KR100781628B1 - Fuel cell separator using the graphite composite and preparing method thereof - Google Patents

Abstract

A method for preparing a graphite composite fuel cell separator and a graphite composite fuel cell separator prepared by the method are provided to reduce compression molding time remarkably and to improve electrical conductivity and flexural strength. A graphite composite fuel cell separator is prepared by using a graphite composite material prepared by dry mixing 70-95 wt% of a natural graphite powder and 5-30 wt% of a thermosetting resin powder uniformly to make a mixing material for a fuel cell separator; variably filling the mixing material into a mold where a separator channel is carved and compression molding it at a room temperature to prepare a molded product having a density of 90-100 % corresponding to the theoretical density; and thermosetting the molded product at 100-200 deg.C for 10-100 min.

Description

       Fuel Cell Separator Using the Graphite Composite and Preparing Method Thereof}

1 is a manufacturing flowchart of a conventional fuel cell separator.

2 is a manufacturing flow chart of the graphite composite fuel cell separator for explaining the present invention.

3 is a perspective view of a fuel cell separation plate completed through one embodiment of the present invention;

Figure 4 is a block diagram showing a cross section of the charging of one embodiment of the conventional uniform charging

5 is a block diagram showing a cross section of a fuel cell separator formed by manufacturing an embodiment of the conventional uniform charging.

Figure 6 is a cross-sectional view showing an embodiment of a variable charge of the present invention

Figure 7 is a block diagram showing a cross-section of the fuel cell separator formed by manufacturing an embodiment of the variable charge of the present invention.

<Description of the code | symbol about the principal part of drawing>

100: mixed material manufacturing process 200: forming and curing process

300: fuel cell separator 301: part with flow path

302: part without euro

The present invention provides a graphite composite by dry mixing spherical graphite powder and thermosetting resin powder in the manufacture of a separator plate of a polymer electrolyte fuel cell or a direct methanol fuel cell. The present invention relates to a fuel cell separator manufactured by variable charging a graphite composite into a mold of a press, compression molding at room temperature, and thermally curing the molded body.

More specifically, in the graphite composite fuel cell separator and a method of manufacturing the graphite composite, the graphite composite is formed of phenol in a spherical graphite powder obtained by spherical or plate-like natural graphite powder through mechanical processing. The thermosetting resin powders such as resins and epoxy resins are mixed using a mixing mixer to prepare a dry mixing method without using a solvent.In the thermosetting resin powder, a powdered phenol resin containing a curing agent is used as the phenol resin. Epoxy resin was used by putting a certain amount of a curing agent in the resin powder, and the fuel cell having a flow path through compression press molding at room temperature by variable tamping the graphite composite prepared as above into a mold engraved with the flow path. A method of preparing a plate molded body and putting it in a drying oven to cure for a certain time The present invention relates to provide a high electrical conductivity and flexural strength, and a graphite composite material that allows to provide a fuel cell bipolar plate having a high dimensional accuracy and a method of producing a fuel cell bipolar plate using the same.

As shown in FIG. 1, the conventional fuel cell separator is manufactured in the form of a mixed material as the thermosetting resin (10). One of a plurality of thermosetting resins, such as phenol resins and epoxy resins, and a needle or plate shape Natural graphite powder or artificial graphite and expanded graphite, carbon black or carbon fiber, carbon nanotube, diamond light carbon, etc. dry mixed as a conductive filler material, methyl ethyl ketone (MEK) or isopropyl alcohol as a solvent for dissolving the thermosetting resin (IPA), methanol, acetone, and the like (11) in excess of 80 to 120% by weight of the conductive filler is deposited by mixing, the mixture is dried to remove the solvent (12) through the granulation and regrinding process After preparing the fuel cell separator, the mold is heated (21) and filled into the preheated mold in forming the fuel cell separator (20). And heating the mold to a temperature according to a curing agent, and the compression set (22) at the same time as a molding is produced which is a fuel cell bipolar plate (30).

As described above, the molding material for fuel cell separator and the manufacturing method thereof described in Japanese Patent Laid-Open No. 2005-116335 can be examined.

