High-heat-resistant fuel cell flexible graphite bipolar plate pore sealing agent

Abstract

The application discloses a high-heat-resistant fuel cell flexible graphite bipolar plate micropore plugging agent, which comprises 30-50 parts of organic silicon double end cap agent with two (methyl) acryloyloxy groups at each end, 50-70 parts of high-Tg methacrylate monomer, 0.5-2 parts of leveling agent and 0.2-1.0 parts of free radical thermal initiator, and the total amount of the organic silicon double end cap agent and the high-Tg methacrylate monomer is 100 parts by weight. The plugging agent has excellent ethylene glycol resistance due to the organic silicon structure, the organic silicon double end cap agent has four (methyl) acryloyloxy groups capable of free radical polymerization on each molecule, the crosslinking density is high, and after copolymerization with the high-Tg methacrylate monomer, the plugging agent has high heat resistance, low curing shrinkage and small residual stress, and is beneficial to keeping the bipolar plate to have good bending strength at high temperature.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of hydrogen fuel cells, and particularly relates to a heat-cured micro-pore plugging agent for flexible graphite bipolar plates of hydrogen fuel cell stacks. BACKGROUND

[0002] Fuel cell bipolar plates are the core structural support of hydrogen fuel cell stacks, and are divided into metal bipolar plates and graphite bipolar plates. Graphite bipolar plates are widely used in fuel cell stacks of commercial vehicles due to the advantages of easy availability of raw materials, low cost, good chemical corrosion resistance, and long service life. However, flexible graphite plates have a micro-porous structure and must be treated with a plugging agent for impregnation to ensure the gas tightness of the bipolar plate. After the plugging agent is cured, it must also impart sufficient mechanical strength, chemical resistance (mainly resistance to ethylene glycol) and long-term heat resistance to the flexible graphite plate.

[0003] Flexible graphite bipolar plates generally use (meth) acrylate monomers compounded into an impregnation resin solution as a plugging agent (referring to Chinese Patent CN 107706430B). Before use, a free radical thermal initiator is added, the flexible graphite plate is impregnated in the plugging agent, and vacuum or pressurized impregnation is performed to allow the plugging agent molecules to penetrate into the micro-pores of the flexible graphite bipolar plate. Then, the surface of the bipolar plate is cleaned to prevent the plugging agent from affecting the electrical conductivity of the graphite after it is cured on the surface of the bipolar plate. After that, the bipolar plate is heated and cured in a water bath, and the plugging agent forms a dense network structure after curing, thereby imparting gas tightness, compressive strength, chemical resistance and heat resistance to the bipolar plate.

[0004] After the flexible graphite bipolar plate is assembled into a stack, it must be able to withstand long-term exposure to ethylene glycol aqueous solution cooling medium at a temperature of 80-95℃ during fuel cell operation. The (meth) acrylate polymer has some solubility in ethylene glycol, which causes the plugging agent of the bipolar plate to partially dissolve in the ethylene glycol during long-term operation of the fuel cell, resulting in pore cracks and gas leakage and failure.

[0005] The Tg of the methacrylate polymer or copolymer mentioned in Chinese Patent CN 107706430B is relatively low, and few components have a Tg exceeding 100℃. The Tg of long-chain alkyl acrylate polymers is even below zero degrees, and the graphite bipolar plate has a significantly reduced bending strength in the rubber state at the operating temperature of the fuel cell, making it difficult to meet the stringent requirements for stable operation of hydrogen fuel cell vehicles at high temperatures. SUMMARY

[0006] The purpose of the present application is to provide a high-heat-resistant fuel cell flexible graphite bipolar plate micro-pore plugging agent.

[0007] The technical solution to achieve the purpose of the present application is as follows:

[0008] The first aspect, the present application provides a kind of high heat-resistant fuel cell flexible graphite bipolar plate micropore plugging agent, comprising: 30-50 weight parts two ends each with two (meth) acryloyloxy organic silicon double end cap agent and 50-70 weight parts high Tg methacrylate monomer, the total of both is 100 weight parts, and 0.5-2 weight parts leveling agent and 0.2-1.0 weight parts radical thermal initiator;

[0009] Wherein, the two ends each with two (meth) acryloyloxy organic silicon double end cap agent has the following structure:

[0010]

[0011] Wherein, R1 represents methyl or hydrogen atom.

