Polymer blend and fuel cell gasket comprising same

Abstract

The invention provides a polymer blend and a fuel cell gasket comprising the same. The polymer blend comprises: 70 wt% to 95 wt% of an amorphous ethylene propylene diene monomer wherein the amorphous ethylene propylene diene monomer has 0.5 wt% to 2 wt% of vinyl-norbornene units, 0 wt% to 7 wt% of vinylidene norbornene units, and 5 wt% to 30 wt% of a maleic anhydride grafted amorphous ethylene propylene diene monomer based on the weight of the amorphous ethylene propylene diene monomer, wherein the maleic anhydride grafted amorphous ethylene propylene diene monomer has 0.5 wt% to 2.5 wt% of maleic anhydride units based on the weight of the maleic anhydride grafted amorphous ethylene propylene diene monomer. By applying the polymer blend of the present invention and the fuel cell gasket comprising the same, good bonding to a structural layer is achieved without using an adhesive, and good water resistance at an extremely low pH value and good low temperature flexibility are exhibited.

Description

Technical Field

[0001] The present invention relates to the field of polymers, in particular to a polymer blend and a fuel cell gasket containing the same. Background Art

[0002] The fuel cell is composed of two electrode rods attached to each other around an electrolytic material, and utilizes the following principle: electricity, water, and heat are generated through an electrochemical reaction when oxygen in the air passes through one electrode and hydrogen passes through the other electrode. When hydrogen flows through the gas diffusion layer and the membrane, it is converted into hydrogen cations, and the generated electrons generate electrical energy.

[0003] Fuel cell stacks require gaskets and seals in each cell to keep the reactant gases (hydrogen and oxygen) in their respective areas. During operation, there are gases and liquids inside the fuel cell. The main fluids are water or steam, which is a proton (H + ) and oxygen anions (O 2- ) is a reaction product when it combines on the air side of the fuel cell. Due to the release of sulfonic acid and sulfuric acid The aqueous phase is usually acidic, resulting in a pH range of 1 to 3, when in contact with a proton exchange membrane. The seal around the periphery of the cell needs to prevent gas / liquid leakage inside the cell and effectively separate the anode and cathode spaces. The cathode side and the anode side can also be sealed separately. Cross-linked elastomers are usually used as sealing or gasket materials. Possible elastomers include silicone rubber, polyolefin rubber and fluoroelastomer.

[0004] In general, suitable fuel cell gaskets should meet long-term aqueous acid stability and durability, stability in humid atmospheres, hydrogen and air, sufficient mechanical and thermal dimensional stability, good flexibility at low temperatures, low compression set at low temperatures to high temperatures, good aging resistance, very low outgassing during use and very low leaching and cost-effectiveness. In addition, it is still challenging to achieve very thin gasket shapes using available rubber technology (including necessary curing processes). Fuel cells are arranged in fuel cell stacks, which can include 500 or more individual fuel cell units, each of which has several gaskets. Efficient manufacturing processes require gaskets to cure quickly, preferably on or with components of fuel cells. This limits the temperature at which the rubber compound flows in the mold and the exposure time under curing conditions to avoid damaging fuel cell components, such as membrane electrode assemblies (MEAs), more specifically to avoid damaging temperature-sensitive layers containing electrolytes.

[0005] Rubber gaskets are usually very thin, they have three-dimensional patterns such as beads, rounded edges, and cannot be easily manually manipulated. In addition to robotic manufacturing techniques, it has been proposed to combine or apply these rubber gaskets on a thermoplastic resin film to make handling easier. For example, a rubber-like material can be applied to one or both sides of the thermoplastic film. The application can be carried out by molding, laminating, extruding or calendering the film or by solution coating and subsequent drying. Then the rubber material can be attached to the thermoplastic film while curing. The rubber material can be applied over the entire surface of the thermoplastic film or along the lines or shapes of the film that require a sealing function. Compared with only thin rubber gaskets, the processing and shaping of such rubber-like materials on thermoplastic films are easier, such as stamping into a desired geometry. The applied rubber material needs to have a certain geometry and be able to be roughly shaped, for example, by die extrusion. After that, the extruded strip can be cut into the required length, placed on a substrate, and then compression molded and cured. One can also use a preforming process, preferably before the rubber-like material is cured or before it is fully cured.

[0006] However, there is no relevant information indicating how to combine these very different materials with sufficient adhesion for the handling and use of fuel cells.