As described above, however, the conventional fuel cell separator is manufactured by using a solvent to dissolve the resin in a mixture of a conductive filler such as a natural impression graphite or artificial graphite and a thermosetting resin in synthesizing the mixed material. If the amount of solvent is small due to the wet mixing method, the viscosity of the thermosetting resin is not sufficiently lowered, so that it is not uniformly dispersed. If the amount of the solvent is too large, sedimentation occurs during drying of the mixture for granulation and uniform dispersion. This becomes difficult and causes a decrease in electrical conductivity and flexural strength in the manufacture of the fuel cell separator. In addition, the volatilization time is long in the volatilization of the solvent to lower productivity, and the cost of the solvent and additional facility costs for the recovery and reuse of the solvent are required, thereby increasing the manufacturing cost.

In addition, the fuel cell separation plate described in Japanese Patent Laid-Open No. 2004-338269 and a manufacturing apparatus of the method for manufacturing the same include a mold heating apparatus for mixing a graphite powder with a low viscosity thermosetting resin in a liquid state and filling the above-mentioned mixture. The mold is separated from the mold heating apparatus and cooled to form a fuel cell separator plate, but the process time for heating and cooling the mold is at least 9 minutes. There is a problem of longer than 20 minutes at low productivity, so a plurality of molds are prepared for smooth molding, and one of the molding machines must be preheated before molding in the preheater, thereby increasing the cost for the mold and cooling the mold. There is a problem that a cooling water system is required and the molding machine becomes complicated.

In the hot compression molding as described above, when the molded body is separated from the mold without being sufficiently cooled after molding, the thickness deviation and the dimensional accuracy decrease due to the deformation of the molded body, resulting in the assembly of the fuel cell stack. This can cause leakage of fuel and gas.

In the hot and cold compression molding, the mixture is filled in the mold and the fuel cell separator 300 as shown in FIG. 3 is formed in the hot and cold compression molding. As shown in FIG. ) And the non-flow path 302 are filled to the same density within 0.5 to 1.0 g / cm ³ , causing severe thickness deviation between the flow path part with yaw iron and parts other than the flow path after molding, In the flow path portion, the thickness variation between the inside and the outside of the flow path portion is generated, and as shown in FIG. 5, the fuel cell separator is manufactured in a state where the center portion with the flow path is bulging, and the separator plate is assembled to the fuel cell stack as it is. Problems such as non-uniform contact with the gas diffusion layer (GDL) and leakage after assembly occur, and the characteristics of the fuel cell separator are understood for reasons of efficiency and safety. Since the electrical conductivity required by the Department of Energy is over 100 S / cm and the flexural strength is over 40 MPa, the efficiency and safety of the fuel cell will be deteriorated if it does not have small thickness variation, high electrical conductivity and high flexural strength. This problem needs to be solved.

The present invention has been made to solve the problems of the prior art as described above has the following object.

The present invention is a graphite composite fuel cell separator and its manufacturing method, the electrical conductivity required by the US Department of Energy (DOE) 100 S / cm or more, the high electrical conductivity and flexion strength of more than 40 MPa flexural strength at thickness 1.0 ~ 2.0 mm In the manufacture of fuel cell separator having strength, spherical graphite powder which spherical or plate-shaped natural graphite is spherical shape by mechanical processing in the composition of graphite composite suitable for this, and phenol resin or powder form containing resin-hardening agent Unlike the wet mixing method using a conventional solvent using an epoxy resin powder and a powdery curing accelerator, and the graphite powder and the resin powder through a mixer to produce a graphite composite by homogeneously mixing in a dry state of the molding material The manufacturing process is simplified, and the fuel cell separator is formed by compression molding at room temperature. The molded product is cured at a temperature of about 10 to 40 ° C. above a curing temperature of a thermosetting resin phenol resin or epoxy resin using a drying oven for a predetermined time to prepare a fuel cell separator to have high electrical conductivity and flexural strength. It is an object of the present invention to provide a fuel cell separator and a manufacturing method thereof.

