rubber composition

Abstract

This rubber composition comprises (B) 35-55 parts by weight of carbon black having an iodine adsorption value of 10-25 mg / g and a DBP oil absorption value of 30-140 ml / 100 g, (C) 5-23 parts by weight of a straight-chain hydrocarbon softener having a dynamic viscosity of 8-500 mm2 / sec at 40°C and a pour point of at most -30°C, and (D) 0.5-10 parts by weight of an organic peroxide, with respect to (A) 100 parts by weight of a copolymerized rubber polymer including at least one from ethylene-butene-nonconjugated diene terpolymer rubber, ethylene-propylene-nonconjugated diene terpolymer rubber, and ethylene-propylene copolymer rubber. A vulcanized product of the rubber composition exhibits resistance in a wide temperature range from low to high temperatures, and, when used as a sealing material such as a sealing material for a fuel cell separator, can sufficiently satisfy functions required as a sealing material.

Description

[Technical Field]

[0001] The present invention relates to a rubber composition, and more particularly to a rubber composition that is suitable for use as a molding material for seals for fuel cell separators. [Background technology]

[0002] Fuel cells have been put to practical use in a wide range of fields because they have excellent properties such as hardly requiring the use of fossil fuels, which are a resource that requires careful consideration for depletion, generating almost no noise during power generation, and having a higher energy recovery rate than other energy generation mechanisms.

[0003] Among these, polymer electrolyte fuel cells (PEFCs) operate at lower temperatures than other types of fuel cells, eliminating the need to worry about corrosion of the materials that make up the battery. They also have the advantage of being able to discharge a relatively large current despite operating at low temperatures, and are therefore attracting attention not only for use in domestic cogeneration systems but also as an alternative power source to internal combustion engines in vehicles.

[0004] Among the components that make up this PEFC, the separator is generally a flat plate with multiple parallel grooves formed on one or both sides. Its role is to transmit the electricity generated by the gas diffusion electrode inside the fuel cell to the outside, as well as to drain water produced during the power generation process into the grooves, ensuring that the grooves serve as a flow path for the reactant gases flowing into the fuel cell.

[0005] Fuel cell separators with grooves that fulfill this role are required to be smaller, and because many separators are stacked together, there is a demand for separator sealing materials that are highly durable and can be used for long periods of time.

[0006] Furthermore, the electrolyte membrane of a PEFC is formed of a polymer membrane such as a polytetrafluororesin membrane having perfluorosulfone side chain groups. When a sealant is placed near the electrolyte membrane for cross-linking, care must be taken to prevent the electrolyte membrane from deteriorating due to heating during cross-linking. In other words, a sealant for a fuel cell that can be cross-linked at a lower temperature and in a shorter time is desirable.

[0007] As such a separator sealing material, for example, one using EPDM has been proposed.

[0008] Patent Document 1 describes an adhesive sealant for fuel cells that can be crosslinked at low temperatures and has high sealing and adhesive reliability. The adhesive sealant is composed of a crosslinked product of a rubber composition containing (A) EPDM, (B) an organic peroxide crosslinking agent with a one-hour half-life temperature of 130°C or less, (C) a crosslinking aid, and (D) an adhesive component that is a resorcinol compound-melamine compound or a silane coupling agent. Comparative Example 4 describes that when adhesive component (D) is not included, poor results are observed in 90° peel tests and T-peel tests (initial, after 100 hours and after 1000 hours of immersion in 90°C hot water).

[0009] Patent Document 2 also describes that 5 to 30 parts by weight of an ethylene-α-olefin copolymer is further compounded per 100 parts by weight of EPDM to the rubber composition described in Patent Document 1. Examples of the α-olefin include α-olefins having 3 to 10 carbon atoms, such as propylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1, heptene-1, octene-1, nonene-1, and decene-1. An aluminate-based coupling agent is also described as component (D).

[0010] According to the examples using ethylene-octene-1 copolymer, in which the α-olefin is octene-1, the tensile strength, elongation at break, 90° peel strength, and volume resistivity (insulating properties) were increased, highlighting the effect of blending ethylene-α-olefin copolymer.