[0007] Silicone rubber can meet many requirements for fuel cell rubber gaskets, such as being very easy to flow and curing at low temperatures, but it has an inherent sensitivity to humid, low-pH environments containing water because these cause it to degrade into polysiloxane fragments that can affect electrical contact and will ultimately lead to a loss of elastomeric properties. For example, Ke Li, Haining Zhang, Mu Pan, Wuhan University, Rubber Chemistry and Technology, vol. 88, no. 3, pp. 475-481 (2015) reported that silicone rubber has significant swelling and leaches into the cell fluid within 30 days at pH 5 and 80 °C. Similarly, S Pehlivan-Davis, J Clarke, S Armour, J. Appl. Polym. Sci. (Polym. Sci.), 2013, pp. 1446-1454 found that the elongation of silicone rubber is lost when it is immersed in acidic water and in water in which a proton exchange membrane is also suspended. S Bhargava, K A Leary, T C Jackson, B Lakshmanan, Rubber Chemistry and Technology, vol. 86, no. 1, pp. 28-37 (2013) determined that when silicone rubber is used in a fuel cell under simulated use conditions, siloxane oligomers are the main degradation products. Another disadvantage of silicone rubber is that it has a very high permeability to gases such as hydrogen, which can lead to gas loss and an increase in hydrogen concentration in an enclosed space, which in turn can lead to the formation of an explosive gas composition.

[0008] Fluoroelastomers are very stable materials. However, the low-temperature flexibility of fluoroelastomers is limited and it can only be achieved at very high costs.

[0009] The following documents disclose fuel cell gaskets or materials that can be used for gaskets.

[0010] US20080026280 describes the use of ethylene propylene diene monomer (EPDM) for fuel cell gaskets, especially inside a fuel cell that can be wetted by cell fluid, but does not give further details on how such an EPDM compound should be formulated or cured.

[0011] WO2007064777 describes a general peroxide-cured EPDM that has a low metal extraction in a 5% nitric acid solution, which can be achieved by selecting high-purity peroxides and fillers, but does not give further details on the type of EPDM. In modern fuel cells, nitric acid is not a preferred component.

[0012] WO2009078185 describes VNB EPDM with a Pt curing system. However, it requires a two-stage curing at 150 °C to achieve the desired low compression set. It is known in the prior art that two-stage curing may damage fuel cell components.

[0013] JP2010168479A describes EPDM for peroxide curing, in which an anti-sticking agent of stearoyl-amide type is added to reduce the adhesion to the separator. However, this document does not disclose the need for adhesion to a thermoplastic film.

[0014] EP3282151 describes a combination of a rubber gasket and a carrier film, where the rubber is formed into various shapes on the carrier film using a metal mold. The thermoplastic film can be made of polybutylene terephthalate or polyamide. However, this document does not disclose the specific composition of the rubber gasket and does not explain how the bonding between the two components is achieved.

[0015] GB2582399 describes fixing a flexible layer to a structural layer, where the flexible layer can be EPDM rubber. These layers are bonded with a thin adhesive layer, which can be an acrylic material. However, this document does not give the specific composition of a suitable material for preparing the gasket.

[0016] Thus, it can be seen that none of the known rubber materials can be well bonded to the structural layer without using an adhesive, and they all show unsatisfactory water resistance and low temperature flexibility at extremely low pH values. Therefore, to solve the problems mentioned above, there is still a need for a rubber material that can solve the deficiencies of the known rubber materials. SUMMARY OF THE INVENTION

[0017] The main object of the present invention is to provide a polymer blend and a fuel cell gasket containing the same, to solve the problems that known rubber materials cannot be well bonded to the structural layer without using an adhesive and show unsatisfactory water resistance and low temperature flexibility at extremely low pH values.

[0018] To achieve the above object, according to one aspect of the present invention, there is provided a polymer blend, which comprises: 70 wt% to 95 wt% of amorphous ethylene propylene diene monomer (EPDM), wherein based on the weight of the amorphous EPDM, the amorphous EPDM has 0.5 wt% to 2 wt% of vinyl-norbornene units, 0 wt% to 7 wt% of ethylidene norbornene units, and 5 wt% to 30 wt% of maleic anhydride grafted amorphous EPDM, wherein based on the weight of the maleic anhydride grafted amorphous EPDM, the maleic anhydride grafted amorphous EPDM has 0.5 wt% to 2.5 wt% of maleic anhydride units.

