High heat-resistant flexible graphite bipolar plate microporous sealing agent

Abstract

This invention discloses a high-heat-resistant flexible graphite bipolar plate microporous plugging agent, comprising 20-40 parts by weight of a glycidyl etheroxypropylcyclotetrasiloxane (meth)acrylate esterified ring-opening compound and 60-80 parts by weight of a high-Tg methacrylate monomer, the total of which is 100 parts by weight, as well as 0.5-2 parts by weight of a leveling agent and 0.2-1.0 parts by weight of a free radical thermal initiator. The plugging agent of this invention, due to its organosiloxane structure, exhibits excellent ethylene glycol resistance. Furthermore, the glycidyl etheroxypropylcyclotetrasiloxane (meth)acrylate esterified ring-opening compound contains four (meth)acryloyloxy groups on each molecule, resulting in high crosslinking density. When copolymerized with the high-Tg methacrylate monomer, it exhibits high heat resistance, low curing shrinkage, and low residual stress, which is beneficial for the bipolar plate to maintain good flexural strength at high temperatures.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen fuel cells, specifically relating to a thermosetting microporous sealant for flexible graphite bipolar plates in hydrogen fuel cell stacks. Background Technology

[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 fuel cell stacks of commercial vehicles due to the availability of raw materials, low cost, good chemical corrosion resistance, and long service life. However, flexible graphite plates have a microporous structure and must be impregnated with a sealing agent to ensure the airtightness of the bipolar plate. At the same time, after the sealing agent cures, it must give the flexible graphite plate sufficient mechanical strength, chemical resistance (mainly resistance to ethylene glycol), and long-term heat resistance.

[0003] Flexible graphite bipolar plates typically use a resin solution formulated with (meth)acrylate monomers as a sealing agent (refer to Chinese Patent CN 107706430B). Before use, a free radical thermal initiator is added. The flexible graphite plate is then impregnated in the sealing agent under vacuum or pressure, allowing the sealing agent molecules to penetrate into the micropores of the flexible graphite bipolar plate. Residual sealing agent on the surface of the bipolar plate is then cleaned to prevent it from affecting the conductivity of the graphite after curing. The bipolar plate is then cured in a water bath. After curing, the sealing agent forms a dense network structure, thereby giving the bipolar plate airtightness, compressive strength, chemical resistance, and heat resistance.

[0004] After flexible graphite bipolar plates are assembled into a fuel cell stack, they are in contact with ethylene glycol aqueous solution as a cooling medium at a temperature of 80-95°C for a long time during fuel cell operation. They need to be resistant to long-term high temperature of ethylene glycol aqueous solution. However, (meth)acrylate polymers have a certain degree of solubility in ethylene glycol. As a result, after long-term operation of the fuel cell, the bipolar plate sealing agent partially dissolves in ethylene glycol, producing pores and cracks, leading to gas leakage and failure.

[0005] In addition, the methacrylate polymers or copolymers mentioned in Chinese patent CN 107706430B have relatively low Tg, with very few components having a Tg exceeding 100°C. The Tg of long-chain alkyl acrylate polymers is even below zero, which means they are in a rubbery state at fuel cell operating temperatures. This significantly reduces the bending strength of the graphite bipolar plates, making it difficult to meet the stringent requirements for stable operation of hydrogen fuel cell vehicles under long-term high temperatures. Summary of the Invention

[0006] The purpose of this invention is to provide a flexible graphite bipolar plate microporous plugging agent with good heat resistance and ethylene glycol resistance.

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

[0008] In a first aspect, the present invention provides a high heat-resistant flexible graphite bipolar plate micropore plugging agent, comprising: 20-40 parts by weight of a glycidyl etheroxypropylcyclotetrasiloxane (meth)acrylate ring-opening compound and 60-80 parts by weight of a high Tg methacrylate monomer, the total of which is 100 parts by weight, as well as 0.5-2 parts by weight of a leveling agent and 0.2-1.0 parts by weight of a free radical thermal initiator.

