JP2006172955A - Manufacturing method of fuel cell separator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a fuel cell separator which can be manufactured using a material molded in tablet shape by an ordinary tablet molding machine and by an ordinary die in a state of being filled uniformly. <P>SOLUTION: A material having carbon and resin as a principal component, with a spiral flow of 3 cm-100 cm, is molded in a tablet shape, and then a plurality of materials of tablet shape are filled in a die and are compression-molded. At this time, molding is carried out by a normal tablet molding machine, and compression molding of the separator is carried out by a normal die. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a fuel cell separator.

  Fuel cells that are used in household cogeneration systems and automotive applications are attracting attention. A fuel cell is used by directly converting it into electrical energy without converting chemical energy into heat energy, and usually takes out electricity by reaction of hydrogen and oxygen. There are several types of fuel cells, such as phosphoric acid fuel cells, solid electrolyte fuel cells, and polymer electrolyte fuel cells (PEFC).

  In each type of fuel cell, a fuel cell separator (hereinafter simply referred to as a separator) is used. A separator comprises a unit cell with an electrode etc. Since one unit cell has a small electrical output, a stack in which many unit cells are stacked is used. The separator isolates the introduced hydrogen gas or oxygen gas between adjacent cells.

  The separator is formed with a large number of grooves that serve as gas flow paths, and is usually formed with through holes (hereinafter sometimes simply referred to as holes) for introducing gas from the outside to the periphery of the separator. . Since the separator functions as a current collector of the fuel cell, a high conductivity of, for example, 10 mΩ · cm or less is required. The separator is also required to have functions such as gas permeability, oxidation resistance, hydrolysis resistance, hot water resistance, and hydrophilicity for effectively draining generated water.

In recent years, various materials such as carbon materials, metals, and conductive polymers have been studied as materials for these separators.
Among these materials, carbon material systems having excellent characteristics such as conductivity and heat resistance are widely used. There are various carbon material systems such as graphite / resin compound systems, expanded graphite systems, sheet carbon systems, and glassy carbon systems.

  Among these carbon material-based separator materials, graphite / resin compound-based materials are considered easy to mold and suitable for mass production.

In this case, the material is a compound system containing graphite that does not melt unless it is extremely high temperature, and hardly flows. Therefore, as a manufacturing technique, the material is heated and melted to be in a fluid state, and pressed into a closed mold to be molded. No molding technology such as injection molding is used.
In addition, even if a molding technique such as an injection molding method is applied by increasing the fluidity of the material by, for example, reducing the ratio of graphite of the material, the electrical characteristics cannot be satisfied.

  For this reason, a compression molding technique is generally employed in which a mold is opened and filled with a material, and then the mold is tightened and pressed and heated for molding.

However, even in the case of producing a carbon material separator using compression molding technology, it is necessary to increase the graphite blending ratio of the material in order to satisfy the high conductivity required as a separator. In most cases, the material is difficult to flow. Moreover, even if it is a flowable material using a thermosetting resin having a relatively low viscosity at the time of molding, the fluidity is not good because the viscosity is very high. In this case, if the temperature of the mold is increased for the purpose of improving the fluidity of the material, the resin is rapidly cured, which is not appropriate.
If the filling state of the material is not uniform, the thickness accuracy of the separator to be molded is lowered, or a portion having a low mechanical strength is generated, which causes a crack of the separator.

  Therefore, it is essential that the material is uniformly filled in the mold by appropriate means, but this is usually not always easy.

For this reason, as a manufacturing method of a separator, a method of processing a groove and a hole by cutting after a flat plate is once manufactured by molding has been proposed.
However, this method does not require precise material filling because it performs cutting, but it takes time to manufacture a separator and is expensive to manufacture, and is not suitable for industrial mass production.

  Therefore, a method for improving the mechanical strength of the separator has been proposed by uniformly charging and filling the molding material into the mold.