[0019] In the above polymer blend, the maleic anhydride grafted amorphous ethylene propylene diene monomer rubber contains less than 7 wt%, preferably less than 3 wt%, more preferably less than 0.5 wt% of non-conjugated diene units selected from one or any combination of dicyclopentadiene, vinyl norbornene and ethylidene norbornene.

[0020] In the above polymer blend, the amorphous ethylene propylene diene monomer rubber has a glass transition temperature measured by differential scanning calorimetry of less than -44 °C and / or a Mooney viscosity in the range of 15 MU to 30 MU measured according to ISO 289.

[0021] In the above polymer blend, the maleic anhydride grafted amorphous ethylene propylene diene monomer rubber has a melt flow index value in the range of 1 g / 10 min to 10 g / 10 min measured according to ASTM D1238 and / or a glass transition temperature measured by differential scanning calorimetry of less than -46 °C.

[0022] In the above polymer blend, the polymer blend further includes a crosslinking agent, and based on the total of 100 parts by weight of the amorphous ethylene propylene diene monomer rubber and the maleic anhydride grafted amorphous ethylene propylene diene monomer rubber, the crosslinking agent is present in an amount of 5 parts by weight to 10 parts by weight.

[0023] In the above polymer blend, the crosslinking agent is a peroxide crosslinking agent.

[0024] In the above polymer blend, the crosslinking agent has a decomposition half-life t 1 / 2 of 5 minutes to 10 minutes at a temperature between 130 °C and 145 °C.

[0025] In the above polymer blend, the polymer blend has a Mooney viscosity measured according to ISO 289 of less than 60 MU.

[0026] According to another aspect of the present invention, a fuel cell gasket is provided, and the fuel cell gasket contains the polymer blend described above in the present invention.

[0027] In the above fuel cell gasket, the fuel cell gasket further includes a filler, an antioxidant, a coupling agent, a processing aid, a plasticizer and / or a curing agent.

[0028] By applying the polymer blend of the present invention and the fuel cell gasket containing the same, good bonding to the structural layer can be achieved without using an adhesive, and it exhibits good water resistance at extremely low pH values and good low temperature flexibility. Description of the Drawings

[0029] The accompanying drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0030] Figure 1 show Comparative Example 1 ( 2650C), Example 1 ( 2650C + 10% of 1519R) and Example 2 ( 2650C + 20% of 1519R), a graph showing the relationship between the degree of vulcanization time and temperature at 95%. Detailed Description of the Invention

[0031] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in conjunction with the embodiments.

[0032] As described in the background art, known rubber materials cannot be well bonded to the structural layer without using adhesives, and they all exhibit unsatisfactory water resistance and low temperature flexibility at extremely low pH values. To address the problems in the prior art, according to a typical embodiment of the present application, a polymer blend is provided, which comprises: 70 wt% to 95 wt% of amorphous ethylene propylene diene monomer (EPDM), wherein based on the weight of the amorphous EPDM, the amorphous EPDM has 0.5 wt% to 2 wt% of vinyl-norbornene units, 0 wt% to 7 wt% of vinylidene norbornene units, and 5 wt% to 30 wt% of maleic anhydride grafted amorphous EPDM, wherein based on the weight of the maleic anhydride grafted amorphous EPDM, the maleic anhydride grafted amorphous EPDM has 0.5 wt% to 2.5 wt% of maleic anhydride units.

[0033] The main component of the polymer blend according to the present invention for gaskets is amorphous ethylene propylene diene monomer (EPDM), which is a copolymer based on ethylene, propylene, and optionally other α-olefins. Preferably, the EPDM copolymer contains two non-conjugated dienes, vinyl-norbornene units (ENB) and vinylidene norbornene units (VNB), so as to ensure that the EPDM copolymer can be rapidly cured by a peroxide-based curing system. In the EPDM copolymer, based on its total weight, the content of VNB is in the range of 0.5 wt% to 2 wt%, within which range VNB achieves rapid curing ability; based on its total weight, the content of ENB can be in the range of 0 wt% to 7 wt%.

