Flame-retardant rubber composition and gasket

Abstract

This flame-retardant rubber composition comprises: an ethylene / α-olefin / non-conjugated diene copolymer; 60 mass% or more of aluminum hydroxide; and 8 mass% or less in total of an alkyl-modified silane coupling agent and a hydrocarbon plasticizer. The alkyl-modified silane coupling agent constitutes 5 mass% or more of the aluminum hydroxide. A rubber composition having excellent flame-retardancy, physical properties preferable for a sealing material, and low environmental load can be provided.

Description

[Technical field]

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

[0002] Ethylene-α-olefin-non-conjugated diene copolymers, such as ethylene-propylene-diene copolymer rubber (Ethylene Propylene Diene Monomer; EPDM), have excellent mechanical properties, heat resistance, and weather resistance, and are also inexpensive, so they are used in rubber parts for sealing purposes such as gaskets in a wide range of products, including automobile parts, electrical appliance parts, and civil engineering and building materials.

[0003] In recent years, as the performance requirements for automobiles and electrical products become more sophisticated, gaskets used in these products, particularly electric vehicles (EVs), hybrid energy vehicles (HEVs), and lithium-ion batteries, are also required to have high low-temperature properties, safety, and flame retardancy. In order to impart flame retardancy to ethylene-α-olefin-non-conjugated diene copolymer rubber, many techniques have been reported for adding halogen-based compounds / antimony-based compounds, ammonium polyphosphate, hydrated metal oxides, expandable graphite, and the like. In particular, it is known that high flame retardancy can be imparted even in small amounts by using one or more halogen-based compounds such as chlorinated polyethylene, chlorinated paraffin, and decabromodiphenyl ether, and further antimony trioxide in combination (for example, Patent Document 1). However, halogen-based compounds generate toxic and corrosive halogen gases when burned, and antimony trioxide is a harmful substance, so there is a risk of environmental pollution.

[0004] Therefore, flame-retardant EPDM containing non-halogen, non-antimony flame retardants such as hydrated metal oxides such as ammonium polyphosphate, aluminum hydroxide, and magnesium hydroxide has been disclosed. However, most of these have been foamed, and are used in the fields of sealing materials for airtightness and waterproofing, indoor products such as home appliances such as heat insulation and soundproofing materials, outdoor products such as automobiles, and buildings such as houses (e.g., Patent Documents 2 and 3). In contrast, non-foamed EPDM has been disclosed (e.g., Patent Documents 4, 5, and 6). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 5-314841 [Patent Document 2] JP 2002-293976 A [Patent Document 3] JP 2007-204621 A [Patent Document 4] JP 2013-194232 A [Patent Document 5] JP 2018-16747 A [Patent Document 6] International Publication No. 2021 / 153234 Summary of the Invention [Problem to be solved by the invention]

[0006] Hydrated metal oxides are hydrophilic and therefore have a strong interaction with metals. Therefore, ethylene-α-olefin-non-conjugated diene copolymer rubbers to which a large amount of hydrated metal oxides has been added strongly adhere to manufacturing equipment such as dies and kneaders, resulting in reduced processability. Hydrated metal oxides also function as fillers, so when added in large quantities, they become unsuitable for use as sealing materials due to their high hardness. 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 aluminum hydroxide or further with non-halogen flame retardants such as ammonium polyphosphate alone, so a halogen flame retardant is used in combination. Alternatively, processing aids such as wax and soap are generally used to reduce adhesion to dies, but as the amount of hydrated metal oxides increases, the amount of processing aids also needs to increase, resulting in reduced flame retardancy due to reduced flame retardant content.

[0007] The flame-retardant EPDM with metal hydroxides disclosed in Patent Document 5 is a composition for the outer hood of railway vehicles, and acid-modified polyolefin is added to reduce the amount of metal hydroxides added to prevent the deterioration of durability, but the molded product is presumably too hard, making it unsuitable for use as a sealing material. One way to reduce the hardness of the molded product is to add a plasticizer, but since plasticizers are flammable, this reduces the flame retardancy.

