TW477776B - Processing of high-impermeability fluorocarbon-graphite composite - Google Patents

Abstract

This invention provides the processing to produce fluorocarbon-graphite composite by mixing thermoplastic fluorocarbon dispersion with vermicular graphite in a wet condition, immersing, centrifugal treatment, drying and hot pressing. In the composite composition, there is 15 to 95 weight percent of vermicular graphite, preferably 65 to 90 weight percent. According to test demonstration, the composite has helium permeability below 1.1x10<SP>-9</SP> torr.1/sec, volume resistivity below 9.67x10<SP>-3</SP> Ω-cm. The inventive process can manufacture graphite composite material with high-impermeability and high-conductivity for the application in fuel cell, polar current collector separator and bipolar current collector separator.

Description

〃 / 76 V. Description of the invention (1) A ^ '~ --- (I) The prior art fuel cell is a device that directly uses oxygen in hydrogen-containing fuel air to generate electricity and heat energy through electrochemical reactions. . Due to its low pollution: high destruction clean power generation technology, which can be applied to generator sets, vehicle power discs, and other types of electricity, it has become a target for research, development, and promotion in the United States, Japan, and Europe. Bipolar 77 separator (Bipolar current collector-separator) 疋 Proton exchange membrane fuel cell (PEMFC) important components, bipolar separator plate main functions have five: (丨) as a fuel gas (such as hydrogen &amp; ) And oxidants such as oxygen (02 or air) gas separators, (2) gas guide grooves distributed on both surfaces of the bipolar separator plate as gas diversion tanks, (3) as near the cathode and ^ Another cell (cel 1) conducts current through the anode, (4) is used as current collection μ '(5), and a coolant deflector can be added inside the bipolar separator to remove the battery heat. Therefore, the bipolar separator must have high gas impermeability to gas, high gas conductivity, and be rotten. In addition, the bipolar separator must have sufficient bending strength to resist operating pressure and thermal cycling stability. It is also hoped that the bipolar separator plate can be made as thin as possible in the use design, so that the size of the fuel cell is reduced, and the electrical and thermal conductivity is improved to achieve a more economical and diversified fuel cell. Commercially most bipolar separators use processable artificial graphite 'graphite with strong corrosion resistance and good electronic conductivity (the volume resistivity of POCO EDM-3 is 2.97 X 10-3 Ω-cm), and Metals are relatively light weight. But graphite material is quite brittle, so it is very difficult to process, and graphite is a porous material (? 0 (: 0 £ 0 ^ 1-3, 1 ^ Air leakage rate is about 2 \ 10-: ^ 〇1 ^ .1 / 36〇), gas

Page 4 of 477776 V. Description of the invention (2) Experience leaking through the micro holes, unable to get the name of the famous name Qi Qi Qi. It is against the effect of milk, so it is impossible to make a very thin air-impermeable bipolar plate. Moyi Shuang uses a thicker graphite bipolar separator for most of the wounds to reduce gas leakage, which also causes the fuel cell stack's low weight, low volume, and low internal resistance not to be achieved. Graphite materials for fuel cells include artificial graphite (such as Japan Toyo Carbon IG15 graphite, US poc graphite), graphite powder composite thermosetting polymer materials, and graphite powder composite thermoplastic polymer materials. For example, U.S. Patents 4, 30 i, 222; 4, 1 97, 1 78 all mention the production of bipolar separator plates for fuel cells. In terms of 勑 composite thermoplastic 咼 molecular materials, U.S. Patents 4,301,222, and 4,2,1,4,169,9 mention graphite powder composites with fluorocarbon polymer composites and graphite-reinforced graphite powder composites. Fluorocarbon polymer composite materials, the volume resistivity of the two is 2.54 ~ 8.9 乂 10_2〇-〇111, this volume resistivity is about 1.97xl0-3 Ω-cm and artificial POCO than the artificial graphite such as Japan Toyo Carbon IG15 graphite Graphite is about 2 · 9 7X 1 Ο-3 Ω -cm high. In the Republic of China Patent Application No. 8 9 1 0 2 5 6 2 (Production method of battery bipolar separator), the dry method is used to mix thermoplastic fluorocarbon resin and worm-shaped graphite. The thermoplastic fluorocarbon resin powder is used by Changxing Chemical Industry Co., Ltd. The vinylidene fluoride and hexafluoropropylene copolymer powder (ETERFLON-420 1 VDF / HFP copolymer) produced by the company is first sieved through a 80-mesh sieve and then uniformly mixed with worm-like graphite at an appropriate ratio. After being stirred and mixed uniformly, it is placed in a mold, and pressed into a flat plate of composite material by a hot press. The hot pressing conditions are a pressure of 100 kg / cm2, a temperature of 180 ° C, and a pressing time of 2 hours. After cooling, remove the pressed composite material. The volume resistivity is 1.17x10-3 to 8.59x10-4Q-cm, and the air leakage rate is 3x10-8 to 9xl0-9torr · l / sec, among which the volume of the fluorocarbon polymer composite graphite material

