JP2005285537A - Rubber gasket for fuel cell separator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber gasket for a fuel cell separator that has high sealing property, extractability, reaction force, durability and the like and can develop sufficient sealing property even at a low temperature of -30°C or lower. <P>SOLUTION: The rubber gasket for the fuel cell separator contains 10-100 pts. wt. of carbon black per 100 pts. wt. of hydrogenated nitrile rubber (HNBR) containing 15-30 wt% comprehensive acrylonitrile and 20 (mg/100 mg) or lower iodine number, and is cross-linked by organic peroxide. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a rubber gasket for a fuel cell separator that is excellent in cold resistance, sealability, extractability, reaction force, durability, and the like.

  A fuel cell is composed of an ion exchange membrane, a separator, a catalyst, and the like. A single cell is made of these constituent materials, and a plurality of single cells are stacked to form a fuel cell stack. A separator used in a fuel cell has a groove structure through which a gas such as hydrogen or oxygen or cooling water flows, and a rubber gasket for a fuel cell separator that seals the gas or cooling water is attached.

  Fuel cells have been developed as power sources for automobiles or households, and have reached a level where they can be put to practical use in general use environments, but for full-scale spread, they are durable and suitable for various environments. It is a situation where problems such as sex remain. Currently, long-term durability is being evaluated around the world. In particular, in cold districts such as Northern Europe and Hokkaido, there are places where the temperature is -30 ° C. or lower, and rubber gaskets used in fuel cells are required to have cold resistance.

  Conventionally, however, silicone rubber is used as the material for the rubber gasket for a fuel cell separator (see, for example, Patent Document 1, Patent Document 2, and Patent Document 3). There is a problem of reducing the power generation performance. Furthermore, although sulfur is generally used for rubber crosslinking, there is a problem that when sulfur is deposited, the power generation performance of the fuel cell is lowered, and rubber crosslinking with an organic peroxide that does not use sulfur is desired. Yes.

  The rubber gasket for the fuel cell separator is sandwiched between the fuel cell separators and is compressed to a certain thickness by the fuel cell separator. At that time, considering the variation in the thickness of the fuel cell separator and the gap into which the fuel cell separator rubber gasket enters, the compression rate of the fuel cell separator rubber gasket is 15 to 60%. If the compression ratio is high, the reaction force of the gasket (force to push back the separator in response to compression) becomes high, but if this reaction force is too high, a problem arises that the combustion battery separator breaks. In order to reduce the reaction force of the rubber gasket for the fuel cell separator, the gasket shape can be reduced, but this reduces the reaction force at high compression, but the reaction force at low compression becomes too small, and the seal This causes a problem that the performance decreases.

  Furthermore, EPDM or fluororubber is also used as a material for the rubber gasket for a fuel cell separator (see, for example, Patent Document 4). However, EPDM is excellent in cold resistance, heat resistance and the like, but has poor durability, particularly hydrofluoric acid resistance. For example, when it is immersed in a hydrofluoric acid solution at a compression rate of 60%, compression fracture occurs. Fluoro rubber is excellent in heat resistance and chemical resistance, but is generally expensive.

  HNBR with an acrylonitrile content of 30% or more is also used, but the rubber gasket for a fuel cell separator based on this has excellent heat resistance and durability, but the cold resistance is around -20 ° C. The temperature reaches a seal limit, and cannot be used in a temperature range of −30 ° C. or lower.

JP 11-179755 A JP 11-309747 A JP 2000-133288 A JP 2002-50369 A

  The present invention has been made in view of such circumstances, and is excellent in sealability, extractability, reaction force, durability, and the like, and for a fuel cell that can exhibit sufficient sealability even at a low temperature of −30 ° C. or lower. An object is to provide a rubber gasket for a separator.

  In order to achieve the above object, the present invention provides 10 to 100 per 100 parts by weight of hydrogenated nitrile rubber (HNBR) having a total acrylonitrile content of 15 to 30% by weight and an iodine value of 20 (mg / 100 mg) or less. Provided is a rubber gasket for a fuel cell separator, characterized by containing carbon black by weight and being crosslinked with an organic peroxide.