For example, a material is once filled in an input part having a plurality of input ports arranged in a matrix in a downward direction and having a predetermined volume space formed at a certain height, and after the input part is arranged on the upper part of the mold, the input part A method of uniformly filling a mold with a material by pulling out a slide plate located on the lower side has been proposed (see Patent Document 1).
In addition, an apparatus for manufacturing a carbon separator for a fuel cell has been proposed that can supply a molding material accurately and uniformly into a mold cavity in a predetermined amount. This device has a lower die and a die that form a cavity that opens upward, a mesh that can enter and retract in the lateral direction above the cavity, and moves laterally relative to the mesh located on the mesh. And a raw material storage container that can enter and retract in the lateral direction above the cavity and supplies the raw material to the cavity through mesh eyes (see Patent Document 2).

However, each of these methods or apparatuses requires a dedicated material filling apparatus having a complicated structure. For this reason, the material filling equipment cost is incurred separately from the main body equipment cost, the device is not versatile, the material filling device must be manufactured for each mold, and the material filling takes time etc. There is.
In these methods or apparatuses, the time required for material filling is longer than that of fluid molding as compared with fluid molding such as injection molding. When filling the material, the mold temperature must be lower than the molding temperature. After filling the material, the mold is heated to the molding temperature, and the mold is released for mold release and material refilling. It is necessary to cool the mold, and the molding cycle is considerably longer than that of injection molding or the like.

  On the other hand, in order to solve the problem peculiar to the separator material that the filling time becomes long due to the poor fluidity of the above materials, and to shorten the molding cycle, holes and grooves are collectively formed at the molding stage. As a method that has been devised, a method has been devised in which a sheet-like primary molded body (this is referred to as a preform) is molded and then the preform is filled into a mold and molded.

As an example, a resin composition containing a non-carbon thermoplastic resin such as polyphenylene sulfide resin and a conductive agent such as graphite particles or conductive carbon black is formed into a sheet, and the resulting sheet is stamped with a grooved mold. There is a method of manufacturing a fuel cell separator by molding (see Patent Document 3).
However, this method takes time and effort to mold the preform, and it is necessary to provide an expensive dedicated apparatus for manufacturing the preform, so that the preform molding cost increases. Furthermore, since the required molding pressure is as very high as 100 MPa, the compression molding machine becomes very large and the molding cost of the separator increases.

In addition, paying attention to the fact that excessive molding pressure is required to spread the plate-shaped preform with a press so that the cavity is uniformly filled, the gas flow path is used to suppress the excessive molding pressure. There has been proposed a method using a drum-shaped preform in which the width in the gas flow path length direction at the center in the alignment direction is narrowed. (See Patent Document 4).
However, in practice, it is not easy to manufacture a preform having the above-mentioned special shape. For example, after extrusion molding or calender molding, further punching molding is necessary, which increases the preform molding cost. . In this case, it is conceivable to form the preform with a tableting machine (tablet making device), but since the shape is complicated and the area is large, it is difficult to produce a uniform preform. The handling of preforms is complicated.

In addition, a method using a tablet with a projected area of 45% or more of the separator area has been proposed. (See Patent Document 5). In this method, as in the case of the drum-shaped preform, it is difficult to manufacture a tablet having a large area, and handling of the manufactured tablet is complicated.
Japanese Patent No. 3356728 JP 2003-346829 A JP 2001-122777 A JP 2002-373671 A JP 2003-346827 A

The problem to be solved is that when manufacturing a separator for a fuel cell with a mold using a separator material having poor fluidity formed into a tablet shape, it cannot be molded in a uniform filling state, or When a tablet-shaped material having a large area is used in order to obtain a uniform filling state, the molding is difficult, and handling of the manufactured tablet is complicated.
In view of the above points, the present invention provides a fuel cell separator capable of manufacturing a fuel cell separator in a uniform filling state with a normal mold using a material molded into a tablet shape by an ordinary tablet molding machine. It aims to provide a method.

  The method for producing a fuel cell separator according to the present invention comprises forming a material having carbon and resin as main components and a spiral flow of 3 cm to 100 cm into a tablet shape, and then charging a plurality of the tablet shape materials into a mold. And compression molding.

