Rubber crosslinked materials and vibration-damping members

Abstract

The present invention provides a rubber crosslinked material having a high storage modulus and a low loss coefficient from the low-frequency range to the high-frequency range. [Solution] The crosslinked rubber material comprises a rubber component containing one or more polymers from among ethylene-propylene-diene rubber and ethylene-butene-diene rubber, polyethylene that is compatible with the rubber component, and a plurality of polyethylene terephthalate fibers having a diameter of 100 nm to 1000 nm and a length of 0.1 mm to 50 mm, wherein the polyethylene content is 0.05 parts by mass to 5.0 parts by mass per 100 parts by mass of the rubber component, and the total content of the plurality of polyethylene terephthalate fibers is 0.15 parts by mass to 5.0 parts by mass per 100 parts by mass of the rubber component.

Description

Technical Field

[0001] The present invention relates to a rubber crosslinked product that contributes to improving handling stability and a vibration isolator including the same.

Background Art

[0002] Vibration isolators are widely used in various applications for the purpose of suppressing vibrations generated from vibrating bodies. In particular, in the fields related to mobility such as automobiles in general, motorcycles, and railways, various vibration isolators are used for the purposes of suppressing noise of automobiles, etc., improving riding comfort, and enhancing handling stability. For such vibration isolators, various rubber crosslinked products that are suitably used for vibration isolation applications, considering physical properties of the crosslinked product itself, types of rubber components, types of additives, blending ratios of additives, etc., are used.

[0003] For example, Patent Document 1 describes a vibration isolation rubber composition containing butyl rubber, EPDM having a Mooney viscosity ML 1+8 (100 °C) of about 50 to 100, and a sulfur-based vulcanization accelerator. Specifically, it is described that the vibration isolation rubber composition has a hardness and a dynamic magnification factor below a certain value and can provide a vulcanized product suitably used as a vibration isolation material.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the effectiveness of vibration-damping rubber crosslinked materials in improving handling stability is often frequency-dependent. Specifically, the handling stability provided by a particular type of rubber crosslinked material exhibits different behavior in the low-frequency and high-frequency ranges. For example, the vibration-damping rubber composition described in Patent Document 1 does not involve measurements of the hardness or dynamic magnification of the vulcanized material considering frequency differences. Therefore, it would be desirable to have a rubber crosslinked material that can exhibit improved handling stability from the low-frequency range to the high-frequency range.

[0006] The handling stability of vibration-damping rubber crosslinked materials is evaluated by their dynamic viscoelasticity, specifically their storage modulus and loss coefficient. Conventionally, incorporating reinforcing fibers into the rubber crosslinked material has been considered to increase the storage modulus. However, there is a problem in that these reinforcing fibers are not well dispersed during the mixing of the rubber material, and no rubber crosslinked material containing reinforcing fibers suitable for vibration-damping applications has been reported.

[0007] Therefore, the present invention aims to provide a rubber crosslinked material having a high storage modulus and a low loss coefficient from the low-frequency range to the high-frequency range.

[0008] The inventors of this invention have conducted diligent studies to solve the above problems and have arrived at the present invention. That is, the present invention encompasses the following preferred embodiments.

[0009] A first aspect of the present invention is a crosslinked rubber material comprising a rubber component containing one or more polymers from among ethylene-propylene-diene rubber and ethylene-butene-diene rubber, polyethylene that is compatible with the rubber component, and a plurality of polyethylene terephthalate fibers having a diameter of 100 nm or more and 1000 nm or less and a length of 0.1 mm or more and 50 mm or less, The polyethylene content is 0.05 parts by mass or more and 5.0 parts by mass or less per 100 parts by mass of the rubber component. The total content of the plurality of polyethylene terephthalate fibers is 0.15 parts by mass or more and 5.0 parts by mass or less per 100 parts by mass of the rubber component.

[0010] A second aspect of the present invention is a rubber crosslinked material according to the first aspect, wherein the storage modulus of the rubber crosslinked material in the grain direction is 1.1 times or more and 6.0 times or less than the storage modulus of the non-grain direction.

[0011] A crosslinked rubber product according to a third aspect of the present invention is a crosslinked rubber product according to a first or second aspect, wherein the rubber component comprises one or more polymers selected from the group consisting of ethylene-propylene-5-ethylidene-2-norbornene rubber, ethylene-propylene-vinylidene-5-vinyl-2-norbornene rubber, and ethylene-butene-5-ethylidene-2-norbornene rubber.

[0012] A fourth aspect of the present invention is a rubber crosslinked material according to any of the first to third aspects, further comprising carbon black. The carbon black content is 35 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the rubber component.

[0013] A fifth embodiment of the present invention is a rubber crosslinked product according to any of the first to fourth embodiments, further comprising one or more components selected from the group consisting of vulcanization accelerators, processing aids, antioxidants, vulcanization accelerators, crosslinking agents, crosslinking aids, fillers, and oils.

[0014] A rubber crosslinked product according to the sixth aspect of the present invention is a rubber crosslinked product according to the fifth aspect, wherein the total content of the one or more components is greater than 0 parts by mass and less than or equal to 200 parts by mass per 100 parts by mass of the rubber component.