[0009] Preferably, the (meth)acrylated ring-opening compound of the glycidyl etheroxypropylcyclotetrasiloxane has the following structure:

[0010]

[0011] In this context, R represents a methyl group or a hydrogen atom.

[0012] Preferably, the (meth)acrylated ring-opening compound of glycidyl etheroxypropylcyclotetrasiloxane is prepared by epoxy ring-opening esterification reaction of glycidyl etheroxypropylcyclotetrasiloxane of Formula I with acrylic acid or methacrylic acid in the presence of a catalyst:

[0013]

[0014] Specifically, catalysts used for the epoxy ring-opening esterification reaction of acrylic acid or methacrylic acid include: tertiary amines and quaternary ammonium salts. Commonly used catalysts include any one of triethylamine, N,N-dimethylbenzylamine, N,N-dimethylaniline, trimethylbenzylammonium chloride, triphenylphosphine, triphenylantimony, chromium acetylacetone, chromium isooctanoate, organotin compounds, and tetraethylammonium bromide, with an amount of 0.1% to 3% of the total mass of the reactants.

[0015] Specifically, to ensure complete ring-opening esterification of the epoxy groups, the amount of acrylic acid or methacrylic acid added should generally be 1.1 to 1.5 times the number of epoxy groups in glycidyl etheroxypropylcyclotetrasiloxane.

[0016] Specifically, to prevent the self-polymerization of acrylic acid or methacrylic acid during the ring-opening esterification reaction, a small amount of free radical polymerization inhibitor can be added. Commonly used free radical polymerization inhibitors include any one of p-methoxyphenol (MEHQ), hydroquinone, 2,5-dimethylhydroquinone, and 2,6-di-tert-butyl-4-methylphenol (BHT), with the amount of free radical polymerization inhibitor added being 0.01% to 1% of the total mass of the reactants.

[0017] Specifically, the ring-opening esterification reaction of epoxy groups is an exothermic reaction, so controlling the temperature in the early stage of the reaction is very important. Usually, glycidyl etheroxypropylcyclotetrasiloxane is heated to 80-90°C, and a mixture of acrylic acid or methacrylic acid, catalyst and free radical polymerization inhibitor is added dropwise. After the addition is completed, the reaction temperature is controlled at 110-120°C and maintained at this temperature for 5 hours. Then, the heating is stopped and the temperature is lowered to room temperature to obtain the target product.

[0018] Preferably, the high-Tg methacrylate monomer is selected from any one of isobornyl methacrylate, o-phenylphenoxyethyl methacrylate, benzyl methacrylate, phenyl methacrylate, tert-butyl methacrylate, cyclohexyl methacrylate, tetrahydrofuran methacrylate, tricyclodecyl methacrylate, dicyclopentadiene methacrylate, methacryloylmorpholine, and N,N-dimethylacrylamide, etc. Considering factors such as heat resistance and low viscosity, isobornyl methacrylate, dicyclopentadiene methacrylate, or tricyclodecyl methacrylate are preferred.

[0019] Preferably, the leveling agent can be any leveling agent that has a wetting effect on the flexible graphite bipolar plate. The choice depends on the impregnation content of the sealing agent after the flexible graphite bipolar plate is impregnated; a higher impregnation content results in a better leveling effect. Preferred leveling agents include BYK-333 and BYK-3505 from BYK (Germany), as well as high-molecular-weight superdispersants such as CH-1, CH-2, CH-3, CH-5, CH-6, CH-7, CH-8, CH-9, etc.

[0020] Preferably, the free radical thermal initiator is an initiator with a decomposition temperature of 80–95°C, specifically an azo or peroxide-based free radical thermal initiator. Azobisisobutyronitrile, azobisisoheptanenitrile, and benzoyl peroxide are preferred free radical thermal initiators.

[0021] Preferably, considering factors such as weather resistance, heat resistance, and fluorescence recognition, various antioxidants, anti-aging agents, fluorescent agents, etc., can be added to the above-mentioned components.