  According to the present invention, a rubber for a fuel cell separator having excellent sealing properties, extractability, reaction force, durability, etc., and also having cold resistance capable of exhibiting sufficient sealing properties even at a low temperature of -30 ° C. or lower. A gasket is provided.

  The first requirement of the present invention is to use HNBR having a total acrylonitrile content (AN amount) of 15 to 30% by weight and an iodine value of 20 (mg / 100 mg) or less as a base polymer. Examples of HNBR that satisfies such requirements include the following HNBR. Examples include “ZETPOL3110 (AN amount: 25%, iodine value 15)”, “ZETPOL3120 (AN amount: 25%, iodine value 28)”, “ZETPOL3310 (AN amount: 24%) manufactured by Nippon Zeon Co., Ltd. , Iodine value 15) "," ZETPOL4310 (AN amount: 19%, iodine value 15) "," ZETPOL4320 (AN amount: 19%, iodine value 27) "," Terban LTVPKA8882 "manufactured by Bayer. (AN amount 21%, iodine value 3 (calculated value)) "," Terban LTVPKA8886 (AN amount 21%, iodine value 14 (calculated value)) "," Terban LT2157 (AN amount 21%, iodine value 14) (Calculated value)) ”and the like, but are not limited thereto.

  As a cross-linking agent for HNBR, there is sulfur in addition to the organic peroxide. However, in a fuel cell, there is a problem that the power generation performance is reduced by sulfur. Therefore, an organic peroxide should be used for the cross-linking. A wide variety of known organic peroxides can be used. Examples include dicumyl peroxide (eg, “Park Mill D” manufactured by NOF Corporation), di-t-butylperoxydiisopropylbenzene (eg: “Perbutyl P” manufactured by NOF Corporation), 2,5- Dimethyl-2,5-di (t-butylperoxy) hexane (example: “Perhexa 25B” manufactured by Nippon Oil & Fats Co., Ltd.), di-t-hexyl dicumyl peroxide (example: “Perhexyl manufactured by Nippon Oil & Fats Co., Ltd.) D "), t-hexyl silk mill peroxide (example:" Perhexyl C "manufactured by NOF Corporation) and the like. Of these, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane is particularly preferable. Further, it is preferable to use a crosslinking aid in combination, for example, triallyl isocyanurate, trimethylolpropane trimethacrylate, polybutadiene, polyester having a double bond, polycyclooctene, isocyanuric acid EO-modified triacrylate, ditrimethylolpropane tetraacrylate. Dipentaerythritol polyacrylate can be used in combination.

  There is no restriction | limiting in particular in the quantity of a crosslinking agent and a crosslinking adjuvant, Those skilled in the art can determine arbitrarily according to the physical property intended, the kind of crosslinking agent, etc. However, usually about 0.1 to 10 parts by weight of a crosslinking agent and about 0.01 to 10 parts by weight of a crosslinking aid, more preferably about 0.5 to 7 parts by weight of crosslinking, with respect to 100 parts by weight of HNBR. And about 0.05 to 7 parts by weight of a crosslinking aid, particularly preferably about 1 to 5 parts by weight of a crosslinking agent and about 0.1 to 5 parts by weight of a crosslinking aid.

  The second requirement of the present invention is to blend 10 to 100 parts by weight of carbon black per 100 parts by weight of HNBR. Considering the reaction force, which is an important physical property item in the gasket of the fuel cell as described above, the reaction force can be suppressed when the hardness is low, so that it is necessary to select a formulation that does not increase the hardness.

