Flexible graphite bipolar plate micropore sealing agent

Abstract

This invention discloses a microporous sealing agent for flexible graphite bipolar plates, comprising 20-40 parts by weight of an epoxycyclohexylethylcyclotetrasiloxane (meth)acrylate ring-opening compound and 60-80 parts by weight of a high-Tg methacrylate monomer, totaling 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 sealing agent of this invention, due to its organosiloxane structure, exhibits excellent resistance to ethylene glycol. Furthermore, the epoxycyclohexylethylcyclotetrasiloxane (meth)acrylate 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] 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, vacuum or pressurized impregnation is performed, and the plugging agent molecules are allowed 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 high-temperature resistance to ethylene glycol aqueous solution cooling medium during fuel cell operation at temperatures of 80-95℃. However, (meth) acrylate polymers have some solubility in ethylene glycol, which causes the plugging agent of the bipolar plate to partially dissolve in the ethylene glycol after long-term operation of the fuel cell, resulting in pore cracks and gas leakage and failure.

[0005] In addition, the Tg of the methacrylate polymers or copolymers 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 flexible graphite bipolar plate micro-pore plugging agent that is resistant to heat and ethylene glycol.

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

[0008] In a first aspect, the present application provides a flexible graphite bipolar plate micropore plugging agent with good heat resistance and ethylene glycol resistance, comprising: 20-40 parts by weight of a (meth) acrylated ring-opening compound of epoxycyclohexylethyl cyclotetrasiloxane and 60-80 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.

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

[0010]

[0011] wherein R represents a methyl group or a hydrogen atom.

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

[0013]

[0014] Specifically, the catalyst for the epoxy ring-opening esterification reaction of acrylic acid or methacrylic acid includes any one of tertiary amines, quaternary ammonium salts, commonly used triethylamine, N,N-dimethylbenzylamine, N,N-dimethylaniline, trimethylbenzylammonium chloride, triphenylphosphine, triphenylantimony, chromium acetylacetate, chromium iso-octoate, organotin compounds, tetraethylammonium bromide, etc., and the amount of the catalyst is 0.1%-3% of the total mass of the reactants.

[0015] Specifically, in order to ensure the completion of the epoxy ring-opening esterification reaction, the amount of acrylic acid or methacrylic acid added is generally 1.1-1.5 times the number of moles of epoxy groups in the epoxycyclohexylethyl cyclotetrasiloxane.

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

[0017] Specifically, the epoxy group open ring esterification reaction is an exothermic reaction, so it is very important to control the temperature at the beginning of the reaction. Usually, the epoxy cyclohexyl ethyl cyclosiloxane is heated to 80-90℃, and the mixture of acrylic acid or methacrylic acid, catalyst and free radical polymerization inhibitor is added dropwise. After the dropwise addition is completed, the reaction temperature is controlled at 110-120℃, and this temperature is maintained for 5h. Then, the heating is stopped and the temperature is reduced to room temperature to obtain the target product.

[0018] 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.

[0019] Preferably, the leveling agent can be any leveling agent that has a wetting effect on the flexible graphite bipolar plate. 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 superdispersant 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 selected from initiators with a decomposition temperature of 80-95℃, such as azo and peroxide free radical thermal initiators. Preferably, the free radical thermal initiator is azobisisobutyronitrile, azobisisoheptyl nitrile or benzoyl peroxide.

[0021] 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.

[0022] Compared with the prior art, the present application has the following advantages:

[0023] (1) The (meth)acrylated open ring compound of epoxy cyclohexyl ethyl cyclosiloxane, which is one of the components of the flexible graphite bipolar plate sealing agent composition of the present application, has excellent ethylene glycol resistance due to the hydrophobic and oleophobic properties and low surface tension of the organosiloxane structure. It will not swell or dissolve in contact with ethylene glycol aqueous solution at high temperature for a long time, and is particularly suitable for sealing the micropores of the flexible graphite bipolar plate of a hydrogen fuel cell.

[0024] (2) One of the components of the flexible graphite bipolar plate plugging agent composition of the present application, the (meth) acrylated ring-opening compound of epoxycyclohexylethyl cyclotetrasiloxane contains 4 (meth) acryloyloxy groups that can be radically polymerized in each molecule, and has high heat resistance after copolymerization with high-Tg methacrylate monomers, and also has low curing shrinkage, small residual stress, and is beneficial to maintaining good bending strength of the bipolar plate at high temperatures. DETAILED DESCRIPTION

[0025] The present application will be described in detail below with reference to examples.

[0026] The (meth) acrylate monomer has the advantages of low viscosity, strong permeability, and low curing temperature, and is the preferred compound for graphite bipolar plate micropore plugging agents. Compared with acrylate compounds, methacrylate compounds are easier to undergo radical thermal curing reaction, and the cured product has a higher Tg (glass transition temperature), that is, higher heat resistance, so most commercial micropore plugging agents use methacrylate monomers as the main component. However, after polymerization of the methacrylate monomer, 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.

