fuel cell gasket

Abstract

To provide a fuel cell gasket with excellent rebound modulus in low-temperature environments. A fuel cell gasket with excellent rebound modulus in low-temperature environments, characterized by containing the following components (A) to (E). (A) A rubber component based on ethylene-butene-diene rubber. (B) A paraffinic hydrocarbon oil containing alpha-olefin as its main component, having a pour point of -70°C or higher and -60°C or lower as a softening agent. (C) Carbon Black. (D) A crosslinking agent consisting of an organic peroxide. (E) A crosslinking aid that is a polyfunctional carboxylic acid compound.

Description

[Technical Field]

[0001] This invention relates to a fuel cell gasket with excellent rebound modulus in low-temperature environments. [Background technology]

[0002] A fuel cell is an electrochemical battery that generates electricity through a chemical reaction between hydrogen and oxygen. Fuel cells are widely used in various applications, including as power supply systems for mobile vehicles such as passenger cars, buses, and ships, as well as in factories, office buildings, and homes.

[0003] In fuel cells, a fuel gas such as hydrogen is supplied from the anode side and an oxidizing gas such as air (oxygen) is supplied from the cathode side to a unit cell containing electrodes, thereby causing a chemical reaction for power generation. Therefore, in fuel cells, a sealed structure is formed by gaskets to prevent gases from leaking to the outside from the supply paths of the fuel gas and oxidizing gas.

[0004] For example, Patent Documents 1 to 5 describe fuel cell sealing members or rubber compositions for fuel cell separator sealing members, using ethylene-propylene rubber, ethylene-propylene-diene rubber, or ethylene-butene-diene rubber as rubber components.

[0005] When using such rubber compositions as sealing components for fuel cells, design must be tailored to the external environment in which the fuel cell operates. In particular, when used in cold regions, the lower limit temperature of the rubber composition must be considered. This is because rubber compositions with low cold resistance will lose elasticity and harden in low-temperature environments, potentially impairing the physical properties of the rubber as a sealing component. There are regions where winter temperatures drop below -30°C, and in order to operate fuel cells without problems even in such cold regions, the cold resistance and rebound modulus of the rubber composition used as a sealing component become crucial. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2021-66844 [Patent Document 2] Japanese Patent Publication No. 2021-86791 [Patent Document 3] Japanese Patent Publication No. 2022-152524 [Patent Document 4] International Publication No. 2019 / 003885 [Patent Document 5] International Publication No. 2019 / 216311 [Overview of the project] [Problems that the invention aims to solve]

[0007] Therefore, in view of the problems of the above-mentioned prior art, the object of the present invention is to provide a fuel cell gasket with excellent rebound modulus in low-temperature environments. [Means for solving the problem]

[0008] One aspect of the present invention is a fuel cell gasket that exhibits excellent rebound modulus in low-temperature environments, and is characterized by containing the following components (A) to (E). (A) A rubber component based on ethylene-butene-diene rubber. (B) A paraffinic hydrocarbon oil containing alpha-olefin as its main component, having a pour point of -70°C or higher and -60°C or lower as a softening agent. (C) Carbon Black. (D) A crosslinking agent consisting of an organic peroxide. (E) A crosslinking aid that is a polyfunctional carboxylic acid compound.

[0009] In one aspect of the present invention, the content of the softening agent in the fuel cell gasket may be 30% by weight or more.

[0010] In addition, in one aspect of the present invention, the content of the rubber component in the fuel cell gasket may be 40% by weight or more.

[0011] In addition, in one aspect of the present invention, the carbon black has a nitrogen adsorption specific surface area of 20 to 30 m 2 / g, and the content thereof in the fuel cell gasket may be 15 to 35% by weight. (In this specification, "~" means not less than the lower limit and not more than the upper limit. The same shall apply hereinafter)

Effects of the Invention

[0012] According to the present invention, it is possible to realize a fuel cell gasket excellent in rebound resilience at low temperature environments.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, the fuel cell gasket according to the present invention will be described in detail. Note that the present invention is not limited to the following examples and can be arbitrarily changed without departing from the gist of the present invention.

