KR102094757B1 - Rubber composion for fuel cell gasket and fuel cell gasket - Google Patents

Abstract

The present invention relates to a rubber composition excellent in gas tightness and heat resistance as well as cold resistance and shape retention, and a fuel cell gasket manufactured thereby. According to the present invention, heat resistance and cold resistance required in the gasket for a fuel cell can be improved by using, as a main ingredient, EPDM rubber composed of 55-59 wt% of ethylene and 3.5-5.5 wt% of ethyleneidene norbornene (ENB) with the Moony viscosity of 36-48 (ML1+4, 125°C). In addition, it is possible to produce a highly durable gasket for a fuel cell by having sealing properties, compression resistance, and low elution properties due to excellent compression permanent percentage of contraction as well as excellent electric insulation.

Description

Rubber composition for fuel cell gasket and gasket for fuel cell using the same {Rubber composion for fuel cell gasket and fuel cell gasket}

The present invention relates to a rubber composition for a fuel cell gasket, specifically, to a rubber composition excellent in airtightness and heat resistance as well as cold resistance and shape retention particularly suitable for a fuel cell gasket and a gasket for a fuel cell produced therefrom. will be.

The fuel cell consists of two electrode rods that are attached to each other around the electrolytic material, and uses the principle of generating electricity, water, and heat through electrochemical reaction when oxygen in the air passes through one electrode and hydrogen passes through the other electrode. As the hydrogen flows through the gas diffusion layer and the membrane, it is converted into hydrogen cations, and the generated electrons generate electricity.

The fuel cell has a membrane, a cathode, and an anode, as shown in the attached FIG. 1. The gas diffusion layer, a unit cell made of a bipolar plate, is composed of a stack in the form of a stack of several hundred sheets, and the supplied fuel gas must be delivered to the electrode without loss. The gasket is required for airtightness between the and the bipolar plate, and in the case of a fuel cell vehicle, the driving temperature is repeatedly driven in the range of -40 to 80 ℃, so the gasket material is resistant to temperature changes with cold resistance and heat resistance. It should be manufactured to minimize the change in compression rate.

Currently, most gasket materials use fluorine rubber, but below -10 ℃, they lose the properties of rubber, causing problems in hydrogen sealing, and silicone rubber is used for testing. Recently, liquid rubbers for integration with gaskets and MEAs (Membrane Electrode Assembly), gaskets and gas diffusion layers, gaskets and separators are being reviewed. Especially, in the case of metal separators made of thin plates, the role of the gasket additionally maintains the structural shape. Because it is required, fuel cell vehicles are also required to maintain shape rather than just airtight.

As a prior art related to a rubber composition for a fuel cell gasket, for example, Patent Literature 1 contains 0.5 to 5 parts by weight of zinc oxide as a crosslinking agent and 100 to 5 parts by weight of zinc dimethacrylate as a crude crosslinking agent in 100 parts by weight of polyalkenamer. , 0.5 to 7 parts by weight of ZnPCTP as a peptizer, 0.5 to 5 parts by weight of ZMBT as an accelerator, and 5 to 70 parts by weight of carbon black and silica (carbon black / silica = 1/1 (weight ratio)) as an inorganic additive in an extruder And, extruding at a temperature of 60 ~ 80 ℃ to prepare a pellet-shaped polyalkenamer rubber composition; Mixing 1 to 3 parts by weight of an organic crosslinking agent master batch containing DCPO (dicumyl peroxide) as an organic crosslinking agent in 100 parts by weight of the rubber composition in an injection machine, and injection molding at a temperature of 60 to 80 ° C. to prepare a preform; And it is disclosed in the fuel cell gasket manufacturing method comprising the step of curing the pre-formed by compression molding at a temperature of 180 ~ 200 ℃, Patent Document 2 EPDM rubber 80 ~ 98 wt.% And FKM A base containing 2 to 20 wt.% Of rubber and 0.1 to 10 wt.% Of peroxide crosslinking agent compared to 100 wt.% Of the base, and the EPDM rubber and the FKM rubber are co-crosslinked through a peroxide crosslinking agent (Co-Crosslink) Disclosed is a blend gasket for a fuel cell, characterized in that the permanent compression reduction rate is 3.6 to 5.9% when heat treatment is performed at 100 ° C for 72 hours.