[0012] Preferably, the synthesis method of two ends each with two (meth) acryloyloxy organic silicon double end cap agent, comprising:

[0013] First step: using hydrogen-containing double end cap and allyl glycidyl ether in the presence of platinum gold catalyst carries out silicon hydrogen addition reaction, generates the step of two ends each containing one epoxy group double end cap agent,

[0014]

[0015] Second step: the double end cap agent of two ends each containing one epoxy group and excess (meth) acrylic acid are carried out ring-opening esterification in the presence of ring-opening esterification catalyst, and the step of obtaining two ends each with one (meth) acryloyloxy and hydroxyl group double end cap agent,

[0016]

[0017] Wherein, R1 represents methyl or hydrogen atom.

[0018] Third step: the double end cap agent of two ends each with one (meth) acryloyloxy and hydroxyl group and excess (meth) acrylic acid are carried out esterification dehydration reaction in the presence of cyclohexane water agent and acid catalyst, generates the double end cap agent of two ends each containing two (meth) acryloyloxy,

[0019]

[0020] Specifically, in order to prevent (meth) acrylic acid self-polymerization during (meth) acrylate dehydration reaction, it is necessary to add radical polymerization inhibitor in esterification dehydration reaction, and the amount of addition is 0.01%~1% of the total mass of reactant.

[0021] More specifically, the radical polymerization inhibitor is any one or more than two of p-methoxyphenol, hydroquinone, 2,5-dimethyl hydroquinone, 2,6-di-tert-butyl-4-methylphenol.

[0022] Specifically, the open ring esterification catalyst is selected from any one of tertiary amine, quaternary ammonium salt, commonly used triethylamine, N, N-dimethyl benzylamine, N, N-dimethyl aniline, trimethyl benzyl ammonium chloride, triphenyl phosphine, triphenyl antimony, chromium acetylacetone, chromium iso-octanoate, stannous octoate, tetraethyl ammonium bromide, etc., and the amount of the catalyst is 0.1% to 5.0% of the reactants.

[0023] Specifically, the acid catalyst is selected from any one of concentrated sulfuric acid, sodium bisulfate, methyl sulfonic acid, methyl benzene sulfonic acid, trifluoromethanesulfonic acid, strong acid ion exchange resin and solid super acid, and preferably any one of methyl sulfonic acid, trifluoromethanesulfonic acid, strong acid ion exchange resin and solid super acid, and the amount of the catalyst is 0.1% to 5.0% of the total mass of the reactants.

[0024] Preferably, the high Tg methacrylate monomer is selected from any one of isobornyl (meth)acrylate, o-phenylphenoxyethyl (meth)acrylate, benzyl (meth)acrylate, phenyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, tricyclodecanyl (meth)acrylate, dicyclopentadiene (meth)acrylate, (meth)acryloyl morpholine and N, N-dimethyl acrylamide, etc. Based on the comprehensive consideration of heat resistance and low viscosity, isobornyl (meth)acrylate, dicyclopentadiene (meth)acrylate or tricyclodecanyl methacrylate is preferred.

[0025] Preferably, the leveling agent can be any leveling agent that has a wetting effect on the flexible graphite bipolar plate, and the amount of the leveling agent can be determined according to the impregnation amount of the flexible graphite bipolar plate after impregnation. The higher the impregnation amount, the better the effect of the leveling agent. Preferably, the leveling agent is BYK-333 or BYK-3505 from BYK Germany, and a high-molecular-weight super dispersant such as CH-1, CH-2, CH-3, CH-5, CH-6, CH-7, CH-8, CH-9, etc.

[0026] Preferably, the free radical thermal initiator is selected from an initiator with a decomposition temperature of 80 to 95°C, and an azo and peroxide free radical thermal initiator is preferred. Preferably, the free radical thermal initiator is azobisisobutyronitrile, azobisisoheptyl nitrile or benzoyl peroxide.

[0027] Preferably, various antioxidants, anti-aging agents, fluorescent agents, etc. can be added to the composition based on the consideration of weather resistance, heat resistance and fluorescent identification.

[0028] Compared with the prior art, the present application has the following advantages:

[0029] (1) One of the components of the flexible graphite bipolar plate plugging agent composition of the present application, the organic silicon double end cap agent with two (methyl) acryloyloxy groups at both ends, has excellent ethylene glycol resistance due to the hydrophobic and oleophobic properties and low surface tension of the organic siloxane structure, and will not swell or dissolve in contact with ethylene glycol aqueous solution at high temperature for a long time, and is particularly suitable for use in the micropore plugging of flexible graphite bipolar plates for hydrogen fuel cells.

