Flame-retardant rubber composition and sealing ring

Abstract

The flame-retardant rubber composition contains an ethylene-α-olefin-non-conjugated diene copolymer, aluminum hydroxide of 60% by mass or more, and an alkyl-modified silane coupling agent and a hydrocarbon plasticizer in a total amount of 8% by mass or less, and the alkyl-modified silane coupling agent is 5% by mass or more of the aluminum hydroxide. It is possible to provide a rubber composition having excellent flame retardancy, suitable physical properties as a sealing material, and a low environmental load.

Description

Technical Field

[0001] The present invention relates to a flame-retardant ethylene-α-olefin-non-conjugated diene copolymer rubber composition and a sealing ring. Background Art

[0002] Ethylene-α-olefin-non-conjugated diene copolymers represented by ethylene-propylene-diene monomer (EPDM) are excellent in mechanical properties, heat resistance, weather resistance, etc., and are also inexpensive. Therefore, they are used in rubber components for sealing such as sealing rings in a wide range of products such as automotive parts, electrical product parts, and civil engineering and building materials.

[0003] In recent years, as the performance requirements for automobiles, electrical products, etc. have gradually increased, the sealing rings used in these products, especially in electric vehicles (EV), hybrid energy vehicles (HEV), or lithium-ion batteries, are also required to have high performance in terms of low-temperature properties, safety, and flame retardancy. In order to impart flame retardancy to ethylene-α-olefin-non-conjugated diene copolymer rubbers, techniques for adding halogen compounds / antimony compounds, ammonium polyphosphate, hydrated metal oxides, expanded graphite, etc. have been widely reported. In particular, it is known that by using one or more of halogen compounds such as chlorinated polyethylene, chlorinated paraffin, and decabromodiphenyl ether and further antimony trioxide, high flame retardancy can be imparted even with a small compounding amount (for example, Patent Document 1). However, halogen compounds generate toxic and corrosive halogen gases when burned, and in addition, antimony trioxide is a harmful substance, so there is a possibility of environmental pollution respectively.

[0004] Therefore, flame-retardant EPDMs containing halogen-free and antimony-free flame retardants such as ammonium polyphosphate, aluminum hydroxide, and magnesium hydroxide have been disclosed. However, most of them are foams as airtight and water-stopping sealing materials, heat insulating materials, and sound insulating materials in fields such as indoor products such as home appliances, outdoor products such as automobiles, and buildings such as houses (for example, Patent Documents 2 and 3). In contrast, non-foamed EPDMs have been disclosed (for example, Patent Documents 4, 5, and 6).

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent Laid-Open No. 5-314841;

[0008] Patent Document 2: Japanese Patent Laid-Open No. 2002-293976;

[0009] Patent Document 3: Japanese Patent Application Laid-Open No. 2007-204621;

[0010] Patent Document 4: Japanese Patent Application Laid-Open No. 2013-194232;

[0011] Patent Document 5: Japanese Patent Application Laid-Open No. 2018-16747;

[0012] Patent Document 6: International Publication No. 2021 / 153234. SUMMARY OF THE INVENTION

[0013] Problems to be Solved by the Invention

[0014] Since hydrated metal oxides are hydrophilic and have a strong interaction with metals, ethylene-α-olefin-non-conjugated diene copolymer rubbers with a large amount of hydrated metal oxides added will strongly adhere to manufacturing equipment such as molds and kneaders, resulting in reduced processability. In addition, hydrated metal oxides also function as fillers, so if a large amount is added, the hardness (rigidity) becomes high and it is not suitable as a sealing material. For example, in the flame-retardant EPDM disclosed in Patent Document 4, aluminum hydroxide is suppressed to a mass ratio of 70% or less of EPDM, and the flame retardancy is insufficient with only halogen-free flame retardants such as aluminum hydroxide or further ammonium polyphosphate, and a halogen-based flame retardant is used in combination. Or, in order to reduce the adhesion to molds and the like, processing aids such as wax and soap are usually used, but as the compounding amount of hydrated metal oxides increases, the compounding amount of processing aids must also be large, and as a result, the compounding amount of the flame retardant decreases and the flame retardancy decreases.