  MT, FT, SRF, GPF, FEF, MAF, HAF, ISAF, etc. can be used as the carbon black used in the rubber material of the present invention, but MT, FT, SRF, etc. are used for reinforcement without increasing the hardness. Is suitable. Car black, especially MT, FT, and SRF are blended in an amount of 10 to 100 parts by weight per 100 parts by weight of HNBR. If the amount is less than 10 parts by weight, strength is difficult to develop and compression after immersion in hydrofluoric acid solution Permanent distortion may increase. If it exceeds 100 parts by weight, the hardness will increase. Preferably 15 to 90 parts by weight, more preferably 20 to 80 parts by weight, particularly preferably 25 to 70 parts by weight of carbon black is blended. In addition, when adding HNBR rubber with a low total acrylonitrile content, mechanical strength such as tensile strength and elongation is low only by adding MT, FT, etc., so it is preferable to use HAF, FEF, etc. in combination for improvement. Preferably, the carbon black is blended so that the sum of the filling amount (phr) / particle size (nm) ratio of each carbon black is 0.1 to 0.6, particularly 0.2 to 0.5. For example, 10 to 50 parts by weight of MT carbon black and 10 to 40 parts by weight of carbon black such as HAF and FEF are used in combination. If the amount of carbon black such as HAF or FEF is less than 10 parts by weight, the effect of improving the mechanical strength may be small, and if it exceeds 40 parts by weight, the reaction force of the rubber gasket for the fuel cell separator will increase. There is.

  As other additives, plasticizers can be added. At that time, it is necessary to select a plasticizer that improves the cold resistance and fluidity of the rubber material. Depending on the type and amount of the plasticizer, the compression set of the rubber gasket for a fuel cell separator may increase, resulting in deterioration of durability or the like, and conversely, durability may be improved. As the plasticizer used in the present invention, for example, sebacate-based plasticizers such as di- (2-ethylhexyl) sebacate, dioctyl sebacate and dibutyl sebacate are preferable. Also suitable are ester plasticizers such as phthalic acid diester, adipic acid diester, adipic acid ether ester, isophthalic acid diester, trimellitic acid triester. In particular, trimellitate plasticizers such as octyl trimellitate, isononyl trimellitate, isodecyl trimellitate, etc. have low volatility at high temperatures and have good heat resistance, and plastic gaskets for fuel cell separator rubber gaskets. Suitable for agents. In addition, polyether-based, polyether ester-based, and adipic acid polyether ester-based low-volatile plasticizers are preferably used. A plasticizer is used individually or in combination of 2 or more types from the above. The amount of plasticizer is suitably 2 to 10 parts by weight per 100 parts by weight of HNBR. When the amount of the plasticizer exceeds 10 parts by weight, the hydrofluoric acid resistance decreases. If it is less than 2 parts by weight, the fluidity of the material is lowered, and the moldability of the rubber is lowered. More preferably, 4 to 8 parts by weight of a plasticizer is used per 100 parts by weight of HNBR.

  If necessary, a suitable amount of a general-purpose rubber reinforcing filler such as silica or talc; a fiber reinforcing material such as glass fiber, carbon fiber, graphite fiber, aramid fiber, or polyester fiber may be blended.

  Furthermore, an appropriate amount of optional additives such as anti-aging agents, fillers such as clay minerals, pigments, dispersants, coupling agents, compatibilizers, flame retardants, surface smoothing agents, processing aids, etc. may be added. it can.

  Each of the above materials is kneaded by, for example, a two-roll, a Banbury mixer, a pressure kneader, an extruder, or the like to be a material for molding a rubber gasket for a fuel cell separator. Moreover, after dissolving each material in a solvent, you may mix. The obtained molding material is then cross-linked to form a rubber gasket for a fuel cell separator having a desired shape, such as an O-ring, V-ring, rod-like, sheet-like, block-like, or other complex-shaped gasket. The crosslinking conditions for molding are arbitrary, and can be set according to the raw materials to be used and the intended cross-linking properties. For example, heating is performed at a temperature of about 100 to 200 ° C. for about 1 to 120 minutes. Depending on conditions, secondary cross-linking may be performed at about 100 to 200 ° C. for 1 to 24 hours. The secondary cross-linking method is also arbitrary, and various conventional cross-linking methods such as press cross-linking, vapor cross-linking, hot air cross-linking, and radiation cross-linking can be employed. Before forming the rubber gasket for a fuel cell separator, it is preferable that a primer is applied to the fuel cell separator and heated at a temperature of 150 to 200 ° C. for about 1 to 30 minutes. As the primer, epoxy resin, phenol resin, silicone or the like can be used.