Another object of the present invention is a graphite composite fuel cell separator and a method of manufacturing the same, which have a high electrical conductivity and high flexural strength by homogeneously dry mixing spherical powder graphite and powdery thermosetting resin, and forming a fuel cell separator. In the case of filling the mixture in the mold, the filling density of the mixture with and without the flow path is filled differently according to the distribution of the flow path. The purpose is to provide.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell graphite composite fuel cell separator and a method for manufacturing the same. The present invention relates to a spheroidal graphite powder, a phenol resin powder, or an epoxy resin powder processed to have a spherical shape through mechanical processing of needle or plate-shaped natural impression graphite. The mixed molding material and the mold is variably charged into a mold, pressurized at room temperature, and molded, and the molded body is cured in a drying oven to form a fuel cell separator.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

As shown in Figures 2 and 3, Figure 2 is a manufacturing flow configuration diagram of a fuel cell separator and a manufacturing method of the fuel cell separator using the same according to the present invention, Figure 3 is a fuel according to the present invention Figure 4 is a perspective view of a battery separator, Figure 4 is a block diagram showing a uniform state of charge of the prior art, Figure 5 is a cross-sectional view of the fuel cell separator obtained through compression molding after the prior art uniform charge of Figure 4, Figure 6 Is a block diagram showing a variable charging state according to the present invention, Figure 7 shows a cross-sectional view of the fuel cell separator obtained through compression molding after the variable charge of the present invention.

Thus, the present invention is a mixture of fuel cell separator plate 101 through a two-step short manufacturing process of the two steps of the preparation of the mixture 100 and the two steps of molding and curing 200 using the mixture as shown in FIG. ) And the fuel cell separator 300 is manufactured.

More specifically, in the manufacture of a fuel cell separator, the spherical or plate-shaped natural impression graphite is mechanically processed, and the spheroidized graphite having an average particle diameter of 10 μm to 100 μm and a spheroidization coefficient of 0.5 to 1.0 as a degree of nodularity. The particle anisotropy is reduced compared to the direct use of plate- or needle-shaped undifferentiated natural graphite material, which makes it possible to equalize the electrical conductivity characteristics in the plane direction and thickness direction when manufacturing fuel cell separator plates. It is possible to make the mixed state with the homogeneous to have a high bending strength and to improve the fluidity of the powder to uniformly fill the powder into the mold. At this time, if the average particle diameter of the spheroidal graphite powder is 10 μm or less, the powder flowability is poor, and workability is bad, and the spherical graphite powder of 100 μm or more has difficulty in manufacturing. Therefore, it is necessary to adjust the average particle diameter of the spheroidal graphite powder in the range of 10 μm to 100 μm. . In addition, when the spheroidization degree of the spherical graphite powder is 0.5 or less, the flowability of the powder is bad, so it is necessary to maintain it to 0.5 or more.

In addition, the phenol resin or epoxy resin, which is a thermosetting resin used in the above mixture, uses a phenol powder resin prepared to contain a curing agent in the case of phenol resin for homogeneous mixing with the spheroidized graphite powder. It is used by mixing with a silver curing agent, and the thermosetting resin is used by adjusting the particle size and apparent density with the graphite powder to have an average particle size of 10 ~ 150 ㎛. If the average particle size of the thermosetting resin is 10 μm or less, homogeneous mixing with the graphite powder is difficult, and if the surface of the graphite powder is difficult to uniformly coat the surface of the graphite powder, it is necessary to keep it within the range of 10 μm to 150 μm.

The mixing ratio of the natural graphite powder and the thermosetting resin powder is 70:30 to 95: 5. If the mixing ratio of the thermosetting resin powder is more than 30%, the electrical resistance is increased to obtain the desired electrical conductivity, and if less than 5%, sufficient adhesion is not achieved to obtain the desired mechanical strength. Therefore, it is necessary to limit the natural graphite powder to 70 wt.% To 95 wt.%, And the thermosetting resin powder to 5 wt.% To 30 wt.%.

As described above, by controlling the particle size of the thermosetting resin powder with the graphite powder to adjust the apparent density to be 0.5 to 1.0 g / cm ³ , homogeneous mixing (101) is possible with the mixing mixer, and the graphite powder and the thermosetting resin By inducing homogeneous mixing of powders, high electrical conductivity and high flexural strength can be realized in manufacturing fuel cell separator. At this time, when the apparent density of the thermosetting resin powder with the graphite powder is 0.5 g / cm ³ or less, the flowability is poor, and powders of 1.0 g / cm ³ or more are difficult to manufacture, so that they are apparent in the range of 0.5 g / cm ³ to 1.0 g / cm ³ The density needs to be adjusted.