Further, as a gasket for a fuel cell containing EPDM rubber and a crosslinking agent in Patent Document 3, the EPDM rubber comprises 50 to 60 wt.% Of ethylene and 4 to 10 wt.% Of diene monomer, and the crosslinking agent is sulfur (S ) Does not contain a peroxide crosslinking agent, the EPDM rubber 100wt.% Compared to the peroxide crosslinking agent 1 ~ 5 wt.% Is added, the EPDM rubber 100wt.% Compared to the organic crosslinking agent 0.1 ~ 1 wt.%, Antioxidant 0.1 ~ 1wt.% And carbon black 1 ~ 10wt.% Is further added to the composition, does not contain metal compounds and stearic acid (Stearic Acid), permanent compression reduction rate ASTM D395 (Method B, 25% Deflection, 72 hours) @ 100 ℃) discloses a gasket for a fuel cell, characterized in that less than 5%.

The applicant of the present invention uses EPDM rubber as a main material to manufacture a gasket for a fuel cell using the fuel cell gasket composition and a fuel cell gasket composition using a combination of the airtightness and heat resistance required by the gasket for a fuel cell, as well as a blending component showing properties suitable for cold resistance and shape retention And completed the present invention.

KR 10-1128404 B KR 10-1601380 B KR 10-1664740 B

The problem to be solved in the present invention relates to the provision of a rubber composition for a fuel cell gasket and a gasket for a fuel cell using the same, and more specifically, airtightness and heat resistance as well as cold resistance required by the gasket for a fuel cell using EPDM rubber as a main material, It is an object of the present invention to provide a fuel cell gasket composition and a fuel cell gasket using the composition for a fuel cell gasket combining a compounding component that exhibits properties suitable for adhesiveness and shape retention.

As a solution of the problems of the present invention, the rubber composition for fuel cell gaskets is an EPDM rubber having a Mooney viscosity of 36 to 48 (ML1 + 4, 125 ° C) as a main material, and is a MT-carbon black, crosslinking agent having a particle diameter of 201 to 500 nm. Di (tert-butylperoxyisopropyl) benzene, 1,2-polybutadiene or triallyl isocyanurate as a processing aid, 4- (1-methyl-1-phenylethyl) -N- [4- as an antioxidant (1-methyl-1-phenylethyl) phenyl] aniline, wherein at least one selected from di-2-ethylhexylphthalate as a cold-resistant emollient, dioctyldiphosphate as a cold-resistant plasticizer and tricresyl phosphate as a heat-resistant plasticizer It consists of comprising a composition.

The mixing ratio of the components according to the rubber composition for the gasket of the present invention is 40 to 50 parts by weight of the filler, 2 to 5 parts by weight relative to 100 parts by weight of EPDM rubber having a Mooney viscosity of 36 to 48 (ML1 + 4, 125 ° C). It is composed of 8 to 12 parts by weight of one or more components selected from cold-resistant softeners, cold-resistant plasticizers and heat-resistant plasticizers, by weight, 4 to 6 parts by weight of processing aid, and 0.2 to 2 parts by weight of antioxidant.

One aspect of the rubber composition for a fuel cell gasket according to the present invention is that in the case of a fuel cell vehicle, since the driving temperature is repeatedly driven in a range of -40 to 80 ° C, the gasket material is cold and heat resistant, and the compression rate change due to temperature change is minimized. It consists of combining suitable additives and fillers while selecting EPDM rubber as the rubber material for fuel cell gaskets in order to show the properties.

In particular, by combining MT-carbon black with a particle diameter of 201 to 500 nm as a cold-resistant softener, cold-resistant plasticizer, and filler, the fuel cell gasket is made of cold-resistant material capable of maintaining rubber properties at low temperatures to the maximum.

And a fuel cell gasket manufactured by using a rubber composition for a fuel cell gasket as a solution of another problem of the present invention is a thin film for a fuel cell by crosslinking and molding the blend of the rubber composition according to the present invention at a mold temperature of 180 ° C for 240 seconds. It consists of manufacturing a gasket.

The rubber composition for a fuel cell gasket according to the present invention has an effect of improving the cold resistance as well as the heat resistance required by the fuel cell gasket by combining EPDM rubber with a cold-resistant softener, a cold-resistant plasticizer, and a heat-resistant plasticizer.