  The method for producing a fuel cell separator according to the present invention is characterized in that the resin is a thermosetting resin.

  The method for producing a fuel cell separator according to the present invention comprises forming a material having carbon and resin as main components and a spiral flow of 3 cm to 100 cm into a tablet shape, and then charging a plurality of tablet-shaped materials into a mold. In order to perform compression molding, a fuel cell separator can be manufactured in a uniform filling state with a normal mold using a material molded into a tablet shape by a normal tablet molding machine.

  Embodiments of the present invention will be described below. In addition, this invention is not limited to the following embodiment examples at all. Moreover, in each figure, in order to make a structure easy to understand, the groove | channel and hole intrinsic | native to a separator are not displayed and description is abbreviate | omitted. The present invention is not limited by the presence or absence of grooves or holes.

In the method for manufacturing a fuel cell separator according to the present invention, for example, a mold of a compression molding type as shown in FIG.
A mold 10 whose side view is shown in FIG. 1 includes an upper mold 12, a middle mold 14, and a lower mold 16. A portion (molding of a material) where a product for molding is formed by filling a molding material (hereinafter simply referred to as a material) in the upper mold 12, the middle mold 14 and the lower mold 16 in a clamped state. (Cavity) 18 is formed. In this case, the middle mold 12 may be omitted and the middle mold and the lower mold may be integrated. However, in order to facilitate the release of the separator, it is better to use the middle mold. .

  In the manufacturing method of the fuel cell separator of the present invention, the material used is that formed into a tablet shape. Here, the tablet shape means a granule shape, and includes not only a so-called tablet shape but also a pellet shape. Hereinafter, a tablet-shaped material is simply referred to as a tablet.

  The tablet material (molding material) is mainly composed of carbon and resin, and these are mixed and kneaded.

Carbon is preferably graphite, and in this case, the type of graphite is not particularly limited as long as it exhibits high conductivity. For example, carbonized carbon such as mesocarbon microbeads, coal-based coke, Graphitized petroleum coke, graphitized by catalytic action of boron, silicon, iron and their compounds, special carbon materials such as isotropic graphite, natural graphite, quiche graphite, etc. can be used In addition, graphite electrode processing powder, conductive carbon black, and the like can also be used.
Moreover, it can replace with graphite and other carbons (carbon material), such as hard carbon materials, such as glassy carbon and isotropic carbon, can also be used.

  These powders obtained by pulverizing carbon can be used alone or in admixture of two or more at a mass ratio of 40:60 to 90:10, preferably 70:30 to 80:20. Moreover, you may use the graphite powder etc. which have 2 or more types of particle size distribution, for example, the large particle diameter graphite powder etc. with an average particle diameter of 50-300 micrometers, and the average particle diameter of less than 50 micrometers, Preferably it is a small particle | grain with 5-20 micrometers You may mix | blend diameter graphite powder etc. by the ratio of 40: 60-90: 10 by the mass ratio, Preferably it is 70: 30-80: 20.

The resin is not particularly limited as long as it is heat-resistant and has a viscosity low enough to be kneaded, and either a thermosetting resin or a thermoplastic resin can be used. More preferably, a thermosetting resin is used. Use.
As the thermosetting resin, for example, a resin such as a phenol resin, a furfuryl alcohol resin, an epoxy resin, a urea resin, or a melamine resin can be used. The resin viscosity should be low in order to increase the conductivity by mixing as much graphite powder as possible. For example, an epoxy resin is blended when the resin alone or a curing agent is blended. In this state, the viscosity at 150 ° C. is 1 to 500 mPa · s, and the viscosity at 25 ° C. is preferably solid or 3 Pa · s or higher. In addition, as an epoxy resin hardening accelerator, well-known accelerators, such as amines, imidazoles, ureas, organic phosphines, a Lewis acid, can be used.
Thermoplastic resins include, for example, polyamide, polyethylene, polypropylene, polybutylene terephthalate, liquid crystal polymer, polyphenylene sulfide, polyimide, polyamideimide, polyphenylene ether, polysulfone, polyphenylene ether, polyether ether ketone, polyether ketone, polyphenylene oxide, polyacetal, etc. Can be used. However, when using a thermoplastic resin, when the molded separator is taken out from the mold, the mold temperature must be cooled to a temperature that can be taken out, and further the mold temperature must be raised to the molding temperature at the time of molding. It should be noted that the molding cycle is lengthened accordingly and energy is lost.