[0034] In various embodiments, based on the weight of the amorphous ethylene propylene diene monomer rubber, the amorphous ethylene propylene diene monomer rubber of the present invention has vinyl-norbornene units in the following content ranges: 0.5 wt% to 2 wt%, 0.6 wt% to 1.9 wt%, 0.7 wt% to 1.8 wt%, 0.8 wt% to 1.7 wt%, 0.9 wt% to 1.6 wt%, 1.0 wt% to 1.5 wt%, 1.1 wt% to 1.4 wt%, 1.2 wt% to 1.3 wt%, 1.0 wt% to 2 wt%, 1.5 wt% to 2 wt%, 0.5 wt% to 1.5 wt%, or 0.5 wt% to 1.0 wt%; and has vinylidene norbornene units in the following content ranges: 0 wt% to 7 wt%, 0.5 wt% to 6.5 wt%, 1.0 wt% to 6.0 wt%, 1.5 wt% to 5.5 wt%, 2.5 wt% to 5.0 wt%, 3.0 wt% to 4.5 wt%, 3.5 wt% to 4.0 wt%, 0.5 wt% to 7 wt%, 1.0 wt% to 7 wt%, 1.5 wt% to 7 wt%, 2.0 wt% to 7 wt%, 3.5 wt% to 7 wt%, 4.0 wt% to 7 wt%, 4.5 wt% to 7 wt%, 5.0 wt% to 7 wt%, 5.5 wt% to 7 wt%, 6.0 wt% to 7 wt%, 6.5 wt% to 7 wt%, 0 wt% to 6.5 wt%, 0 wt% to 6.0 wt%, 0 wt% to 5.5 wt%, 0 wt% to 5.0 wt%, 0 wt% to 4.5 wt%, 0 wt% to 4.0 wt%, 0 wt% to 3.5 wt%, 0 wt% to 3.0 wt%, 0 wt% to 2.5 wt%, 0 wt% to 2.0 wt%, 0 wt% to 1.5 wt%, or 0 wt% to 1.0 wt%.

[0035] To ensure that the polymer blend of the present invention can be effectively bonded to the thermoplastic carrier film, the polymer blend of the present invention further comprises maleic anhydride grafted amorphous ethylene propylene diene monomer rubber, and based on the weight of the maleic anhydride grafted amorphous ethylene propylene diene monomer rubber, the maleic anhydride grafted amorphous ethylene propylene diene monomer rubber is grafted with 0.5 wt% to 2.5 wt% of maleic anhydride units, and further optionally comprises less than 7 wt%, preferably less than 3 wt%, more preferably less than 0.5 wt% of non-conjugated diene units selected from one or any combination of dicyclopentadiene, vinyl-norbornene, and vinylidene norbornene.

[0036] In various embodiments, the maleic anhydride grafted amorphous ethylene propylene diene monomer rubber of the present invention has maleic anhydride units in the following content ranges: 0.5 wt% to 2.5 wt%, 0.6 wt% to 2.4 wt%, 0.7 wt% to 2.3 wt%, 0.8 wt% to 2.2 wt%, 0.9 wt% to 2.1 wt%, 1.0 wt% to 2.0 wt%, 1.1 wt% to 1.9 wt%, 1.2 wt% to 1.8 wt%, 1.3 wt% to 1.7 wt%, 1.4 wt% to 1.6 wt%, 1.0 wt% to 2.5 wt%, 1.5 wt% to 2.5 wt%, 2.0 wt% to 2.5 wt%, 0.5 wt% to 2.0 wt%, 0.5 wt% to 1.5 wt%, or 0.5 wt% to 1.0 wt%.

[0037] Each polymer component in the polymer blend of the present invention has a low glass transition temperature (Tg). The amorphous ethylene propylene diene monomer rubber has a glass transition temperature of less than -44 °C measured by differential scanning calorimetry, and the maleic anhydride grafted amorphous ethylene propylene diene monomer rubber has a glass transition temperature of less than -46 °C measured by differential scanning calorimetry. Since each component has a low glass transition temperature, the polymer blend of the present invention exhibits good low temperature flexibility. In addition, there is substantially no crystallization within the chains of each polymer in the polymer blend. Even a small amount of crystallization (low crystallinity) will deteriorate the low temperature compression set performance of the polymer blend. Therefore, the preferred ethylene propylene diene monomer rubber is a completely amorphous ethylene propylene diene monomer rubber, and the maleic anhydride grafted ethylene propylene diene monomer rubber is also a completely amorphous maleic anhydride grafted ethylene propylene diene monomer rubber.