[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 is a (meth)acrylated ring-opening compound of glycidyl etheroxypropylcyclotetrasiloxane. Due to the hydrophobic and oleophobic properties of the organosiloxane structure and the low surface tension, it has excellent ethylene glycol resistance. It will not swell or dissolve when in contact with ethylene glycol aqueous solution at long-term high temperature, and is particularly suitable for micropore plugging of flexible graphite bipolar plates for hydrogen fuel cells.

[0024] (2) One of the components of the flexible graphite bipolar plate sealing agent of the present invention is a (meth)acrylated ring-opening compound of glycidyl etheroxypropylcyclotetrasiloxane, each molecule containing 4 (methyl) groups that can be polymerized by free radicals.

[0025] Acryloyloxy, when copolymerized with high-Tg methacrylate monomers, exhibits high heat resistance, low curing shrinkage, and low residual stress, which helps the bipolar plate maintain good flexural strength at high temperatures. Detailed Implementation

[0026] The present invention will now be described in detail with reference to the embodiments.

[0027] (Meth)acrylate monomers possess advantages such as low viscosity, strong penetration, and low curing temperature, making them the preferred compounds for microporous sealing agents in graphite bipolar plates. Compared to acrylate compounds, methacrylate compounds undergo free radical thermosetting reactions more easily, and the cured products have a higher Tg (glass transition temperature), meaning they possess higher heat resistance. Therefore, most commercial microporous sealing agents use methacrylate monomers as the main component. However, after polymerization, methacrylate monomers rarely have a Tg exceeding 100℃, resulting in lower heat resistance compared to epoxy resin cured products. Furthermore, due to insufficient crosslinking density and the presence of numerous polar ester bonds, their resistance to ethylene glycol is not good.

[0028] This invention introduces a tetrafunctional monomer containing a methylsiloxane structure, which has high Tg and excellent resistance to ethylene glycol.

[0029] The glycidyl etheroxypropylcyclotetrasiloxane (meth)acrylate ring-opening compound of the present invention is prepared by glycidyl etheroxypropylcyclotetrasiloxane and acrylic acid or methacrylic acid undergoing an epoxy ring-opening esterification reaction in the presence of a catalyst. After the reaction is completed, the compound is washed with water, alkali, and water again until excess acrylic acid or methacrylic acid is completely washed away. Then, it is dried and filtered with a dehydrating agent to obtain a colorless and transparent glycidyl etheroxypropylcyclotetrasiloxane acrylate ring-opening compound or a glycidyl etheroxypropylcyclotetrasiloxane methacrylate ring-opening compound.

[0030] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0031]

Tetrafunctional Organosilicon-1

[0032]

Tetrafunctional Organosilicon-2

[0033] The sealant formulations in the examples and comparative examples are prepared by mixing all components and stirring until all solid substances are dissolved into a transparent liquid.

[0034] The formulations of each embodiment and comparative example are shown in Table 1 below.

[0035] Table 1

[0036]

[0037] The evaluation method for ethylene glycol resistance is as follows:

[0038] 10g of the sealant was poured into a Teflon mold with a diameter of 4.0cm and a height of 2.0cm. The mold was then placed in an 80℃ drying oven and heated for 2 hours, followed by heating to 120℃ for another 2 hours, resulting in a colorless, transparent cylindrical cured product. This cylindrical cured product was placed in a glass bottle containing a 50% wt ethylene glycol aqueous solution, sealed, and placed in a 90℃ oven for 1000 hours. The solubility of the cured product and the turbidity of the ethylene glycol aqueous solution were then examined to evaluate the sealant's resistance to ethylene glycol.

[0039] Ethylene glycol resistance is classified into four levels:

[0040] 1. Excellent ◎ (The solidified material is intact and undamaged; the ethylene glycol aqueous solution is clear, free of foreign matter, and not cloudy)

[0041] 2. Good (No obvious dissolution of the solidified material; the ethylene glycol aqueous solution is slightly turbid)

[0042] 3. Generally △ (The solidified material shows obvious dissolution, and the ethylene glycol aqueous solution becomes cloudy)

[0043] 4. Very poor × (The solidified material swells and dissolves; the ethylene glycol aqueous solution is slightly very cloudy)

[0044] According to Table 1, by comparing Example-1 and Comparative Example-1, it was found that the amount of tetrafunctional organosilicon added has a crucial impact on the ethylene glycol resistance. A tetrafunctional organosilicon added amount of more than 20 phr (parts per hundred) is required to achieve good resistance. When the amount of tetrafunctional organosilicon added is 10 phr, the cured product shows obvious dissolution after aging, the ethylene glycol aqueous solution becomes turbid, and the Tg of the resulting cured product is relatively low, and the heat resistance is also poor.

