Vibration damping rubber composition for electric vehicle and vibration damping rubber member for electric vehicle

Abstract

The purpose of the present invention is to provide a vibration damping rubber member for an electric vehicle in which a loss factor (tanδ) of a rubber component is moderately high and which can suppress a surge in a high-frequency region while satisfactorily maintaining low dynamic magnification.　The present invention is: a vibration damping rubber composition for an electric vehicle that contains a rubber component in which a mixture of a natural rubber and a non-diene-based rubber is a main component; and a vibration damping rubber member for an electric vehicle that is obtained by crosslinking the vibration damping rubber composition. The non-diene-based rubber is preferably a butyl rubber or a butyl halide rubber, and the loss factor at 2,000 Hz of the vibration damping rubber member for an electric vehicle is preferably 0.26-0.55.

Description

Anti-vibration rubber composition for electric vehicles and anti-vibration rubber member for electric vehicles

[0001] The present invention relates to an anti-vibration rubber composition for electric vehicles and an anti-vibration rubber member for electric vehicles obtained by crosslinking the same.

[0002] Mounting parts in electric vehicles play an important role in reducing vibration and noise. Because electric vehicles use electric motors as their power source, they are prone to internal vibration and resonance phenomena, which must be suppressed. Anti-vibration rubber compositions are materials used to prevent the transmission of vibration, and high-frequency vibration reduction performance is particularly required for mounting parts in electric vehicles. Mounting parts play a role in attaching important equipment such as electric motors to the vehicle body, and are important parts that provide users with a comfortable ride by absorbing and dispersing vibrations.

[0003] In the development of anti-vibration rubber compositions, reducing the dynamic magnification ratio is an important factor. The dynamic magnification ratio (dynamic spring constant (Kd) / static spring constant (Ks)) is an index that indicates the flexibility of anti-vibration rubber components, and the smaller the value, the more vibration transmission can be suppressed. The development of anti-vibration rubber compositions for mounting parts of electric vehicles is an important technology that contributes to improving ride comfort and reducing vehicle noise, and for example, the compounding of coupling agents for carbon black is being considered (Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2019-178199

[0005] Unlike vibration-isolating rubber components for conventional engine vehicles, vibration-isolating rubber components for electric vehicles are required to be able to withstand the high-frequency vibrations (500 to 2000 Hz) generated by electric motors. However, if the rubber material is designed with a low dynamic magnification, the loss factor becomes small, making it more likely to experience a phenomenon known as surging, in which the vibration transmissibility at specific frequencies in the high-frequency range becomes extremely high.

[0006] Generally, there is a positive correlation between the loss factor and dynamic magnification of rubber materials, and a compound with a high loss factor results in a high dynamic magnification, which deteriorates vibration-damping performance. Electric vehicles require quietness, so a strict low dynamic magnification is required. For this reason, it is extremely difficult to reduce the resonance of rubber materials simply by increasing the loss factor.

[0007] The present invention has been made in view of the above circumstances, and has an object to provide an anti-vibration rubber member for electric vehicles that has a moderately high loss factor (tan δ) and can suppress surging in the high frequency range while maintaining a low dynamic magnification.

[0008] As a result of extensive research into achieving the above object, the present inventors have discovered that by blending natural rubber and non-diene synthetic rubber, it is possible to maintain a low dynamic magnification and ensure vibration-damping performance while appropriately increasing the loss factor, and have thus completed the present invention.

[0009] The present invention provides an anti-vibration rubber composition for electric vehicles, which contains a rubber component consisting essentially of a mixture of natural rubber and non-diene rubber.

[0010] The present invention also provides an anti-vibration rubber member for electric vehicles, which is obtained by crosslinking the anti-vibration rubber composition.

[0011] The anti-vibration rubber composition for electric vehicles of the present invention (hereinafter referred to as "anti-vibration rubber composition") contains a rubber component whose main component is a mixture of natural rubber and non-diene rubber. The anti-vibration rubber composition for electric vehicles of the present invention can be used as an anti-vibration rubber member for electric vehicles (hereinafter referred to as "anti-vibration rubber member") by curing it through crosslinking.