[0015] A vibration-damping member according to the sixth aspect of the present invention includes a rubber crosslinked material according to any of the first to fifth aspects. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a rubber crosslinked material having a high storage modulus and a low loss coefficient from the low-frequency range to the high-frequency range. [Brief explanation of the drawing]

[0017] [Figure 1] Figure 1 is a schematic diagram showing a composite material composed of polyethylene, which is a raw material of the rubber cross-linked product according to the present embodiment, and a plurality of polyethylene terephthalate fibers. [Figure 2] Figure 2 is a graph showing the storage modulus at each frequency of samples in the alignment direction and the anti-alignment direction of the rubber cross-linked product of Example 1. [Figure 3] Figure 3 is a graph showing the storage modulus at each frequency of samples in the alignment direction and the anti-alignment direction of the rubber cross-linked product of Comparative Example 1. [Figure 4] Figure 4 is a graph showing the storage modulus at each frequency of samples in the alignment direction and the anti-alignment direction of the rubber cross-linked product of Example 2. [Figure 5] Figure 5 is a graph showing the storage modulus at each frequency of samples in the alignment direction and the anti-alignment direction of the rubber cross-linked product of Comparative Example 2. [Figure 6] Figure 6 is a graph showing the storage modulus at each frequency of samples in the alignment direction and the anti-alignment direction of the rubber cross-linked product of Example 3. [Figure 7] Figure 7 is a graph showing the storage modulus at each frequency of samples in the alignment direction and the anti-alignment direction of the rubber cross-linked product of Comparative Example 3. [Figure 8] Figure 8 is a graph showing a comparison of the storage modulus at each frequency of samples in the alignment direction of the rubber cross-linked product of Example 1 and the rubber cross-linked product of Comparative Example 1. [Figure 9] Figure 9 is a graph showing a comparison of the loss factor at each frequency of samples in the alignment direction of the rubber cross-linked product of Example 1 and the rubber cross-linked product of Comparative Example 1. [Figure 10] Figure 10 is a graph showing a comparison of the storage modulus at each frequency of samples in the alignment direction of the rubber cross-linked product of Example 2 and the rubber cross-linked product of Comparative Example 2. [Figure 11] Figure 11 is a graph showing a comparison of the loss factor at each frequency of samples in the alignment direction of the rubber cross-linked product of Example 2 and the rubber cross-linked product of Comparative Example 2. [Figure 12]FIG. 12 is a graph showing a comparison of the storage elastic modulus at each frequency of samples in the alignment direction of the rubber crosslinked product of Example 3 and the rubber crosslinked product of Comparative Example 3. [Figure 13] FIG. 13 is a graph showing a comparison of the loss factor at each frequency of samples in the alignment direction of the rubber crosslinked product of Example 3 and the rubber crosslinked product of Comparative Example 3. [Figure 14] FIG. 14 is a partial cross-sectional image of a sample of the rubber crosslinked product of Example 3 observed using a digital microscope.

MODE FOR CARRYING OUT THE INVENTION

[0018] As a result of intensive studies by the present inventors, a composite material having a sea-island structure composed of polyethylene and a plurality of polyethylene terephthalate fibers (hereinafter also referred to as "PET fibers") of a predetermined size is added to a rubber component at a predetermined blending ratio to produce a rubber crosslinked product, whereby it has been found that a rubber crosslinked product having a high storage elastic modulus and a low loss factor can be obtained from the low-frequency region to the high-frequency region. In the obtained rubber crosslinked product, polyethylene is compatible with the rubber component, and accordingly, the plurality of PET fibers are dispersed (preferably substantially uniformly) in the rubber component and polyethylene.

[0019] In the present specification, the "rubber crosslinked product" means a molded body (crosslinked product or vulcanized product) after blending raw materials of a rubber composition and crosslinking (or vulcanizing) with a crosslinking agent (or vulcanizing agent). The shape of the rubber crosslinked product is not particularly limited, and for example, any shape known to those skilled in the art such as a sheet shape, a polygonal shape, a circular shape, a cylindrical shape, a conical shape, etc. may be used for manufacturing any vibration-proof member (vibration-proof product). [[ID=I9]]

[0020] In this specification, "storage modulus" and "loss factor" refer to the values ​​of storage modulus (Pa) and loss factor (tanδ), respectively, measured by frequency-dependent measurement of a dynamic viscoelasticity test using the Rheogel-E4000 dynamic viscoelasticity measuring device manufactured by UBM Co., Ltd., as will be described in detail in later examples. Furthermore, in this specification, "low frequency region to high frequency region" refers to a frequency region that includes at least the range of 0 Hz to 200 Hz, and preferably the frequency region of 0 Hz to 400 Hz.

[0021] The embodiments of the present invention will be described in detail below. However, the scope of the present invention is not limited to the embodiments described herein, and various modifications can be made without impairing the spirit of the invention.

[0022] <Rubber Crosslinked Products> The crosslinked rubber material according to this embodiment includes a rubber component, polyethylene that is compatible with the rubber component, and a plurality of PET fibers. The polyethylene and the plurality of PET fibers are components derived from a composite material consisting of polyethylene and a plurality of PET fibers, which are the raw materials. The components contained in the crosslinked rubber material and the physical properties of the crosslinked rubber material will be described in detail below.

[0023] (Rubber component) The crosslinked rubber material according to this embodiment contains one or more polymers selected from ethylene-propylene-diene rubber (hereinafter also referred to as "EPDM") and ethylene-butene-diene rubber (hereinafter also referred to as "EBDM") as rubber components.

[0024] The type of EPDM is not particularly limited, and any EPDM known to those skilled in the art and commonly used as an industrial rubber material may be used. Specifically, as EPDM, any polymer obtained by copolymerizing ethylene and propylene with a small amount of various non-conjugated diene components can be used. Examples of such non-conjugated dienes include 5-ethylidene-2-norbornene, 5-vinyl-2-norbornene rubber, dicyclopentadiene, and 1,4-hexadiene.