[0015] The flame-retardant EPDM containing a metal hydroxide disclosed in Patent Document 5 is a composition for constructing the outer windshield of a railway vehicle. In order to suppress the reduction in durability caused by the metal hydroxide, the addition amount is minimized and an acid-modified polyolefin is added, but it is presumed that the hardness of the molded product is high and it is not suitable as a sealing material. In order to suppress the hardness of the molded product, adding a plasticizer can be cited, but since the plasticizer is flammable, the flame retardancy will decrease.

[0016] The flame-retardant rubber composition disclosed in Patent Document 6 is obtained by adding a vinyl-modified silane coupling agent such as vinyltrimethoxysilane together with a hydrated metal oxide to an ethylene-α-olefin-non-conjugated diene copolymer. The hydrated metal oxide is surface-treated with silane, improving compatibility, thus making it easier to disperse uniformly. It can improve flame retardancy while suppressing compounding, and furthermore, can improve compression set. In addition, by applying it to an ethylene-butene-diene copolymer rubber (Ethylene Butene Diene Monomer; EBDM) with butene as the α-olefin, a flame-retardant rubber composition with excellent low-temperature properties is produced. However, the vinyl-modified silane coupling agent reacts with the ethylene-α-olefin-non-conjugated diene copolymer, hardening the flame-retardant rubber composition. Therefore, in order to form a hardness suitable for a sealing material, a large amount of plasticizer needs to be compounded, reducing the compounding ratio of the hydrated metal oxide. At the same time, the flame retardancy decreases due to the large amount of plasticizer, making it difficult to balance a more appropriate hardness and high flame retardancy.

[0017] The present invention has been completed in view of the above problems, and its object is to provide an ethylene-α-olefin-non-conjugated diene copolymer composition and a sealing ring that have excellent flame retardancy, low environmental load, good mold release properties, and physical properties suitable for sealing materials.

[0018] Means for Solving the Problem

[0019] In order to solve the above problems, the inventors of the present invention studied additives necessary together with aluminum hydroxide as a flame retardant and their contents. As a result, it was found that by adding an alkyl-modified silane coupling agent in a ratio of a specified amount or more relative to aluminum hydroxide, adhesion to a mold or the like is reduced, and an increase in hardness is suppressed. By containing a silane coupling agent or a further plasticizer in a specified content, an appropriate hardness is achieved without impairing flame retardancy. The present invention has been completed based on such an insight.

[0020] That is, the flame-retardant rubber composition according to the present invention is characterized in that the ethylene-α-olefin-non-conjugated diene copolymer contains 60% by mass or more of aluminum hydroxide and 8% by mass or less of an alkyl-modified silane coupling agent, and the alkyl-modified silane coupling agent is 5% by mass or more of the aluminum hydroxide.

[0021] In addition, the sealing ring according to the present invention is composed of the flame-retardant rubber composition.

[0022] Effects of the Invention

[0023] The flame-retardant rubber composition according to the present invention has excellent flame retardancy, low environmental load, good mold release properties, and physical properties suitable for sealing materials. The sealing ring according to the present invention has excellent flame retardancy, low environmental load, and physical properties suitable as a sealing material. Detailed Description of the Invention

[0024] Hereinafter, embodiments of the present invention will be described in detail. However, the scope of the present invention is not limited to the embodiments as specific examples described below.

[0025] [Flame-retardant rubber composition]

[0026] The flame-retardant rubber composition according to this embodiment contains an ethylene-α-olefin-non-conjugated diene copolymer, a crosslinking agent, aluminum hydroxide as a flame retardant, an alkyl-modified silane coupling agent, a hydrocarbon plasticizer, a crosslinking aid, and a processing aid. By using aluminum hydroxide as the flame retardant, the environmental load of the flame-retardant rubber composition can be reduced. In addition, in a halogen-free and antimony-free flame retardant, flame retardancy can be imparted in a relatively small amount, so that the amount of a plasticizer or the like for reducing hardness can be small. The alkyl-modified silane coupling agent can hydrophobize aluminum hydroxide, weaken the adhesion of the flame-retardant rubber composition to a mold or the like due to a large amount of aluminum hydroxide, and ensure mold release properties. In addition, it can reduce the hardness without the need for a plasticizer or reduce its addition amount. Further, by appropriately blending a processing aid and a plasticizer, rubber properties suitable as a sealing material can be obtained without impairing the flame retardancy imparted by the flame retardant. Hereinafter, each component constituting the flame-retardant rubber composition will be described.