  The blending ratio of the resin and the raw material containing a hardener or the like to be blended in addition to graphite powder or the like if necessary is that the raw material other than the resin is 2 to 15 times the mass of the resin, It is preferable from the viewpoint of providing necessary conductivity. Even if the resin is too much or too little, the specific resistance increases. Therefore, the mass is more preferably 3 to 8 times. In general, if the proportion of the resin is too large, contact between the graphite powders is hindered and the conductivity is lowered, and if it is too small, not only a molded product having a predetermined strength can be obtained, but also the flow characteristics deteriorate and molding is difficult. Become. The graphite powder and the resin may be mixed at the same time. When using graphite powder having two or more types of particle size distribution, the graphite powder is mixed in advance and then mixed with the resin. May be.

  In addition to the graphite powder and the resin and the resin, a modifying additive and other conductive fillers can be blended within a range that does not impede the effects of the present invention. Examples of modifying additives include liquids such as liquid paraffin, powder release agents such as carnauba wax, low molecular weight polyethylene wax, and stearic acid, antioxidants, plasticizers, and other various additives. . Moreover, you may use together the additive which assists hydrophilicity, such as surfactant and hydrophilic resin, in the range which does not prevent the effect of this invention.

It is advisable to adjust the particle size distribution obtained by kneading graphite powder etc. and resin to a predetermined particle size distribution. The particle size distribution can be changed to Rosin-Rammler's distribution.
distribution) formula:
R = 100exp (−ad ⁿ )
(Wherein, R is the distribution amount cumulative value on the sieve (%), d is the particle size (μm), a is a constant), the value of n is 1.2 to 2.0, especially A range of 1.3 to 1.6 is preferable. In this case, the particle size is measured by a sieving method. In the Rosin-Rammler distribution formula, when the powder particles have a normal distribution, n indicates the distribution range, and the larger n, the sharper the distribution. When the value of n is less than 1.2, the distribution is too wide and large particles are included and the surface of the molded product tends to be rough. On the other hand, when the value of n exceeds 2.0, the distribution becomes sharp. Therefore, the specific gravity does not increase and the resistance tends to increase. In addition, control of n value is possible by selecting a classification condition, a grinder, and its operation conditions.

As the material (raw material), a material having a spiral flow (sometimes referred to as a spiral flow length or a flow distance) having a flow characteristic of 3 cm to 100 cm is used.
If the value of the spiral flow is less than 3 cm, it hardly flows, so that tablet molding becomes extremely difficult, and not only a separator having a uniform density is obtained, but also a state of poor filling is obtained. On the other hand, if the flow distance exceeds 100 cm, burrs will remarkably occur, which makes mold design and mold manufacturing accuracy difficult, and even if it is designed and manufactured with strict accuracy, the load of burrs removal work will increase. Problems such as easy occurrence of problems such as mold galling in the molding operation may occur. Needless to say, the effect of the present invention can be more suitably expressed when using a material having relatively poor flow characteristics. In that sense, a more preferable range of the spiral flow is, for example, about 4 cm to 20 cm. it can. Further, when a material having a spiral flow of about 3 cm to 10 cm is used, there is a possibility that the molding itself may be difficult by a method using only one conventional pellet.
The spiral flow is evaluated by transfer molding using a spiral flow mold having a cross-sectional shape of φ3.2 mm described in ASTM D3213 (width 3.2 mm, thickness 1.6 mm). The shape of the material does not need to be tableted, and may be in a state just before tablet creation. That is, it is in the form of powder, granules, pellets, or the like. The material filling amount is 16 g when the plunger diameter is 35 mm. The molding conditions are a molding temperature of 180 ° C. and a plunger pressure of 200 kg / cm ² . It is not necessary to keep the preheat after the material is put into the molding machine, and the molding is performed immediately.