[0025] The ethylene content of EPDM is not particularly limited as long as it does not impair the effects on dynamic viscoelasticity from low to high frequencies in this embodiment. For example, it is preferably 30% by weight or more and 80% by weight or less, and more preferably 40% by weight or more and 70% by weight or less.

[0026] The molecular weight of EPDM is not particularly limited as long as it does not impair the effects on dynamic viscoelasticity from low to high frequencies in this embodiment, but for example, from the viewpoint of balancing durability and work efficiency, it is preferably between 200,000 and 1,000,000.

[0027] EPDM as a rubber component may be synthesized by known methods, or commercially available products may be used. Examples of commercially available EPDM products include "Espren 6373" (ethylene content 65% by weight, manufactured by Sumitomo Chemical Co., Ltd.), "Espren 552" (ethylene content 55% by weight, manufactured by Sumitomo Chemical Co., Ltd.), "KELTAN 2450" (ethylene content 48% by weight, manufactured by Lanxess), and "PX-008M" (ethylene content 60% by weight, manufactured by Mitsui Chemicals, Inc.).

[0028] Furthermore, the type of EBDM is not particularly limited, and any EBDM known to those skilled in the art and commonly used as an industrial rubber material may be used. Specifically, as the EBDM, any polymer obtained by copolymerizing ethylene and butene with a small amount of various non-conjugated diene components can be used. Examples of such non-conjugated dienes include 5-ethylidene-2-norbornene, 5-vinyl-2-norbornene rubber, dicyclopentadiene, and 1,4-hexadiene.

[0029] The molecular weight of EBDM is not particularly limited as long as it does not impair the effects on dynamic viscoelasticity from low to high frequencies in this embodiment, but for example, from the viewpoint of balancing durability and work efficiency, it is preferably between 200,000 and 1,000,000.

[0030] The ethylene content of EBDM is not particularly limited as long as it does not impair the effects on dynamic viscoelasticity from low to high frequencies in this embodiment. For example, it is preferably 30% by weight or more and 80% by weight or less, and more preferably 40% by weight or more and 60% by weight or less.

[0031] EBDM as a rubber component may be synthesized by known methods, but commercially available products may also be used. Examples of commercially available EBDM include "EBT K-9330M" (ethylene content 50% by weight, manufactured by Mitsui Chemicals, Inc.).

[0032] The EPDM and EBDM polymers used as rubber components may be used individually or in combination of two or more types.

[0033] Furthermore, the rubber component preferably contains one or more polymers selected from the group consisting of ethylene-propylene-5-ethylidene-2-norbornene rubber, ethylene-propylene-vinylidene-5-vinyl-2-norbornene rubber, and ethylene-butene-5-ethylidene-2-norbornene rubber. Including one or more polymers selected from any of these makes it possible to more reliably obtain a rubber crosslinked product having a high storage modulus and a low loss coefficient from the low-frequency range to the high-frequency range.

[0034] The content of rubber components in the crosslinked rubber material can be appropriately adjusted to satisfy the conditions for the content of polyethylene and multiple PET fibers derived from the composite material of the raw materials described later, taking into consideration the type of rubber component and other components contained, and within a range that does not impair the effect on dynamic viscoelasticity from low to high frequencies in this embodiment. For example, the content of rubber components is preferably 10 parts by mass or more and 75 parts by mass or less, and more preferably 20 parts by mass or more and 65 parts by mass or less, based on the total amount of the crosslinked rubber material.

[0035] (polyethylene) The crosslinked rubber material according to this embodiment contains polyethylene derived from a composite material consisting of polyethylene as a raw material and multiple PET fibers. The polyethylene is compatible with the rubber component in the crosslinked rubber material.

[0036] In this specification, "polyethylene is miscible with the rubber component" means that polyethylene and the rubber component, which were separate raw materials, become mixed together in the final crosslinked rubber product due to the melting of polyethylene during the rubber mixing process, making them indistinguishable. Specifically, this means that when a cross-section of the crosslinked rubber product is observed using a scanning electron microscope (SEM), the polyethylene and the rubber component cannot be distinguished.

[0037] The polyethylene content is between 0.05 parts by mass and 5.0 parts by mass per 100 parts by mass of rubber component. A polyethylene content of 0.05 parts by mass or more allows for good dispersion of multiple PET fibers within the rubber component and polyethylene. A polyethylene content of 5.0 parts by mass or less prevents the inherent elasticity of the rubber component from being compromised, allowing for the production of a crosslinked rubber product with desired physical properties.

[0038] The polyethylene content is preferably 0.50 parts by mass or more, more preferably 1.0 part by mass or more, even more preferably 1.5 parts by mass or more, and particularly preferably 1.7 parts by mass or more, per 100 parts by mass of rubber component. Furthermore, the polyethylene content is preferably 4.5 parts by mass or less, more preferably 4.0 parts by mass or less, even more preferably 3.5 parts by mass or less, and particularly preferably 3.0 parts by mass or less, per 100 parts by mass of rubber component.

[0039] (Multiple PET fibers) The crosslinked rubber material according to this embodiment includes multiple PET fibers derived from a composite material consisting of polyethylene as a raw material and multiple PET fibers. Each of the multiple PET fibers has a diameter of 100 nm to 1000 nm and a length of 0.1 mm to 50 mm.