[0011] However, one of the challenges with fuel cell vehicles is the need to design and control them so that the FC stack and system components do not freeze and become inoperable, whether during start-up and driving under low-temperature conditions or when left in sub-zero temperatures after driving. This requires that sealing materials also be cold-resistant, but EPDM does not have sufficient cold resistance.

[0012] To improve the low-temperature properties of EPDM, it is well known to add plasticizers such as oils to improve the formulation so that the material remains rubbery even at low temperatures. However, this approach introduces new problems, such as reduced rubber strength and modulus, as well as poor mixability, dispersibility, and bleeding resistance. For this type of application, it is also important that the material can be used as a separator sealant. To improve low-temperature sealing while retaining the necessary functionality, rubber compositions have been proposed that contain 1 to 10 parts by weight of an organic peroxide crosslinking agent with a specified one-hour half-life temperature per 100 parts by weight of an ethylene-butene-non-conjugated diene copolymer (Patent Documents 3 to 5). While vulcanized molded products of such rubber compositions exhibit satisfactory low-temperature sealing properties, further improvement in sealing properties at high temperatures is desired. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-94056 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-249283 [Patent Document 3] WO2019 / 003884 [Patent Document 4] Japanese Patent Application Laid-Open No. 2017-183162 [Patent Document 5] Patent Publication No. 2021-086791 [Patent Document 6] Japanese Patent Application Laid-Open No. 2011-213822 Summary of the Invention [Problem to be solved by the invention]

[0014] The present invention has been made in view of the above-mentioned problems, and has an object to provide a rubber composition which, when vulcanized, exhibits resistance over a wide temperature range from low to high temperatures and which, when used as a sealing material, for example, a sealing material for a fuel cell separator, can fully satisfy the functions required of the sealing material. [Means for solving the problem]

[0015] The object of the present invention is to provide (A) an ethylene-butene-non-conjugated diene terpolymer rubber. (EBDM) and Ethylene-propylene-non-conjugated diene terpolymer rubber (EPDM) blends in which EBDM is blended in a proportion of 75% by weight or more of the total amount of EPDM. (B) 35 to 55 parts by weight of carbon black having an iodine adsorption of 10 to 25 mg / g and a DBP oil absorption of 30 to 140 ml / 100 g, and (C) a kinematic viscosity at 40°C of 8 to 500 mm 2 / sec, is achieved by a rubber composition containing 5 to 23 parts by weight of a linear hydrocarbon softener having a pour point of -30°C or less and 0.5 to 10 parts by weight of (D) an organic peroxide. [Effects of the Invention]

[0016] For example, sealing members for fuel cells are required to have both high elongation and compression set resistance, which are contradictory properties, but the rubber composition of the present invention makes it possible to achieve both of these properties by optimizing the particle size and structure size of the carbon black. That is, by blending a predetermined amount of carbon black having a predetermined iodine adsorption amount and DBP oil absorption amount, the obtained vulcanized molded product has excellent effects of ensuring compression crack resistance (high elongation) and excellent compression set resistance, which is a factor in extending the product's life, over a wide temperature range from low to high temperatures. DETAILED DESCRIPTION OF THE INVENTION

[0017] The polymer used is EBDM (ethylene / butene / non-conjugated diene terpolymer) for the purpose of balancing heat resistance, cold resistance, durability, temperature dependency of spring constant, and rebound stress. and EPDM (ethylene / propylene / non-conjugated diene terpolymer) of Blend And In this case, a copolymer rubber polymer is used in which EBDM is blended with EPDM in a proportion of 70% by weight or more of the total amount. Each copolymer rubber polymer is typically in a solid state.

[0018] The ethylene content in the copolymer rubber polymer is preferably 40 to 60% by weight. If the ethylene content is less than this, the rubber properties will be reduced, and it may be difficult to satisfy the elongation and tensile properties required for the sealing member. On the other hand, if the ethylene content is higher than this, the low-temperature properties tend to deteriorate. Also, from the viewpoint of acid resistance and water resistance in the operating environment of the fuel cell, EPDM Polymer is used, and from the viewpoint of low-temperature sealing EBDM A polymer is used.