[0038] In the specific embodiments of the present invention, for different embodiments, the polymer blend of the present invention comprises an amorphous ethylene propylene diene monomer (EPDM) rubber in the following ranges of amounts: 70 wt% to 95 wt%, 71 wt% to 94 wt%, 72 wt% to 93 wt%, 73 wt% to 92 wt%, 74 wt% to 91 wt%, 75 wt% to 90 wt%, 76 wt% to 89 wt%, 77 wt% to 88 wt%, 78 wt% to 87 wt%, 79 wt% to 86 wt%, 80 wt% to 85 wt%, 81 wt% to 84 wt%, 82 wt% to 83 wt%, 70 wt% to 90 wt%, 70 wt% to 85 wt%, 70 wt% to 80 wt%, 70 wt% to 75 wt%, 75 wt% to 95 wt%, 80 wt% to 95 wt%, 85 wt% to 95 wt%, or 90 wt% to 95 wt%; and the polymer blend of the present invention comprises a maleic anhydride grafted amorphous ethylene propylene diene monomer (EPDM) rubber in the following ranges of amounts: 5 wt% to 30 wt%, 6 wt% to 29 wt%, 7 wt% to 28 wt%, 8 wt% to 27 wt%, 9 wt% to 26 wt%, 10 wt% to 25 wt%, 11 wt% to 24 wt%, 12 wt% to 23 wt%, 13 wt% to 22 wt%, 14 wt% to 21 wt%, 15 wt% to 20 wt%, 16 wt% to 19 wt%, 17 wt% to 18 wt%, 10 wt% to 30 wt%, 15 wt% to 30 wt%, 20 wt% to 30 wt%, 25 wt% to 30 wt%, 5 wt% to 25 wt%, 5 wt% to 20 wt%, 5 wt% to 15 wt%, or 5 wt% to 10 wt%.

[0039] In some embodiments of the present invention, the amorphous ethylene propylene diene monomer (EPDM) rubber in the polymer blend of the present invention has a Mooney viscosity in the range of 15 MU to 30 MU as measured according to ISO 289, and / or the maleic anhydride grafted amorphous ethylene propylene diene monomer (EPDM) rubber in the blend has a melt flow index value in the range of 1 g / 10 min to 10 g / 10 min as measured according to ASTM D 1238.

[0040] The polymer blend in the present invention comprises all possible polymer components that can be combined to achieve the desired properties in a fuel cell gasket. The rubber composition of the present invention is based on the polymer blend and may comprise other components such as those described below: fillers, antioxidants, coupling agents, processing aids such as anti-sticking agents, an optional small amount of plasticizers, and a curing system, which may include various components such as peroxides, accelerators, scorch retardants, etc.

[0041] The polymer blend of the present invention may comprise reinforcing fillers of carbon black and mineral fillers, while ensuring low swelling in an aqueous medium and excluding those mineral fillers that may leach metal ions that may occur in a fuel cell into an acidic aqueous fluid. Surface-treated calcined clay can be used. However, the preferred filler is high-purity carbon black.

[0042] It is possible to add a plasticizer in a limited amount to reduce the viscosity of the polymer blend of the present invention while avoiding leaching of the organic plasticizer component into the fuel cell. The plasticizer can be selected from high-purity mineral oils with low volatility and low aromatic content to avoid oxidation reactions in the fuel cell. Ester plasticizers are less preferred because they may hydrolyze during long-term use. The amount of the plasticizer should be less than 15%, more preferably less than 10% and most preferably less than 5%.

[0043] If the polymer blend of the present invention contains only a very small amount of liquid plasticizer or no plasticizer at all, the viscosity of the polymer blend can only be achieved low enough by selecting a polymer with a lower molecular weight. Low compound viscosity is important for ensuring good fluidity of the rubber compound into the mold cavity.

[0044] The curing system of the polymer blend of the present invention should be cured based on peroxides. Optional peroxides include dicumyl peroxide (DCP), 2,5-bis(tert-butylperoxy)-2,5-dimethyl-hexane (DTBPH), bis(tert-butylperoxyisopropyl)benzene (DTBPIB), 2,5-bis(benzoylperoxy)-2,5-dimethylhexane, 2,5-(tert-butylperoxy)-2,5-dimethyl-3-hexyne (DTBPHY), di-tert-butyl-peroxide and di-tert-butyl peroxide-3,3,5-trimethylcyclohexane (DTBTCH) or a mixture of these peroxides. Since commercial peroxides are usually supplied with an inert mineral as a carrier, those peroxides with the least tendency to leach metal ions into the fuel cell fluid need to be selected. Uddin et al., (J. Power Sources, 296 (2015) 64-69) found that if Ca ions are continuously introduced into the air stream, the fuel cell will still experience performance loss, although the Ca ions in the experiment are relatively high. Ohashi et al. (ECS Transactions, 11(1) 877-987 (2007)) found that 500 ppm Ca 2+ has a harmful effect on the fuel cell, presumably by exchanging protons in the proton exchange membrane (PEM). Therefore, those skilled in the art will evaluate the entry of metal ions from the components in the gasket material to find the upper limit of those components.