[0012] In the present invention, the term "electric vehicle" refers to a vehicle that runs using an electric motor as its power source, and includes electric vehicles (EVs) and fuel cell vehicles (FCVs) that use an electric motor as the only power source, as well as plug-in hybrid vehicles (PHVs) and hybrid vehicles (HVs) that use an electric motor as one of their power sources.

[0013] The natural rubber used in the present invention may be appropriately selected from known natural rubbers, for example, RSS (Ribbed Smoked Sheets), TSR (Technically Specified Rubber), etc. The content of natural rubber in the rubber component is preferably 50 to 95% by mass, more preferably 70 to 95% by mass, and particularly preferably 90 to 95% by mass.

[0014] The non-diene rubber used in the present invention is a synthetic rubber that has no double bonds or only a small amount of double bonds in the polymer main chain, and examples thereof include halogenated butyl rubbers such as butyl rubber (IIR), chlorinated butyl rubber (CIIR), and brominated butyl rubber (BIIR), ethylene-propylene rubber (EPM), ethylene-propylene-diene rubber (EPDM), ethylene-acrylic rubber (AEM), polyacrylic rubber (ACM), silicone rubber (VMQ), fluororubber (FKM), polyurethane rubber (AU), ester-based polyurethane rubber (EU), and polyether ether ketone rubber (PEEK). In the present invention, in order to maintain a suitably high loss factor (tan δ) of the resulting vibration-proof rubber member, it is preferable to use butyl rubber or halogenated butyl rubber as the non-diene rubber, and it is more preferable to use butyl rubber.

[0015] The content of the non-diene rubber in the rubber component is preferably 5 to 50% by mass, more preferably 5 to 30% by mass, and particularly preferably 5 to 10% by mass. By setting the content within this range, a vibration-proof rubber member having an excellent balance between dynamic magnification and loss factor can be obtained.

[0016] The rubber component in the vibration-proof rubber composition of the present invention is primarily a mixture of natural rubber and non-diene rubber. Although other rubbers such as isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), and acrylonitrile-butadiene rubber (NBR) may be contained, it is preferable in the present invention that no diene rubber is contained.

[0017] The content of the mixture of natural rubber and non-diene rubber in the rubber component is preferably 80% by mass or more, and more preferably 90% by mass or more. In particular, it is preferable that the rubber component consists only of natural rubber and non-diene rubber, as this makes it easier to obtain a vibration-proof rubber member that has an excellent balance between dynamic magnification and loss factor.

[0018] The anti-vibration rubber composition of the present invention preferably contains carbon black. Known carbon blacks can be used, and are not particularly limited. Examples of carbon black include various grades of carbon black, such as SRF, GPF, FEF, HAF, ISAF, SAF, FT, and MT. In the present invention, FT and MT grade carbon blacks are preferred because they are expected to reduce the dynamic magnification. These may be used alone or in combination of two or more. The amount of carbon black compounded is usually 10 to 80 parts by mass, and preferably 20 to 60 parts by mass, per 100 parts by mass of the rubber component.

[0019] In addition to the rubber component and carbon black described above, the vibration-damping rubber composition of the present invention may contain vulcanizing agents, vulcanization accelerators, vulcanization accelerator assistants, crosslinking agents, oils, antioxidants, and the like that are commonly used in vibration-damping rubber compositions.

[0020] Examples of vulcanizing agents include sulfur and sulfur-containing compounds such as alkylphenol disulfide compounds, but sulfur is preferably used in the present invention. The amount of sulfur added is usually 0.1 to 10.0 parts by mass, preferably 0.3 to 5.0 parts by mass, and more preferably 0.5 to 2.0 parts by mass per 100 parts by mass of the rubber component, in order to maintain basic physical properties such as desired hardness and tensile properties. Peroxides such as dialkyl peroxides and peroxyketals can also be used as vulcanizing agents, and in this case, the amount added is usually 1.0 to 10.0 parts by mass, preferably 2.0 to 8.0 parts by mass per 100 parts by mass of the rubber component.