[0030] (2) One of the components of the flexible graphite bipolar plate plugging agent composition of the present application, the organic silicon double end cap agent compound with two (methyl) acryloyloxy groups at both ends, contains 4 (methyl) acryloyloxy groups that can be free radical polymerized on each molecule, and after copolymerization with high Tg methacrylate monomers, has high heat resistance, and also has low curing shrinkage and small residual stress, which is beneficial to the bipolar plate to maintain good bending strength at high temperature. DETAILED DESCRIPTION

[0031] The present application will be described in detail below with reference to examples.

[0032] The (methyl) acrylate monomer has the advantages of low viscosity, strong permeability, and low curing temperature, and is the preferred compound for fuel cell graphite bipolar plate micropore plugging agent. Compared with acrylate compounds, methacrylate compounds are easier to undergo free radical thermal curing reaction, and the cured product has a higher Tg (glass transition temperature), that is, has higher heat resistance, so most commercial micropore plugging agents use methacrylate monomers as the main component. However, after polymerization of methacrylate monomers, very few have a Tg exceeding 100℃, and the heat resistance is not as good as that of epoxy resin cured products. Also, due to the low crosslinking density and the presence of a large number of polar ester bonds, the resistance to ethylene glycol is not good enough.

[0033] The present application introduces a tetrafunctional monomer containing a methylsiloxane structure, which has high Tg and excellent ethylene glycol resistance.

[0034] The organic silicon double end cap agent with two (methyl) acryloyloxy groups at both ends of the present application first undergoes a silicon-hydrogen addition reaction with a hydrogen-containing double end cap and AGE (allyl glycidyl ether) in the presence of platinum gold catalyst to form a double end cap compound containing one epoxy group at both ends, then undergoes an epoxy ring-opening reaction with excess (methyl) acrylate in the presence of a catalyst, and the generated hydroxyl group further undergoes an esterification and dehydration reaction with excess (methyl) acrylate and cyclohexane water-carrying agent in the presence of an acid catalyst to form a double end cap compound with two (methyl) acryloyloxy structures at both ends.

[0035] In the examples, the specific conditions are not specified, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be purchased on the market.

[0036] Synthesis of epoxy-terminated sealant.

[0037] A three-necked glass flask with oil bath and condenser was charged with 160 g of allyl glycidyl ether (AGE) and 0.01 g of chloroplatinic acid, stirred and heated to 70°C, and 100 g of hydrogen-containing sealant (1,1,3,3-tetramethyldisiloxane) was added dropwise over one hour. The temperature was then raised to 80°C and the reaction was continued for 4 hours. The unreacted hydrogen-containing sealant was removed by vacuum distillation, and a colorless transparent sealant with two epoxy groups at each end (referred to as epoxy-terminated sealant) was obtained, with a molecular weight of 362.7.

[0038] Synthesis of hydroxyacryloyloxy-terminated sealant.

[0039] A three-necked glass flask with oil bath and condenser was charged with 100 g of epoxy-terminated sealant, 0.5 g of triethylamine, and 0.05 g of MeHQ radical inhibitor, stirred and heated to 70°C, and 50 g of acrylic acid was added dropwise over one hour. The temperature was then raised to 80°C and the reaction was continued for 6 hours. Excess sodium carbonate was added to neutralize the residual acrylic acid and triethylamine, and the precipitate was filtered and washed with water several times. The product, a light yellow transparent sealant with one hydroxyl group and one acryloyloxy group at each end (referred to as hydroxyacryloyloxy-terminated sealant), was obtained after vacuum drying, with a molecular weight of 506.8.

[0040] Synthesis of diacryloyloxy-terminated sealant-1.

[0041] A three-necked glass flask with oil bath and condenser was charged with 100 g of hydroxyacryloyloxy-terminated sealant, 0.05 g of MeHQ radical inhibitor, 0.05 g of BHT radical inhibitor, 0.5 g of triflic acid, and 100 g of cyclohexane as a water-carrying agent, stirred and heated to 85°C to reflux, and 35 g of acrylic acid was added dropwise over one hour. The water produced was periodically removed with a separatory funnel, and the reaction was considered complete when no more water was distilled out. The temperature was then lowered to room temperature, and excess sodium carbonate was added to neutralize the residual acrylic acid and triflic acid. The precipitate was filtered and washed with water several times. The product, a light yellow transparent sealant with two acryloyloxy groups at each end (referred to as diacryloyloxy-terminated sealant), was obtained after vacuum drying, with a viscosity of 393 mPas and a molecular weight of 614.9.

[0042] Synthesis of hydroxymethacryloyloxy-terminated sealant.