[0027] The present application introduces a tetrafunctional monomer containing a methylsiloxane structure, which has high Tg and excellent ethylene glycol resistance.

[0028] The (meth) acrylated ring-opening compound of epoxycyclohexylethyl cyclotetrasiloxane of the present application is prepared by ring-opening esterification reaction of epoxycyclohexylethyl cyclotetrasiloxane with acrylic acid or methacrylic acid in the presence of a catalyst. After the reaction is completed, multiple water washing, alkali washing, and then water washing are performed until the excess acrylic acid or methacrylic acid is completely washed away, and then the dehydrating agent is used for drying and filtration to obtain colorless and transparent acrylic acid esterified ring-opening compound of epoxycyclohexylethyl cyclotetrasiloxane or methacrylic acid esterified ring-opening compound of epoxycyclohexylethyl cyclotetrasiloxane.

[0029] 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 conventional products that can be purchased on the market.

[0030]

Four officials have silicone-1

[0031]

Four officials have silicone-2

[0032] The plugging agent formula in each example and comparative example is mixed and stirred uniformly after each component is mixed, and the solid substance is dissolved into transparent liquid.

[0033] The formula of the examples and comparative examples is as follows Table 1.

[0034] Table 1

[0035]

[0036] The evaluation method of ethylene glycol resistance is as follows:

[0037] The plugging agent 10 g is poured into a Teflon mold with a diameter of 4.0 cm and a height of 2.0 cm, and heated in a 80 ℃ drying oven for 2 h, and then heated to 120 ℃ for 2 h, to obtain a colorless transparent cylindrical cured product. The cylindrical cured product is placed in a glass bottle containing 50%wt ethylene glycol aqueous solution and sealed, and then moved into a 90 ℃ oven for 1000 h. The solubility of the cured product and the turbidity of the ethylene glycol aqueous solution are observed to evaluate the ethylene glycol resistance of the plugging agent.

[0038] The ethylene glycol resistance is divided into four grades:

[0039] 1. Excellent (the cured product is intact, the ethylene glycol aqueous solution is transparent and free of foreign matter and turbidity)

[0040] 2. Good (No obvious dissolution of cured product, the ethylene glycol aqueous solution is slightly turbid)

[0041] 3. General (The cured product has obvious dissolution, the ethylene glycol aqueous solution becomes turbid)

[0042] 4. Very poor (The cured product has swelling dissolution, the ethylene glycol aqueous solution is very turbid)

[0043] According to Table 1, by comparing Example-1 and Comparative Example-1, it is found that the addition amount of tetra-functional organosilicon has a crucial influence on the ethylene glycol resistance, and the addition amount of tetra-functional organosilicon should be more than 20 phr (Parts per hundred) to achieve better resistance, while the addition amount of tetra-functional organosilicon is 10 phr, the cured product has obvious dissolution after aging, the ethylene glycol aqueous solution becomes turbid, and the Tg of the obtained cured product is also relatively low, and the heat resistance is also poor.

[0044] 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 ethylene glycol resistance is poor, and the cured product has swelling dissolution after aging, and the ethylene glycol aqueous solution is very turbid.

[0045] The formula of Comparative Example-3 contains low-Tg di-functional acrylate, and the Tg of the obtained cured product is relatively low, the heat resistance is poor, the ethylene glycol resistance is also poor, the cured product has swelling dissolution after aging, and the ethylene glycol aqueous solution is also very turbid.

Claims

1. A flexible graphite bipolar plate micropore plugging agent that is resistant to heat and ethylene glycol, characterized by, Comprise: 20~40 parts by weight of (meth)acrylated ring-opening compound of epoxycyclohexylethyl cyclotetrasiloxane 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 leveling agent and 0.2~1.0 parts by weight of free radical thermal initiator; Wherein, the (meth)acrylated ring-opening compound of epoxycyclohexylethyl cyclotetrasiloxane has the following structure: ； Wherein, R represents methyl or hydrogen atom.

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

4. The lost circulation material of claim 2, wherein, The catalyst is selected from any one of triethylamine, N,N-dimethylbenzylamine, N,N-dimethylaniline, trimethylbenzylammonium chloride, triphenyl phosphine, triphenyl antimony, chromium acetylacetone, chromium isooctanoate, organotin compound, 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 epoxycyclohexylethyl 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: epoxycyclohexylethyl cyclotetrasiloxane is heated to 80~90℃, and a mixture of (meth)acrylic acid, catalyst, and free radical polymerization inhibitor is added dropwise. After the dropwise addition is completed, the reaction temperature is controlled at 110~120℃, and this temperature is maintained for 5h. The 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, tert-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 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.

12. The lost circulation material of claim 1, wherein, The free radical thermal initiator is selected from 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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