[0021] Examples of vulcanization accelerators include benzothiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole, dibenzothiazyl disulfide, N-cyclohexyl-2-benzothiazyl sulfenamide, N-t-butyl-2-benzothiazyl sulfenamide, and N-t-butyl-2-benzothiazyl sulfenamide; guanidine-based vulcanization accelerators such as diphenyl guanidine; and thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide, tetrabutylthiuram disulfide, tetradodecylthiuraum disulfide, tetraoctylthiuraum disulfide, and tetrabenzylthiuraum disulfide. These may be used alone or in combination of two or more. In the present invention, benzothiazole-based vulcanization accelerators are preferably used. The amount of the vulcanization accelerator to be compounded is preferably 0.5 to 10 parts by mass, more preferably 1 to 5 parts by mass, per 100 parts by mass of the rubber component, from the viewpoints of ease of production of the vibration-proof rubber and obtaining a desired hardness.

[0022] Examples of vulcanization accelerators include zinc oxide (ZnO) and fatty acids. The fatty acids may be saturated, unsaturated, linear, or branched, and the number of carbon atoms is not particularly limited. Examples of fatty acids include fatty acids having 1 to 30 carbon atoms, preferably 15 to 30 carbon atoms. More specifically, saturated fatty acids such as cyclohexanoic acid (cyclohexanecarboxylic acid), naphthenic acids such as alkylcyclopentanes having side chains, hexanoic acid, octanoic acid, decanoic acid (including branched carboxylic acids such as neodecanoic acid), dodecanoic acid, tetradecanoic acid, hexadecanoic acid, and octadecanoic acid (stearic acid), unsaturated fatty acids such as methacrylic acid, oleic acid, linoleic acid, and linolenic acid, and resin acids such as rosin, tall oil acid, and abietic acid. These may be used alone or in combination. In the present invention, zinc oxide and stearic acid are preferred. The amount of the vulcanization accelerator added is preferably 1 to 10 parts by mass, more preferably 2 to 8 parts by mass, per 100 parts by mass of the rubber component, from the viewpoints of ease of production of the vibration-proof rubber and obtaining a desired hardness.

[0023] Examples of crosslinking agents include bismaleimide compounds and phenolic resins. Examples of bismaleimide compounds include N,N'-o-phenylene bismaleimide, N,N'-m-phenylene bismaleimide, N,N'-p-phenylene bismaleimide, N,N'-(4,4'-diphenylmethane)bismaleimide, 2,2-bis-[4-(4-maleimidophenoxy)phenyl]propane, and bis(3-ethyl-5-methyl-4-maleimidophenyl)methane. In the present invention, bismaleimide compounds are preferred from the viewpoint of storage stability. The amount of these bismaleimide compounds is preferably 0.5 to 5.0 parts by mass, more preferably 0.5 to 3.0 parts by mass, per 100 parts by mass of the rubber component.

[0024] Examples of oils that can be used include process oils such as aromatic oil, naphthenic oil, and paraffin oil, vegetable oils such as coconut oil, synthetic oils such as alkylbenzene oil, and castor oil. These oils may be used alone or in combination of two or more. The amount of oil added is preferably 0.5 to 10 parts by mass, and more preferably 1 to 5 parts by mass, per 100 parts by mass of the rubber component.

[0025] Examples of the antioxidant include phenol-based antioxidants, imidazole-based antioxidants, amine-based antioxidants, and waxes. These may be used alone or in combination of two or more. The amount of antioxidant mixed is preferably 0.5 to 10 parts by mass, more preferably 1 to 5 parts by mass, and even more preferably 1 to 3 parts by mass per 100 parts by mass of the rubber component.

[0026] In addition, additives commonly used in rubber products, such as antioxidants, foaming agents, plasticizers, lubricants, tackifiers, petroleum-based resins, ultraviolet absorbers, dispersants, compatibilizers, and homogenizers, may be appropriately blended as needed, provided that the effects of the present invention are not impaired.

