JP6334870B2 - Seal composition for fuel cell - Google Patents

Description

  The present invention relates to a fuel cell sealing composition used for a fuel cell separator.

  The polymer electrolyte fuel cells that have been developed in recent years have less loss and higher power generation efficiency compared to transmitting the power generated at the power plant to the power consumption area, and the discharged gas is clean and environmentally friendly. There is an advantage that the load is extremely small.

  FIG. 5 shows an example of a polymer electrolyte fuel cell. As shown in FIG. 5A, the polymer electrolyte fuel cell has separators on both sides of a membrane / electrode assembly (Mebrane Electrode Assembly, MEA) composed of a gas diffusion layer 12, a catalyst 13, and an electrolyte membrane 14. 11 is a cell 10, and a plurality of cells 10 are stacked to form a fuel cell stack 20 (FIG. 5B). The electric power generated by the stack 20 is supplied from the current collecting plate 15 to the outside. The separator 11 is formed with a hydrogen and oxygen gas flow path and a refrigerant flow path for cooling heat generated during power generation. The electrolyte membrane 14 needs to be used in a humidified environment in order to maintain proton conductivity. Therefore, it is necessary to prevent and maintain the leakage of gas, water vapor and refrigerant, and therefore it is important to ensure the sealing performance in and between the separators.

  In addition, with the spread of fuel cells, when it is required to be used in a cryogenic environment, the members constituting the polymer electrolyte fuel cell have a wide range of temperatures from the operating temperature of the fuel cell to the cryogenic environment. Performance in the environment is required. In particular, the seal member is required to absorb the thermal shrinkage of the members constituting the fuel cell and the dimensional variation due to the tolerance of the dimensions of the laminated members, and in order to ensure sufficient sealing performance, There is a demand for the use of a seal member that can increase the compressibility when stacking cells and maintain the elasticity of rubber even in a cryogenic environment.

  As a gasket material for ensuring sealing performance, ethylene-propylene rubber, ethylene-propylene-diene rubber, silicone rubber, fluorine rubber, and the like have been proposed.

  For example, Patent Document 1 describes an adhesive seal member for a fuel cell in which a softening agent having a pour point of −40 ° C. or less is added to a rubber component such as EPDM for the purpose of improving low temperature performance. Patent Document 2 describes a fuel cell adhesive seal member using EPDM of Patent Document 1 having a low ethylene content (53% or less) for the purpose of improving low-temperature performance. Yes.

JP 2012-226907 A JP 2012-226908 A

  With the spread of fuel cells, when it is required to be used in various environments, seal members that are used in a wide range of temperatures from an extremely low temperature environment of -40 ° C. or lower to a high temperature environment are used in an extremely low temperature environment. However, it is required to maintain rubber elasticity.

  For example, Patent Document 1 describes an adhesive seal member for a fuel cell to which a softening agent having a pour point of −40 ° C. or lower is added for the purpose of improving low temperature performance. However, as a technique for improving the low temperature property, a technique of adding a softening agent having a pour point of −40 ° C. or lower is effective in a region where the recovery rate of the seal reaction force in a low temperature environment is small, but the elastic component of rubber is reduced. Therefore, the effect is not sufficiently exhibited in a region where the recovery rate of the seal reaction force is large.

  Furthermore, in a cryogenic environment, the compression rate of the seal portion is reduced due to the thermal contraction of the member. Therefore, in order to ensure a sufficient seal reaction force, the rubber member is used under a high compression condition. . However, when rubber is used under high compression conditions, it is possible to maintain the sealing performance under a cryogenic environment, but under high temperature environment, the breaking elongation and strength of the rubber are reduced, so The followability of rubber becomes poor, and a highly compressed gasket tends to break. Patent Document 1 describes a technique for increasing the number of crosslinking points and preventing crystallization for the purpose of maintaining the sealing property at the above-mentioned cryogenic temperature. This is disadvantageous for cracking in a high-temperature environment.

  Possible measures to prevent cracking in a highly compressed environment include reducing the vulcanizing agent, reducing the vulcanization density by inhibiting crosslinking with an anti-aging agent, and reducing the modulus (stress against constant elongation) by changing carbon, etc. Although there is a method of reducing the stress inside the rubber, any method reduces the seal reaction force in a low temperature environment. As a result, it is impossible to achieve both maintenance of the seal reaction force at extremely low temperatures and cracking under high temperature environments, and it becomes difficult to maintain seal performance in a wide temperature range from extremely low temperatures to high temperatures.

  In addition, members in the fuel cell stack are exposed to water vapor generated by power generation for a long period of time. Therefore, the physical properties (elongation and tensile strength) of the rubber member are lowered. This decrease in physical properties also impairs the ability of the rubber to follow the strain during high compression, leading to cracking of the rubber member.