In addition, when homogeneously dry mixing the natural graphite powder and the thermosetting resin powder, additives such as carbon fiber and carbon black of 0.1 wt.% To 5.0 wt.% Are added to improve the mechanical strength and electrical conductivity of the fuel cell separator. It is possible to configure the mixture material for the fuel cell separator containing. At this time, if the content of the additive is less than 0.1 wt.%, The effect of adding mechanical strength or electrical conductivity is insignificant. If the content of the additive is more than 5.0 wt.%, It is difficult to mix and the material value increases. Therefore, the content of the additive is 0.1 wt.%. It is necessary to limit it to% to 5.0 wt.%.

In addition, the present invention, in the manufacture of the fuel cell separator plate in order to minimize the thickness variation of the molded body in the filling and molding the molding material engraved in the flow path as shown in Figure 6, as shown in Figure 6 The filling density of the part without flow path is 0.8 ~ 1.2 g / cm ³ or more when the molding material is filled by using the variable tamping method that uniformly fills the mixture with and without the flow path of the mold. Filling density of the part with flow path is 0.5 ~ 1.0 g / cm ³ , filling the powder to have different packing density so that the molding density is the same after molding, and the thickness variation, the shape of the separator and the width and depth of the flow path A fuel cell separator, as shown in FIG. 7, with high dimensional accuracy within ± 30 μm, was molded. In this case, unbalanced gas tapping or multi-layered powder tamping may be used as the variable filling method. At this time, if the filling density is uniform, the molding thickness deviation after molding is more than ± 30 μm. If the thickness deviation is more than ± 30 μm, the contact with the gas diffusion layer is poor, the electrical resistance increases, there is a fear of gas leakage. Therefore, it is necessary to limit the thickness deviation to within ± 30 μm for good contact. Therefore, if the filling density of the flow path portion and the non-flow passage portion is varied and filled in order to correct the thickness deviation, the thickness deviation of the molded body can be adjusted within ± 30 μm.

In addition, during molding, the molding pressure is formed by applying a pressure of 1.0 to 5.0 kgf per square centimeter of the molded unit, and appropriately a predetermined pressure of 2.0 to 3.0 kgf, and the fully formed molded body is formed between the porous ceramic plate or the porous metal plate. To prevent distortion during curing, the curing temperature is uniformly dispersed in the molded body for 10 to 100 minutes at a temperature of 100 ℃ ~ 200 ℃, suitably 150 ℃ ~ 180 ℃ by curing the distributed thermosetting resin A fuel cell separator having a high electric conductivity and a bending strength of 100 to 275 S / cm and a bending strength of 40 to 55 MPa was prepared. The higher the electrical conductivity and the flexural strength, the higher the efficiency and stability of the fuel cell. At this time, when the curing temperature is less than 100 ℃ incomplete curing occurs, over 200 ℃ over curing is not good to occur. In addition, incomplete curing may occur even if the curing time is less than 10 minutes, and there is a problem such as excessive curing or productivity decrease at 100 minutes or more, it is necessary to limit the curing time from 10 minutes to 100 minutes at the curing temperature 100 ℃ ~ 200 ℃ have.

As described above, the present invention is a method for producing a fuel cell separator and a method for producing a fuel cell separator using the same, and the following describes preferred embodiments and comparative examples of the present invention.

Example 1

(Fuel cell separator is manufactured from a mixture prepared by mixing spheroidized graphite powder and phenol resin powder with a mixer)

In the preparation of the separator, the mixture is dry by using a mixer such that when the ratio of the graphite powder and the phenol resin powder is 100% by weight of the mixture, the spheroidized powder graphite is 90% by weight and the phenol resin powder is 10% by weight. After mixing, the prepared mixture was variably filled in a mold and press-molded at room temperature to prepare a fuel cell separator.

At this time, the dry mixer used is a super mixer, Henschel mixer, zero gravity mixer.