[0045] If the gasket and the carrier film are molded together with the MEA and the catalyst carrying layer of the fuel cell, the curing temperature should be as low as possible, preferably in the temperature range of 120 °C to 155 °C. In addition, too high a curing temperature may cause the carrier film to deform. A person of ordinary skill in the art will select a peroxide with a low decomposition temperature such as DTBTCH. The selection of a suitable peroxide can be carried out by the decomposition half-life t 1 / 2 to carry out the selection of a suitable peroxide. The crosslinking agent selected in the present invention has a decomposition half-life t 1 / 2 between 130 °C and 145 °C that can be 5 minutes to 10 minutes. Thus, the time for the full utilization of the peroxide at a certain temperature can be obtained. This will be a curing temperature that should be low enough so that the fuel cell components cured together will not be damaged.

[0046] In some embodiments of the present invention, based on the sum of 100 parts by weight of amorphous ethylene propylene diene monomer rubber and maleic anhydride grafted amorphous ethylene propylene diene monomer rubber, the crosslinking agent is present in an amount of 5 parts by weight to 10 parts by weight. In different embodiments, based on the sum of 100 parts by weight of amorphous ethylene propylene diene monomer rubber and maleic anhydride grafted amorphous ethylene propylene diene monomer rubber, the amount of the crosslinking agent can be in the following ranges: 5 parts by weight to 10 parts by weight, 6 parts by weight to 9 parts by weight, 7 parts by weight to 8 parts by weight, 5 parts by weight to 9 parts by weight, 5 parts by weight to 8 parts by weight, 5 parts by weight to 7 parts by weight, 5 parts by weight to 6 parts by weight, 6 parts by weight to 10 parts by weight, 7 parts by weight to 10 parts by weight, 8 parts by weight to 10 parts by weight, or 9 parts by weight to 10 parts by weight.

[0047] In addition, additives can be added, especially those that increase the crosslinking density and those that accelerate curing, such as triallyl isocyanurate, triallyl cyanurate, bismaleimide, liquid polybutadiene with a high enough vinyl content.

[0048] Processing aids can be used to further improve the flow of the compound, but should be used in an amount low enough to minimize the amount of processing aids leached into the fuel cell fluid. Preferably, in the present invention, based on the sum of 100 parts by weight of amorphous ethylene propylene diene monomer rubber and maleic anhydride grafted amorphous ethylene propylene diene monomer rubber, the amount of the processing aid can be less than 5 parts by weight, more preferably less than 2 parts by weight. Antioxidants are conventionally used in EPDM rubber compounds including those of the present invention. These antioxidants should be selected to avoid the leaching of oxidizable components into the fuel cell. Polymerized 2,2,4-trimethyl-1,2-dihydroquinoline is preferred due to its low mobility.

[0049] In some alternative embodiments, the polymer blend of the present invention may comprise the following processing aids: one or any combination of antioxidants, UV stabilizers, release agents, and post-processing aids. Optional processing aids may include, for example, antioxidants such as 1076, UV stabilizers, dispersants, or other processing aids for rubber composition processing, such as talc or metal salts, such as, for example, zinc stearate, magnesium stearate, or calcium stearate, which will remain in the rubber composition after manufacture. The rubber composition may also contain other additives, such as desiccants (e.g., calcium oxide), tackifiers (e.g., resins), adhesives, pigments, processing aids (e.g., oil gums, fatty acids, stearates, polyethylene glycol, or diethylene glycol), antioxidants (e.g., poly-2,2,4-trimethyl-1,2-dihydroquinoline or zinc 2-mercaptobenzothiazole), heat stabilizers, UV stabilizers, anti-ozonants, blowing agents, and mold release additives.

[0050] The polymer blend of the present invention has a Mooney viscosity of less than 60 MU as measured according to ISO289.