[0014] One aspect of the present invention is a fuel cell gasket excellent in rebound resilience at low temperature environments, characterized by containing the following components (A) to (E). (A) A rubber component based on ethylene-butene-diene rubber. (B) A paraffinic hydrocarbon oil containing alpha olefin as a main component and having a pour point of -70°C or higher and -60°C or lower, which is a softening agent. (C) Carbon black. (D) A crosslinking agent composed of an organic peroxide. (E) A crosslinking aid which is a polyfunctional carboxylic acid compound.

[0015] As described above, this invention investigates fuel cell gaskets with excellent rebound modulus in low-temperature environments. Generally, when the temperature of rubber materials is lowered from room temperature, the rubbery elasticity is gradually lost, and the randomly moving molecular arrangement freezes, becoming glassy and solidifying at low temperatures. More specifically, rubber materials exhibit their unique elasticity through two processes: interatomic motion within the molecules and free rotational motion of the molecular chain structure. However, at low temperatures, interatomic motion within the molecules decreases, and the free rotational motion of the molecular chain structure also decreases at low temperatures. As a result, the rubber hardens and loses its elasticity.

[0016] Rubber hardens and breaks into pieces when it falls below a certain temperature (the glass transition temperature: the temperature at which the liquid state crystallizes). Basically, the glass transition temperature of rubber equals the glass transition temperature of raw rubber. As an exception, the softer the intermolecular chains and the weaker the forces acting on them, the more resistant to low temperatures they become. Therefore, it is possible to lower the glass transition temperature by adding chemicals that increase the molecular chain mobility of raw rubber. The following describes each component used in this invention.

[0017] (A. Rubber component) Regarding the rubber component, a rubber component based on ethylene-butene-diene rubber (EBT) is used. Other rubber components such as ethylene-propylene-diene rubber (EPDM, EPT) could also be considered, but the inventors of this invention investigated the physical properties under low-temperature conditions and found that ethylene-butene-diene rubber (EBT) is preferable.

[0018] Rubber components based on EBT (Earth-Bead Tissue) exhibit excellent high-temperature resistance, chemical resistance, and gas barrier properties, and can maintain flexibility even at low temperatures where conventional materials could not achieve this. Therefore, they are suitable as materials for harsh environments such as fuel cell applications.

[0019] Regarding the rubber component, it is preferable to formulate it so that its content in the fuel cell gasket (weight ratio to the total rubber composition synthesized) is 40% by weight or more. This is the ratio found in the examples described later.

[0020] (B. Softener) The plasticizer used is a paraffinic hydrocarbon oil containing alpha-olefin as its main component, with a pour point between -70°C and -60°C. The plasticizer reduces hardness and improves flexibility and low-temperature elasticity. It can also improve processability and fluidity. Polyalpha-olefin (PAO) can be used as an example of a plasticizer.

[0021] Softeners loosen the intermolecular bonds of polymers, thereby increasing the softness (flexibility and pliability) of rubber, and are particularly used to improve low-temperature properties (maintaining flexibility at low temperatures). Thus, by appropriately selecting a softener, the glass transition temperature (Tg) can be lowered, preventing the rubber from hardening in cold environments and maintaining its performance at low temperatures.

[0022] Regarding the amount of softener added, it is preferable to blend the softener so that its content relative to the fuel cell gasket is 20 to 40% by weight, and more preferably 30% by weight or more. By blending 30% by weight or more of the softener, a rebound modulus of 30% at -30°C can be achieved, as shown in the examples described later.

[0023] (C. Carbon Black) Carbon black is added as a filler. This enhances the strength, tensile strength, abrasion resistance, and UV resistance of the rubber, and also imparts some conductivity.

[0024] For example, it is preferable to use high-structure carbon of GPF (General Purpose Furnace) grade as the carbon black, with a nitrogen adsorption specific surface area of ​​20-30 m². 2It is desirable that the amount be / g. In addition, it is preferable that the carbon black content in the fuel cell gasket be 15 to 35% by weight.

[0025] (D. Crosslinking agent) The crosslinking agent used is an organic peroxide. The use of organic peroxides promotes the crosslinking reaction of rubber, forming a three-dimensional network structure. Furthermore, the crosslinking agent affects the rubber's resilience, permanent deformation rate, and heat resistance.

[0026] As an example of a crosslinking agent, molecular formula C 14 H 28 O4 1,1-(t-butylperoxy)cyclohexane and the like can be used, and those that function as radical crosslinking agents have the properties of a polymerization initiator for vinyl monomers, a heat curing agent for unsaturated polyester resins, or a crosslinking agent for polyolefins or synthetic rubbers.