[0045] Comparative Example-2 consists of high-Tg methacrylates. The cured product has a relatively high Tg, but because it does not contain organosiloxane structures, it has poor resistance to ethylene glycol. After aging, the cured product swells and dissolves, and the ethylene glycol aqueous solution is slightly very turbid.

[0046] Comparative Example-3 contains a low-Tg difunctional acrylate, resulting in a cured product with a relatively low Tg, poor heat resistance, and poor ethylene glycol resistance. After aging, the cured product swells and dissolves, and the ethylene glycol aqueous solution is also very turbid.

Claims

1. A high-heat-resistant flexible graphite bipolar plate pore plugging agent, characterized in that, Comprise: 20~40 parts by weight of glycidyl ether oxypropyl cyclotetrasiloxane (meth) acrylated ring-opening compound and 60~80 parts by weight of high Tg methacrylate monomer, the total of both being 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 glycidyl ether oxypropyl cyclotetrasiloxane (meth) acrylated ring-opening compound has the following structure: ； Wherein, R represents a methyl group or a hydrogen atom.

2. The lost circulation material of claim 1, wherein, The glycidyl ether oxypropyl cyclotetrasiloxane (meth) acrylated ring-opening compound is prepared by epoxy ring-opening esterification reaction of glycidyl ether oxypropyl cyclotetrasiloxane of formula I structure with (meth) acrylic acid under the action of a catalyst and a free radical polymerization inhibitor: ； I。 3. The lost circulation material of claim 2, wherein, The catalyst is selected from any one of tertiary amines, quaternary ammonium salts, triphenyl phosphine, triphenyl antimony, chromium acetylacetone, chromium isooctanoate, and organotin compounds.

4. The lost circulation material of claim 2, wherein, The catalyst is selected from any one of triethylamine, N,N-dimethylbenzylamine, N,N-dimethylaniline, trimethylbenzyl ammonium chloride, and tetraethylammonium bromide.

5. The lost circulation material of claim 2, wherein, The amount of catalyst is 0.1%~3% of the total mass of reactants.

6. The lost circulation material of claim 2, wherein, The amount of (meth) acrylic acid added is 1.1~1.5 times the number of moles of epoxy groups in the glycidyl ether oxypropyl cyclotetrasiloxane.

7. The lost circulation material of claim 2, wherein, The free radical polymerization inhibitor is any one of p-methoxyphenol, hydroquinone, 2,5-dimethyl hydroquinone, and 2,6-di-tert-butyl-4-methylphenol, and the amount added is 0.01%~1% of the total mass of reactants.

8. The lost circulation material of claim 2, wherein, The specific reaction process is as follows: the glycidyl ether oxypropyl cyclotetrasiloxane is heated to 80~90℃, a mixture of (meth) acrylic acid, catalyst, and free radical polymerization inhibitor is added dropwise, after the dropwise addition is complete, the reaction temperature is controlled at 110~120℃, this temperature is maintained for 5h, heating is stopped and the temperature is reduced to room temperature to obtain the target product.

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

10. The lost circulation material of claim 1, wherein, The high Tg methacrylate monomer is selected from isobornyl methacrylate, dicyclopentadiene methacrylate, or tricyclodecane methacrylate.

11. The lost circulation material of claim 1, wherein, The leveling agent is selected from any one of German BYK leveling agents BYK-333, BYK-3505, and tri-normal high molecular weight superdispersant CH-1, CH-2, CH-3, CH-5, CH-6, CH-7, CH-8, and CH-9.

12. 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℃.

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

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