In addition, it has the characteristics of being able to manufacture a gasket for a fuel cell with high durability by being excellent in sealing property, compression resistance, and low elution property due to excellent electrical insulation properties and excellent compression permanent shrinkage characteristics.

1 is a view schematically showing the structure of a unit cell of a fuel cell.

Hereinafter, the present invention will be described in more detail with reference to specific details and examples and test examples for carrying out the present invention, but the present invention is not limited by the following description and examples.

1 is a view schematically showing the structure of a unit cell of a fuel cell. In general, a fuel cell includes a membrane, a cathode, and an anode as shown in FIG. 1. The gas diffusion layer, a unit cell made of a bipolar plate, is composed of a stack in the form of a stack of hundreds of sheets, and the supplied fuel gas must be delivered to the electrode without loss. ) And a gasket is required for airtightness between the bipolar plate.

The rubber composition for gaskets for fuel cells according to the present invention is an EPDM rubber having a Mooney viscosity of 36 to 48 (ML1 + 4, 125 ° C) as a main material, and a filler having a particle diameter of 201 to 500 nm, MT-carbon black, crosslinking agent (tert-) Butyl peroxyisopropyl) benzene, 1,2-polybutadiene or triallyl isocyanurate as a processing aid, 4- (1-methyl-1-phenylethyl) -N- [4- (1-methyl as an antioxidant) -1-phenylethyl) phenyl] aniline is formulated, wherein at least one component selected from di-2-ethylhexylphthalate as a cold-resistant softener, dioctyl adipate as a cold-resistant plasticizer, and tricresyl phosphate as a heat-resistant plasticizer is composed. It consists of including.

 The composition ratio according to the rubber composition for the gasket of the present invention is 40 to 50 weight of MT-carbon black having a particle diameter of 201 to 500 nm with respect to 100 parts by weight of EPDM rubber having a Mooney viscosity of 36 to 48 (ML1 + 4, 125 ° C). Parts, di (tert-butylperoxyisopropyl) benzene 2 to 5 parts by weight, 1,2-polybutadiene or triallyl isocyanurate 4 to 6 parts by weight, 4- (1-methyl-1-phenylethyl) -N- [4- (1-methyl-1-phenylethyl) phenyl] aniline is composed of 0.2 to 2 parts by weight and is selected from di-2-ethylhexyl phthalate, dioctyl adipate, and tricresyl phosphate. It is composed of 8 to 12 parts by weight of the above components.

The EPDM rubber (Ethylene Propylene Diene Monomer Terpolymer) is a terpolymer of ethylene, propylene and diene components, and the diene components are dicyclopentadiene (DCPD), ethylidene norbornene (ENB) and vinyl norbornene (VNB). It is made of, there is a significant difference in the physicochemical properties of the EPDM rubber according to the diene component.

The EPDM rubber is a rubber composed of dicyclopentadiene (DCPD), ethylidene norbornene (ENB) or vinylnorbornene (VNB), and is widely marketed as a known material. For example, the trade name SUPRENE ^® 501A, 505A, KEP-2320, KEP-330, KEP-240, and Keltan DE 8270C.

EPDM rubber having a Mooney viscosity of 36 to 48 (ML1 + 4, 125 ° C) according to the present invention has an ethylene content of 55 to 59 wt%, an ethylidene norbornene (ENB) content of 3.5 to 5.5 wt%, ethylene (Ethylene) ), Ternary copolymers of propylene (Propylene) and ethylidene norbornene (ENB) are selected.

MT-carbon black having a particle size of 201 to 500 nm selected as a filler in the present invention is the largest particle of carbon black, has a small specific surface area, excellent electrical insulation, and has very little impurities such as ash or sulfur. Particularly suitable for strength reinforcement and electrical insulation of the battery gasket, the MT-carbon black having a particle diameter of 201 to 500 nm is composed of 40 to 50 parts by weight based on 100 parts by weight of the EPDM rubber according to the present invention, preferably 45 parts by weight Is created.

Di (tert-butylperoxyisopropyl) benzene selected as a crosslinking agent in the present invention is a crosslinking agent having excellent heat stability and is composed of 2 to 5 parts by weight based on 100 parts by weight of the EPDM rubber, preferably 3 parts by weight And is marketed under the trade name PERKADOX 14-40.