[0027] (E. Crosslinking agent) A polyfunctional carboxylic acid compound is used as the crosslinking aid. When used in combination with the organic peroxide, which is the crosslinking agent, the crosslinking aid promotes the crosslinking reaction, improving crosslink density, heat resistance, and dimensional stability. Examples of polyfunctional carboxylic acid compounds include acrylates.

[0028] As an example of a crosslinking agent, molecular formula C 12 H 18 O4 1,6-hexanediol diacrylate and the like can be used as crosslinking aids for bifunctional monomers.

[0029] (F. Other ingredients) In this invention, other formulations such as antioxidants and inorganic white fillers may be included. Antioxidants suppress oxidative degradation and ozone, extending durability and service life, and are particularly effective against thermal aging. Inorganic white fillers contribute to cost reduction and improved dimensional stability, but excessive addition can affect strength and processability. Unlike carbon black, inorganic white fillers improve insulation properties.

[0030] For example, phenolic antioxidants are used as anti-aging agents. In addition, calcium carbonate is used as an inorganic white filler.

[0031] (Fuel cell gasket) Generally, fuel cells have a cell stack structure in which multiple units (cells) composed of an electrolyte membrane, electrode plates (cathode, anode), and separators are combined. As mentioned above, fuel cells generate electricity through the reaction of hydrogen and oxygen, and in order to prevent leakage of these hydrogen and oxygen gases and to properly drain the water generated in the fuel cell, the fuel cell gasket according to the present invention is mainly used as a sealing member to seal between each separator that constitutes the cell stack.

[0032] Furthermore, in this invention, even when a fuel cell is used in a cold region where the temperature drops below -30°C, as described above, the fuel cell gasket used in the fuel cell will not solidify and become non-functional due to the low temperature, thus realizing a fuel cell gasket with excellent rebound elasticity in low-temperature environments. [Examples]

[0033] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to the following examples.

[0034] (Preparation of rubber composition) In the examples, rubber compositions constituting the fuel cell gasket according to the present invention were prepared. The following materials were used for each composition. • Rubber component (base material): EBT-K8370EM rubber or EBT-K9330M rubber (manufactured by Mitsui Chemicals, Inc.) • Plasticizer: PAO401 (manufactured by Nippon Steel Chemical & Material Co., Ltd.) • Carbon Black: SPHERON 5200 (manufactured by Cabot Japan Co., Ltd.) • Inorganic filler: Calcium carbonate (whiteSB) (manufactured by Shiraishi Calcium Co., Ltd.) • Crosslinking agent: Organic peroxide (PERHEXA-C or PERCUMYL-D) (manufactured by NOF Corporation) • Crosslinking agent: Viscort #230 (manufactured by Osaka Organic Chemical Industry Co., Ltd.) • Anti-aging agent: RD (manufactured by Seikoh PMC Co., Ltd.)

[0035] Furthermore, as a comparative example, EPT (ethylene-propylene-diene rubber) was used instead of EBT (ethylene-butene-diene rubber) for the rubber component. The rubber component used was EPT 9090M (manufactured by Mitsui Chemicals, Inc.).

[0036] (Consideration of the blending ratio of rubber compositions) Regarding the blending ratio of rubber compositions, we used AI-based machine learning to investigate blending ratios that can achieve excellent rebound modulus in low-temperature environments. Past experimental results were mainly used as training signals for deep learning. As an example of the investigation, we selected three components—softener, carbon black, and crosslinking aid—with the goal of improving two properties, rebound modulus and volume resistivity, as described later, and performed reinforcement learning with three variables and two goals. Through this, we investigated the correlation between softener and carbon black, softener and crosslinking aid, and carbon black and crosslinking aid for improving the rebound modulus of rubber, and the correlation between softener and carbon black, softener and crosslinking aid, and carbon black and crosslinking aid for improving the volume resistivity of rubber, and predicted the blending ratios necessary to achieve the two goals using AI.

[0037] Following the above considerations, in the examples and comparative examples, each of the above compositions was blended in the proportions shown in Table 1 below. The values ​​for the examples in Table 1 represent the mass proportion of each composition when the rubber component (base material) is 100 parts by mass.