[0027] (Ethylene-α-olefin-non-conjugated diene copolymer)

[0028] The ethylene-α-olefin-non-conjugated diene copolymer is a rubber obtained by copolymerizing a small amount of a non-conjugated diene component with ethylene and an α-olefin. The α-olefin is an α-olefin having 3 or more carbon atoms, and more preferably an α-olefin having 4 or more carbon atoms. By setting the number of carbon atoms of the α-olefin to 3 or more, the crystallization of polyethylene can be hindered. Examples of the α-olefin having 3 or more carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, etc., and propylene and 1-butene are preferred. Examples of the non-conjugated diene include 5-ethylidene-2-norbornene, dicyclopentadiene, 1,4-hexadiene, etc.

[0029] (Crosslinking agent)

[0030] As the crosslinking agent, a crosslinking agent that can generally be used for crosslinking an ethylene-α-olefin-non-conjugated diene copolymer can be applied. For example, an organic peroxide is preferred. This is because the organic peroxide does not contain a sulfur compound and does not corrode the metal material in contact with the flame-retardant rubber composition. Specific examples of the organic peroxide include: tert-butyl peroxide, dicumyl peroxide, tert-butyl cumyl peroxide, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, etc. The blending amount of the organic peroxide is preferably 3 to 6 parts by mass with respect to 100 parts by mass of the ethylene-α-olefin-non-conjugated diene copolymer.

[0031] (aluminum hydroxide)

[0032] Aluminum hydroxide has a higher heat absorption during thermal decomposition than other hydrated metal oxides such as magnesium hydroxide. Therefore, even a small amount can exhibit flame retardancy. Thus, by selecting aluminum hydroxide as the flame retardant and making its formulation a small amount, the influence of properties such as hardness possessed by ethylene-α-olefin-non-conjugated diene copolymer on rubber properties is suppressed. The flame-retardant rubber composition achieves high flame retardancy. Specifically, in order to meet the V-0 grade in the UL94 standard, aluminum hydroxide containing 60% by mass or more is formulated. The upper limit of the formulation of aluminum hydroxide is a value that does not exceed the specified upper limit value of the content of the alkyl-modified silane coupling agent formulated in proportion to aluminum hydroxide as described later.

[0033] Aluminum hydroxide is preferably in particle form. In order to improve the dispersibility and workability during kneading, the average particle size of aluminum hydroxide is preferably 0.6 μm or more, more preferably 0.9 μm or more. On the other hand, in order not to easily affect the mechanical properties of the flame-retardant rubber composition, the average particle size of aluminum hydroxide is preferably 10 μm or less, more preferably 5.0 μm or less. In addition, aluminum hydroxide treated with silane on the surface can also be used.

[0034] (alkyl-modified silane coupling agent)

[0035] The silane coupling agent hydrophobizes the surface of aluminum hydroxide by silane treatment. Through the hydrophobization of aluminum hydroxide, the flame-retardant rubber composition weakens the adhesiveness to molds, etc. without reducing the demolding property. In addition, the compatibility between aluminum hydroxide and ethylene-α-olefin-non-conjugated diene copolymer is improved, and it is easily uniformly dispersed in the flame-retardant rubber composition, and the flame retardancy can be improved relative to the formulation amount. In addition, the Payne effect of aluminum hydroxide as a filler is reduced, and the hardening caused by the addition of aluminum hydroxide is suppressed. Furthermore, the alkyl-modified silane coupling agent does not have functional groups other than the silanol group that reacts with aluminum hydroxide as the surface treatment object. Therefore, it does not form a covalent bond with polymers such as EPDM, does not harden the flame-retardant rubber composition, and further reduces the hardness. In addition, even if there are aluminum hydroxide and unreacted silane coupling agent, the silanol group binds to molds, etc., but since there are no functional groups that bind to polymers, the demolding property is not reduced.

