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

rubber composition

[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.

[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 the 90° peel test and T-peel test (initial, after 100 hours and after 1000 hours of immersion in 90°C hot water).

[0009] Patent Document 2 also describes compounding 5 to 30 parts by weight of an ethylene-α-olefin copolymer per 100 parts by weight of EPDM with 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 in which ethylene-octene-1 copolymer, in which the α-olefin is octene-1, is used, the tensile strength, elongation at break, 90° peel strength, and volume resistivity (insulating properties) are increased, highlighting the effect of blending the ethylene-α-olefin copolymer.

[0011] However, one of the challenges with fuel cell vehicles is that they must be designed and controlled to prevent the FC stack and system components from freezing and becoming 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 it 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, further improvement in sealing at high temperatures is desired.

[0013] JP 2009-94056 A JP 2011-249283 A WO2019 / 003884 JP 2017-183162 A JP 2021-086791 A JP 2011-213822 A

[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.

[0015] The object of the present invention is to provide a rubber composition comprising: (A) 100 parts by weight of a copolymer rubber polymer consisting of at least one of an ethylene-butene-non-conjugated diene terpolymer rubber, an ethylene-propylene-non-conjugated diene terpolymer rubber, and an ethylene-propylene copolymer rubber; (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; (C) a rubber composition having 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.

[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.

[0017] The polymer used is at least one polymer selected from the group consisting of EBDM (ethylene / butene / non-conjugated diene terpolymer), EPDM (ethylene / propylene / non-conjugated diene terpolymer), and EPM (ethylene / propylene copolymer), with the aim of balancing heat resistance, cold resistance, durability, temperature dependency of spring constant, and rebound stress. That is, any one of EBDM, EPDM, and EPM may be used alone or in blends. Preferably, EBDM is used as a blend with EPDM, and a copolymer rubber polymer in which EBDM is blended with EPDM in a proportion of 70% by weight or more of the total amount of EBDM and EPDM is used. Each copolymer rubber polymer is typically solid.

[0018] The ethylene content of the copolymer rubber polymer is preferably 40 to 60% by weight. If the ethylene content is lower than this, the rubber physical properties may be reduced, making it difficult to achieve the elongation and tensile properties required for the sealing member. On the other hand, if the ethylene content is higher than this, low-temperature properties tend to deteriorate. Furthermore, from the viewpoint of acid resistance and water resistance in the operating environment of the fuel cell, EPDM polymer is preferably used. From the viewpoint of low-temperature sealing properties, EBDM polymer is preferably 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 is synthesized using a metallocene compound such as (tert-butylamido)dimethyl(η5-2-methyl-s-indacen-1-yl)silanetitanium(II)1,3-pentazine as a polymerization catalyst.

[0020] This EBDM is described, for example, in Patent Document 6. The butene is mainly butene-1, and the non-conjugated diene is a cyclic or linear non-conjugated diene such as 5-ethylidene-2-norbornene or 5-vinyl-2-norbornene, with cyclic non-conjugated dienes being preferred. From the viewpoint of low-temperature sagging properties, 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 a rubber polymer made of ethylene, propylene, and non-conjugated diene terpolymer. A small amount of non-conjugated diene, such as dicyclopentadiene, 1,4-hexadiene, dicyclooctadiene, methylene norbornene, vinyl norbornene, or ethylidene norbornene, is copolymerized. Its Mooney viscosity (ML) is 1+4 (125°C) is about 25 to 80, preferably about 25 to 70. As the EPM, an ethylene-propylene copolymer rubber polymer is used.

[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 linear hydrocarbon softener, the kinematic viscosity at 40°C is 8 to 500 mm 2A linear hydrocarbon-based softener, preferably a liquid poly-α-olefin oligomer, with a pour point of -30°C or less (due to its 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 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. Using a softener in a proportion greater than this level can result in poor compression set at low temperatures, such as -30°C, while using a softener in a proportion less than this can result in poor elongation at high temperatures.

[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, which is an index indicating the decomposition temperature of an organic peroxide, is one hour. 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, preferably peroxyketals, having a one-hour half-life temperature of 110 to 130°C 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 this range, foaming during vulcanization that makes it impossible to mold the product can be prevented, and the crosslinking density is good, 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 by primary vulcanization at about 150 to 230°C for about 0.5 to 30 minutes, and then oven vulcanization (secondary vulcanization) at about 150 to 250°C for about 0.5 to 24 hours, which is carried out as needed.

[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 EP27) 25 parts by weight SRF carbon black (Asahi Carbon Asahi #50HG; 50 parts by weight Iodine adsorption 19 mg / g, DBP oil absorption 110 ml / 100 g) Softener (INEOS Singapore DURASYN 170; 20 parts by weight C 10 Derived from poly alpha-olefin, kinematic viscosity @ 40℃ 65.1mm 2 / sec @100℃ 9.8mm 2 / sec, pour point -45°C) 1,2-polybutadiene (NISSO-PB B-3000, a product of Nippon Soda) 2 same as above Amine-based anti-aging agent (Nocrac 224S, a product of Ouchi Shinko Chemical Industry) Peroxyketal (Perhexa C, a product of Nippon Oil & Fats; 7.1 same as above Purity 70%, 1,1-di(tert-butylperoxy)cyclohexane, 1-hour half-life temperature 111°C) The above ingredients were kneaded using a kneader and open roll, and the kneaded mixture was vulcanized at 180°C for 10 minutes, then oven vulcanized (secondary vulcanization) at 150°C for 24 hours to create a 2mm thick sample sheet.

[0041] The vulcanizates obtained were measured and evaluated for the following properties. High-temperature elongation test: Compliant with JIS K-6251, which corresponds to ISO 37. Using a sample sheet, measure the elongation at 95°C. 120% or more is evaluated as ○, 119% or less as × High-temperature compression set: Compliant with JIS K-6262, which corresponds to ISO 815-1. Using a stack of three sample sheets, measure after leaving in air at 130°C for 24 hours. 5% or less is evaluated as ◎, 6% to 10% is evaluated as ○, 11% or more is evaluated as × Low-temperature compression set: Compliant with JIS K-6262, which corresponds to ISO 815-1. Using a stack of three sample sheets, measure after leaving in air at -30°C for 24 hours. 30% or less is evaluated as ◎, 31% to 40% is evaluated as ○, 41% or more is evaluated as × Low-temperature elastic recovery test: Compliant with JIS K-6261, which corresponds to ISO 2921. Measure the TR-10 and TR-70 values The TR-10 value is rated as ○ for -40°C or below, and × for -39°C or above. The TR-70 value is rated 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 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 44 mg / g, DBP oil absorption 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 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 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, a difunctional acrylate monomer, was further used.

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

[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 at a ratio of 75% by weight or more in the total amount of EPDM and EBDM, 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, (C) a kinetic 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 100 / s and a pour point of -30°C or less is a liquid polyolefin oligomer.

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