[0008] The flame-retardant rubber composition disclosed in Patent Document 6 is obtained by adding a vinyl-modified silane coupling agent such as vinyltrimethoxysilane to an ethylene-α-olefin-non-conjugated diene copolymer together with a hydrated metal oxide, and the surface of the hydrated metal oxide is silane-treated to improve compatibility, which makes it easier to disperse uniformly, thereby improving flame retardancy while suppressing compounding, and improving compression set. In addition, the flame-retardant rubber composition has excellent low-temperature properties by applying an ethylene-butene-diene copolymer rubber (Ethylene Butene Diene Monomer; EBDM) in which the α-olefin is butene. However, the vinyl-modified silane coupling agent reacts with the ethylene-α-olefin-non-conjugated diene copolymer to harden the flame-retardant rubber composition. Therefore, a large amount of plasticizer needs to be compounded to obtain a hardness suitable for sealing materials, and as the compounding ratio of the hydrated metal oxide decreases, the flame retardancy decreases due to the large amount of plasticizer, making it difficult to achieve both a more appropriate hardness and high flame retardancy.

[0009] The present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide an ethylene-α-olefin-non-conjugated diene copolymer composition that has excellent flame retardancy, low environmental impact, and good releasability, and has physical properties suitable for a sealing material, and a gasket. [Means for solving the problem]

[0010] In order to solve the above problems, the present inventors have investigated additives and their contents necessary together with aluminum hydroxide as a flame retardant. As a result, they have found that adding an alkyl-modified silane coupling agent to aluminum hydroxide in a predetermined ratio or more reduces adhesion to a mold and inhibits an increase in hardness, and that adding a silane coupling agent or a plasticizer in a predetermined content provides an appropriate hardness without impairing flame retardancy. The present invention has been completed based on these findings.

[0011] That is, the flame-retardant rubber composition according to the present invention is a rubber composition that contains an ethylene-α-olefin-non-conjugated diene copolymer, 60 mass % or more of aluminum hydroxide, 、8 % by weight or less of alkyl-modified silane coupling agent and 0% by mass or more of plasticizer Contains The plasticizer is a hydrocarbon-based agent, and the total content of the alkyl-modified silane coupling agent and the plasticizer is 8% by mass or less; The amount of the alkyl-modified silane coupling agent is 5% by mass or more of the aluminum hydroxide. The gasket according to the present invention is made of the flame-retardant rubber composition. Effect of the Invention

[0012] The flame-retardant rubber composition according to the present invention has excellent flame retardancy, low environmental impact, good releasability, and physical properties suitable for a sealing material. The gasket according to the present invention has excellent flame retardancy, low environmental impact, and physical properties suitable for a sealing material. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, embodiments of the present invention will be described in detail. However, the scope of the present invention is not limited to the specific embodiments described below.

[0014] [Flame-retardant rubber composition] The flame-retardant rubber composition according to the present 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-based plasticizer, a crosslinking aid, and a processing aid. By applying aluminum hydroxide as a flame retardant, the environmental load of the flame-retardant rubber composition can be reduced, and since flame retardancy can be imparted with a relatively small amount among non-halogen and non-antimony flame retardants, the amount of plasticizer, etc., to be blended for reducing hardness can be reduced. The alkyl-modified silane coupling agent hydrophobizes aluminum hydroxide, weakening the adhesion of the flame-retardant rubber composition to a mold or the like caused by a large amount of aluminum hydroxide, thereby ensuring releasability, and also reducing the hardness, making the plasticizer unnecessary or reducing the amount of plasticizer added. Then, by blending the processing aid and plasticizer in appropriate amounts, rubber characteristics suitable for a sealant can be obtained without impairing the flame retardancy imparted by the flame retardant. Below, each component constituting the flame-retardant rubber composition will be described.

[0015] (Ethylene-α-olefin-non-conjugated diene copolymer) Ethylene-α-olefin-non-conjugated diene copolymer is a rubber obtained by copolymerizing ethylene and α-olefin with a small amount of non-conjugated diene component. 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 making the α-olefin have 3 or more carbon atoms, the crystallization of polyethylene can be inhibited. Examples of α-olefins having 3 or more carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, and 1-decene, and propylene and 1-butene are preferred. Examples of non-conjugated dienes include 5-ethylidene-2-norbornene, dicyclopentadiene, and 1,4-hexadiene.

[0016] (Crosslinking agent) The crosslinking agent may be any agent that is generally usable for crosslinking ethylene-α-olefin-non-conjugated diene copolymers, and is preferably, for example, an organic peroxide. This is because the organic peroxide does not contain a sulfur-based compound and does not corrode metal materials that come into contact with the flame-retardant rubber composition. Specific examples of the organic peroxide include tertiary butyl peroxide, dicumyl peroxide, tertiary butyl cumyl peroxide, 1,1-di(tertiary butylperoxy)-3,3,5-trimethylcyclohexane, and 2,5-dimethyl-2,5-di(tertiary butylperoxy)hexane. The amount of the organic peroxide to be blended is preferably 3 to 6 parts by mass per 100 parts by mass of the ethylene-α-olefin-non-conjugated diene copolymer.