[0040] Multiple PET fibers are dispersed, preferably substantially uniformly, within the rubber component and polyethylene. In this specification, "multiple PET fibers are dispersed within the rubber component and polyethylene" means that each PET fiber, which had a sea-island structure with polyethylene in the composite material at the raw material stage, is spread throughout the rubber component and polyethylene when the cross-section of the final rubber crosslinked product is observed using a SEM. When multiple PET fibers with extremely small diameters are dispersed (preferably substantially uniformly) within the rubber component and polyethylene, a rubber crosslinked product with a high storage modulus and low loss coefficient can be reliably obtained from the low-frequency range to the high-frequency range.

[0041] The diameter of the PET fiber is preferably 200 nm or more, more preferably 300 nm or more, and even more preferably 400 nm or more. Furthermore, the diameter of the PET fiber is preferably 900 nm or less, more preferably 800 nm or less, and even more preferably 700 nm or less.

[0042] Furthermore, if the length of the PET fibers is 0.1 mm or more, the aspect ratio of the PET fibers is high, which can improve the mechanical properties of the rubber crosslinked material in the direction of grain. The length of the PET fibers is preferably 0.3 mm or more, and particularly preferably 0.5 mm or more.

[0043] Furthermore, the length of the PET fibers is preferably 30 mm or less, and particularly preferably 10 mm or less.

[0044] The total content of multiple PET fibers is between 0.15 parts by mass and 5.0 parts by mass per 100 parts by mass of rubber component. When the total content of multiple PET fibers is 0.15 parts by mass or more, the storage modulus of the crosslinked rubber can be increased and the loss coefficient can be reduced from the low-frequency range to the high-frequency range. When the total content of multiple PET fibers is 5.0 parts by mass or less, the inherent elasticity of the rubber component is prevented from being impaired, and a crosslinked rubber with the desired physical properties can be obtained.

[0045] The total content of multiple PET fibers is preferably 0.25 parts by mass or more, more preferably 1.0 part by mass or more, even more preferably 1.5 parts by mass or more, and particularly preferably 1.8 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, the total content of multiple PET fibers is preferably 4.5 parts by mass or less, more preferably 4.0 parts by mass or less, even more preferably 3.5 parts by mass or less, and particularly preferably 3.0 parts by mass or less, per 100 parts by mass of the rubber component.

[0046] As mentioned above, the polyethylene and multiple PET fibers described above are components derived from a composite material consisting of polyethylene and multiple PET fibers, which are the raw materials. Therefore, the total content of polyethylene and multiple PET fibers is the content of the composite material consisting of polyethylene and multiple PET fibers used as raw materials. The total content of polyethylene and multiple PET fibers (content of the raw material composite) is between 0.2 parts by mass and 10.0 parts by mass per 100 parts by mass of rubber components.

[0047] In the composite material of raw materials, the mass ratio of polyethylene to multiple PET fibers is preferably polyethylene:PET fiber (mass ratio) = 5:5 to 3:7.

[0048] (Carbon Black) The crosslinked rubber material according to this embodiment preferably further contains carbon black. The carbon black functions as a reinforcing material for the crosslinked rubber material.

[0049] The type of carbon black used is not particularly limited, as long as it is any carbon black known to those skilled in the art for addition to rubber crosslinking materials. Examples include channel black, furnace blacks such as SAF, ISAF, N-339, HAF, N-351, MAF, FEF, SRF, GPF, ECF, and N-234, thermal blacks such as FT and MT, and acetylene black. Carbon black may be added alone or in combination of two or more types.

[0050] The carbon black content should be adjusted appropriately, taking into account the conditions for the content of polyethylene and multiple PET fibers derived from the composite material of the raw materials mentioned above, the type of rubber component and other components contained, and within a range that does not impair the effect on dynamic viscoelasticity from low to high frequencies in this embodiment. For example, the carbon black content is preferably 35 parts by mass or more and 200 parts by mass or less per 100 parts by mass of rubber component. When the carbon black content is 35 parts by mass or more, the mechanical strength, elongation, and abrasion resistance of the crosslinked rubber material are improved, and in particular, a crosslinked rubber material with a high storage modulus can be reliably obtained. When the carbon black content is 200 parts by mass or less, the inherent dynamic viscoelasticity of the rubber component can be well maintained.

[0051] The carbon black content is more preferably 40 parts by mass or more, even more preferably 45 parts by mass or more, and particularly preferably 50 parts by mass or more, per 100 parts by mass of rubber component. Furthermore, the carbon black content is more preferably 150 parts by mass or less, even more preferably 130 parts by mass or less, and particularly preferably 115 parts by mass or less, per 100 parts by mass of rubber component.

[0052] (Any component) The crosslinked rubber according to this embodiment may contain any other components known to those skilled in the art that are generally added to crosslinked rubber. Such optional components may include, for example, one or more components selected from the group consisting of vulcanization accelerators, processing aids, antioxidants, vulcanization accelerators, crosslinking agents, crosslinking aids, fillers, and oils.

[0053] Vulcanization accelerators have the function of promoting the formation of crosslinked structures by crosslinking agents or vulcanizing agents. The type of vulcanization accelerator is not particularly limited as long as it is any vulcanization accelerator known to those skilled in the art that can be added to rubber crosslinked products, for example, metal oxides such as magnesium oxide and zinc oxide. Vulcanization accelerators may be added individually or in combination of two or more types.