[0019] EBDM has a copolymerization composition of 30 to 95% by weight, preferably 40 to 95% by weight, of structural units derived from ethylene, 4.9 to 49.9% by weight, preferably 4.9 to 35% by weight, of structural units derived from butene, and 0.1 to 20% by weight, preferably 1 to 15% by weight, of structural units derived from non-conjugated dienes, and (tert-butylamido)dimethyl ( η 5 - It is synthesized using a metallocene compound such as 2-methyl-s-indacen-1-yl)silanetitanium(II) 1,3-pentazine as a polymerization catalyst.

[0020] This EBDM is described in, for example, Patent Document 6. As the butene, butene-1 is mainly used, and as the non-conjugated diene, cyclic or chain non-conjugated dienes such as 5-ethylidene-2-norbornene and 5-vinyl-2-norbornene are used, with cyclic non-conjugated dienes being preferred. From the viewpoint of low-temperature setting resistance, EBDM containing about 1 to 20 wt %, preferably about 3 to 15 wt %, of these non-conjugated dienes is used. In practice, commercially available products, such as Mitsui Chemicals' EBT, are used as is.

[0021] EPDM is made of ethylene-propylene-non-conjugated diene terpolymer rubber polymer. As non-conjugated dienes, small amounts of dicyclopentadiene, 1,4-hexadiene, dicyclooctadiene, methylenenorbornene, vinylnorbornene, ethylidenenorbornene, etc. are copolymerized. Its Mooney viscosity ML 1+4 (125°C) is about 25 to 80, preferably about 25 to 70 be.

[0022] The copolymer rubber polymer is blended with carbon black, a linear hydrocarbon-based softener, and an organic peroxide to form a rubber composition. Note that when a bifunctional (meth)acrylate monomer, which is considered an essential component in Patent Document 5, is used, elongation at high temperatures may deteriorate as shown in the Reference Examples below.

[0023] The carbon black has an iodine adsorption of 10 to 25 mg / g, preferably 10 to 20 mg / g, and a DBP oil absorption of 30 to 140 ml / 100 g, preferably 30 to 110 ml / 100 g, and is used in an amount of 35 to 55 parts by weight, preferably 40 to 55 parts by weight, per 100 parts by weight of the copolymer rubber polymer.

[0024] Here, the iodine adsorption and DBP oil absorption are representative indices that indicate the properties of carbon black. The iodine adsorption is a value measured based on JIS K6221, which corresponds to ISO 1304, and the DBP oil absorption is a value measured in accordance with Method A (mechanical method) of JIS K6221, which corresponds to ISO 4656.

[0025] Iodine adsorption is an index of the total specific surface area of ​​carbon black, including pores, and DBP oil absorption indirectly quantifies structure by measuring the porosity between individual aggregates, which is positively correlated with structure.

[0026] If carbon black with an iodine adsorption capacity lower than this range is used, a large amount of carbon black must be blended to increase the hardness and thereby ensure the repulsive force required for sealing, resulting in a deterioration in compression set properties. On the other hand, if carbon black with a higher iodine adsorption capacity is used, or if carbon black with a DBP oil absorption outside this range is used, the sealing properties under high temperature conditions will be reduced.

[0027] Furthermore, when carbon black is used in a ratio other than the above, the sealing performance under high temperature conditions also deteriorates.

[0028] As a straight-chain hydrocarbon-based softener, the kinematic viscosity at 40°C is 8 to 500 mm 2 A linear hydrocarbon-based softener, preferably a liquid poly-α-olefin oligomer, having a pour point of −30°C or less from the viewpoint of volatility, is used in a proportion of about 5 to 23 parts by weight, preferably about 10 to 21 parts by weight, per 100 parts by weight of the copolymer rubber polymer. For example, commercially available products such as DURASYN 170 (manufactured by Ineos Singapore) and Diana Process Oil PW-380 (manufactured by Idemitsu Kosan) can be used as is. The kinematic viscosity here is measured in accordance with JIS K2283, which corresponds to ISO 2909 and ISO 3104. The inclusion of a linear hydrocarbon-based softener improves kneadability, suppresses bleed-out, and improves compression crack resistance and settling resistance over a wide temperature range, from low to high. If such a softener is used in a proportion greater than this, compression set properties at low temperatures, such as −30°C, deteriorate, while if used in a proportion less than this, elongation at high temperatures deteriorates.

