High-Tg flexible graphite bipolar plate micropore plugging agent

Abstract

The invention discloses a high-Tg flexible graphite bipolar plate micropore plugging agent which comprises the following components in parts by weight: 20-30 parts of epoxy cyclohexyl ethyl cyclotetrasiloxane, 70-80 parts of oxetane or alicyclic epoxy resin, 0.1-2.0 parts of a cationic thermal initiator and 0.5-2 parts of a flatting agent, and the sum of the parts by weight of the epoxy cyclohexyl ethyl cyclotetrasiloxane and the oxetane or alicyclic epoxy resin is 100. The flexible graphite bipolar plate plugging agent has excellent ethylene glycol resistance due to an organosiloxane structure, and each molecule of epoxy cyclohexyl ethyl cyclotetrasiloxane contains four epoxy groups capable of being subjected to cationic curing, so that after curing, the flexible graphite bipolar plate plugging agent is high in crosslinking density, good in heat resistance, low in curing shrinkage rate and small in residual stress; compared with a (methyl) acrylate plugging agent, the plugging agent has higher bending strength.

Description

Technical Field

[0001] The invention belongs to the field of hydrogen fuel cells, and in particular relates to a thermally cured microporous plugging agent for a flexible graphite bipolar plate of a hydrogen fuel cell stack. Background Art

[0002] Fuel cell bipolar plates are the core structural support components of hydrogen fuel cell stacks, and are divided into metal bipolar plates and graphite bipolar plates. Graphite bipolar plates are widely used in commercial vehicle fuel cell stacks because of their easy availability of raw materials, low cost, good chemical corrosion resistance, and long life. However, the flexible graphite plate itself has a microporous structure and must be impregnated with a plugging agent to ensure the airtightness of the bipolar plate. At the same time, after the plugging agent is cured, the flexible graphite plate must be given sufficient mechanical strength, chemical resistance (mainly ethylene glycol resistance) and long-term heat resistance.

[0003] Flexible graphite bipolar plates generally use (meth) acrylate monomers to compound into impregnated resin liquid as plugging agent (refer to Chinese patent CN 107706430B). Free radical thermal initiator is added before use, and the flexible graphite plate is impregnated in the plugging agent, and vacuum or pressure impregnation is performed to allow the plugging agent molecules to penetrate into the micropores of the flexible graphite bipolar plate, and then the plugging agent remaining on the surface of the bipolar plate is cleaned to prevent the plugging agent from affecting the conductivity of graphite after curing 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 giving the bipolar plate air tightness, bending strength, chemical resistance and heat resistance.

[0004] After the flexible graphite bipolar plates are assembled into a fuel cell stack, they will be in contact with an ethylene glycol aqueous solution cooling medium at a temperature of 80 to 95°C for a long time during the operation of the fuel cell. They need to have resistance to the long-term high temperature of the ethylene glycol aqueous solution. (Meth)acrylate polymers have a certain solubility in ethylene glycol. As a result, after the fuel cell has been running for a long time, the bipolar plate plugging agent is partially dissolved in ethylene glycol, resulting in holes and cracks, which lead to gas leakage and failure.

[0005] In addition, the Tg of the methacrylate polymer or copolymer mentioned in Chinese patent CN 107706430B is relatively low, and there are few components with a Tg exceeding 100°C. The Tg of the long-chain alkyl acrylate polymer is even lower than zero degrees, and it is in a rubbery state at the operating temperature of the fuel cell. The bending strength of the graphite bipolar plate is greatly reduced, and it is difficult to meet the stringent requirements of hydrogen fuel cell vehicles for stable operation under long-term high temperatures. Summary of the invention

[0006] The purpose of the present invention is to provide a high Tg flexible graphite bipolar plate micropore plugging agent.

[0007] The technical solution to achieve the purpose of the present invention is:

[0008] In the first aspect, the present invention provides a high Tg flexible graphite bipolar plate micropore plugging agent, which includes, by weight, 20 to 30 parts of epoxycyclohexylethylcyclotetrasiloxane, and 70 to 80 parts of oxetane or alicyclic epoxy resin, the total of which is 100 parts by weight, as well as 0.1 to 2.0 cationic thermal initiator and 0.5 to 2 parts of leveling agent.