[0054] The amount of vulcanization accelerator can be adjusted as appropriate within a range that does not impair the effects on dynamic viscoelasticity from low to high frequencies in this embodiment. For example, when the rubber crosslinked product contains a vulcanization accelerator, the amount of vulcanization accelerator is preferably 1.0 part by mass or more and 15 parts by mass or less, and more preferably 3.0 parts by mass or more and 8.0 parts by mass or less, per 100 parts by mass of the rubber component.

[0055] The type of processing aid is not particularly limited, as long as it is any processing aid known to those skilled in the art that can be added to rubber crosslinked products. Examples include saturated fatty acids such as stearic acid, unsaturated fatty acids, etc. Processing aids may be added individually or in combination of two or more types.

[0056] The content of the processing aid can also be adjusted as appropriate, within a range that does not impair the effects on dynamic viscoelasticity from low to high frequencies in this embodiment. For example, when the rubber crosslinked product contains a processing aid, the content of the processing aid is preferably more than 0 parts by mass and 3.0 parts by mass or less, and more preferably 0.5 parts by mass or more and 2.0 parts by mass or less, per 100 parts by mass of the rubber component.

[0057] The type of antioxidant is not particularly limited, as long as it is any antioxidant known to those skilled in the art that can be added to rubber crosslinked products. Examples include amine-based antioxidants, imidazole-based antioxidants, phenol-based antioxidants, etc. The antioxidant may be added alone or in combination of two or more types.

[0058] The amount of the antioxidant can be adjusted as appropriate, within a range that does not impair the effect on dynamic viscoelasticity from low to high frequencies in this embodiment. For example, if the rubber crosslinked product contains an antioxidant, the amount of the antioxidant is preferably 1.0 part by mass or more and 8.0 parts by mass or less, and preferably 3.0 parts by mass or more and 6.0 parts by mass or less, per 100 parts by mass of the rubber component.

[0059] A vulcanization accelerator has the function of promoting the formation of a crosslinked structure by a crosslinking agent or vulcanizing agent. The type of vulcanization accelerator is not particularly limited as long as it is any vulcanization accelerator known to those skilled in the art that can be added to rubber crosslinked products. Examples include guanidin-based, aldehyde-amine-based, aldehyde-ammonia-based, thiazole-based, sulfenamide-based, thiourea-based, thiram-based, dithiocarbamate-based, and xantate-based vulcanization accelerators. A single vulcanization accelerator may be added, or two or more may be added in combination.

[0060] The amount of vulcanization accelerator can also be adjusted as appropriate within a range that does not impair the effect on dynamic viscoelasticity from low to high frequencies in this embodiment. For example, when the rubber crosslinked product contains a vulcanization accelerator, the amount of vulcanization accelerator is preferably 0.1 parts by mass or more and 15 parts by mass or less, and more preferably 0.5 parts by mass or more and 10 parts by mass or less, per 100 parts by mass of the rubber component.

[0061] Crosslinking agents (including vulcanizing agents) have the function of crosslinking the raw polymer to form a rubber crosslinked product. The type of crosslinking agent is not particularly limited as long as it is any crosslinking agent known to those skilled in the art that can be added to a rubber crosslinked product, and examples include organic peroxides, sulfur, sulfur compounds, oximes, nitroso compounds, polyamines, thirams, etc. Crosslinking agents may be added individually or in combination of two or more types.

[0062] The amount of crosslinking agent can be adjusted as appropriate within a range that does not impair the effects on dynamic viscoelasticity from low to high frequencies in this embodiment. For example, when the rubber crosslinked product contains a crosslinking agent, the amount of crosslinking agent is preferably 3.0 parts by mass or more and 10 parts by mass or less, and more preferably 5.0 parts by mass or more and 9.0 parts by mass or less, per 100 parts by mass of rubber component.

[0063] Crosslinking aids have the function of promoting the formation of crosslinked structures by crosslinking agents or vulcanizing agents. The type of crosslinking aid is not particularly limited as long as it is any crosslinking aid known to those skilled in the art that can be added to rubber crosslinked products, and examples include phenylenedimaleimide, quinone dioxime, ammonium benzoate, nitrosobenzenes, morpholin disulfide, etc. Crosslinking aids may be added individually or in combination of two or more types.

[0064] The amount of crosslinking aid can also be adjusted as appropriate within a range that does not impair the effect on dynamic viscoelasticity from low to high frequencies in this embodiment. For example, when the rubber crosslinked product contains a crosslinking aid, the amount of crosslinking aid is preferably 0.3 parts by mass or more and 3.0 parts by mass or less, and more preferably 0.5 parts by mass or more and 1.5 parts by mass or less, per 100 parts by mass of rubber component.

[0065] The oil functions as a softening agent. The type of oil is not particularly limited as long as it is any oil known to those skilled in the art for addition to rubber crosslinking materials, such as process oils such as paraffinic oils and naphthenic oils, vegetable oils, synthetic oils such as alkylbenzene oils, and castor oil. The oil may be added alone or in combination of two or more types.

[0066] The oil content can also be adjusted as appropriate within a range that does not impair the effects on dynamic viscoelasticity from low to high frequencies in this embodiment. For example, when the rubber crosslinked material contains oil, the oil content is preferably 5 parts by mass or more and 150 parts by mass or less, and more preferably 10 parts by mass or more and 120 parts by mass or less, per 100 parts by mass of rubber component.

[0067] In addition to the components mentioned above, the crosslinked rubber may appropriately contain any additives commonly used in the rubber industry, such as fillers (e.g., talc, silica, etc.), waxes, plasticizers, antioxidants, foaming agents, lubricants, tackifiers, petroleum resins, UV absorbers, dispersants, compatibilizers, homogenizers, vulcanization retarders, silica, silane coupling agents, etc., within a range that does not impair the effects on dynamic viscoelasticity from low to high frequencies in this embodiment.

