyl group having 1 to 4 carbon atoms, and may include at least one selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, and cyclobutyl groups, or at least one selected from the group consisting of methyl, ethyl, isopropyl, and isobutyl groups.

[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 86, even more preferably 30 to 84, even more preferably 40 to 82, and even more preferably 45 to 80. By setting the Mooney viscosity ML(1+4) 100°C of chloroprene rubber within the above range, the handling of chloroprene rubber can be improved when manufacturing rubber compositions.

[0020] (Carbon Black) The rubber composition of this embodiment preferably further contains carbon black. This further improves the vibration damping properties of the rubber composition after vulcanization. It also improves the mechanical properties of the rubber composition after vulcanization, such as weather resistance, abrasion resistance, and dynamic fatigue resistance.

[0021] 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 70 nm to 600 nm, more preferably 72 nm to 550 nm, even more preferably 74 nm to 500 nm, even more preferably 76 nm to 480 nm, even more preferably 78 nm to 460 nm, and even more preferably 80 nm to 450 nm. By setting the average particle size of carbon black to be above the lower limit, the vibration damping properties of the rubber composition after vulcanization can be further improved. By setting the average particle size of carbon black to be below the upper limit, the mechanical properties of the rubber composition after vulcanization, such as weather resistance, abrasion resistance, and dynamic fatigue resistance, can be improved.

[0022] The amount of DBP (dibutyl phthalate) absorbed by carbon black, as measured in accordance with JIS K 6217-4:2017, is preferably 15 mL / 100 g or more and 60 mL / 100 g or less, more preferably 20 mL / 100 g or more and 55 mL / 100 g or less, and even more preferably 25 mL / 100 g or more and 50 mL / 100 g or less. By setting the DBP absorption amount of carbon black to be above the lower limit, the processability of the rubber composition can be improved. By setting the DBP absorption amount of carbon black to be below the upper limit, the vibration damping properties of the rubber composition after vulcanization can be further improved.

[0023] The carbon black preferably includes at least one selected from the group consisting of MT carbon black and FT carbon black. This further improves the vibration damping properties of the rubber composition after vulcanization. It also improves the mechanical properties of the rubber composition after vulcanization, such as weather resistance, abrasion resistance, and dynamic fatigue resistance. MT carbon black refers to carbon black designated as N990 in ASTM D 1765. FT carbon black refers to carbon black designated as N880 in ASTM D 1765.

[0024] The carbon black content per 100 parts by mass of chloroprene rubber is preferably 15 parts by mass or more and 150 parts by mass or less, more preferably 18 parts by mass or more and 100 parts by mass or less, and even more preferably 20 parts by mass or more and 50 parts by mass or less. By setting the carbon black content per 100 parts by mass of chloroprene rubber to be above the lower limit, the mechanical properties of the rubber composition after vulcanization, such as weather resistance, abrasion resistance, and dynamic fatigue resistance, can be improved. By setting the carbon black content per 100 parts by mass of chloroprene rubber to be below the upper limit, the vibration damping properties of the rubber composition after vulcanization can be further improved.

[0025] (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.

[0026] (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.

[0027] 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.

[0028] 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.

[0029] The rubber composition of this embodiment preferably further comprises a vulcanization accelerator. This can accelerate the vulcanization reaction of the rubber composition.

[0030] The vulcanization accelerator may include at least one selected from the group consisting of thiourea-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiram-based vulcanization accelerators, and guanidine-based vulcanization accelerators. Preferably, the vulcanization accelerator includes a thiourea-based vulcanization accelerator, more preferably at least one selected from the group consisting of ethylenethiourea, diethylthiourea, trimethylthiourea, and triethylthiourea, even more preferably at least one selected from the group consisting of ethylenethiourea and trimethylthiourea, and even more preferably ethylenethiourea and trimethylthiourea. This allows the rubber composition to be properly vulcanized and improves the mechanical properties of the rubber composition after vulcanization.