[0029] Examples of organic peroxides include dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, di-tert-butylperoxide, di-tert-butylperoxy-3,3,5-trimethylcyclohexane, and tert-butyl hydroperoxide. Preferably, an organic peroxide having a one-hour half-life temperature of 110 to 130°C is used. Here, the one-hour half-life temperature is the temperature at which the half-life is one hour, which is an index indicating the decomposition temperature of an organic peroxide. The lower the one-hour half-life temperature, the more easily the organic peroxide decomposes at low temperatures.

[0030] As the organic peroxide having such a one-hour half-life temperature, peroxyketals and peroxyesters having a one-hour half-life temperature of 110 to 130°C, preferably peroxyketals, are preferably used.

[0031] Examples of peroxyketals that can be used include n-butyl-4,4-di(tert-butylperoxy)valerate, 2,2-di(tert-butylperoxy)butane, 2,2-di[4,4-bis(tert-butylperoxy)cyclohexyl]propane, 1,1-di(tert-butylperoxy)cyclohexane, di(3,5,5-trimethylhexanoyl)peroxide, 1,1-di(tert-hexylperoxy)cyclohexane, 1,1-di(tert-hexylperoxy)-3,3,5-trimethylcyclohexane, and 1,1-di(tert-butylperoxy)-2-methylcyclohexane.

[0032] Furthermore, examples of peroxyesters that can be used include tert-butylperoxybenzoate, tert-butylperoxyacetate, tert-hexylperoxybenzoate, tert-butylperoxy-2-ethylhexyl monocarbonate, tert-butylperoxylaurate, tert-butylperoxyisopropyl monocarbonate, tert-butylperoxy-3,5,5-trimethylhexanoate, tert-butylperoxymaleic acid, and tert-hexylperoxyisopropyl monocarbonate.

[0033] The amount of crosslinking agent to be added is 0.5 to 10 parts by weight, preferably 4.5 to 8.5 parts by weight, per 100 parts by weight of copolymer rubber polymer. By using the crosslinking agent in the above range, foaming during vulcanization that makes molding impossible can be prevented, and the crosslinking density is improved, making it easier to obtain products with sufficient physical properties.

[0034] Furthermore, a crosslinking accelerator may be contained as necessary. Examples of the crosslinking accelerator that can be used include triallyl isocyanurate, triallyl cyanurate, liquid polybutadiene, N,N'-m-phenylenedimaleimide, and trimethylolpropane trimethacrylate. Addition of an appropriate amount of the crosslinking accelerator can improve crosslinking efficiency and further improve heat resistance and mechanical properties.

[0035] In addition to the above components, compounding agents generally used in the rubber industry, such as antioxidants, vulcanization aids, and acid acceptors, may be added to the rubber composition as needed.

[0036] Examples of antioxidants that can be used include polymerized-2,2,4-trimethyl-1,2-dihydroquinoline and 2-mercaptobenzimidazole, examples of vulcanization aids that can be used include stearic acid, and examples of acid acceptors that can be used include oxides or hydroxides of divalent metals and hydrotalcite.

[0037] The rubber composition can be prepared by kneading various materials using a kneader such as a single-screw extruder, a twin-screw extruder, a roll, a Banbury mixer, a kneader, or a high-shear mixer.

[0038] Its vulcanization molding is carried out through a primary vulcanization at about 150 to 230°C for about 0.5 to 30 minutes, and an oven vulcanization (secondary vulcanization) at about 150 to 250°C for about 0.5 to 24 hours, which is performed as needed. [Example]

[0039] The present invention will now be described in detail with reference to examples, although the present invention, including its effects, is not limited to these examples.