1,2-polybutadiene (1,2-polybutadiene), which is selected as a processing aid in the present invention, significantly improves the tear strength, permanent compression shrinkage, and rebound resilience of the crosslinking and crosslinking rubber when crosslinking EPDM with peroxide. , It also shows the function of improving the heat resistance. 1,2-polybutadiene is composed of 4 to 6 parts by weight with respect to 100 parts by weight of EPDM rubber according to the present invention, preferably 3 parts by weight

In addition, triallyl isocyanurate, which is selected as a processing aid, is added to the crosslinking process of EPDM, and the crosslinking efficiency, heat resistance, and mechanical properties of triallyl isocyanurate are triallyl groups. It exhibits an improved effect, and triallyl isocyanurate is composed of 4 to 6 parts by weight with respect to 100 parts by weight of EPDM rubber according to the present invention, preferably 3 parts by weight.

In the present invention, 4- (1-methyl-1-phenylethyl) -N- [4- (1-methyl-1-phenylethyl) phenyl] aniline selected as an antioxidant is used to prevent a decrease in hardness due to aging. Composition, the antioxidant is composed of 0.2 to 2 parts by weight based on 100 parts by weight of the EPDM rubber according to the present invention, preferably 1 part by weight.

The rubber composition according to the present invention has at least one component selected from a cold-resistant softener, a cold-resistant plasticizer, and a heat-resistant plasticizer for improving heat resistance as well as heat resistance required by the gasket for a fuel cell (strengthening low temperature), 100 parts by weight of EPDM rubber according to the present invention It is composed of 8 to 12 parts by weight.

Di-2-ethylhexyl phthalate (DOE) is used as the cold-resistant softener, dioctyl adipate (DOA) as the cold-resistant plasticizer, and tricresyl phosphate (TCP) as the heat-resistant plasticizer.

Of course, the components selected as the rubber composition of the present invention are selected and combined so as to be particularly suitable for the characteristics such as the compression reduction ratio, the total insulation, etc. according to the mechanical properties and sealing properties required for the fuel cell gasket. It is selected and combined to be particularly suitable for the characteristics of heat resistance under cold resistance due to semi-purpose driving in a temperature range of -40 ℃ to 80 ℃.

In addition, in the case of a gasket for a fuel cell vehicle stack, a direct injection molding and primary crosslinking are performed to produce a thin film gasket to be integrated into a membrane electrode assembly, a gas diffusion layer, or a separator. It is very important to maintain a proper crosslinking speed when injection molding in a mold.

In the fuel cell gasket using the rubber composition according to the present invention, a material of the rubber composition is kneaded by combining a Kneader Mixing process and an Open roll mixing process, and is first crosslinked and molded at a mold temperature of 180 ° C for 240 seconds to produce a thin film gasket. do.

Hereinafter, the rubber composition for a fuel cell gasket according to the present invention and a fuel cell gasket using the same will be described in more detail with reference to Examples and Test Examples.

 <Example 1>

Mooney viscosity 45 (ML1 + 4, 125 ℃), ethylene (Ethylene) content of 57wt%, ethylidene norbornene (ENB) content of 4.5wt% EPDM rubber as shown in Table 1 below the composition and blending ratio Using 3L Kneader and 8inch Open Mill, add EPDM rubber and 400nm MT-carbon black from Kneader and mix them, and then apply uniform stress to the whole by uniformly dispersing the compounding agents using an open roll. To obtain constant properties, the mixture was steamed for 3 minutes, and then the remaining material such as a crosslinking agent was added and mixed for 5 minutes to obtain a rubber composition for a fuel cell gasket of the present invention.

The rubber composition for gaskets is crosslinked and molded at a mold temperature of 180 ° C for 240 seconds to prepare a thin film gasket and used as a specimen.