  The rubber gasket for a fuel cell separator obtained as described above exhibits excellent cold resistance in addition to low pressure and high durability, and is suitable as a rubber gasket for a fuel cell separator for automobiles or households. Specifically, TR10 as a result of the low temperature elastic recovery test according to JIS K6261 is −30 ° C., particularly −35 ° C. or less. Therefore, fuel or the like can be sufficiently sealed at these temperatures.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example at all.

[Examples 1-6, Comparative Examples 1-5]
The compounding agents shown in Table 1 were roll-kneaded according to a conventional method. The raw materials used are as follows:
HNBR-1: “ZETPOL4310 (total acrylonitrile content 19 wt%, iodine value 15)” manufactured by Nippon Zeon Co., Ltd.
HNBR-2: “ZETPOL3310 (total acrylonitrile content 24 wt%, iodine value 15)” manufactured by Nippon Zeon Co., Ltd.
HNBR-3: “ZETPOL2020L (total amount of acrylonitrile 36 wt%, iodine value 28)” manufactured by Nippon Zeon Co., Ltd.
Silicone: Dimethyl silicone rubber (platinum catalyst additive) manufactured by Shin-Etsu Chemical Co., Ltd.
EPDM: “EP33” manufactured by JSR Corporation
Peroxide-1: NOF Corporation “Perhexa 25B (2,5-dimethyl-2,5-di (t-butylperoxy) hexane)”
Peroxide-2: “Perhexyl C (t-hexyl mill peroxide)” manufactured by NOF Corporation
Crosslinking aid-1: “NK Ester A-9300 (isocyanuric acid EO-modified triacrylate)” manufactured by Shin-Nakamura Chemical Co., Ltd.
Crosslinking aid-2: “TAIC (triallyl isocyanurate)” manufactured by Nippon Kasei Co., Ltd.
Anti-aging agent-1: “NOCRACK CD (4,4′-bis (α, α-dimethylbenzyl) diphanylamine)” manufactured by Ouchi Shinsei Chemical Co., Ltd.
Anti-aging agent-2: “NOCRACK MB (2-mercaptobenzimidazole)” manufactured by Ouchi Shinsei Chemical Co., Ltd.
Processing aid-1: Stearic acid processing aid-2 made by Shin Nippon Rika Co., Ltd .: "Stractol WB222" made by S & S Japan Ltd.
Plasticizer-1: “C-9N (isononyl trimellitate)” manufactured by Asahi Denka Kogyo Co., Ltd.
Plasticizer-2: "TP-95 (Diester)" manufactured by Morton International
Filler-1 (carbon black): “N-990MT” manufactured by CANCARB
Filler-2 (carbon black): “Asahi # 60” manufactured by Asahi Carbon Co., Ltd.
Filler-3 (carbon black): “Asahi # 50G” manufactured by Asahi Carbon Co., Ltd.

  The obtained kneaded material was re-kneaded after several hours and then cross-linked by hot pressing to form a sheet (150 × 150 × 2 t) and a Φ30 test piece (gasket) having the cross-sectional shape shown in FIG. The illustrated .PHI.30 test piece 1 is formed by laminating and integrating two peaks 2 and 3. The dimensions of each part are as shown in Table 2.