[0043] Into a three-necked glass flask with oil bath and condenser, add 100 g of epoxy di-capper, 0.5 g of triethylamine, 0.05 g of MeHQ radical inhibitor, and stir to heat to 70°C. Add 60 g of acrylic acid dropwise over one hour, then heat to 80°C and continue to react for 6 hours. Add excess sodium carbonate to neutralize the residual acrylic acid and triethylamine, precipitate and filter, wash with water several times, and then vacuum dry to obtain a yellowish transparent di-capper with a hydroxyl group and a methacryloyloxy group at each end (referred to as hydroxyl methacryloyloxy di-capper), with a molecular weight of 534.8.

[0044] Synthesis of methacryloyloxy di-capper-2.

[0045] Into a three-necked glass flask with oil bath and condenser, add 100 g of hydroxyl methacryloyloxy di-capper, 0.05 g of MeHQ radical inhibitor, 0.05 g of BHT radical inhibitor, 0.5 g of trifluoromethanesulfonic acid, and 100 g of cyclohexane water-carrying agent, and stir to heat to 85°C to reflux. Add 42 g of methacrylic acid dropwise over one hour, and periodically remove the water carried out with a separatory funnel. Carefully observe the amount of water trapped in the separatory funnel until no more water is distilled out, which indicates that the reaction is complete. Cool to room temperature, add excess sodium carbonate to neutralize the residual acrylic acid and trifluoromethanesulfonic acid, precipitate and filter, wash with water several times, and then vacuum dry to obtain a yellowish transparent di-capper with two methacryloyloxy groups at each end (referred to as methacryloyloxy di-capper), with a viscosity of 402 mPas and a molecular weight of 642.9.

[0046] The sealant formulations in the examples and comparative examples are mixed and stirred until the solid substances are dissolved into transparent liquids.

[0047] The formulations of the examples and comparative examples are as shown in Table 1 below.

[0048] Table 1

[0049] Example-1 Example-2 Example-3 Example-4 Example-5 Comparative Example-1 Comparative Example-2 Comparative Example-3 Bisacryloyloxy bis-capper-1 30 45 35 10 Bismethacryloyloxy bis-capper-2 40 35 Isobornyl acrylate 70 90 Isobornyl methacrylate 60 55 50 50 Bicyclopentadiene acrylate 65 Tricyclodecanyl methacrylate 65 50 Dipropylene glycol diacrylate 50 Azobisisobutyronitrile thermal initiator 0.5 0.5 0.5 0.5 05 Benzoyl peroxide thermal initiator 0.5 0.5 0.5 BYK-333 leveling agent 1.0 1.0 1.0 1.0 1.0 1.0 BYK-3505 leveling agent 1.0 1.0 Tg (DMA, tan delta peak) °C 123 171 146 168 179 106 166 89 Ethylene glycol resistance ○ ◎ ◎ ◎ ◎ △ × ×

[0050] The evaluation method for ethylene glycol resistance is as follows:

[0051] Pour 10 g of the sealant into a Teflon mold with a diameter of 4.0 cm and a height of 2.0 cm, place it in a 80°C drying oven for 2 hours, and then heat it to 120°C for another 2 hours to obtain a colorless transparent cylindrical cured product. Place the cylindrical cured product in a glass bottle containing 50% wt ethylene glycol aqueous solution, seal it, and place it in a 90°C oven for 1000 hours. Take it out and observe the solubility of the cured product and the turbidity of the ethylene glycol aqueous solution to evaluate the ethylene glycol resistance of the sealant.

[0052] The ethylene glycol resistance is divided into four grades:

[0053] 1. Excellent (Cured product intact, no foreign matter and no turbidity in the glycol aqueous solution)

[0054] 2. Good (Cured product has no obvious dissolution, and the glycol aqueous solution is slightly turbid)

[0055] 3. Fair (Cured product has obvious dissolution, and the glycol aqueous solution becomes turbid)

[0056] 4. Very poor (Cured product has swelling and dissolution, and the glycol aqueous solution is very turbid)

[0057] According to Table 1, by comparing Example 1 and Comparative Example 1, it is found that the addition amount of the diacryloyloxy double blocking agent has a crucial influence on the glycol resistance, and the addition amount of the diacryloyloxy double blocking agent needs to be more than 30 phr (Parts per hundred) to achieve good resistance, and when the addition amount of the diacryloyloxy double blocking agent is 10 phr, the cured product has obvious dissolution after aging, the glycol aqueous solution becomes turbid, and the Tg of the obtained cured product is also relatively low, and the heat resistance is also poor.