Example 2

As a separator prepared in Example 1, a fuel cell separator having 85 wt% graphite powder and 15 wt% phenol resin was prepared.

Example 3

As a separator prepared in Example 1, a fuel cell separator having 80 wt% graphite powder and 20 wt% phenol resin was prepared.

Example 4

(Fuel cell separator is manufactured from a mixture prepared by mixing spheroidized graphite powder and epoxy resin powder with a mixer)

In the preparation of the mixture, when the ratio of the graphite powder and the epoxy resin powder is 100% by weight of the total mixture, 90% by weight of the spheroidized powder graphite, 9% by weight of the epoxy resin powder, and 1% by weight of the curing agent are used. A mixed material prepared by dry mixing was variably filled into a mold and pressure molded at room temperature to prepare a fuel cell separator.

Example 5

As a separator prepared in Example 4, a fuel cell separator having 85 wt% graphite powder, 13.5 wt% epoxy resin powder, and 1.5 wt% hardener was prepared.

Example 6

As a separator prepared in Example 4, a fuel cell separator having 80 wt% graphite powder, 18 wt% epoxy resin powder, and 2 wt% hardener was prepared.

Example 7

In the production of the separator, the mixture material is spherical graphite powder, carbon fiber, carbon black, and phenol resin powder, when the total amount of the mixture is 100% by weight, the spheroidized powder graphite is 85.5% by weight, and the pulverized carbon fiber 4.0 weight %, Ketchen black 0.5% by weight, phenolic resin powder was dry mixed by using a mixer to 10% by weight, and the fuel mixture was prepared by variable filling the prepared mixture into a mold and pressure molding at room temperature.

Comparative Example 1

(Fuel cell separator is manufactured from a mixed material prepared by dry mixing by mixing needle or plate graphite powder and resin powder with a mixer)

In the preparation of the mixture, when the ratio of graphite powder and phenol resin powder of thin plate having an average particle diameter D 50 of 50 to 100 μm which is not spheroidized into acicular and plate-like natural graphite is 100% by weight of the mixture, 90 wt% graphite powder and 10 wt% phenol resin powder were dry mixed using a mixer to prepare a mixture, variable filling in a mold, and pressure molding at room temperature to prepare a fuel cell separator.

Comparative Example 2

(Manufacture of Fuel Cell Separator Using Mixed Material Prepared by Wet Method)

When the total amount of the mixture is 100, 90% by weight of the spheroidized graphite of Example 1 and 10% by weight of the phenolic resin powder of Example 1 are mixed with methyl ethyl ketone by a ball mill using a ball mill and wet mixed in a 50 ° C. oven. 5 hr dry and dried mixed material is pulverized through a blender, and the mixed material is prepared by a wet method of 90% by weight of graphite powder and 10% by weight of phenol resin through a 100-mesh sieve and variable filling in the mold using the same. And press-molded at room temperature to prepare a fuel cell separator.

In Comparative Example 3, the mixture prepared in Example 1 was uniformly filled in a mold and pressure-molded at room temperature to prepare a fuel cell separator.

In Comparative Example 4, the mixture prepared in Example 4 was uniformly filled in a mold and pressure molded at room temperature to prepare a fuel cell separator.

The moldability, electrical conductivity, and flexural strength of the fuel cell separators prepared in Examples 1 and 2, 3, 4, 5, and 6 and Comparative Examples 1 and 2 were measured and shown in Table 1 below.

TABLE 1

Formability Conductivity (S / cm) Flexural Strength (MPa) Example 1 o 245 41 Example 2 o 180 47 Example 3 o 144 51 Example 4 o 275 40 Example 5 o 175 41 Example 6 o 147 55 Example 7 o 255 48 Comparative Example 1 △ 120 25 Comparative Example 2 o 82 37

   The moldability was expressed as good: o, bad: △, not: x by comparing the shape of the molded body discharged from the mold after molding, the electrical conductivity was measured using a four-terminal measuring instrument, the flexural strength was ASTM D790 It was measured by the specimen thickness 2mm.

In addition, Table 2 shows the thickness variation of the fuel cell separator manufactured by Examples 1 and 4 and Comparative Examples 3 and 4.