[0068] If any of the above components are included, their total content is preferably more than 0 parts by mass and 200 parts by mass or less, more preferably 5 parts by mass or more and 160 parts by mass or less, even more preferably 10 parts by mass or more and 132 parts by mass or less, and particularly preferably 15 parts by mass or more and 125 parts by mass or less, per 100 parts by mass of the rubber component.

[0069] (Physical properties of crosslinked rubber materials) The storage modulus in the grain direction of the crosslinked rubber product according to this embodiment is preferably 1.1 to 6.0 times the storage modulus in the non-grain direction. The greater the storage modulus in the grain direction relative to the storage modulus in the non-grain direction of the crosslinked rubber product, the higher the modulus and durability of the crosslinked rubber product.

[0070] When PET fibers with a high aspect ratio are dispersed (preferably substantially uniformly) within a crosslinked rubber material and are arranged as substantially parallel as possible, the storage modulus in the direction of grain relative to the storage modulus in the direction of grain can be increased. If the shape of the crosslinked rubber material according to this embodiment is sheet-like, rod-like, etc., multiple PET fibers can be easily arranged in this manner within the crosslinked rubber material.

[0071] Thus, the crosslinked rubber material according to this embodiment has a high storage modulus and a low loss coefficient from the low-frequency range to the high-frequency range. Therefore, a vibration-damping member including the crosslinked rubber material according to this embodiment can obtain good steering stability regardless of frequency and can be suitably used in various members where vibration damping is required.

[0072] <Method for manufacturing crosslinked rubber products> In the method for manufacturing a crosslinked rubber product according to this embodiment, the rubber component described above, carbon black as an optional component, and other optional components, along with a composite material consisting of polyethylene and multiple PET fibers, are used as raw materials.

[0073] Figure 1 shows a schematic diagram of a composite material consisting of polyethylene and a plurality of PET fibers, which are the raw materials for the crosslinked rubber according to this embodiment. As shown in Figure 1, the composite material 1 has a sea-island structure consisting of polyethylene 2 and a plurality of PET fibers 3. As mentioned above, the PET fibers 3 have a diameter of 100 nm to 1000 nm and a length of 0.1 mm to 50 mm. Instead of directly mixing the PET fibers as raw materials during rubber kneading, the crosslinked rubber according to the above embodiment can be obtained by kneading the composite material of polyethylene and PET fibers in this state. Specifically, when the polyethylene of the composite material melts due to heating during rubber kneading, the PET fibers are well dispersed (preferably substantially uniformly dispersed) in the crosslinked rubber.

[0074] The crosslinked rubber product according to the above embodiment can be manufactured using these raw materials by any method for manufacturing crosslinked rubber products known to those skilled in the art. An example of a method for manufacturing the crosslinked rubber product according to this embodiment will be described below.

[0075] (Preparation of raw materials) First, the aforementioned rubber components, optional carbon black, other optional components, and composite materials consisting of polyethylene and multiple PET fibers are weighed out in proportion to their respective content ratios in the aforementioned crosslinked rubber products.

[0076] (Primary mixing) Next, the raw materials, excluding the crosslinking agent and crosslinking aid, are mixed using any mixer known to those skilled in the art (also referred to as "primary mixing"). The mixer is not particularly limited, but examples include Banbury mixers, internal mixers, and roll mixers. The mixing temperature at this stage can be set appropriately according to the type of rubber component, the mixing ratio of each component, etc. For example, the starting temperature can be set to 40°C to 90°C and the finishing temperature to 100°C to 160°C. The mixing time can also be set appropriately according to the type of rubber component, the mixing ratio of each component, etc. For example, it can be set to about 3 to 10 minutes.

[0077] (Second mixing) After the initial mixing, the mixture is kneaded, then a crosslinking agent and a crosslinking aid are added, and the mixture is further kneaded using open rolls or other rollers, a kneader, etc. (this is also called "secondary mixing"). The mixing temperature at this stage can be set appropriately according to the type of rubber component and the mixing ratio of each component, for example, it can be 30°C to 70°C. The mixing time can also be set appropriately according to the type of rubber component and the mixing ratio of each component, for example, it can be 5 minutes to 130 minutes.

[0078] (molding) After secondary kneading, the kneaded material is molded into the desired shape. Then, by heating the molded kneaded material at, for example, 150°C to 200°C for 1 to 30 minutes, a rubber crosslinked material having the desired shape according to the above embodiment can be obtained.

[0079] <Vibration Isolator> The vibration-damping member according to this embodiment includes the rubber crosslinked material according to the aforementioned embodiment. Specifically, the vibration-damping member includes the rubber crosslinked material according to the aforementioned embodiment molded into a desired shape. Therefore, the vibration-damping member according to this embodiment can also have a high storage modulus and a low loss coefficient from the low-frequency range to the high-frequency range.

[0080] The type of vibration-damping material is not particularly limited, but it is preferable to use a vibration-damping material for vehicles, especially automobiles, that requires high vibration damping performance. Specifically, examples of vibration-damping materials include vibration-damping rubber for automobiles such as tires, bushings, engine mounts, torsional dampers, body mounts, cap mounts, member mounts, strut mounts, and muffler mounts; vibration-damping rubber for railway vehicles; vibration-damping rubber for industrial machinery such as timing belts and conveyor belts; and seismic isolation rubber for buildings. [Examples]

[0081] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples.