[0031] The content of the vulcanization accelerator per 100 parts by mass of chloroprene rubber is preferably 0.5 parts by mass or more and 5.0 parts by mass or less, more preferably 0.7 parts by mass or more and 4.0 parts by mass or less, even more preferably 0.8 parts by mass or more and 3.5 parts by mass or less, even more preferably 0.9 parts by mass or more and 3.0 parts by mass or less, and even more preferably 1.0 part by mass or more and 2.5 parts by mass or less. By setting the content of the vulcanization accelerator 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.

[0032] The content of the thiourea - type vulcanization accelerator with respect to 100 parts by mass of chloroprene rubber is preferably 0.5 parts by mass or more and 5.0 parts by mass or less, more preferably 0.7 parts by mass or more and 4.0 parts by mass or less, still more preferably 0.8 parts by mass or more and 3.5 parts by mass or less, still more preferably 0.9 parts by mass or more and 3.0 parts by mass or less, and still more preferably 1.0 parts by mass or more and 2.5 parts by mass or less. By setting the content of the thiourea - type vulcanization accelerator with respect to 100 parts by mass of chloroprene rubber within the above range, the rubber composition can be vulcanized appropriately and the mechanical properties of the rubber composition after vulcanization can be improved.

[0033] (Processing aid) The rubber composition of the present embodiment preferably further contains a processing aid. Thereby, the processability of the rubber composition can be improved.

[0034] The processing aid preferably contains 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 contains at least one selected from the group consisting of fatty acids and fatty acid metal salts. Thereby, the processability of the rubber composition can be improved.

[0035] When the vulcanizing agent contains a metal oxide, the processing aid preferably contains a fatty acid, and more preferably contains stearic acid. Thereby, the processability of the rubber composition can be improved.

[0036] The content of the processing aid with respect to 100 parts by mass of chloroprene rubber is preferably 0.1 parts by mass or more and 5.0 parts by mass or less, more preferably 0.2 parts by mass or more and 4.0 parts by mass or less, and still more preferably 0.3 parts by mass or more and 3.0 parts by mass or less. By setting the content of the processing aid with respect to 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.

[0037] (Plasticizer) The rubber composition of the present embodiment preferably further contains a plasticizer. Thereby, the processability of the rubber composition can be improved.

[0038] The plasticizer may include at least one selected from the group consisting of ester plasticizers such as aliphatic dibasic acid plasticizers and epoxy plasticizers; and process oils such as aromatic process oils, naphthenic process oils, and paraffinic process oils.

[0039] The plasticizer preferably includes an aliphatic dibasic acid plasticizer, more preferably includes at least one selected from the group consisting of dioctyl sebacate, dioctyl azelate, dioctyl adipate, diisononyl adipate, and diisodecyl adipate, still more preferably includes at least one selected from the group consisting of dioctyl sebacate, dioctyl azelate, and dioctyl adipate, and still more preferably includes dioctyl sebacate. Thereby, the processability of the rubber composition can be improved, and the cold resistance of the rubber composition after vulcanization can be improved.

[0040] 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 balance between the processability of the rubber composition and the mechanical properties of the rubber composition after vulcanization can be improved.

[0041] The content of the aliphatic dibasic acid 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 aliphatic dibasic acid plasticizer with respect to 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.

[0042] (Antioxidant) The rubber composition of the present embodiment preferably further includes an antioxidant. Thereby, the deterioration of the rubber composition after vulcanization can be suppressed.

[0043] 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.

[0044] The antioxidant preferably comprises at least one selected from the group consisting of amine-based antioxidants and sulfur-based antioxidants, and more preferably comprises at least one selected from the group consisting of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, and 2-mercaptobenzimidazole. This suppresses the deterioration of the rubber composition after vulcanization.

[0045] The content of the antioxidant per 100 parts by mass of chloroprene rubber is preferably 0.1 parts by mass or more and 30.0 parts by mass or less, more preferably 0.2 parts by mass or more and 20.0 parts by mass or less, even more preferably 0.5 parts by mass or more and 15.0 parts by mass or less, and even more preferably 1.0 part by mass or more and 10.0 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.