  The present invention has been made to solve the above problems, and provides a fuel cell sealing composition capable of sealing at a high compression in a temperature range from an extremely low temperature to a high temperature and in a steam environment. For the purpose.

  The present invention has the following configuration in order to solve the above problems.

(1) (a) a rubber component selected from ethylene-propylene-diene rubber having a diene content of 7 wt% or more and an ethylene content of 50 wt% or less;
(B) a co-crosslinking agent which is a polyfunctional unsaturated compound having two or more double bonds;
(C) an organic peroxide;
(D) a softener having a pour point of −40 ° C. or less;
(E) a thermoplastic resin;
A fuel cell sealing composition comprising a crosslinked rubber composition containing

  (2) The fuel cell sealing composition according to (1), wherein the thermoplastic resin (e) is a hydrocarbon-based one.

  (3) The fuel cell sealing composition as described in (1) or (2) above, wherein the amount of the thermoplastic resin (e) is 1 phr or more and 30 phr or less.

  (4) The fuel cell sealing composition according to any one of (1) to (3), wherein TR70 in a low temperature elastic recovery test is −40 ° C. or lower.

  In addition, the adhesive seal member for fuel cells of Patent Documents 1 and 2 has no description on the diene content and Mooney viscosity, and does not contain a thermoplastic resin. Moreover, the low temperature performance is evaluated by the Gehman torsion test.

  According to the fuel cell seal composition of the present invention, by adding a small amount of thermoplastic resin, it is possible to prevent cracking of the rubber member under high compression conditions at high temperatures without degrading performance and physical properties at low temperatures. it can. Further, if the thermoplastic resin is of a hydrocarbon type, the hydrophobicity of the rubber improves the water resistance of the rubber, so that it is possible to control the loss of rubber followability with respect to the amount of deformation during high compression.

The graph which shows the reference data of TR test of an Example Table showing the composition, physical properties, and compression cracking test results of the comparative sample and the working sample of the working example The figure which shows the jig | tool used for the compression cracking test of an Example Table showing immersion test results of examples Diagram showing a general polymer electrolyte fuel cell

  DESCRIPTION OF EMBODIMENTS Embodiments for carrying out the present invention will be described below with reference to the drawings.

  The fuel cell seal composition of this example is a crosslinked product of a rubber composition comprising the following components (a) to (e), even under a high temperature environment (100 ° C.) and at a high compression rate (50%). It has the characteristics that it is not cracked and has excellent sealing performance at low temperatures (−40 ° C.). Each component will be described below.

[Structural component]
(A) Rubber component: EPDM
It is a copolymer of ethylene-propylene-diene, and two or more kinds of polymers having different amounts of ethylene and diene may be blended and used. The smaller the ethylene content, the less likely it is to crystallize at low temperatures, and 50 wt% or less is more preferred. However, 40 wt% or more is desirable in order to ensure the elongation and tensile strength required for the seal member.

  Furthermore, in EPDM, when a polymer having a large amount of diene and a large molecular weight is selected, it not only inhibits crystallization, but also becomes easy to recover due to an increase in the number of crosslinking points and a restoring force due to the main chain structure of the polymer. Recovery of rubber elasticity is promoted. In particular, this effect is noticeable in a region where the recovery rate of the seal reaction force is large.

  The diene content is more preferably 4% or more, and more preferably 7% or more. In addition, a polymer having a high molecular weight can be highly filled, and physical properties as a sealing member are not impaired even when a large amount of a softening agent or the like is contained. The molecular weight can be evaluated using Mooney viscosity as an index, and the Mooney viscosity is preferably 50 or more at 125 ° C. ML (1 + 4).

(B) Softening agent Polyalphaolefin, adipic acid ester, sebacate acid ester, phthalic acid ester or the like is used. As the softening agent, polyolefin, alkyl acid ester and the like having a pour point of −40 ° C. or lower (preferably −50 ° C. or lower) are preferable. Moreover, a thing with high purity is good. This is because when the purity is low and impurities include sulfur, phosphorus, metal, etc., the performance of the electrolyte membrane, catalyst, etc. used in the fuel cell stack may be degraded, and the cell performance may be degraded.

(C) Co-crosslinking agent A maleimide compound, an isocyanate compound, an isocyanurate compound, or the like is used. These are polyfunctional unsaturated compounds having two or more double bonds.

(D) Organic peroxide An organic peroxide having a one-minute half-life temperature of 160 ° C. or higher is used. The purity is desirably 95% or more. When there are many impurities, there exists a possibility of causing the deterioration of the electrolyte membrane used as an electrode or a catalyst.