[0038] For the preparation of the test specimens, the rubber component was kneaded, then carbon black was added and kneaded again. Plasticizers, crosslinking aids, and antioxidants were then added, and the mixture was placed in a mold for test specimen preparation and crosslinked with a crosslinking agent to form a compound. The crosslinking conditions were 170°C for 10 minutes.

[0039]

Table 1

[0040] Regarding the prepared rubber composition, the following listed tests were applied to measure the physical properties of the rubber composition.

[0041] (Compression stress relaxation test) The compression stress relaxation test was carried out based on Chinese standard specification GB / T1685 - 2008 (equivalent to Japanese Industrial Standard JIS K6263). This test is to apply a specified compression deformation to a cylindrical or ring-shaped test piece and determine the change between the compression force and the initial compression force when maintaining the deformation at a specified temperature and time, and is carried out to examine the compression stress relaxation characteristics.

[0042] Cylindrical test pieces with a diameter of 13.0 mm ± 0.5 mm and a thickness of 6.3 mm ± 0.3 mm were prepared, and at standard temperature and humidity, the test pieces were compressed to 25% ± 2% of the specified deformation amount by a compression force measuring device. Then, the stresses after 30 minutes, 3 hours, 6 hours, 24 hours, 72 hours, and 168 hours were measured. The initial compression force after 30 minutes was F0 (N), and the compression force after t hours was F t (N). Taking the compression stress relaxation R C (t) as R C (t)=[(F0 - F[[ID=�0]] t ) / F0] × 100 (%) Each was calculated respectively, and the median value of the obtained values was rounded to the integer place and represented.

[0043] (Compression set test) The compression set test was carried out based on Chinese standard specification GB / T7759.1 - 2015 (equivalent to Japanese Industrial Standard JIS K6262). This test determines the sagging property of the rubber material by measuring the permanent strain due to compression of the rubber material.

[0044] A cylindrical test specimen with a diameter of 29.0 mm ± 0.5 mm and a thickness of 12.5 mm ± 0.5 mm was prepared. This test specimen was subjected to strain using a compression device consisting of a compression plate for compressing the specimen, a spacer for applying a specified strain, and a holder for fixing the compression plate. After a predetermined time, the test specimen was released from the compression device and left on a wooden board for 30 minutes ± 3 minutes, and its height was measured. The compression set CS (%) was calculated using the original thickness of the test specimen h0 (mm), the thickness of the test specimen after removal from the compression device h1 (mm), and the thickness of the spacer h s (mm) CS = [(h0-h1) / (h0-h s )] × 100 (%) This was calculated using three test specimens, and the average value was rounded to an integer.

[0045] (Rebound modulus test) The rebound modulus test was conducted in accordance with the Chinese standard GB / T1681-2009 (equivalent to the Japanese Industrial Standard JIS K6257). The rebound modulus represents the ratio of the rebound energy to the energy applied when a pendulum with a spherical striking end strikes a test specimen at a specified mass and speed.

[0046] A cylindrical test specimen with a diameter of 29.0 mm ± 0.5 mm and a thickness of 12.5 mm ± 0.5 mm was prepared. The rebound modulus of this specimen was measured at room temperature, -40°C, -30°C, and -20°C using a Schob-type rebound modulus tester SB-M1 (manufactured by Toyo Seiki Co., Ltd.). For low temperatures, the test specimen was placed in a freezer set to the respective temperature for one week before measurement.

[0047] Furthermore, the rebound modulus test was evaluated using ◎, ○, and × based on the following criteria. At room temperature: ○: 50% or more, ×: less than 50% -40℃···◎: 15% or more, ○: 10% or more but less than 15%, ×: less than 10% -30℃···◎: 30% or more, ○: 20% or more but less than 30%, ×: less than 20% -20℃···◎: 30% or more, ○: 20% or more but less than 30%, ×: less than 20%

[0048] (Acid resistance test) The acid resistance test was conducted in accordance with the Chinese standard GB / T1690-2010 (equivalent to the Japanese Industrial Standard JIS K6258). In the acid resistance test, the rubber material's resistance to acidic solutions is determined by immersing it in an acidic solution and measuring the change in mass before and after immersion.