[0040] Example 1 EBDM copolymer (Mitsui Chemicals EBT K-9330M) 75 parts by weight EPDM copolymer (JSR product EP27) 25 〃 SRF carbon black (Asahi Carbon Products Asahi #50HG; 50 Iodine adsorption amount 19mg / g, DBP oil absorption amount 110ml / 100g) Softener (INEOS Singapore product DURASYN 170; 20% C 10 Derived from polyα-olefin, kinematic viscosity @ 40℃ 65.1mm 2 / sec @100℃ 9.8mm 2 / sec, pour point -45℃) 1,2-Polybutadiene (Nippon Soda Product NISSO-PB B-3000) 2 Same Amine-based antioxidant (Ouchi Shinko Chemical Industry Products 1 〃 Noklac 224S) Peroxyketal (Nippon Oil & Fats Products Perhexa C; 7.1%) 70% purity, 1,1-di(tert-butylperoxy) Cyclohexane, 1-hour half-life temperature 111°C) The above components were kneaded using a kneader and an open roll, and the kneaded mixture was vulcanized at 180°C for 10 minutes, and then oven-vulcanized (secondary vulcanization) at 150°C for 24 hours to prepare a sample sheet with a thickness of 2 mm.

[0041] The vulcanizates obtained were measured and evaluated for the following properties. High temperature elongation test: JIS K-6251 compliant, corresponding to ISO 37, sample sheet The elongation was measured at 95°C. 120% or more is evaluated as ○, 119% or less is evaluated as × High temperature compression set: JIS K-6262 compliant, corresponding to ISO 815-1, sample sheet Three sheets were stacked and left in air at 130°C for 24 hours. Measured after installation 5% or less: ◎, 6% to 10%: ○, 11% or more: × and evaluation Low temperature compression set: JIS K-6262 compliant, corresponding to ISO 815-1, sample sheet Three sheets were stacked and left in the air at -30°C for 24 hours. Measured after installation 30% or less: ◎, 31% to 40%: ○, 41% or more: Rated as × Low temperature elastic recovery test: Compliant with JIS K-6261 corresponding to ISO 2921, TR-10 value and and TR-70 values TR-10 values ​​are evaluated as ○ for -40°C or below and × for -39°C or above. TR-70 values ​​are evaluated as ○ for -60°C or below and × for -59°C or above.

[0042] Example 2 In Example 1, the same amount (50 parts by weight) of MT carbon black (Cancarb product, Termax LSR N990; iodine adsorption capacity 10 mg / g, DBP oil absorption capacity 38 ml / 100 g) was used as the carbon black.

[0043] Comparative Example 1 In Example 1, the same amount (50 parts by weight) of FT carbon black (Tokai Carbon Products Seast TA; iodine adsorption 18 mg / g, DBP oil absorption 19 ml / 100 g) was used as carbon black.

[0044] Comparative Example 2 In Example 1, the same amount (50 parts by weight) of FEF carbon black (Showa Cabot Show Black N550; iodine adsorption capacity 44 mg / g, DBP oil absorption capacity 115 ml / 100 g) was used as carbon black.

[0045] Comparative Example 3 In Example 1, the same amount (50 parts by weight) of SRF carbon black (Tokai Carbon Products Seast G-SVH; iodine adsorption 30 mg / g, DBP oil absorption 140 ml / 100 g) was used as the carbon black.

[0046] Comparative Example 4 In Example 1, the same amount (50 parts by weight) of SRF carbon black (Tokai Carbon Products Seast GS; iodine adsorption 26 mg / g, DBP oil absorption 68 ml / 100 g) was used as the carbon black.

[0047] Example 3 In Example 1, the amount of carbon black was changed to 40 parts by weight.

[0048] Comparative Example 5 In Example 1, the amount of carbon black was changed to 30 parts by weight.

[0049] Comparative Example 6 In Example 1, the amount of carbon black was changed to 60 parts by weight.

[0050] Comparative Example 7 In Example 1, the amount of carbon black was changed to 70 parts by weight.