  The blending amount of the organic peroxide is preferably 2 to 4 phr. If it is 2 phr or less, the number of crosslinking points is small, resulting in a decrease in the seal reaction force in a low temperature environment, and if it is 4 phr or more, it causes a decrease in the elongation at break of the rubber, so that cracking is likely to occur in a high temperature environment. .

(E) Thermoplastic resin component Polyethylene (PE), polypropylene (PP), polystyrene (PS), ABS, etc. are used for a thermoplastic resin component. These components have a softening point equal to or higher than the operating environmental temperature of the fuel cell. When the softening point is low, the rubber physical properties are lowered due to plasticization of the resin itself.

  Note that when the vulcanization density is increased in order to suppress crystallization of the polymer in a low temperature environment, the elongation is reduced, and in a high temperature environment, the polymer is cracked at high compression (40% or more). By adding the thermoplastic resin to the rubber in the range of 0.5 phr to 10 phr, cracking can be suppressed. 1 phr indicates an addition amount of 1 g per 100 g of the polymer. In addition, since the hydrocarbon type has a hydrophobic structure, it is possible to add hydrophobicity to the rubber material.

  Addition of a small amount of PE, PP, or other thermoplastic resin does not cause cross-linking inhibition, etc., and can prevent cracking during high compression, making it possible to achieve both sealing performance under low temperature and high compression environments. It is. The effect of the thermoplastic resin at the time of high compression is considered that the stress is relieved and cracking is prevented by microscopic plasticization by the pressure and temperature at the time of high compression. Therefore, it is possible to prevent cracking without reducing the vulcanization density.

  In addition, since the members in the fuel cell stack are exposed to water vapor generated by power generation for a long time, the physical properties of the rubber are reduced. Further, the water vapor may contain an acid caused by an electrolyte membrane, a catalyst or the like serving as an electrode. The presence of this acid promotes deterioration of the physical properties of the rubber. On the other hand, hydrocarbon-based thermoplastic resins such as PE, PP, and PS have a hydrophobic main chain and thus have an effect of preventing water vapor from entering the surface. Therefore, by adding a small amount of a hydrocarbon-based thermoplastic resin, it is possible to improve the water resistance of the rubber and suppress the deterioration of the rubber physical properties.

  The blending amount of the thermoplastic resin component is desirably 1 phr or more and 30 phr or less. By adding 1 phr or more of resin such as PP to the rubber, cracking can be suppressed. Addition of 20% or more reduces the elastic component of the rubber and is inferior in compression set characteristics in a long-term seal, so addition of 5 phr or more and 10 phr or less is preferable.

[Test sample]
In this example, comparative samples 1 to 5 and working samples 1 and 2 were prepared as samples. The components in Comparative Samples 1 to 5 and Working Samples 1 and 2 shown in FIG. 2 are as follows. Only the working samples 1 and 2 contain the thermoplastic resin component.

(A) Rubber component Polymers (1) to (5) in the figure correspond to the following EPDM (1) to (5), respectively.
EPDM (1): ethylene content 51%, diene content 3.5%,
Mooney viscosity 82.5ML125 ℃ (1 + 4)
EPDM (2): ethylene content 45%, diene content 7.6%,
Mooney viscosity 30.1ML125 ℃ (1 + 4)
EPDM (3): ethylene content 48%, diene content 4.1%,
Mooney viscosity 28.2ML125 ° C (1 + 4)
EPDM (4): ethylene content 48%, diene content 9.0%,
Mooney viscosity 68.3ML125 ° C (1 + 4)
EPDM (5): ethylene content 48%, diene content 9.0%,
Mooney viscosity 98.4ML125 ° C (1 + 4)
(B) Softener Adipic acid ester (pour point -63 ° C)
(C) Co-crosslinking agent triallyl isocyanurate (d) organic peroxide dicumyl peroxide (1 minute half-life temperature 175.2 ° C.)
(E) Reinforcing agent Carbon black: MAF
(F) Thermoplastic resin polypropylene (softening point 156 ° C.)

[Manufacturing method and evaluation method of seal for cryogenic and high compression for fuel cell]
<Method for producing rubber material>
The seal corresponding to cryogenic temperature and high compression is produced by crosslinking the rubber compositions containing the above (a) to (f) and various additives as required. The rubber composition may be adjusted as follows.

  First, materials other than (c) a co-crosslinking agent and (d) an organic peroxide are mixed with EPDM at a temperature equal to or higher than the melting point of the thermoplastic resin. The resulting mixture is cooled and (c) a co-crosslinking agent and (d) an organic peroxide are added. For adjusting the mixture, for example, a kneader usually used for kneading, such as a roll and a kneader, can be used. The adjusted rubber composition is heated and vulcanized by a method such as compression molding, injection molding, transfer molding, or the like, whereby a seal member can be obtained. For vulcanization, for example, primary vulcanization is performed at a temperature of about 150 to 170 ° C. for about 1 to 15 minutes. Further, secondary vulcanization is performed in an oven at a temperature of 100 to 150 ° C. for 1 to 4 hours as necessary.