Page 5 477776 V. Description of the invention (3) The resistivity is significantly better than that of US patents 4,301,222 and 4, 2 1 4, 969. It also has good performance in terms of air leakage rate, far better than that of Toyo Tanso 1 (^ 15 graphite leak rate is about 3x1 0_3torr · 1 / sec and American p0C0 graphite leak rate is about 2xl0-3torr · 1 / sec, but it has not reached full air tightness, so how to improve the fluorocarbon polymer composite graphite gas Density is the main object of the present invention. The conductive graphite of the present invention uses worm-like graphite, uses scaly natural graphite powder as a raw material, and is treated with acidification, etc., and then appropriately washed and dried to obtain expandable graphite powder. graphite). The expandable graphite powder is heated under high temperature (700 ~ 100 ° C) for an instant, and a vermicular expanded graphite is obtained, and its expansion ratio can reach 100%. 500 times. Since the snail-like graphite is derived from natural graphite, it has a high degree of graphitization and electrical conductivity, and its shape is similar to a sheet. After compression, the sheets and the sheets are bonded to each other, so that the overall Good conductivity. In fluorocarbon In terms of resin and worm-like graphite mixing technology, a wet mixing method is used to improve the airtightness of the composite material. (II) Purpose of the invention The purpose of the present invention is to produce a highly airtight and highly conductive fluorocarbon resin composite graphite material. In order to apply the components to the proton exchange membrane fuel cell. (3) Technical content

Page 6 4 //// 0 V. Description of the invention (4) * ~ ----- This ^ invention is a kind of high air-tight fluorocarbon polymer composite graphite. In the mixing method, a thermoplastic fluorocarbon resin is dispersed into a graphite to form a composite material. The fluorocarbon resin dispersion liquid is uniformly mixed with the worm and graphite at an appropriate ratio. After immersion mixing, centrifugation, or non-centrifugation processing, drying, Then, the mixed uniform powder is put into a mold and pressed by a hot press into a composite flat plate or a single-pole grooved unipolar separator plate or a double-sided grooved bipolar separator plate and other components. In terms of the mixing technology of fluorocarbon resin and worm-like graphite, the wet mixing method can be used to uniformly disperse the fluorocarbon tree moon powder on the worm-like graphite. Therefore, a hot air-tight composite material can be obtained after hot pressing. The weight ratio of the worm-like graphite in the composition is 15% to 95%, and the hot pressing temperature can be from 1000c to 3600c depending on the resin.