TABLE 2

Variable charging Thickness deviation Uniform charging Thickness deviation Example 1 22 μm Comparative Example 3 115 μm Example 4 25 μm Comparative Example 4 120 μm

As described above, the present invention relates to a graphite composite fuel cell separator and a method for manufacturing the same, wherein a powdery thermosetting resin having a similar flow density and spherical natural graphite having high fluidity during the preparation of the mixture is prepared using a mixer. By using dry mixing, the graphite composite can be produced relatively simply, and the compression molding time can be significantly shortened. The fuel cell separator manufactured using the graphite composite is 100 S / cm as shown in the examples. It has a high electrical conductivity and a high flexural strength of 40 MPa or more at a thickness of 1.2mm, and also the variable filling method to ensure that the density of powder charged in the mold is different depending on the distribution of the flow path in the molding of the fuel cell separator Uniform thickness of separator plate with low thickness deviation within ± 30 μm after molding It has the effect of maximizing the efficiency and safety in use by having high precision dimensional accuracy, and it is possible to mold at room temperature without special heating or cooling of the mold to shorten the molding time and increase the production efficiency. It is obvious that this is a very useful invention that can be harvested at the same time.

Claims (9)

  Mixture for fuel cell separator produced by homogeneously dry mixing 70 wt.% ~ 95 wt.% Of natural graphite powder and 5 wt.% ~ 30 wt.% Of thermosetting resin powder, and mold with engraved fuel cell separator flow path Variable filling and compression molding at room temperature to form a compact having a density of 90% ~ 100% of the theoretical density, and the molded body is heat-cured by holding for 10 to 100 minutes at 100 ℃ ~ 200 ℃ characterized in that the solid graphite composite material Method for producing a graphite composite fuel cell separator. The method of claim 1, The natural graphite powder is spheroidized by mechanically processing needle-like or plate-like natural graphite, the average particle diameter of the graphite powder is 10 ~ 100 μm, the spheroidization degree is 0.5 ~ 1.0, the apparent density is 0.5 ~ 1.0 g / A fuel cell separator and a method for producing a fuel cell separator using the same, characterized in that to form a mixture for fuel cell separator using a spherical graphite powder of cm ³ . The method of claim 1, The powdered thermosetting resin powder has a powder average particle size of 10 to 150 μm and a phenol resin or epoxy resin containing a curing agent having an apparent density of 0.1 to 1.0 g / cm ³ to form a mixture for a fuel cell separator. A mixture of fuel cell separators and a method of manufacturing a fuel cell separator using the same. The method of claim 1, When the natural graphite powder and the thermosetting resin powder is homogeneously dry mixed, the fuel characterized in that a fuel cell separator comprising a mixture of 0.1 wt.% To 5.0 wt.% Carbon fiber, carbon black additive respectively Mixture for a battery separator and a method for producing a fuel cell separator using the same.      The method of claim 1, A method of manufacturing a fuel cell separator and a fuel cell separator using the same, characterized in that the natural graphite powder and the thermosetting resin powder are homogeneously dry mixed in a dry mixer in the production of the fuel cell separator.      The method of claim 1       When filling the fuel cell separator plate mixture into a mold engraved with the fuel cell separator flow path, the filling density of the mixture material is differently charged for the flow path section and the part without the flow path according to the shape and shape of the flow path. A method for manufacturing a fuel cell separator, characterized in that there is little thickness variation after molding and molding with high dimensional accuracy is possible.      The method according to claim 1 or 6,      The variable filling method of the fuel cell separating plate mixture in the mold engraved with the flow path is a method of manufacturing a fuel cell separating plate, characterized in that the variable filling the powder by unbalanced gas tapping.      The method according to claim 1 or 6,      The variable filling method of the fuel cell separating plate mixture in the mold engraved with the flow path is a method of manufacturing a fuel cell separating plate, characterized in that the variable filling by filling multiple powders in the mold.  Fuel cell, characterized in that the dimensional accuracy is within ± 30 μm, the bending strength is 40 MPa or more, the surface electrical conductivity is 100 S / cm or more, without the distortion of the natural graphite powder and the graphite composite composed mainly of the thermosetting resin Separator.

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