<Low temperature elastic recovery test>
The low temperature elastic recovery test was conducted according to JIS K 6261 (2006). The TR test is a temperature shrinkage test. When a rubber to be tested is held at a low temperature in a stretched state, when the temperature is raised under a certain condition in an open state, the rubber molecules start to move gradually. The temperature at which 10% of the original extended value is recovered is referred to as TR10 value. FIG. 1 shows reference data (example) of the TR test. As an index for evaluating the low temperature property, in many cases, the TR10 value with a low recovery rate is often evaluated. However, in a region where the recovery rate is as small as about 10% (TR10) to 50% (TR50), the elasticity of rubber is not sufficiently exhibited, so that it is difficult to express the sealing performance. If TR70 is −40 ° C. or lower, rubber elasticity is maintained even at extremely low temperatures (−40 ° C. or lower), and sealing properties can be secured. FIG. 2 shows the temperatures of TR10, TR30, TR60, and TR70 in the low-temperature elastic recovery test.

<Compression cracking test>
The high compression seal was confirmed by crushing the test piece to a compression rate of 50%, leaving it at 110 ° C. for 504 h under pH 3 sulfuric acid immersion and pH 3 sulfuric acid vapor, and then checking for cracks after release. FIG. 2 shows the compression crack test results. In the table of FIG. 2, “OK” indicates no occurrence of cracking and “NG” indicates occurrence of cracking. The test results also show the results when left for 24h, 72h, 168h, and 336h. The jig used in the compression cracking test is shown in FIG. The test piece 50 is compressed while being sandwiched between the upper compression jig 30 and the lower compression jig 40.

<Immersion test>
For confirmation of water resistance, the immersion test in each aqueous solution was tested up to 90 ° C. × 168 h in accordance with JIS K6258 (2003), and various physical properties, hardness, tensile strength, elongation, volume and weight change rate were measured. FIG. 4 shows the immersion test results for Comparative Sample 5 and Working Sample 2.

[Confirmation of effect]
In the low temperature recovery test of the examples, it is preferable that the rubber elasticity recovery rate is 70% or more in order to exhibit sufficient sealing performance. Therefore, if the rubber material has a recovery rate of 70% or more in a -40 ° C environment, it is considered possible to seal at -40 ° C. It can be seen that the comparative samples 4 and 5 and the working samples 1 and 2 both achieved TR70 of −40 ° C. or less and achieved the target.

  Moreover, in the compression crack test result of FIG. 2, since the compression crack did not arise in the implementation samples 1 and 2 even after 504h, it turns out that the effect of the resin component has fully satisfy | filled performance. In Comparative Sample 5, TR70 was −46 ° C. and the performance in the low temperature elastic recovery test was satisfied, but in the compression cracking test, cracking occurred after 72 hours.

  Furthermore, from the results of the immersion test, it was confirmed that the effect of the thermoplastic resin not only plasticizes the rubber but also improves the water resistance of the rubber. In the result of FIG. 4, the comparative sample 5 has a large change rate of tensile strength and elongation after 168 h, and the physical properties are lowered, whereas the working sample 2 containing the thermoplastic resin has a decrease after 168 h. It can be seen that the rate of change in tensile strength and elongation is small.

  Therefore, according to the present example, by adding a small amount of thermoplastic resin, it is possible to prevent cracking of the rubber at the time of high compression without impairing the low temperature property of the rubber. It is possible to provide a fuel cell sealing composition that can be sealed with

10 cell 11 separator 12 gas diffusion layer 13 catalyst 14 electrolyte membrane 15 current collector plate 30 upper compression jig 40 lower compression jig 50 test piece

Claims (1)

(A) a rubber component selected from ethylene-propylene-diene rubber having a diene content of 7 wt% or more and an ethylene content of 50 wt% or less, and having a Mooney viscosity of 50 or more at ML (1 + 4) 125 ° C .;
(B) a co-crosslinking agent which is a polyfunctional unsaturated compound having two or more double bonds;
(C) an organic peroxide;
(D) a softener having a pour point of −40 ° C. or less;
(E) a thermoplastic resin;
(F) carbon black;
Containing
(E) the thermoplastic resin is a hydrocarbon-based thermoplastic resin;
(E) A sealing composition for a fuel cell, comprising a crosslinked rubber composition having a thermoplastic resin content of 1 phr to 30 phr.

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