[0082] In this example, a sheet-like crosslinked rubber material was actually manufactured, a sample was taken from the manufactured crosslinked rubber material, and dynamic viscoelasticity was measured, and the cross-section of the crosslinked rubber material sample was observed using a digital microscope.

[0083] First, the raw materials used in the production of the rubber crosslinked product in this embodiment are summarized below.

[0084] <Ingredients> [Rubber components] • EPDM rubber 1: Ethylene-propylene-5-ethylidene-2-norbornene rubber (EP24 manufactured by ENEOS Material Co., Ltd., ethylene content: 54% by weight, Mooney viscosity at 125°C: 42, polymer represented by the following formula (1)) [ka]

[0085] • EPDM rubber 2: Ethylene-propylene-vinylidene-5-vinyl-2-norbornene rubber ("PX-008M" manufactured by Mitsui Chemicals, Inc., ethylene content: 60% by weight, Mooney viscosity at 125°C: 46, polymer represented by the following formula (2)) [ka]

[0086] • EBDM rubber: Ethylene-butene-5-ethylidene-2-norbornene rubber (K-9330M manufactured by Mitsui Chemicals, Inc., ethylene content: 50% by weight, Mooney viscosity at 125°C: 30, polymer represented by the following formula (3)) [ka]

[0087] [Composite material] • Composite material consisting of polyethylene and multiple PET fibers: "Nanofront®" manufactured by Teijin Limited (a composite material having a sea-island structure of polyethylene and multiple PET fibers with a diameter of 700 nm and a length of 0.5 mm, polyethylene:PET fiber (mass ratio) = 3:7)

[0088] [Other ingredients] • Zinc oxide (vulcanization accelerator): "Zinc Oxide No. 3" manufactured by Sakai Chemical Industry Co., Ltd. • Stearic acid (processing aid): Manufactured by Lion Oil & Fat Co., Ltd. • FEF Carbon Black: "#60" manufactured by Asahi Carbon Co., Ltd. • Paraffin-based oil: Diana Process Oil manufactured by Idemitsu Kosan Co., Ltd. • Anti-aging agent CD: "Nocrack CD" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (amine-based anti-aging agent, 4,4'-bis(α,α-dimethylbenzyl)diphenylamine) • Anti-aging agent MB: "Nocrack MB" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (imidazole-based anti-aging agent, 2-mercaptobenzimidazole) • Organic peroxide (dicumyl peroxide) (crosslinking agent): "DCP40" manufactured by Nippon Oil & Fats Co., Ltd. • Crosslinking agent: "Balnock PM" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0089] Next, the method for producing the rubber crosslinked product common to each example and comparative example is described below.

[0090] <Method for manufacturing crosslinked rubber products> In each example and comparative example, first, the primary mixing materials in the proportions (parts by mass) shown in Table 1 were mixed for 6 to 7 minutes using a Banbury mixer (Laboplastmill, manufactured by Toyo Seiki Co., Ltd.) under the conditions of a start temperature of 75°C to 80°C and a dump (completion of mixing) temperature of 140°C to 150°C. Next, the mixture after primary mixing was kneaded for 0.5 to 1 minute at a roll temperature of 40°C. After that, the secondary mixing materials in the proportions (parts by mass) shown in Table 1 were added to the mixture and kneaded again for 10 minutes to form a sheet. Finally, a sheet-shaped rubber crosslinked material was produced by molding at 170°C.

[0091] [Table 1]

[0092] In Table 1 above, "-" indicates that it is not included in the raw materials of the crosslinked rubber product.

[0093] The following measurements were performed using the sheet-like rubber crosslinked materials of each example and comparative example manufactured by the method described above. Furthermore, the following observations were also made using the rubber crosslinked material of Example 3.

[0094] <Measurement of dynamic viscoelasticity of crosslinked rubber materials> The dynamic viscoelasticity, specifically the storage modulus (Pa) and loss coefficient (tanδ), of the crosslinked rubber materials of each example and comparative example was measured by the following method. First, two samples, one in the row direction and the other in the opposite row direction, were cut from the sheet-like crosslinked rubber materials of each example and comparative example, each the size of a JIS No. 3 dumbbell. The row direction is the direction in which the length direction of the sample is parallel to the length direction of multiple PET fibers arranged substantially parallel to each other. The opposite row direction is the direction in which the length direction of the sample is perpendicular to the length direction of multiple PET fibers arranged substantially parallel to each other. Next, using the two cut samples, the storage modulus (Pa) and loss coefficient (tanδ) were measured using a viscoelasticity tester manufactured by UBM Co., Ltd., under the following dynamic viscoelasticity test conditions, with frequencies ranging from 0Hz to 400Hz (0Hz to 200Hz for Example 1 and Comparative Example 1). (Measurement conditions for dynamic viscoelasticity testing) • Measurement method: Dynamic viscoelasticity measurement (sine wave) • Measurement mode: Frequency-dependent (0Hz to 400Hz, however, Example 1 and Comparative Example 1 use 0Hz to 200Hz) • Chuck: pull ·Waveform: Sine wave • Type of excitation: Continuous excitation Conditions: Distortion control 40μm ·Measurement temperature: room temperature