[0049] A cylindrical test specimen with a diameter of 29.0 mm ± 0.5 mm and a thickness of 12.5 mm ± 0.5 mm was prepared. This specimen was immersed in a 20% hydrochloric acid (HCl) solution for 168 hours, and the change in mass of the specimen after immersion relative to the mass of the specimen before immersion (%) was used as an indicator of acid resistance.

[0050] (Resistance measurement test) The resistance measurement test was conducted in accordance with the Chinese standard GB / T1692-2008 (equivalent to the Japanese Industrial Standard JIS K6271-1). In this example, however, the test was conducted in accordance with JIS K6911.

[0051] A flat test specimen measuring 150 mm in length, 150 mm in width, and 1 mm in height was prepared. The surface resistivity (Ω / □) and volume resistivity (Ω·cm) were measured when 1000 V was applied to this specimen for 60 seconds.

[0052] The resistance measurement test was evaluated using ◎, ○, and × based on the following criteria. <Surface resistivity> ◎: 1.0 × 10 14 Ω / □ or more ○: 1.0 × 10 13 Ω / □ or more 1.0×10 14 Ω / □ or less ×: 1.0 × 10 13 Ω / □ or less <Volume resistivity> ◎: 1.0 × 10 13 Ω cm or more ○: 1.0 × 10 12 Ω cm or more 1.0×10 13 Less than Ω·cm ×: 1.0 × 1012 Less than Ω·cm

[0053] Table 2 shows the results of the compression stress relaxation test, compression set test, rebound modulus test, acid resistance test, and resistance measurement test conducted on each rubber composition prepared based on the compounding ratios in Table 1.

[0054] [Table 2]

[0055] As shown in the results in Table 2, it was found that by creating rubber compositions using each of the compositions specified in the present invention, it is possible to obtain rubber compositions (fuel cell gaskets) that have properties that allow them to be used in general even in low-temperature environments. For example, in the case of the comparative example (EPT), the evaluation of the rebound modulus was × (less than 20%) at -20℃ and also × (less than 20%) at -30℃, whereas in the case of the example (EBT), the rebound modulus was ○ to ◎ at -20℃ and mostly ○ at -30℃, showing a significant improvement in the rebound modulus in low-temperature environments. In particular, the rubber compositions of Example 17 and Example 18 were evaluated as ◎ for the rebound modulus at -20℃ to -40℃, demonstrating that rubber compositions (fuel cell gaskets) with excellent properties even in low-temperature environments could be created. Thus, it was found that the present invention can maintain performance equivalent to or better than that of ordinary EPDM while maintaining low-temperature properties.

[0056] As described above, the present invention has made it possible to realize a fuel cell gasket with excellent rebound modulus in low-temperature environments.

[0057] Although one embodiment of the present invention and each example have been described in detail above, it will be readily apparent to those skilled in the art that many modifications are possible without substantially departing from the novel aspects and effects of the present invention. Therefore, all such modifications are included within the scope of the present invention.

[0058] For example, any term that appears at least once in the specification or drawings alongside a broader or synonymous term may be replaced with that different term anywhere in the specification or drawings. Furthermore, the configuration of the fuel cell gasket is not limited to that described in the embodiment of the present invention and each example, and various modifications are possible.

Claims

1. A fuel cell gasket with excellent rebound modulus in low-temperature environments, A fuel cell gasket characterized by containing the following components (A) to (E), wherein the content of the softener (B) below is 60 parts by mass or more per 100 parts by mass of the rubber component (A) below, and having a rebound modulus of 10% or more at -40°C as measured according to the Chinese Standard GB / T1681-2009 or the Japanese Industrial Standard JIS K6257. (A) A rubber component based on ethylene-butene-diene rubber. (B) A paraffinic hydrocarbon oil containing alpha-olefin as its main component, having a pour point of -70°C or higher and -60°C or lower as a softening agent. (C) Carbon Black. (D) A crosslinking agent consisting of an organic peroxide. (E) A crosslinking aid that is a polyfunctional carboxylic acid compound.

2. The fuel cell gasket according to claim 1, characterized in that the content of the rubber component in the fuel cell gasket is 40% by weight or more.

3. The carbon black has a nitrogen adsorption specific surface area of ​​20 to 30 m². ２ The fuel cell gasket according to claim 2, characterized in that the content is / g and the content relative to the fuel cell gasket is 15 to 35% by weight.

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