[0009] Preferably, the epoxycyclohexylethylcyclotetrasiloxane has the following structure:

[0010]

[0011] Preferably, the oxetane comprises the following structure:

[0012]

[0013] Preferably, the alicyclic epoxy resin comprises the following structure:

[0014]

[0015] Preferably, the cationic thermal initiator comprises the molecular structure shown below:

[0016]

[0017] The cation part R 1 , R 2 , R 3 , R 4 H, OH, CH 3 、Cl、CN、NO 2 、OCH 3 、-CH 2 Ph, -CH 2 CH=CHCH 3 、-CH 2 CH=(CH 3 ) 2 etc;

[0018] X in the anion part - SbF 6 - , AsF 6 - PF 6 - The order of thermal initiation activity of different anions is: SbF 6 - >AsF 6 - >PF 6 - .

[0019] Preferably, the leveling agent can be any leveling agent that has a wetting effect on the flexible graphite bipolar plate, and can be determined according to the impregnation amount of the plugging agent after the flexible graphite bipolar plate is infiltrated. The higher the impregnation amount, the better the effect of the leveling agent. German BYK leveling agents BYK-333 and BYK-3505, and three positive polymer superdispersants such as CH-1, CH-2, CH-3, CH-5, CH-6, CH-7, CH-8, CH-9, etc. are preferred, but the leveling agent component cannot contain Lewis bases, and the alkaline component will cause the cationic thermal initiator to fail.

[0020] Preferably, various antioxidants, anti-aging agents, fluorescent agents, etc. may be added to the above composition based on considerations of weather resistance, heat resistance, and fluorescent recognition.

[0021] Preferably, based on the consideration of water resistance, various epoxy silane coupling agents, titanate coupling agents, zirconate coupling agents, aluminate coupling agents, etc. can be added to the above composition.

[0022] Compared with the prior art, the advantages of the present invention are:

[0023] (1) One of the components of the flexible graphite bipolar plate plugging agent of the present invention, epoxycyclohexylethylcyclotetrasiloxane, has an organic siloxane structure, has hydrophobic and oleophobic properties and low surface tension properties, has excellent resistance to ethylene glycol, and will not swell or dissolve when in contact with ethylene glycol aqueous solution under long-term high temperature. It is particularly suitable for plugging micropores in flexible graphite bipolar plates of hydrogen fuel cells.

[0024] (2) One of the components of the flexible graphite bipolar plate plugging agent of the present invention, epoxy cyclohexylethyl cyclotetrasiloxane, contains 4 epoxy groups that can be initiated by cationic heat in each molecule. It is combined with highly heat-resistant oxetane or alicyclic epoxy resin. After curing, it has high heat resistance, low curing shrinkage, and small residual stress. It has higher bending strength than the plugging agent of (meth)acrylate thermal curing system. DETAILED DESCRIPTION

[0025] The present invention is described in detail below with reference to the embodiments.

[0026] (Meth)acrylate monomers have the advantages of low viscosity, strong permeability, and low curing temperature, and are the preferred compounds for micropore plugging agents for graphite bipolar plates. Compared with acrylate compounds, methacrylate compounds are more susceptible to free radical thermal curing reactions, and the cured products have higher Tg, that is, higher heat resistance. Therefore, most commercial micropore plugging agents use methacrylate monomers as the main component. However, after the polymerization of methacrylate monomers, few have a Tg exceeding 100°C, and their heat resistance is not as good as that of epoxy resin cured products. Also, because the cross-linking density is not high enough and they contain a large number of polar ester bonds, their resistance to ethylene glycol is not good enough.

[0027] Compared with the free radical thermal polymerization of (meth)acrylate compounds, the cationic ring-opening polymerization of epoxy resin has the characteristics of low curing shrinkage, good heat resistance, good adhesion to flexible graphite bipolar, high modulus, high bending strength, etc. Although it has many advantages over (meth)acrylate plugging agents, epoxy resin produces a large number of polar structures after cationic thermal curing, which is not conducive to resistance to ethylene glycol. There is still a risk of gas leakage for the bipolar plates of fuel cell stacks that operate under high temperature conditions for a long time.

[0028] In view of the above problems, the present invention introduces a tetrafunctional monomer containing a methylsiloxane structure, which has a high Tg and excellent ethylene glycol resistance.

[0029] The composition of the present invention contains epoxycyclohexylethylcyclotetrasiloxane, heterocyclobutane or alicyclic epoxy resin, cationic thermal initiator, and leveling agent. After curing, the Tg is high, the ethylene glycol resistance is excellent, and the bending strength of the bipolar plate is also higher than that of the (meth) acrylate plugging agent.