[0046] (Other components of the rubber composition) In this embodiment, the static-dynamic ratio α is determined by the following method. (Method) In accordance with JIS K 6299:2012, the rubber composition is press-vulcanized under conditions of vulcanization temperature of 170°C, pressure of 10 MPa, and vulcanization time of 15 minutes to prepare large test pieces (cylindrical, diameter 29.0 ± 0.5 mm, thickness 12.5 ± 0.5 mm), and a dynamic properties test is performed at 23°C in accordance with JIS K 6394:2007. Three test pieces are used. After pre-compression to 3.5 mm at 1 mm / second, compression to 3.5 mm at 0.333 mm / second is performed, and the static spring constant Ks is determined in the range of 0.5 mm to 1.5 mm in the forward stroke. The dynamic spring constant Kd is also determined under conditions of initial compression of 1.25 mm, frequency of 100 Hz, and amplitude of 0.05 mm. The static-dynamic ratio α is determined based on the formula: α = Kd / Ks.

[0047] The static-dynamic ratio α is preferably less than 1.39, more preferably 1.00 to 1.37, even more preferably 1.00 to 1.35, and even more preferably 1.00 to 1.32. By reducing the static-dynamic ratio α, the vibration damping characteristics of the vulcanized rubber composition in the high-frequency range can be further improved.

[0048] The rubber composition of this embodiment is preferably used in vibration-damping rubber members.

[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 and a kneader mixer.

[0050] According to the inventors' studies, by using the mixing conditions described below, the formula Eb > 12.5 × Δm １００ It is easy to obtain a rubber composition that satisfies -1150.

[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 25°C to 125°C, more preferably 30°C to 120°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 4 MPa or more and 15 MPa or less, or 5 MPa or more and 10 MPa or less. The vulcanization time may be 5 minutes or more and 60 minutes or less, or 10 minutes or more and 30 minutes or less.

[0055] (Molded body and vibration-damping rubber member) The molded body of this embodiment includes the vulcanized product of this embodiment. The vibration-damping rubber member 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 1-6 and Comparative Examples 1-6) Using a 3L kneader (D3-7.5GHB-S type manufactured by Nippon Spindle Co., Ltd.), the raw materials were kneaded at 100°C and with blade speeds of 32 rpm in the front and 21 rpm in the back to obtain a rubber composition. The discharge temperature of the kneaded material and the amount of each raw material used in each example and comparative example are shown in Table 1.

[0059] (Examples 7-10 and Comparative Examples 7-10) 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 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 in each example and comparative example is shown in Table 2. 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 2.

[0060] Details of each ingredient are shown below.

[0061] (Chloroprene rubber (CR)) Xanthogene-modified CR1: Mooney viscosity 47, moderate crystallization rate Xanthogene-modified CR2: Mooney viscosity 70, very slow crystallization rate Mercaptan-modified CR1: Mooney viscosity 48, very slow crystallization rate Mercaptan-modified CR2: Mooney viscosity 80, 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) MT carbon black: Cancarb's "Thermax N-990", average particle size 450 nm, DBP absorption 44 mL / 100 g FT carbon black: Asahi Carbon's "Asahi Thermal", average particle size 80 nm, DBP absorption 28 mL / 100 g SRF carbon black: Tokai Carbon's "Seas S", average particle size 66 nm, DBP absorption 68 mL / 100 g FEF carbon black: Asahi Carbon's "Asahi #60UG", average particle size 43 nm, DBP absorption 115 mL / 100 g Anti-aging agent 1: 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, Ouchi Shinko Chemical Industry's "Nocrack CD" Anti-aging agent 2: N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, manufactured by Ouchi Shinko Chemical Industry Co., Ltd. "Nocrack 6C" Anti-aging agent 3: 2-mercaptobenzimidazole, manufactured by Ouchi Shinko Chemical Industry Co., Ltd. "Nocrack MB" Dioctyl sebacate (DOS): manufactured by Shin Nippon Rika Co., Ltd. "Sensor DOS" Zinc oxide: manufactured by Sakai Chemical Industry Co., Ltd. "Zinc Oxide Type 2" Magnesium oxide: manufactured by Kyowa Chemical Industry Co., Ltd. "Kyowa Mag 150" Stearic acid: manufactured by Kao Corporation "Lunaq S-70V" Vulcanization accelerator 1: Ethylene thiourea, manufactured by Kawaguchi Chemical Industry Co., Ltd. "Accel 22-S" Vulcanization accelerator 2: Trimethylthiourea, manufactured by Ouchi Shinko Chemical Industry Co., Ltd. "Nocceller TMU"