[0051] According to another exemplary embodiment of the present invention, a fuel cell gasket is provided, which comprises the polymer blend described above in the present invention. Since the fuel cell gasket of the present invention comprises the polymer blend described above in the present invention, it can be well bonded to the structural layer without using an adhesive, and exhibits good water resistance at extremely low pH values and good low-temperature flexibility. In some embodiments of the present invention, the fuel cell gasket of the present invention further comprises fillers, antioxidants, coupling agents, processing aids, plasticizers, and / or curing agents.

[0052] Examples

[0053] The components used in the examples are summarized in Table 1.

[0054] Table 1

[0055]

[0056] Examples 1-2 and Comparative Examples 1-5

[0057] Prepare polymer blends according to the components of Examples 1-2 and Comparative Examples 1-5 shown in Table 2 below.

[0058] Table 2

[0059]

[0060]

[0061] The data in Table 2 above are all in parts by weight based on the total weight of 100 parts of the polymer.

[0062] Test method

[0063] The properties of each polymer blend were tested according to the standard methods and descriptions shown in Table 3 below.

[0064] Table 3

[0065] Test Name Standard Description Mooney Viscosity ISO 289-1:2015 MDR, Rotorless Curemeter ISO 6502-3:2018 180 °C, 20 min, 0.5 degree Tensile Strength ISO 37:2017 Type 2 Hardness ISO 48-4:2018 Shore A, 3 s O-Ring Compression Set ASTM D1414B 25% Compression, 100 °C, 70 h Fluid Immersion ISO 1817:2015 Aqueous H2SO4 Solution at pH 1 and pH 3

[0066] Immersion test:

[0067] According to the method disclosed by Jou-Hyeon Ahn (International Journal of Hydrogen Energy, 40 (2015), pp. 10627-10635), a fluid immersion test was carried out in H 2 SO 4 to simulate the leaching effect of steam or water on the membrane. HF was not added due to safety concerns, and it is believed that HF is not important for the results of these tests. The temperature was set at 90 °C, which is the higher value in the literature test. A suitable example is 2,2,4-trimethyl-1,2-dihydroquinoline with low volatility and no metal ion content.

[0068] Test results

[0069] Table 4 Test results of Examples 1 and 2 of the present invention and Comparative Example 5

[0070] Test Items Example 1 Example 2 Comparative Example 5 ML 1+4+2, 100 °C, MU 50 54 42 Hardness, Shore-A: 3 s 57 58 57 Tensile Strength, MPa 7.8 7.3 8.3 Elongation at Break, % 278 268 289 O-Ring Compression Set CS, 100 °C, 70 h, % 19 27 14 Maximum Peel Force on Kapton Film, N / 25 mm 1.7 3.4 1.0

[0071] Table 5 Immersion test results of Examples 1 and 2 of the present invention and Comparative Example 5

[0072]

[0073] Examples 1 and 2 and Comparative Example 5 were prepared using non-leaching components and high-purity low-surface-area carbon black N990. Instead of using 0500R, in Examples 1 and 2, maleic anhydride-grafted EPM 1519R was used in combination with 2650C.

[0074] MDR cure curves were obtained at 140 °C, 150 °C and 160 °C to study the cure kinetics. Based on these results, curing can be carried out on the thermoplastic membrane or together with fuel cell components at a sufficiently low temperature to avoid membrane deformation or damage to fuel cell components. See the MDR cure curve results in Figure 1 .

[0075] Examples 1 and 2 show that maleic anhydride-grafted EPM as an added polymer component increases the adhesion to polar thermoplastic films, while maintaining excellent stability in fuel cell liquids and retaining excellent mechanical properties. When the maleic anhydride-grafted EPM is used at a level of 20% (Example 2), there is a slight increase in the O-ring compression set. Therefore, the content of this polymer component can be restricted.

[0076] The EPDM grades used in each example are amorphous and have a Tg value between -48 °C and -53 °C. Therefore, the blends prepared in each example have excellent low-temperature flexibility. The EPDM rubber compositions can be cured to obtain a tight rubber network with excellent O-ring compression set. Therefore, when compressed into a fuel cell stack, a gasket having a shape similar to a hemisphere will have excellent force retention. Peroxide-mediated curing can be carried out at a sufficiently low temperature to avoid thermal damage to any substrate on which the gasket is molded. The main EPDM component (“K2650C”) has a medium ENB content (ENB content of about 6.0 wt%) and a VNB content of 0.9%, which gives an excellent curing response to peroxide. Those skilled in the art will understand that EPDM polymers with an even higher VNB content will further facilitate curing, while the ENB content can be maintained or even reduced. Unexpectedly, EPM can be added, which does not have a third monomer, and the low molar weight allows for a reduction in compound viscosity without loss of mechanical properties.