[0027] When obtaining the vibration-damping rubber composition of the present invention, there is no particular limitation on the method for compounding the above-mentioned components. All of the component raw materials may be compounded and kneaded at once, or the components may be compounded and kneaded in two or three separate stages. For kneading, a kneading machine such as a roll, an internal mixer, or a Banbury rotor may be used. Furthermore, when molding into a sheet or strip, a known molding machine such as an extruder or a press may be used.

[0028] The vibration-isolating rubber member for electric vehicles of the present invention is obtained by crosslinking (vulcanizing) the vibration-isolating rubber composition described above. Although not particularly limited, the vibration-isolating rubber composition is typically cured by vulcanization at 140 to 180°C for 5 to 120 minutes to form the vibration-isolating rubber member. Because this vibration-isolating rubber member is made using the vibration-isolating rubber composition of the present invention described above, it is possible to achieve a low dynamic magnification and suppress rubber surge in the high-frequency range.

[0029] As described above, in order to suppress surging in the high-frequency range and achieve a low dynamic magnification, it is necessary to appropriately increase the loss factor (tan δ) of the vibration-isolating rubber member in the high-frequency range. Specifically, adjusting tan δ at 2000 Hz to 0.26 to 0.55 is highly effective, and adjusting it to 0.28 to 0.40 is even more preferable. As tan δ decreases, sudden surging becomes more likely, and if tan δ is less than 0.26, the resonance magnification becomes very high. On the other hand, the greater the tan δ, the more surging can be suppressed, but if tan δ exceeds 0.60, the effect becomes smaller. Furthermore, as the dynamic magnification increases, the transfer coefficient increases across the entire frequency range, making it difficult to achieve the quietness required for electric vehicles.

[0030] Since the tan δ of the vibration-isolating rubber member increases as the content of non-diene rubber in the rubber component increases, the tan δ of the rubber component can be adjusted by the content of non-diene rubber. Furthermore, the tan δ can be adjusted by using the crosslinking agent, but since the crosslinking agent is likely to affect other physical properties of the vibration-isolating rubber member, it is preferable to keep the amount used to a minimum.

[0031] Tan δ can be measured using a dynamic viscoelasticity measuring device, but due to the specifications of the device, it is difficult to measure at high frequencies. Therefore, tan δ at 2000 Hz can be calculated by creating a master curve of tan δ at a reference temperature of 20°C and using the temperature-time conversion rule (WLF rule). In the present invention, tan δ is a value measured in accordance with JIS K 7244-1.

[0032] In the present invention, the ratio of the 100 Hz dynamic spring constant to the static spring constant (Kd100 / Ks) of the vibration-isolating rubber member, i.e., the dynamic magnification factor, is preferably 1.2 to 1.5. A dynamic magnification factor exceeding 1.5 is undesirable because it results in poor vibration-proofing performance. The dynamic magnification factor tends to increase when a large amount of non-diene rubber is used, but the increase in the dynamic magnification factor can be suppressed by appropriately selecting the type and amount of carbon black used.

[0033] The vibration-isolating rubber member for electric vehicles of the present invention can be suitably used for electric vehicle motor mounts, suspension bushings, subframe mounts, etc. In particular, by using the vibration-isolating rubber member for electric vehicles of the present invention in the motor mount of an electric vehicle, high-frequency vibrations (500 to 2000 Hz) generated by the electric motor can be effectively reduced.

[0034] EXAMPLES The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0035] [Examples 1 to 4, Comparative Examples 1 and 2] Anti-vibration rubber compositions were produced by kneading the components according to the formulation shown in Table 1. The kneading was carried out in two stages: first, all materials except for sulfur, crosslinking agent, vulcanization accelerator and vulcanization acceleration aid were blended and mixed for 3 minutes at 120°C using a Banbury mixer, and then sulfur, crosslinking agent, vulcanization accelerator and vulcanization acceleration aid were blended and mixed for 2 minutes at 90°C using a Banbury mixer.