[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 DBP absorption amount of carbon black is measured in accordance with JIS K 6217-4:2017.

[0066] (2) Preparation of vulcanized sheets (Examples 1-6 and Comparative Examples 1-6) In accordance with JIS K 6299:2012, 70 g of 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") under the conditions of vulcanization temperature of 160°C, pressure of 10 MPa, and vulcanization time of 25 minutes to prepare vulcanized sheets.

[0067] (Examples 7-10 and Comparative Examples 7-10) Vulcanized sheets were prepared in the same manner as in Examples 1-6 and Comparative Examples 1-6, except that the vulcanization time was changed to 20 minutes.

[0068] (3) Evaluation of the rubber composition (measurement of elongation at break) The elongation at break Eb [%] was measured in accordance with JIS K 6251:2023. A dumbbell-shaped No. 3 test piece was cut from the vulcanized sheet, and the elongation at break Eb [%] of the test piece was measured using a tensile testing machine (Strograph AE Elastomer, manufactured by Toyo Seiki Co., Ltd.) at 23°C and a tensile speed of 500 mm / min.

[0069] (Toluene immersion test) In accordance with JIS K 6258:2016, the mass change rate Δm １００ The percentage [%] was measured. A 10 mm x 20 mm x 2 mm test piece was cut from the vulcanized sheet and subjected to a toluene immersion test at 23°C for 24 hours, and the mass change rate Δm of the test piece was measured. １００ [%] was measured.

[0070] (Dynamic Properties Test) In accordance with JIS K 6299:2012, 14 g of rubber composition was press-vulcanized at a vulcanization temperature of 170°C, a pressure of 10 MPa, and a vulcanization time of 15 minutes to prepare large test specimens (cylindrical, diameter 29.0 ± 0.5 mm, thickness 12.5 ± 0.5 mm). In accordance with JIS K 6394:2007, dynamic properties tests were performed at 23°C using a dynamic properties testing machine (Sagimiya Seisakusho Co., Ltd. "KC-2NC-CPU"). Three test specimens were used. After pre-compression to 3.5 mm at 1 mm / second, compression to 3.5 mm at 0.333 mm / second was performed, and the static spring constant Ks was determined in the forward stroke range of 0.5 mm to 1.5 mm. The dynamic spring constant Kd was also determined under the conditions of initial compression of 1.25 mm, frequency of 100 Hz, and amplitude of 0.05 mm. The static-dynamic ratio α was determined based on the formula: α = Kd / Ks.

[0071] The evaluation results of the rubber compositions in each example and comparative example are shown in Tables 1 and 2.

[0072]

[0073]

[0074] Figure 1 shows the Δm in each example and comparative example. １００ A graph showing the relationship between Eb and the given values ​​is shown. In Figure 1, Examples 1 to 6 (examples listed in Table 1) are plotted as filled circles, Comparative Examples 1 to 6 (comparative examples listed in Table 1) are plotted as open circles, Examples 7 to 10 (examples listed in Table 2) are plotted as filled triangles, and Comparative Examples 7 to 10 (comparative examples listed in Table 2) are plotted as open triangles. The dashed line represents the formula: Eb = 12.5 × Δm １００ It shows -1150.