[0077] Test results of Comparative Examples 1 and 2 in Table 6

[0078]

[0079] Immersion test results of Comparative Examples 1 and 2 in Table 7

[0080]

[0081] Comparative Example 2 shows that the EVM-based composition can provide a very low-viscosity compound with excellent mechanical properties and a cured rubber with low hardness, but immersion in simulated fuel cell fluids causes relatively high swelling and changes in mechanical properties, which increase with the immersion time, such that there may be stability problems for long-term use in a fuel cell.

[0082] Comparative Example 1 based on EPDM shows very low swelling values and very stable mechanical properties. However, the selected antioxidant contains zinc ions, such that there may be zinc ion leaching in the fuel cell fluid.

[0083] Test results of Comparative Examples 3 and 4 in Table 8

[0084]

[0085]

[0086] Comparative Examples 3 and 4 were carried out based on EPDM having a zinc-free antioxidant and a change in carbon black targeting a low Shore A hardness of 55. It was found that both compositions could be molded into O-rings, which gave excellent low values in the compression test. These examples still did not solve the adhesion to the carrier film. At 90 °C and pH 1, the cured rubber composition was immersed in a simulated fuel cell fluid for 7 days. Then, any compounds that had leached from the cured rubber composition into the fluid were analyzed in these fluids by GC-MS. Only decomposition products from the peroxide, co-agent TAIC, and the antioxidant of the TMQ type (trimethylquinolines) used were found. The peroxide used for rubber curing purposes was commercially available together with an inert carrier such as CaCO 3 and they were used as such in the experimental part of the present disclosure.

[0087] The above-described content is only the preferred embodiments of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A polymer blend, characterized in that, it comprises: 70 wt% to 95 wt% of amorphous ethylene propylene diene monomer (EPDM), wherein based on the weight of the amorphous EPDM, the amorphous EPDM has 0.5 wt% to 2 wt% of vinyl-norbornene units, 0 wt% to 7 wt% of ethylidene norbornene units, and 5 wt% to 30 wt% of maleic anhydride grafted amorphous EPDM, wherein based on the weight of the maleic anhydride grafted amorphous EPDM, the maleic anhydride grafted amorphous EPDM has 0.5 wt% to 2.5 wt% of maleic anhydride units.

2. The polymer blend according to claim 1, characterized in that, the maleic anhydride grafted amorphous EPDM comprises less than 7 wt%, preferably less than 3 wt%, more preferably less than 0.5 wt% of non-conjugated diene units selected from one or any combination of dicyclopentadiene, vinyl-norbornene and ethylidene norbornene.

3. The polymer blend according to claim 1, characterized in that, the amorphous EPDM has a glass transition temperature measured by differential scanning calorimetry of less than -44 °C and / or a Mooney viscosity in the range of 15 MU to 30 MU measured according to ISO 289.

4. The polymer blend according to claim 1, characterized in that, the maleic anhydride grafted amorphous EPDM has a melt flow index value in the range of 1 g / 10 min to 10 g / 10 min measured according to ASTM D 1238 and / or a glass transition temperature measured by differential scanning calorimetry of less than -46 °C.

5. The polymer blend according to claim 1, characterized in that, the polymer blend further comprises a crosslinking agent, and based on the total of 100 parts by weight of the amorphous EPDM and the maleic anhydride grafted amorphous EPDM, the crosslinking agent is present in an amount of 5 parts by weight to 10 parts by weight.

6. The polymer blend according to claim 5, characterized in that, the crosslinking agent is a peroxide crosslinking agent.

7. The polymer blend according to claim 5, characterized in that, The decomposition half-life t of the crosslinking agent is between 5 minutes and 10 minutes at a temperature between 130 °C and 145 °C. 1 / 2 ​ 8. The polymer blend according to claim 1, characterized in that, the polymer blend has a Mooney viscosity measured according to ISO 289 of less than 60 MU.

9. A fuel cell gasket, characterized in that, the fuel cell gasket comprises the polymer blend according to any one of claims 1 to 8.

10. The fuel cell gasket according to claim 9, characterized in that, the fuel cell gasket further comprises a filler, an antioxidant, a coupling agent, a processing aid, a plasticizer and / or a curing agent.

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