[0030] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0031] The formulations of the embodiments and comparative examples are shown in Table 1 below.

[0032] Table 1

[0033]

[0034] Note:

[0035] TTA11, TTA15, TTA22, TTA28 are the alicyclic epoxy resin product models of Changzhou Qiangli Electronic New Materials Co., Ltd.;

[0036] TCM101, TCM201, THM202 are the oxetane product models of Jiangsu Taitel New Materials Technology Co., Ltd.;

[0037] T-188 is a latent cationic thermal initiator from Shanghai Dongheng Chemical; CXC1612 is a latent cationic thermal initiator from King's Chemicals of the United States; BYK-333 and BYK-3505 are leveling agent product models from BYK Chemicals of Germany.

[0038] The evaluation method of ethylene glycol resistance of the present invention is as follows:

[0039] Pour 10g of the plugging agent into a Teflon mold with a diameter of 4.0cm and a height of 2.0cm, place it in an 80℃ drying oven and heat it for 2h, then heat it to 120℃ and continue heating it for 2h to obtain a cylindrical solid. Put the cylindrical solid into a glass bottle with 50%wt ethylene glycol aqueous solution and seal it, move it into a 90℃ oven and keep it for 1000h, take it out to examine the solubility of the solid and the turbidity of the ethylene glycol aqueous solution, so as to evaluate the ethylene glycol resistance of the plugging agent.

[0040] Ethylene glycol resistance is divided into 4 levels:

[0041] 1. Excellent◎ (the solidified material is intact, the ethylene glycol aqueous solution is transparent and free of foreign matter and turbidity)

[0042] 2. Good ○ (the solidified material has no obvious dissolution, and the ethylene glycol aqueous solution is slightly turbid)

[0043] 3. General △ (the solidified material is obviously dissolved, and the ethylene glycol aqueous solution becomes turbid)

[0044] 4. Very poor × (the solidified material swells and dissolves, and the ethylene glycol aqueous solution is very turbid)

[0045] According to Table 1, by comparing Examples 1 to 7, it is found that the plugging agent compounded with 20 to 30 parts of epoxycyclohexylethylcyclotetrasiloxane has good ethylene glycol resistance, while the plugging agent using alicyclic epoxy resin or compounded with oxetane (Comparative Examples 1 to 3) alone, although Tg is also relatively high and has good bending strength, the ethylene glycol resistance cannot meet the requirements. After aging, the solidified material swells and dissolves, and the ethylene glycol aqueous solution is relatively turbid.

Claims

1. A high Tg flexible graphite bipolar plate micropore plugging agent, characterized in that: The invention comprises 20 to 30 parts of epoxycyclohexylethylcyclotetrasiloxane and 70 to 80 parts of oxetane or alicyclic epoxy resin in parts by weight, the total of which is 100 parts by weight, as well as 0.1 to 2.0 parts of cationic thermal initiator and 0.5 to 2 parts of leveling agent.

2. The plugging agent according to claim 1, characterized in that: The epoxycyclohexylethylcyclotetrasiloxane has the following structure:

3. The plugging agent according to claim 1, characterized in that: The oxetane comprises the following structure:

4. The plugging agent according to claim 1, characterized in that: The alicyclic epoxy resin comprises the following structure:

5. The plugging agent according to claim 1, characterized in that: The cationic thermal initiator comprises the following molecular structure: Wherein, R1, R2, R3, and R4 are H, OH, CH3, Cl, CN, NO2, OCH3, -CH2Ph, -CH2CH=CHCH3, and -CH2CH=(CH3)2; X - SbF6 - 、AsF6 - PF6 - .

6. The plugging agent according to claim 1, characterized in that: The leveling agent is any one of German BYK leveling agent BYK-333, BYK-3505, and Sanzheng polymer super dispersant CH-1, CH-2, CH-3, CH-5, CH-6, CH-7, CH-8, CH-9.

7. The plugging agent according to claim 1, characterized in that: The plugging agent also includes one or more of an antioxidant, an anti-aging agent, and a fluorescent agent.

8. The plugging agent according to claim 1, characterized in that: The plugging agent also includes one or more of an epoxy silane coupling agent, a titanate coupling agent, a zirconate coupling agent, and an aluminate coupling agent.

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