[0017] (Aluminum Hydroxide) Aluminum hydroxide has a higher heat absorption during thermal decomposition than other hydrated metal oxides such as magnesium hydroxide, so it can exhibit flame retardancy even in a relatively small amount. Therefore, by selecting aluminum hydroxide as a flame retardant, its blending amount is small, and the effect on the rubber properties such as hardness of the ethylene-α-olefin-non-conjugated diene copolymer is suppressed. The flame-retardant rubber composition is blended so that it contains 60 mass% or more of aluminum hydroxide to obtain high flame retardancy, specifically to meet the V-0 grade in the UL94 standard. The upper limit of the blending of aluminum hydroxide is a value that does not exceed the specified upper limit of the content of the alkyl-modified silane coupling agent blended in proportion to the aluminum hydroxide, as described later.

[0018] The aluminum hydroxide is preferably particulate. In order to improve dispersibility and workability during kneading, the aluminum hydroxide preferably has an average particle size of 0.6 μm or more, more preferably 0.9 μm or more. On the other hand, in order to make it difficult to affect the mechanical properties of the flame-retardant rubber composition, the aluminum hydroxide preferably has an average particle size of 10 μm or less, more preferably 5.0 μm or less. The aluminum hydroxide may be surface-silane-treated.

[0019] (Alkyl-modified silane coupling agents) Silane coupling agents hydrophobize the surface of aluminum hydroxide by silane treatment. By hydrophobizing aluminum hydroxide, the adhesion of the flame-retardant rubber composition to the mold, etc. is weakened, so that the mold releasability is not reduced. Also, the compatibility of aluminum hydroxide with ethylene-α-olefin-non-conjugated diene copolymer is improved, so that the flame retardant rubber composition can be easily dispersed uniformly, and the flame retardancy can be increased relative to the amount of compounding. In addition, the Payne effect of aluminum hydroxide as a filler is reduced, so that the hardness increase caused by the addition of aluminum hydroxide is suppressed. Furthermore, alkyl-modified silane coupling agents have no functional groups other than silanol groups that react with aluminum hydroxide, which is the surface treatment target. Therefore, they do not form covalent bonds with polymers such as EPDM, do not increase the hardness of the flame-retardant rubber composition, and even reduce the hardness. In addition, even if there is silane coupling agent that has not reacted with aluminum hydroxide, the silanol groups bond to the mold, etc., but do not reduce the mold releasability because there are no functional groups that bond with the polymer.

[0020] The alkyl-modified silane coupling agent preferably has an alkyl group having 8 to 20 carbon atoms, and examples thereof include octyltriethoxysilane and hexadecyltrimethoxysilane. In order for the flame-retardant rubber composition to have sufficient releasability, the alkyl-modified silane coupling agent is blended in an amount of 5% by mass or more of aluminum hydroxide. Furthermore, the flame-retardant rubber composition can be blended with an alkyl-modified silane coupling agent according to the desired hardness, and in the case where the composition does not contain a hydrocarbon-based plasticizer described below, it is preferable to contain 6% by mass or more. On the other hand, the alkyl-modified silane coupling agent is flammable, and if it is blended in excess, the flame retardancy decreases. Therefore, the flame-retardant rubber composition is blended so that the alkyl-modified silane coupling agent is blended in an amount of 8% by mass or less, and in the case where the flame-retardant rubber composition contains a hydrocarbon-based plasticizer described below, the total content of these is 8% by mass or less.

[0021] The flame-retardant rubber composition according to the present embodiment may contain known additives for ethylene-α-olefin-non-conjugated diene copolymer rubber, if necessary. For example, by adding a divalent metal oxide such as zinc oxide as a crosslinking aid, a hydrocarbon-based plasticizer, a processing aid, a colorant, an antioxidant, etc., it is possible to improve kneadability, processability, handling, etc.

[0022] (Hydrocarbon plasticizers) The hydrocarbon plasticizer has good compatibility with the ethylene-α-olefin-non-conjugated diene copolymer and is one of the common additives for ethylene-α-olefin-non-conjugated diene copolymer rubber, for example, mineral oil such as paraffin-based process oil and naphthene-based process oil. In the flame-retardant rubber composition according to the present invention, the hydrocarbon plasticizer is a plasticizer for reducing the high hardness caused by the addition of a large amount of aluminum hydroxide. For this reason, 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 amount of the hydrocarbon plasticizer is mixed, the lower the flame retardancy becomes, so that the total content of the alkyl-modified silane coupling agent and the hydrocarbon plasticizer in the flame-retardant rubber composition is set to 8% by mass or less.