[0036] The alkyl-modified silane coupling agent preferably has an alkyl group with 8 to 20 carbon atoms. Examples include octyltriethoxysilane, cetyltrimethoxysilane, etc. In order to endow the flame-retardant rubber composition with sufficient mold release properties, the alkyl-modified silane coupling agent is compounded at 5% by mass or more based on aluminum hydroxide. Furthermore, the flame-retardant rubber composition can compound the alkyl-modified silane coupling agent according to the desired hardness, and preferably contains 6% by mass or more when not containing the hydrocarbon plasticizer described below. On the other hand, the alkyl-modified silane coupling agent is flammable, and if compounded in excess, the flame retardancy decreases. Therefore, the flame-retardant rubber composition is compounded in such a way that the content of the alkyl-modified silane coupling agent is 8% by mass or less. Furthermore, when containing the hydrocarbon plasticizer described below, their total content is 8% by mass or less.

[0037] The flame-retardant rubber composition according to this embodiment can add known additives in ethylene-α-olefin-non-conjugated diene copolymer rubber as needed. For example, by adding divalent metal oxides such as zinc oxide as a crosslinking aid, hydrocarbon plasticizers, processing aids, colorants, anti-aging agents, etc., the kneadability, processability, operability, etc. can be improved.

[0038] (Hydrocarbon plasticizer)

[0039] The hydrocarbon plasticizer has good compatibility with the ethylene-α-olefin-non-conjugated diene copolymer and is one of the general additives for ethylene-α-olefin-non-conjugated diene copolymer rubber. For example, it is mineral oil such as paraffinic processing oil and naphthenic processing oil. In the flame-retardant rubber composition according to the present invention, the hydrocarbon plasticizer is a plasticizer used to reduce the high hardness caused by the large addition of aluminum hydroxide. Therefore, the total content of the hydrocarbon plasticizer and the alkyl-modified silane coupling agent in the flame-retardant rubber composition is preferably 6% by mass or more. On the other hand, the hydrocarbon plasticizer is easily combustible, and the more the compounding amount, the lower the flame retardancy. Therefore, the total content of the alkyl-modified silane coupling agent and the hydrocarbon plasticizer in the flame-retardant rubber composition is 8% by mass or less.

[0040] (Processing aid)

[0041] Processing aids include, for example, stearic acid, fatty acid amide compounds, fluorine-containing compounds, ethylene-α-olefin copolymers, etc. Stearic acid, fatty acid amide compounds, and fluorine-containing compounds are lubricants, which improve the fluidity of the flame-retardant rubber composition and, in addition, impart mold release properties. When stearic acid, fatty acid amide compounds, and fluorine-containing compounds are added, in order to fully exhibit their effects, preferably 2 parts by mass or more are used respectively relative to 100 parts by mass of the ethylene-α-olefin-non-conjugated diene copolymer. On the other hand, stearic acid, fatty acid amide compounds, and fluorine-containing compounds are flammable. If they are excessively compounded, the flame retardancy will decrease. Therefore, the total content of them in the flame-retardant rubber composition is set to 3% by mass or less, preferably 3 parts by mass or less respectively relative to 100 parts by mass of the ethylene-α-olefin-non-conjugated diene copolymer, and the total is preferably 8 parts by mass or less.

[0042] The ethylene-α-olefin copolymer reduces the hardness of the flame-retardant rubber composition containing the ethylene-α-olefin-non-conjugated diene copolymer. As the α-olefin, an α-olefin having 2 to 10 carbon atoms is preferred. When the ethylene-α-olefin copolymer is added, preferably 3 to 6 parts by mass are used relative to 100 parts by mass of the ethylene-α-olefin-non-conjugated diene copolymer.