[0075] As shown in Figure 1, in each embodiment, Eb > 12.5 × Δm １００ -1150 was satisfied. On the other hand, in each comparative example, Eb < 12.5 × Δm １００ -1150 was satisfied (i.e., Eb > 12.5 × Δm) １００ (The value -1150 was not met). As shown in Tables 1 and 2, the static-to-vibration ratio α of each example was smaller than the static-to-vibration ratio α of each comparative example. The rubber composition of each example can improve the vibration damping characteristics after vulcanization compared to the rubber composition of each comparative example.

[0076] This application claims priority based on Japanese Patent Application No. 2025-017440, filed on 5 February 2025, and incorporates all of its disclosures herein.

Claims

1. A rubber composition containing chloroprene rubber, when a vulcanized sheet is prepared by press vulcanizing the rubber composition in accordance with JIS K 6299:2012 under conditions of vulcanization temperature of 160°C, pressure of 10 MPa, and vulcanization time of 20 minutes or more and 25 minutes or less, the elongation at break Eb [%] measured at 23°C and tensile speed of 500 mm / min on a dumbbell-shaped No. 3 test piece cut from the vulcanized sheet in accordance with JIS K 6251:2023, and the rate of change in mass Δm measured by toluene immersion test at 23°C and 24 hours on a 10 mm × 20 mm × 2 mm test piece cut from the vulcanized sheet in accordance with JIS K 6258:2016. １００ [%] is given by the formula: Eb > 12.5 × Δm １００ A rubber composition that satisfies -1150.

2. The rubber composition according to claim 1, wherein Eb is 250% or more and 750% or less.

3. Δm １００ The rubber composition according to claim 1 or 2, wherein the amount is 115% or more and 140% or less.

4. The rubber composition according to claim 1 or 2, wherein the chloroprene rubber comprises xanthogene-modified chloroprene rubber.

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

6. The rubber composition according to claim 5, wherein the average particle size of the carbon black, calculated from the mass distribution density curve of the aggregate mass distribution in accordance with JIS K 6217-6:2019, is 70 nm or more and 600 nm or less.

7. The rubber composition according to claim 5, wherein the carbon black content is 15 parts by mass or more and 150 parts by mass or less per 100 parts by mass of chloroprene rubber.

8. The rubber composition according to claim 1 or 2, further comprising a vulcanization accelerator.

9. The rubber composition according to claim 8, wherein the vulcanization accelerator comprises a thiourea-based vulcanization accelerator.

10. The rubber composition according to claim 8, wherein the content of the vulcanization accelerator is 0.5 parts by mass or more and 5.0 parts by mass or less per 100 parts by mass of the chloroprene rubber.

11. The rubber composition according to claim 1 or 2, further comprising a plasticizer.

12. The rubber composition according to claim 11, wherein the plasticizer comprises an aliphatic dibasic acid plasticizer.

13. The rubber composition according to claim 11, wherein the content of the plasticizer is 3 parts by mass or more and 30 parts by mass or less per 100 parts by mass of the chloroprene rubber.

14. The rubber composition according to claim 1 or 2, wherein the static-dynamic ratio α, determined by the following method, is less than 1.

39. (Method) The rubber composition is press-vulcanized in accordance with JIS K 6299:2012 under conditions of vulcanization temperature of 170°C, pressure of 10 MPa, and vulcanization time of 15 minutes to prepare large test pieces (cylindrical, diameter 29.0 ± 0.5 mm, thickness 12.5 ± 0.5 mm), and a dynamic properties test is performed at 23°C in accordance with JIS K 6394:2007. Three test pieces are used. After pre-compression to 3.5 mm at 1 mm / second, compression to 3.5 mm at 0.333 mm / second is performed, and the static spring constant Ks is determined in the range of 0.5 mm to 1.5 mm in the forward stroke. The dynamic spring constant Kd is also determined under conditions of initial compression of 1.25 mm, frequency of 100 Hz, and amplitude of 0.05 mm. The static-dynamic ratio α is determined based on the formula: α = Kd / Ks.

15. A vulcanized product of the rubber composition according to claim 1 or 2.

16. A molded article comprising the vulcanized product described in claim 15.

17. A vibration-damping rubber member comprising the molded body described in claim 16.

Images