[0023] (Processing aids) Examples of processing aids include 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 that increase the fluidity of the flame-retardant rubber composition and impart mold releasability. When stearic acid, fatty acid amide compounds, and fluorine-containing compounds are added, in order to fully express their effects, it is preferable that each of them is 2 parts by mass or more per 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, and if they are excessively mixed, the flame retardancy decreases, so that the total content of these in the flame-retardant rubber composition is 3% by mass or less, and it is preferable that each of them is 3 parts by mass or less per 100 parts by mass of the ethylene-α-olefin-non-conjugated diene copolymer, and the total content is 8 parts by mass or less.

[0024] The ethylene-α-olefin copolymer reduces the hardness of the flame-retardant rubber composition containing the ethylene-α-olefin-non-conjugated diene copolymer. The α-olefin preferably has 2 to 10 carbon atoms. When the ethylene-α-olefin copolymer is added, the amount of the copolymer is preferably 3 to 6 parts by mass per 100 parts by mass of the ethylene-α-olefin-non-conjugated diene copolymer.

[0025] (Characteristics of Flame Retardant Rubber Composition) In order to realize high sealing properties when manufactured into a gasket or the like, the flame-retardant rubber composition according to the present embodiment has a JIS A hardness Hs of 80 or less, and preferably 75 or less. In order to have sufficient strength as a gasket or the like, the hardness Hs is preferably 60 or more, and more preferably 65 or more. The JIS A hardness is measured with a durometer (Durometer type A) in accordance with JIS K6253.

[0026] The flame retardant rubber composition according to the present embodiment preferably has flame retardancy satisfying V-0 grade in the UL 94 standard. By having such flame retardancy, the flame retardant rubber composition can be applied to sealing materials such as gaskets, particularly gaskets used in high-temperature environments such as EVs and HEVs.

[0027] 〔gasket〕 The flame-retardant rubber composition according to the present embodiment can be molded and processed into sealing materials such as gaskets and O-rings, etc. In particular, it can be applied to gaskets used in EVs and HEVs, and gaskets that seal the outside of the housings of lithium-ion batteries. EXAMPLES

[0028] The flame-retardant rubber composition according to the present invention has been described above as an embodiment of the present invention, but examples in which the effects of the present invention have been confirmed will be described below. Note that the present invention is not limited to these examples.

[0029] (Creating test pieces) The formulations of the rubber compositions of the Examples and Comparative Examples are shown in Table 1. In Table 1, values ​​outside the range of the present invention are underlined. The raw materials used in the Examples and Comparative Examples are as follows. (1) Ethylene-α-olefin-non-conjugated diene copolymer (1-a) EPDM (ethylene-propylene-ethylidene norbornene copolymer); EP33, manufactured by JSR Corporation (1-b) EBDM (ethylene-butene-diene copolymer); EBT K-9330M, manufactured by Mitsui Chemicals, Inc. (2) Crosslinking agent Dicumyl peroxide (DCP), Percumyl (registered trademark) D, manufactured by Nippon Oil & Fats Co., Ltd. (3) Processing aids (3-a) Stearic acid; DTST, manufactured by Miyoshi Oil Co., Ltd. (3-b) Oleic acid amide; Diamid O-200, manufactured by Nippon Kasei Co., Ltd. (3-c) Fluorine-containing compound (functionalized perfluoropolyether); Tecnoflon (registered trademark) FPA1, manufactured by SOLVAY (3-d) Ethylene-α-olefin copolymer (ethylene-octene copolymer); Engage® XLT8677, manufactured by The Dow Chemical Company (4) Crosslinking assistant Zinc oxide, manufactured by Sakai Chemical Industry Co., Ltd. (5) Flame retardants (5-a) Silane-treated aluminum hydroxide; BF013STV, manufactured by Nippon Light Metal Co., Ltd. (5-b) Halogen-based (Decabromodiphenyl Ethane; DBDPE); Prasafety (registered trademark) AM-1000, manufactured by Manac Corporation (5-c) Antimony trioxide; ATOX-S, manufactured by Nihon Seiko Co., Ltd. (6) Silane coupling agents (6-a) Alkyl-modified silane (octyltriethoxysilane); Dynasylan® OCTEO, manufactured by Evonik Industries, Inc. (6-b) Vinyl-modified silane (vinyltriethoxysilane); SILQUEST A-151, Momentive Performance Materials (7) Plasticizers (7-a) Paraffin-based process oil; Diana Process Oil PW-380, manufactured by Idemitsu Kosan Co., Ltd. (7-b) Adipic acid ether ester type; Adeka Cizer RS-107, manufactured by ADEKA Corporation (8) Coloring agents Carbon black: Seast G-SVH, manufactured by Tokai Carbon Co., Ltd. (9) Antiaging Agents 2,2,4-trimethyl-1,2-dihydroquinoline polymer (TMQ), Nocrac 224-S, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0030] For each Example and Comparative Example, the composition was prepared by a kneader (closed mixer) with the composition excluding the crosslinking agent, and the crosslinking agent was further added and kneaded by an open roll. The obtained composition before crosslinking was crosslinked at 180°C for 6 minutes while compression molding in a sheet-type mold coated with a release agent, and a test piece having a thickness of 2 mm was produced. For each test piece of the Examples and Comparative Examples, the hardness was measured and the flame retardancy was evaluated as follows. In addition, the composition before crosslinking was sandwiched between two SUS plates not coated with a release agent, and crosslinked under the same conditions while compression molding to a thickness of 2 mm.