[0095] [Results and Discussion] Figures 2 to 7 show graphs of the storage modulus at various frequencies for samples of crosslinked rubber materials in the grain direction and anti-grain direction for Examples 1 to 3 and Comparative Examples 1 to 3, respectively. As can be seen from the comparison between Figure 2 and Figure 3, Figure 4 and Figure 5, and Figure 6 and Figure 7, in all of the crosslinked rubber materials of Examples 1 to 3, in which 4 parts by mass of a polyethylene and PET fiber composite material (polyethylene:PET fiber (mass ratio) = 3:7) was added as the material during primary kneading, the storage modulus of the sample in the grain direction was significantly improved compared to the storage modulus of the sample in the anti-grain direction, from the low-frequency range to the high-frequency range. Specifically, in the crosslinked rubber materials of Examples 1 to 3, the storage modulus in the grain direction relative to the storage modulus in the anti-grain direction was 1.1 times at the smallest point and 6.0 times at the largest point. The smallest measurement point is the measurement point around 100 Hz in the crosslinked rubber material of Example 1, and the largest measurement point is the measurement point around 100 Hz in the crosslinked rubber material of Example 3.

[0096] Furthermore, Figures 8 and 9 show graphs comparing the storage modulus (Figure 8) or loss coefficient (Figure 9) of samples of the crosslinked rubber material of Example 1 and Comparative Example 1 at each frequency in the grain direction. Figures 10 and 11 show graphs comparing the storage modulus (Figure 10) or loss coefficient (Figure 11) of samples of the crosslinked rubber material of Example 2 and Comparative Example 2 at each frequency in the grain direction. Figures 12 and 13 show graphs comparing the storage modulus (Figure 12) or loss coefficient (Figure 13) of samples of the crosslinked rubber material of Example 3 and Comparative Example 3 at each frequency in the grain direction. As can be seen from the comparison of these graphs, the crosslinked rubber materials of Examples 1 to 3, in which 4 parts by mass of a polyethylene and PET fiber composite material was added as the material during primary kneading, all showed improved storage modulus and decreased loss coefficient from the low frequency region to the high frequency region.

[0097] From the results shown in Figures 2 to 13, it can be seen that, regardless of the type of rubber component (EPDM or EBDM), by using a composite material consisting of polyethylene and multiple PET fibers with extremely small diameters as raw materials, and by adding the composite material so that the ratio of polyethylene to PET fibers in the final crosslinked rubber product is a predetermined value, a crosslinked rubber product with a high storage modulus and a low loss coefficient can be obtained from the low-frequency range to the high-frequency range. The crosslinked rubber product manufactured in this manner according to this embodiment has good handling stability and is therefore expected to be suitably used for vibration isolation applications such as components of vibration isolation members.

[0098] <Observation of a cross-section of a rubber crosslinked material sample using a digital microscope> Using the rubber crosslinked material of Example 3, the cross-section of a sample of the rubber crosslinked material was observed by the following method. First, a sample measuring 5 cm square x 2 mm thick was cut from the manufactured rubber crosslinked material of Example 3 at an arbitrary location. Then, the cross-section of the cut sample was observed at 500x magnification using a digital microscope "VHX-8000" manufactured by Keyence Corporation.

[0099] [result] Figure 14 shows a portion of the cross-sectional image of the rubber crosslinked material sample from Example 3, observed using a digital microscope. As shown in Figure 14, the composite material of the raw materials polyethylene and PET fibers ultimately showed that the polyethylene was indistinguishable from the rubber component and was well-matched. Furthermore, as shown in Figure 14, the multiple PET fibers with extremely small diameters did not exist in aggregate within the rubber component and polyethylene, but were dispersed and spread throughout the rubber component and polyethylene.

[0100] The embodiments and examples disclosed herein should be understood in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended. [Explanation of Symbols]

[0101] 1 Composite material 2 Polyethylene 3 PET fiber

Claims

1. A rubber component containing one or more polymers from ethylene-propylene-diene rubber and ethylene-butene-diene rubber, polyethylene that is compatible with the rubber component, and a plurality of polyethylene terephthalate fibers having a diameter of 100 nm or more and 1000 nm or less, and a length of 0.1 mm or more and 50 mm or less, The polyethylene content is 0.05 parts by mass or more and 5.0 parts by mass or less per 100 parts by mass of the rubber component. A crosslinked rubber product in which the total content of the plurality of polyethylene terephthalate fibers is 0.15 parts by mass or more and 5.0 parts by mass or less per 100 parts by mass of the rubber component.

2. The rubber crosslinked material according to claim 1, wherein the storage modulus of the rubber crosslinked material in the grain direction is 1.1 times or more and 6.0 times or less than the storage modulus of the rubber crosslinked material in the non-grain direction.

3. The rubber crosslinked product according to claim 1, wherein the rubber component comprises one or more polymers selected from the group consisting of ethylene-propylene-5-ethylidene-2-norbornene rubber, ethylene-propylene-vinylidene-5-vinyl-2-norbornene rubber, and ethylene-butene-5-ethylidene-2-norbornene rubber.

4. It also contains carbon black, The rubber crosslinked product according to claim 1, wherein the carbon black content is 35 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the rubber component.

5. The rubber crosslinked product according to claim 1, further comprising one or more components selected from the group consisting of vulcanization accelerators, processing aids, antioxidants, vulcanization accelerators, crosslinking agents, crosslinking aids, fillers, and oils.

6. The rubber crosslinked product according to claim 5, wherein the total content of one or more of the aforementioned components is greater than 0 parts by mass and less than or equal to 200 parts by mass per 100 parts by mass of the rubber component.

7. A vibration-damping member comprising a rubber crosslinked material according to any one of claims 1 to 6.

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