[0043] (Properties of the flame-retardant rubber composition)

[0044] In order to achieve high sealing performance when manufacturing a sealing ring or the like, the JIS A hardness Hs of the flame-retardant rubber composition according to the present embodiment is 80 or less, preferably 75 or less. In addition, in order to have sufficient strength as a sealing ring or the like, the hardness Hs is preferably 60 or more, more preferably 65 or more. The JIS A hardness is measured with a durometer (Durometer A type) in accordance with JIS K6253.

[0045] The flame-retardant rubber composition according to the present embodiment preferably satisfies the V-0 grade in the UL94 standard for flame retardancy. By having such flame retardancy, the flame-retardant rubber composition can be applied to sealing materials such as sealing rings, especially sealing rings used in high-temperature environments such as EVs and HEVs.

[0046] [Sealing ring]

[0047] The flame-retardant rubber composition according to the present embodiment can be molded and processed into sealing materials such as sealing rings and O-rings. In particular, it can be applied to sealing rings used in EVs and HEVs and sealing rings for sealing the outside of a lithium-ion battery case.

[0048] Examples

[0049] As described above, the manner for implementing the present invention with respect to the flame-retardant rubber composition of the present invention has been described. Hereinafter, examples in which the effects of the present invention have been confirmed will be described. In addition, the present invention is not limited to these examples.

[0050] (Fabrication of Test Pieces)

[0051] The formulations of the rubber compositions of the examples and comparative examples are shown in Table 1. In Table 1, values outside the scope of the present invention are underlined. The raw materials used in the examples and comparative examples are as described below.

[0052] (1) Ethylene-α-olefin-non-conjugated diene copolymer

[0053] (1-a) EPDM (ethylene-propylene-ethylidene norbornene copolymer); EP33, manufactured by JSR Corporation

[0054] (1-b) EBDM (ethylene-butene-diene copolymer); EBT K-9330M, manufactured by Mitsui Chemicals, Inc.

[0055] (2) Crosslinking agent

[0056] Dicumyl peroxide (DCP), PERCUMYL (registered trademark) D, manufactured by NOF Corporation

[0057] (3) Processing aid

[0058] (3-a) Stearic acid: DTST, manufactured by Miyoshi Oil & Fat Co., Ltd.

[0059] (3-b) Oleic acid amide: Diamond O-200, manufactured by Nippon Kasei Co., Ltd.

[0060] (3-c) Fluorine-containing compound (functionalized perfluoropolyether); Tecnoflon (registered trademark) FPA1, manufactured by Solvay

[0061] (3-d) Ethylene-α-olefin copolymer (ethylene-octene copolymer); Engage (registered trademark) XLT8677, manufactured by The Dow Chemical Company

[0062] (4) Crosslinking aid

[0063] Zinc oxide, manufactured by Sakai Chemical Industry Co., Ltd.

[0064] (5) Flame retardant

[0065] (5-a) Silane-treated aluminum hydroxide: BF013STV, manufactured by Nippon Light Metal Co., Ltd.

[0066] (5-b) Halogen type (Decabromodiphenyl Ethane; DBDPE); Plasfty (registered trademark) AM-1000, manufactured by MANAC Incorporated

[0067] (5-c) Antimony trioxide: ATOX-S, manufactured by Nippon Seiko Co., Ltd.

[0068] (6) Silane coupling agent

[0069] (6-a) Alkyl-modified silane (triethoxyoctylsilane); Dynasylan (registered trademark) OCTEO, manufactured by Evonik Industries

[0070] (6-b) Vinyl-modified silane (vinyltriethoxysilane); SILQUEST A-151, manufactured by Momentive Performance Materials

[0071] (7) Plasticizer

[0072] (7-a) Paraffin-based processing oil: DIANA PROCESS OIL PW-380, manufactured by Idemitsu Kosan Co., Ltd.

[0073] (7-b) Adipic acid ether ester: ADK CIZER RS-107, manufactured by ADEKA

[0074] (8) Colorant

[0075] Carbon black: SEAST G-SVH, manufactured by Tokai Carbon Co., Ltd.