[0036] The obtained vibration-proof rubber composition was press-vulcanized under conditions of 155°C x 15 minutes to produce a cylindrical molded body (vibration-proof rubber member) with a diameter of 8 mm and a height of 5.9 mm, which was used to measure tan δ. First, dynamic viscoelasticity measurement was performed at a strain of 0.1% in accordance with JIS K 7244-1 using an ARES-G2 from TA Instruments, and a tan δ master curve at a reference temperature of 20°C was created. Next, tan δ at 2000 Hz was calculated from this master curve using the temperature-time conversion rule (WLF rule). The results are shown in Table 1.

[0037] The obtained vibration-damping rubber composition was press-vulcanized at 155°C for 30 minutes to produce a cylindrical molded body (vibration-damping rubber member) with a diameter of 30 mm and a height of 30 mm. Using this molded body, the static spring constant (Ks) and the dynamic spring constant (Kd100) at a frequency of 100 Hz were measured in accordance with JIS K 6385, and the dynamic magnification ratio (Kd100 / Ks) was calculated. The results are shown in Table 1.

[0038] Details of each component in Table 1 are as follows: Natural rubber: "RSS#4" Diene rubber: Polybutadiene rubber (BR), "BR01" manufactured by JSR Corporation Non-diene rubber: Chlorinated butyl rubber (CIIR), "CIIR 1066" manufactured by ENEOS Materials Corporation Carbon black: FT-grade carbon black, "Asahi #8" manufactured by Asahi Carbon Co., Ltd. Stearic acid: "Stearic acid 50S" manufactured by New Japan Chemical Co., Ltd. Wax: "Santite S" manufactured by Seiko Chemical Co., Ltd. Antioxidant: "Nocrac 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Oil: "SUNTHENE 4240" manufactured by SUNOCO Corporation Maleimide: "BMI-3000H" manufactured by Daiwa Kasei Kogyo Co., Ltd. Phenolic resin: "CASHEW RESIN 5208" manufactured by Cashew Chemical Co., Ltd. Zinc oxide: "Zinc oxide No. 3" manufactured by Hakusui Tech Co., Ltd. Sulfur: "Powdered sulfur" manufactured by Tsurumi Chemical Co., Ltd. Vulcanization accelerator CZ: "Noccela CZ-G" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator PX: "Noccela PX" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator TBT: "Noccela TBT" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator NS: "Noccela NS-F" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0039]

[0040] As shown in Table 1, the vibration-proof rubber members of Examples 1 to 4, which used a mixture of natural rubber and non-diene rubber as the rubber component, had a moderately high loss factor (tan δ) and maintained a low dynamic magnification.

[0041] According to the present invention, it is possible to provide an anti-vibration rubber member for electric vehicles that has a moderately high loss factor and can suppress rubber surge in the high frequency range while maintaining a low dynamic magnification.

Claims

1. An anti-vibration rubber composition for electric vehicles, comprising a rubber component consisting essentially of a mixture of natural rubber and non-diene rubber.

2. The anti-vibration rubber composition according to claim 1, wherein the content of the non-diene rubber in the rubber component is 5 to 50 mass %.

3. The vibration-proof rubber composition according to claim 1, wherein the non-diene rubber is a butyl rubber or a halogenated butyl rubber.

4. The anti-vibration rubber composition according to claim 1, wherein said rubber component consists essentially of natural rubber and non-diene rubber.

5. An anti-vibration rubber component for electric vehicles, obtained by crosslinking the anti-vibration rubber composition according to any one of claims 1 to 4.

6. The anti-vibration rubber member for electric vehicles according to claim 5, which has a loss factor (tan δ) of 0.26 to 0.55 at 2000 Hz, measured in accordance with JIS K 7244-1 and calculated using the temperature-time conversion rule (WLF rule), at a reference temperature of 20°C and a measured strain of 0.1%.

7. The anti-vibration rubber member for electric vehicles according to claim 5, wherein the ratio of the 100 Hz dynamic spring constant to the static spring constant (Kd100 / Ks) is 1.2 to 1.5.

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