[0031] (hardness) The test pieces were measured using a hardness tester (Durometer type A) conforming to JIS K6253. The hardness is shown in Table 1. The pass standard was set at 80 or less.

[0032] (Mold releasability) Test pieces molded from SUS plates not coated with a release agent were rated as "pass" if they did not break when peeled off from the SUS plate after crosslinking, and "fail" if they broke. The results are shown in Table 1.

[0033] (Flame retardant) The test pieces were judged to be V-0 in the flammability test of the UL94 standard. Those that met V-0 were rated as "pass" (○), and those that did not were rated as "fail" (×). The results are shown in Table 1.

[0034] [Table 1]

[0035] As shown in Table 1, the flame-retardant rubber compositions of Examples 1 to 5, which are within the range of the present invention, showed appropriate hardness, good releasability, and high flame retardancy. That is, it can have the same characteristics as Comparative Example 8, in which a halogen-based or antimony-based flame retardant was applied. In particular, Examples 1, 2, and 5, in which the paraffin-based process oil, which is a plasticizer, is a suitable content in total with the silane coupling agent, showed a hardness reduced to 75 or less. In contrast, Comparative Examples 1 and 2, in which the silane coupling agent was not added, and Comparative Example 5, in which the silane coupling agent was insufficient, did not provide releasability. Comparative Example 2 further showed a decrease in flame retardancy due to an excess of processing aids such as fatty acid amide. Comparative Example 3 showed insufficient flame retardancy due to a shortage of flame retardant. Comparative Example 4 showed a decrease in flame retardancy due to an excess of paraffin-based process oil. Comparative Example 6 showed an increase in EPDM hardness due to the application of a vinyl-modified silane coupling agent, and the unreacted silane coupling agent bonded the EPDM to the mold, resulting in a decrease in releasability. In Comparative Example 7, an ether ester type plasticizer, which has poor compatibility with EPDM, was used, and bleeding occurred.

Claims

1. A flame-retardant rubber composition comprising an ethylene-α-olefin-non-conjugated diene copolymer, 60% by mass or more of aluminum hydroxide, 8% by mass or less of an alkyl-modified silane coupling agent, and 0% by mass or more of a plasticizer, The plasticizer is a hydrocarbon-based plasticizer, The total content of the alkyl-modified silane coupling agent and the plasticizer is 8% by mass or less; The alkyl-modified silane coupling agent is 5% by mass or more of the aluminum hydroxide. A flame-retardant rubber composition comprising:

2. 2. The flame-retardant rubber composition according to claim 1, further comprising a processing aid containing at least stearic acid and a fatty acid amide compound, or further containing a fluorine-containing compound, in a total amount of 3 mass % or less.

3. The total content of the alkyl-modified silane coupling agent and the plasticizer is 6 mass% or more. The flame-retardant rubber composition according to claim 1 or 2.

4. 4. The flame-retardant rubber composition according to claim 3, which has a JIS A hardness of 75 or less and a flame retardancy satisfying V-0 of the UL94 standard.

5. A gasket for an electric vehicle, a hybrid vehicle, or a lithium ion battery, comprising the flame-retardant rubber composition according to claim 4.

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