[0076] (9) Antioxidant

[0077] 2,2,4-Trimethyl-1,2-dihydroquinoline polymer (TMQ), NOCRAC 224-S, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0078] For each example and each comparative example, preparation was carried out using a kneader (closed mixer) with a formulation excluding the crosslinking agent, and the crosslinking agent was further added and kneaded using an open roll. The pre-crosslinked composition obtained was compression-molded while crosslinking at 180 °C for 6 minutes in a sheet-shaped mold coated with a mold release agent to produce a test piece with a thickness of 2 mm. For the test pieces of each of the examples and comparative examples, the hardness was measured and the flame retardancy was evaluated as described below. In addition, the pre-crosslinked composition was sandwiched between two SUS plates not coated with the mold release agent, and while compression-molding to a thickness of 2 mm, crosslinking was carried out under the same conditions.

[0079] (Hardness)

[0080] For the test pieces, according to JIS K6253, measurement was carried out using a durometer (Durometer A type). The hardness is shown in Table 1. The acceptance criterion was set to 80 or less.

[0081] (Mold release property)

[0082] For the test pieces molded using SUS plates not coated with the mold release agent, the test pieces that did not break when peeled from the SUS plate after crosslinking were marked as acceptable "O", and the test pieces that broke were marked as unacceptable "×". The results are shown in Table 1.

[0083] (Flame retardancy)

[0084] For the test pieces, in the flammability test according to the UL94 standard, it was determined whether they were V-0. The test pieces that met V-0 were marked as acceptable "O", and the test pieces that did not meet V-0 were marked as unacceptable "×".

[0085] The results are shown in Table 1.

[0086]

[0087] As shown in Table 1, the flame-retardant rubber compositions of Examples 1 to 5 within the scope of the present invention exhibit appropriate hardness, good mold release properties, and high flame retardancy. That is, they can achieve the same properties as Comparative Example 8 using halogen-based and antimony-based flame retardants. In particular, in Examples 1, 2, and 5 where the total content of paraffin-based processing oil as a plasticizer and the silane coupling agent is at an appropriate level, the hardness is reduced to 75 or less. In contrast, Comparative Examples 1 and 2 without the addition of the silane coupling agent and Comparative Example 5 with insufficient silane coupling agent do not achieve mold release properties. In Comparative Example 2, the flame retardancy is reduced due to an excessive amount of processing aids such as fatty acid amides. In Comparative Example 3, the flame retardancy is insufficient due to insufficient flame retardant. In Comparative Example 4, the flame retardancy is reduced due to an excessive amount of paraffin-based processing oil. In Comparative Example 6, the hardness of EPDM increases due to the use of vinyl-modified silane coupling agent, and in addition, the unreacted silane coupling agent causes EPDM to adhere to the mold, resulting in reduced mold release properties. In Comparative Example 7, bleeding occurs due to the use of ether esters with poor compatibility with EPDM as a plasticizer.

Claims

1. A flame-retardant ethylene-α-olefin-non-conjugated diene copolymer composition, characterized in that, Containing aluminum hydroxide of 60% by mass or more and 62.8% by mass or less, processing aids of 3% by mass or less, an alkyl-modified silane coupling agent, and a hydrocarbon plasticizer, the total content of the hydrocarbon plasticizer and the alkyl-modified silane coupling agent is 8% by mass or less, the alkyl-modified silane coupling agent has an alkyl group with 8 to 20 carbon atoms and is 5% by mass or more of the aluminum hydroxide, 2. The flame-retardant ethylene-α-olefin-non-conjugated diene copolymer composition according to claim 1, wherein the processing aids at least include stearic acid and fatty acid amide compounds, or further include fluorine-containing compounds, 3. The flame-retardant ethylene-α-olefin-non-conjugated diene copolymer composition according to claim 1 or 2, characterized in that, the total content of the alkyl-modified silane coupling agent and the hydrocarbon plasticizer is 6% by mass or more, 4. The flame retardant ethylene-α-olefin-non-conjugated diene copolymer composition according to claim 3, wherein, the JIS A hardness is 75 or less, and the flame retardancy meets V-0 of the UL94 standard, 5. A sealing ring composed of the flame-retardant ethylene-α-olefin-non-conjugated diene copolymer composition according to claim 4, wherein, the sealing ring is used for electric vehicles, hybrid vehicles or lithium-ion batteries.

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