Composition Example 1
(Weight ratio) Remark EPDM rubber 100 Mooney viscosity 45 (ML1 + 4, 125 ℃),
Ethylene content 57wt%, ENB content 4.5wt% MT-carbon black 45 Particle size 400nm Di (tert-butylperoxyisopropyl) benzene 3 Crosslinking agent, trade name PERKADOX 14-40 1,2-polybutadiene 5 Processing aid Di-2-ethylhexylphthalate 4 Cold-resistant softener Tricresyl Phosphate 5 Heat-resistant plasticizer 4- (1-methyl-1-phenylethyl) -N- [4- (1-methyl-1-phenylethyl) phenyl] aniline One Antioxidant

<Comparative Example 1 and Comparative Example 2>

<Comparative Example 1> Mooney viscosity 28 (ML1 + 4, 125 ℃), ethylene content 55wt%, ENB content 7.9wt% EPDM rubber (trade name KEP330), <Comparative Example 2> Mooney viscosity 25 (ML1 + 4, 125 ℃), ethylene content 59wt%, ENB content 4.7wt% EPDM rubber (trade name KEP2320), except that each of the compound composition obtained in the same composition and method as in <Example 1>, 180 ℃ mold A thin film gasket is prepared by crosslinking and molding at a temperature for 240 seconds and used as a specimen.

<Test Example 1>

In order to evaluate the crosslinking properties for the gasket <Example 1> according to the present invention, the temperature change of the mold as the primary crosslinking condition, the change in rubber properties (hardness) according to the mold temperature, and the change in physical properties (IRHD hardness) according to the change in crosslinking time Was tested and the results are shown in [Table 2] below.

Mold temperature (℃) Crosslinking time (sec) IRHD (Max) IRHD (Min) ΔIRHD IRHD (Avg ') 190 250 57.4 55.3 2.1 56.5 240 57.5 55.1 2.4 56.3 230 56.8 55.1 1.7 55.9 185 250 56.9 54.9 2.0 55.9 240 56.6 54.5 2.1 55.6 230 56.2 55.0 1.2 55.6 180 250 56.2 55.0 1.2 55.6 240 55.5 54.9 0.6 55.2 230 55.1 54.1 1.0 54.6 175 250 55.4 54.3 1.1 54.8 240 54.9 53.7 1.2 54.3 230 54.3 52.1 2.2 53.3

As shown in [Table 2], the variation in hardness (0.6) was the lowest at the mold temperature of 180 ° C and 240 seconds, and the optimum optimum for the optimum hardness (IRHD hardness: 55 ± 5) required for the fuel cell gasket. It can be confirmed that the condition is indicated.

<Test Example 2>

In order to evaluate the properties of the gaskets <Example 1> and <Comparative Examples 1 and 2> according to the present invention, they were tested by the test items and methods described below, and the results are shown in [Table 3].

One). Hardness (KS M6518), tensile strength and elongation (KS M6518); The hardness was tested using a Shore A hardness tester, and the tensile strength and elongation were measured for the force and length of the specimen to break.

2). Compressed permanent shrinkage (KS M6518); In the case of the fuel cell stack gasket, the elasticity of the gasket showing the reaction force against compression is the most important evaluation item because hundreds of cell components receive a lot of compression load when they are fastened under a certain compression load. Permanent compression set is generally reviewed as a test that can simulate the elasticity of the gasket, and the permanent compression set is measured continuously after applying a constant compressive force for a certain period of time. In Test Example 2>, after 25% compression, the process was performed at 100 ° C and 70 hrs, and the results were obtained by the following calculation formula.

[formula]

In the above formula C: compression permanent shrinkage (%), t ₀ : original thickness of the test piece (mm), t ₁ : thickness of the test piece after the test (mm), t ₂ : thickness of the spacer (mm)

3). Cold resistance TR-10 test (KS M6676); After stretching the specimen 50%, the specimen is immersed at -70 ° C for 10 minutes, and the temperature at which 10% of the elongated length is restored while heating at 1 ° C is measured.

4). Heat resistance test (KS M6518); It is a test to measure the aging (heat resistance) due to heat of rubber. After heating, hardness, tensile strength, elongation, etc. are measured, and changes in these values before heat treatment are evaluated. In <Test Example 2>, the properties at 70h and 168h were additionally analyzed to stand at 100 ° C and 336hrs and grasp the tendency to change physical properties (hardness, tensile strength, elongation).