According to the technology of the present invention, the thermoplastic fluorocarbon resin dispersion liquid includes polyvinylidene fluoride (PVDF), vinylidene fluoride / hexafluoropropylene copolymer (VDF / HFP copolymer) and polytetrafluoroethylene,

PTFE) and other dispersions, the weight ratio of thermoplastic fluorocarbon resin to the overall composite material is 5 to 85%. The feature of the present invention is that it can produce fluorocarbon polymer composite graphite material with higher air-tightness, and its air-tightness is 10 times higher than that of the dry mixing method. Example 1-4: The thermoplastic fluorocarbon resin dispersion uses Changxing Chemical Industry Co., Ltd.'s vinylidene fluoride and hexafluoropropylene copolymer dispersion (ETERFL0N-420 1 VDF / HFP copolymer), the solid content of this product contains

Page 7 477776 V. Description of the invention (5)

The amount is 10%. If you want to reduce the solid content during use, you can use water as a diluent. The fluorocarbon resin dispersion and the worm-shaped graphite are uniformly mixed at an appropriate ratio. After soaking and stirring, the two are centrifuged. Dry at 50 t and time 2 hours, then put the mixed powder into the mold and press it into a flat plate of composite material or a unipolar separator with grooves on one side or a bipolar separator with grooves on both sides by hot pressing. Baffle, etc., pressure is 100kg / cm2, temperature is 130 ° C, pressing time is 2 hours. After cooling, remove the pressed composite material, measure density and measure volume resistance with H p 4 3 8 B milliohmmeter Rate (Q-cm), and the leak rate (torr.1 / sec) was measured with an ASM 1 801 He gas leak detector from alc TEL, France, as shown in Table 1. Table 1. Properties of the liquid method VDF / HFP composite worm-like graphite material. Worm-like graphite volume resistivity leak rate density (wt%) (Ω -cm) (torr. 1 / sec) (g / cc) Example 1 95. 5 1 · 10x1 Ο3 1 · lxlO 9 1. 40 Example 2 90. 9 9. 0 5x1 Ο 4 8. 0x10 10 1. 59 Example 3 82. 5 1 · 07xl0-3 Ί. OxlO11 1. 68 Example 4 77. 2 1 · 17χ1〇-3 2 · 0x10-η 1. 77 Example 5-8: The operation mode is the same as that of Example 4. The thermoplastic fluorocarbon resin dispersion is a Teflon resin dispersion ( DUPONT PTFE 30B aqueous fluorocarbon dispersion), dried to treat at 200 ° c and time 2 hours, pre-pressed to 50kg / cm2 and heated to 32 ()

477776 V. Description of the invention (6) ° C, then pressurize to 100 kg / cm2, and press time for 1 hour, its density, volume resistivity and air leakage rate are shown in Table 2. Table II. Properties of PTFE 30B composite worm-like graphite material Item Volume resistivity Leakage rate Density (wt%) (Ω -cm) (torr. 1 / sec) (g / cc) Example 5 87 5 9 · 96xl0-4 7. OxlO10 1. 56 Example 6 75. 5 1 · 20xl0-3 5.0 · 10x10-10 1.60 Example 7 65. 3 1 · 22xl0-3 3. 4x1010 1.69 Example 8 15. 4 9. 67xl0-3 5.0 0x10 10 1. 91

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Claims (1)

477776 The scope of patent application 丨 θ mouth 1 · A method for producing high airtight γ-poor high-molecular-weight composite graphite, the process of which is to uniformly mix a thermoplastic fluorocarbon resin dispersion with worm-like graphite in the front composition The weight ratio of worm-like graphite is 95% to 15%, and the weight ratio of fluorocarbon resin is 5% to 85%, and then the uniformly mixed powder is put into a mold. The pressing temperature can be from 100 ° C to 360 ° C depending on the resin. 2) For the manufacturing method of high air-tight fluorocarbon polymer composite graphite according to item 丨 of the patent application, the thermoplastic fluorocarbon resin dispersion can be a resin dispersion, vinylidene diene and hexafluoropropylene copolymerized fluorocarbon Resin dispersion. 3. For example, in the method for manufacturing high-airtight fluorocarbon polymers in the scope of the patent application, the fluorocarbon polymer composite graphite products can be σ 'single-sided grooved unipolar separator plate and double-sided grooved double Poles; partitions, etc. 4. For the high air-tight eight production method in the scope of the patent application, the pre-processing step can be a dry-to-knife / composite graphite process, followed by drying. * Or centrifuge first