About the sheets and test pieces of Examples 1 to 4 and Comparative Examples 1 to 7, the physical properties such as hardness, compression set, tensile strength, elongation, cold resistance, stain resistance, reaction force, sealing properties, and gasket destruction are visually observed. Evaluation was performed. The evaluated items are described below, and the results are also shown in Table 1.
<Hardness>
Measurement was performed using a micro hardness meter MD-1 manufactured by Kobunshi Keiki Co., Ltd.
<Compression set>
According to JIS K6262, the measurement was performed at 150 ° C. for 22 hours.
<Tensile strength / elongation>
Measured according to JIS K6251 (Test piece is No. 5 dumbbell, tensile speed is 500 mm / min).
<Cold resistance>
The temperature of TR10 was used for evaluation of cold resistance. TR10 conformed to JIS K6261 (low temperature elastic recovery test).
<Mooney viscosity>
Measured according to JIS K6300.
<Contamination>
An LLC solution (1: 1 = pure water: ethylene glycol) was immersed in 90 ° C. for 2000 hours, and the amount of extract of the extract was measured by ICP analysis for evaluation. A sample with a large amount of extraction was designated as “×”, and a sample with a small amount of extraction as “◯”.
<Reaction force>
The reaction force of the Φ30 test piece was measured using a compression / tensile tester. When the reaction force when compressed to 60% was 8 N / mm or more, “X” was given, 5-8 N / mm was given as “Δ”, and 5 N / mm or less was given as “◯”.
<Sealability>
A Φ30 test piece was set on the flange, tightened to a low compression of 15%, and submerged together with the flange. Φ30 test piece that generates bubbles when nitrogen gas is loaded at 0.1 MPa “×”, those that generate bubbles when loaded at 0.3 MPa “△”, those that do not generate bubbles when loaded at 0.5 MPa “○”.
<Sealability after endurance>
A Φ30 test piece was evaluated by a sealing property after immersion in a hydrofluoric acid solution (added sulfuric acid so that the hydrofluoric acid was 3000 ppm and pH = 2) and 90 ° C. × 280 hours. The evaluation criteria are the same as above.
<Gasket destruction>
The appearance of the Φ30 test piece after immersion in a hydrofluoric acid solution used for sealing performance after durability was observed. Those with destruction were marked with “×”, those with little destruction “△”, and those without destruction with “◯”.

  As shown in Table 1, the silicone rubber composition product of Comparative Example 1 has poor contamination and does not have the durability of the hydrofluoric acid solution. As shown in Comparative Example 2, the EPDM composition product is also not durable to a hydrofluoric acid solution.

  In addition, as shown in Comparative Examples 3 to 5, the composition using HNBR-3 having an overall acrylonitrile amount of 36% and an iodine value of 28 is satisfactory in items other than cold resistance, but the temperature of TR10 is -20. It is around ℃. By adding a plasticizer, cold resistance is improved, but when 10 parts by weight of a plasticizer is added, durability (hydrofluoric acid resistance) is lowered. When HNBR-3 is used, it is estimated that it cannot be used in a temperature range of −30 ° C. or lower.

  Further, as shown in Example 1, Example 4, Example 5 and Example 6, the compound using HNBR-1 having a total acrylonitrile amount of 19% and an iodine value of 15 is 30% by weight of carbon black MT. By using together the reinforcing carbon black FEF in the part, the mechanical strength is increased, and problems such as gasket breakage are improved. On the other hand, when it adds to 40 weight part, hardness and reaction force will become high.

  Moreover, as shown in Example 2, the blending of 5 parts by weight of a plasticizer with respect to Example 1 does not deteriorate the physical properties and has a low Mooney viscosity. Since the fluidity is improved, the productivity is estimated to be good.

  Further, as shown in Example 3, when SRF is used as an alternative to carbon black MT, mechanical strength can be obtained independently without using FEF.

It is a figure which shows the cross-sectional shape of the test piece used in the Example.

Claims (4)

  10-100 parts by weight of carbon black per 100 parts by weight of hydrogenated nitrile rubber (HNBR) having a total acrylonitrile content of 15-30% by weight and an iodine value of 20 (mg / 100 mg) or less, and organic peroxidation A rubber gasket for a fuel cell separator, characterized by being crosslinked with a product.   2. The rubber gasket for a fuel cell separator according to claim 1, comprising 2 to 10 parts by weight of a plasticizer per 100 parts by weight of the hydrogenated nitrile rubber (HNBR).   The rubber gasket for a fuel cell separator according to claim 1 or 2, wherein two or more types of carbon black are blended.   4. The rubber gasket for a fuel cell separator according to claim 1, wherein a TR10 value in a TR test according to JIS K6261 is −30 ° C. or less. 5.

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