[0051] Example 4 In Example 2, the amount of the softener was changed to 10 parts by weight.

[0052] Example 5 In Example 2, the amount of the softener was changed to 22 parts by weight.

[0053] Comparative Example 8 In Example 2, the amount of the softener was changed to 24 parts by weight.

[0054] Reference example In Example 1, 2.5 parts by weight of 1,6-bis(acryloyloxy)hexane, which is a difunctional acrylate monomer, was further used.

[0055] The results obtained in the above examples, comparative examples and reference examples are shown in Tables 1 and 2 below. Table 1 Evaluation and measurement items Fruit 1 Fruit 2 ratio 1 ratio 2 ratio 3 ratio 4 Elongation at high temperature (%) 130 130 99 105 110 115 Rating ○ ○ × × × × High temperature compression set (%) 4.0 8.5 6.2 6.6 4.8 5.5 Rating ◎ ○ ○ ○ ◎ ○ Low temperature compression set (%) 26.9 27.9 28.7 27.4 23.5 28.1 Rating ◎ ◎ ◎ ◎ ◎ ◎ TR-10 value (℃) -60 -61 -61 -61 -61 -61 Rating ○ ○ ○ ○ ○ ○ TR-70 value (℃) -42 -42 -42 -42 -43 -43 Rating ○ ○ ○ ○ ○ ○ Table 2 Evaluation and measurement items Fruit 3 ratio 5 ratio 6 ratio 7 Fruit 4 Fruit 5 ratio 8 three Elongation at high temperature (%) 120 109 111 92 121 132 136 92 Rating ○ × × × ○ ○ ○ × High temperature compression set (%) 3.3 3.0 4.1 3.7 5.0 9.8 11.8 3.8 Rating ◎ ◎ ◎ ◎ ◎ ○ ○ ◎ Low temperature compression set (%) 28.2 28.5 24.3 18.9 26.6 29.0 33.0 24.1 Rating ◎ ◎ ◎ ◎ ◎ ○ × ◎ TR-10 value (℃) -61 -61 -60 -60 -60 -61 -62 -60 Rating ○ ○ ○ ○ ○ ○ ○ ○ ○ TR-70 value (℃) -42 -42 -42 -43 -40 -42 -42 -41 Rating ○ ○ ○ ○ ○ ○ ○ ○ ○ [Industrial Applicability]

[0056] The rubber composition of the present invention has excellent compression set resistance, which is a factor in extending the service life, over a wide temperature range from low to high temperatures while ensuring resistance to compression cracking (high elongation), and is therefore effectively used as a sealing material, for example, a sealing material for fuel cell separators.

Claims

1. (A) a blend of ethylene-butene-non-conjugated diene terpolymer rubber (EBDM) and ethylene-propylene-non-conjugated diene terpolymer rubber (EPDM), in which EBDM is blended in an amount of 75% by weight or more of the total amount of EPDM, per 100 parts by weight of the copolymer rubber polymer, (B) 35 to 55 parts by weight of carbon black having an iodine adsorption of 10 to 25 mg / g and a DBP oil absorption of 30 to 140 ml / 100 g, and (C) a kinematic viscosity at 40°C of 8 to 500 mm 2 / sec, 5 to 23 parts by weight of a linear hydrocarbon softener having a pour point of -30°C or less, and (D) 0.5 to 10 parts by weight of an organic peroxide.

2. (C) Kinematic viscosity at 40°C is 8 to 500 mm 2 2. The rubber composition according to claim 1, wherein the linear hydrocarbon softener having a viscosity of 1 / sec and a pour point of -30°C or less is a liquid polyolefin oligomer.

3. 2. The rubber composition according to claim 1, wherein the organic peroxide (D) is an organic peroxide having a one-hour half-life temperature of 110 to 130°C.

4. The rubber composition according to claim 1, which is used as a molding material for a sealing material.

5. A sealing material which is a vulcanization molded product of the rubber composition according to claim 4.

6. The sealing material according to claim 5, which is used as a sealing material for a fuel cell separator.