[0058] The composition of Comparative Example 2 is all high-Tg methacrylate, and the Tg of the cured product is relatively high, but because it does not contain organosiloxane structure, the glycol resistance is poor, the cured product has swelling and dissolution after aging, and the glycol aqueous solution is very turbid.

[0059] Comparative Example 3 contains low-Tg di-functional acrylate in the formula, and the Tg of the obtained cured product is relatively low, the heat resistance is poor, the glycol resistance is also relatively poor, the cured product has swelling and dissolution after aging, and the glycol aqueous solution is also very turbid.

Claims

1. A high-heat-resistant fuel cell flexible graphite bipolar plate micropore plugging agent, characterized in that, Comprising: 30~50 parts by weight of a silicone double end-capper with two (meth) acryloyloxy groups at each end and 50~70 parts by weight of a high Tg methacrylate monomer, the total of which is 100 parts by weight, and 0.5~2 parts by weight of a leveling agent and 0.2~1.0 parts by weight of a free radical thermal initiator; Wherein, the silicone double end-capper with two (meth) acryloyloxy groups at each end has the following structure: ； Wherein, R1 represents a methyl group or a hydrogen atom.

2. The lost circulation material of claim 1, wherein, The silicone double end-capper with two (meth) acryloyloxy groups at each end is prepared by the following steps: First step: a silicon-hydrogen addition reaction is carried out with a hydrogen-containing double end-capper and an allyl glycidyl ether in the presence of a platinum gold catalyst to generate a double end-capper with one epoxy group at each end, ； Second step: a ring-opening esterification reaction is carried out with the double end-capper with one epoxy group at each end and excess (meth) acrylic acid in the presence of a ring-opening esterification catalyst to obtain a double end-capper with one (meth) acryloyloxy group and one hydroxyl group at each end, ； Wherein, R1 represents a methyl group or a hydrogen atom. Third step: an esterification and dehydration reaction is carried out with the double end-capper with one (meth) acryloyloxy group and one hydroxyl group at each end and excess (meth) acrylic acid in the presence of a cyclohexane water-carrying agent and an acidic catalyst to generate a double end-capper with two (meth) acryloyloxy groups at each end, 。 3. The lost circulation material of claim 2, wherein, A free radical polymerization inhibitor is added in the esterification and dehydration reaction, and the amount of addition is 0.01%~1% of the total mass of the reactants.

4. The lost circulation material of claim 3, wherein, The free radical polymerization inhibitor is any one or more of p-methoxyphenol, hydroquinone, 2,5-dimethyl hydroquinone, and 2,6-di-tert-butyl-4-methylphenol.

5. The lost circulation material of claim 2, wherein, The ring-opening esterification catalyst is any one of a tertiary amine, a quaternary ammonium salt, triphenylphosphine, triphenylantimony, chromium acetylacetone, chromium iso-octoate, and stannous octoate, and the amount of use is 0.1%~5.0% of the reactants.

6. The lost circulation material of claim 2, wherein, The acidic catalyst is any one of concentrated sulfuric acid, sodium bisulfate, methylsulfonic acid, methylbenzenesulfonic acid, triflic acid, a strongly acidic ion exchange resin, and a solid superacid, and the amount of addition is 0.1%~5.0% of the total mass of the reactants.

7. The lost circulation material of claim 2 or 6, wherein, The acidic catalyst is any one of methylsulfonic acid, triflic acid, a strongly acidic ion exchange resin, and a solid superacid.

8. The lost circulation material of claim 1, wherein, The high Tg methacrylate monomer is any one of isobornyl methacrylate, o-phenylphenoxyethyl methacrylate, benzyl methacrylate, phenyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, tricyclodecane methacrylate, and dicyclopentadiene methacrylate.

9. The lost circulation material of claim 1 or 8, wherein, The high Tg methacrylate monomer is any one of isobornyl methacrylate, dicyclopentadiene methacrylate, or tricyclodecane methacrylate.

10. The lost circulation material of claim 1, wherein, The leveling agent is any one of Germany BYK leveling agent BYK-333, BYK-3505, and tri-normal high molecular super dispersant CH-1, CH-2, CH-3, CH-5, CH-6, CH-7, CH-8, and CH-9.

11. The lost circulation material of claim 1, wherein, The free radical thermal initiator is an azo or peroxide free radical thermal initiator with a decomposition temperature of 80~95℃.

12. The lost circulation material of claims 1 or 11, wherein, The free radical thermal initiator is any one of azobisisobutyronitrile, azobisisoheptyl nitrile or benzoyl peroxide.

13. The lost circulation material of claim 1, wherein, The plugging agent also comprises any one or several of the anti-aging agent or the fluorescent agent.

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