5). Acid resistance test; Fuel cells generate electricity by reacting hydrogen with oxygen in the air. H ⁺ ions dissociated from hydrogen move from the anode to the cathode to generate energy. The H ⁺ ions generated in this way acidify the environment inside the fuel cell, and components of the fuel cell stack including gaskets require durability in an acidic atmosphere. In this <Test Example 2>, the gasket was impregnated with a solution of 20 wt% sulfuric acid at 90 ° C and 336 hrs, and the hardness change was measured.

6). Electrical insulation resistance; Among the required characteristics of the fuel cell gasket, insulation resistance is a key item for securing product stability, and 10 ⁸ Ω / cm ² or more is required by measuring with an insulation resistance meter.

7). Thickness tolerance test; The gasket plays a major role in securing durability, such as preventing leakage and sealing of hydrogen, air, and cooling water in the fuel cell stack. In order to secure the stability of such performance, molding precision is required in the molding process, and the shrinkage rate of the material itself must be minimized. In this <Test Example 2>, thickness deviations of five 100 × 100 mm molding sheets were measured and averaged to obtain thickness tolerance (%).

Test Items unit Optimum Example 1 Comparative Example 1 Comparative Example 2 Remark Hardness (Shore A) 55 ± 10 57 55 58 KS M 6518 The tensile strength kgf / cm ² 70 105 63  65 Elongation % 150 211 180 162 Compressed permanent shrinkage
100 ℃, 70hrs % below 10 4.1 7.8 8 Cold resistance
(TR-10) ℃ -40 -50 -38 -36 KS M 6676 Heat resistance (hardness change)
100 ℃, 336hrs point -5 ~ +5 +2 +5 +6 KS M 6518 Acid resistance (hardness change)
90 ℃, 336hrs (sulfuric acid) point -5 ~ +5 0.9 4 5 Self test Electrical insulation resistance Ω / cm ² 10 ⁸ Ω /
cm ² or more 3.2x10 ¹³ 5x10 ¹⁰ 3.2x10 ¹¹ ASTM D257 Gasket thickness tolerance % -5 ~ +5 One 3 3 Self test

As shown in [Table 3], <Example 1> of the present invention can be confirmed as satisfying the optimum value of the test items, such as cold resistance, heat resistance, and compression reduction required by the fuel cell gasket. It can be predicted that the fuel cell gasket rubber composition can provide an excellent fuel cell gasket.

Claims (6)

Mooney viscosity 36 ~ 48 (ML1 + 4, 125 ℃), ethylene (Ethylene), propylene (Propylene) and ethylidene norbornene (ENB) terpolymer of 100 parts by weight of EPDM rubber, as a filler, particle size 201 ~ 40-50 parts by weight of MT-carbon black at 500 nm, 2-5 parts by weight of di (tert-butylperoxyisopropyl) benzene as a crosslinking agent, 1,2-polybutadiene or triallyl isocyanurate 4-6 as a processing aid 4 parts by weight of antioxidant, 4- (1-methyl-1-phenylethyl) -N- [4- (1-methyl-1-phenylethyl) phenyl] aniline 0.2-2 parts by weight of di-2- as a cold-resistant softener Ethyl hexyl phthalate, a cold-resistant plasticizer comprising at least 8 to 12 parts by weight of at least one component selected from dioctyl adipate and heat-resistant plasticizer tricresyl phosphate,
EPDM rubber is a ethylene (Ethylene) content of 55 to 59wt%, ethylidene norbornene (ENB) content of 3.5 to 5.5wt%, the fuel cell rubber composition for gaskets. delete The rubber composition for a fuel cell gasket according to claim 1, wherein a tricresyl phosphate is formed of 1,2-polybutadiene as a processing aid, di-2-ethylhexyl phthalate as a cold resistance softener, and a heat-resistant plasticizer. A gasket for a fuel cell, characterized in that it is manufactured using the rubber composition according to claim 1 or 3. The gasket for a fuel cell according to claim 4, wherein the rubber composition is crosslinked at a mold temperature of 180 ° C. for 240 seconds to produce a thin film gasket. The gasket for a fuel cell according to claim 5, wherein the permanent compression reduction rate is 25% and then proceeds under conditions of 100 ° C. and 70 hrs, and calculated by [Calculation Formula] below.
[formula]

In the above formula C: compression permanent shrinkage (%), t ₀ : original thickness of the test piece (mm), t ₁ : thickness of the test piece after the test (mm), t ₂ : thickness of the spacer (mm)

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