  The molding shape of the tablet molded using the above material (raw material) may be any of a columnar shape, an elliptical columnar shape or a polygonal columnar shape having a low height.

The tablet has a planar dimension of φ150 mm or less for a cylindrical shape, a major dimension of 150 mm or less and a major axis / minor axis of 3 or less for a elliptical cylinder, and a longest dimension of 150 mm or less for a polygonal column. It is preferable that side / shortest side = 3 or less. In any of these shapes, the thickness (height) is preferably 1 mm or more. More preferably, in the case of a cylindrical shape, φ100 mm or less, in the case of an elliptical column shape, the major axis dimension is 100 mm or less and the major axis / minor axis = 2 or less. Side / shortest side = 2 or less. In consideration of tablet manufacturability, the tablet shape is most preferably a columnar shape, followed by an elliptical columnar shape and a polygonal columnar shape in that order. Among the polygonal columnar shapes, a quadrangular columnar shape is more preferable from the viewpoint of tablet molding. Moreover, it is preferable to provide R in the corner part of a polygonal columnar tablet.
If the planar dimensions of the tablet exceed the above values for each shape, it is difficult to manufacture the tablet.

The tablet molding conditions are not particularly limited, and for example, the tablet can be molded under the following conditions.
That is, the molding temperature is preferably room temperature to 130 ° C, more preferably room temperature to 120 ° C. When the molding temperature exceeds 130 ° C., the curing of the material progresses in the molding process, and thus it is necessary to cool the tablet immediately. The molding pressure is preferably 10 MPa to 100 MPa. If the molding pressure is less than 10 MPa, tableting becomes difficult. On the other hand, when the molding pressure is higher than 100 MPa, when a relatively thin tablet is molded, it becomes difficult to take out from the tablet molding apparatus, and the tablet molding apparatus becomes expensive.

A method for producing a fuel cell separator according to the present invention using the tablet described above as a material will be described.
First, for example, a plurality of tablets are loaded into the cavity 18 of the mold 10 described above and arranged. This operation can be performed manually or by a robot, or using a dedicated jig or the like.

  In this case, when the number of tablets is as small as about 2 or 3, for example, it is possible to use a method using a hand or a robot. However, when the number of tablets is as large as 4 or more, use a dedicated jig. Is preferred.

For example, the jig 20 shown in FIGS. 2 and 3 can be used.
The jig 20 includes a tablet set portion 24 having a plurality of holes 22 formed on the upper surface of a box having an open lower surface, and a slide plate 26 that is provided so as to close the lower surface and is slidable in the horizontal direction. Here, the plurality of holes 22 are formed at desired positions in consideration of a good filling state, with the number corresponding to the shape and number of tablets set in consideration of tablet characteristics, mold dimensions, molding conditions, and the like. Is done.
As shown in FIG. 2, a plurality of tablets W are respectively arranged in the plurality of holes 22 with the slide plate 26 closing the lower surface of the tablet set portion 24, and slide on the lower mold 16 as shown in FIG. 3. By sliding the plate 26 and removing the bottom of the tablet setting unit 24, a plurality of tablets W are sequentially loaded into the mold and filled. Thereby, the some tablet W can be easily positioned in the predetermined position in a metal mold | die. The tablet W may be preheated prior to charging.

After filling the lower mold 16 with the tablet W, normal compression molding is performed. That is, mold clamping is performed and molding is performed for a predetermined time at a predetermined pressure and temperature. When performing mold clamping, bumping may be performed by opening and closing the mold several times for the purpose of releasing air.
In order to easily form a plurality of holes provided in the vicinity of the peripheral edge of the separator, which is a finished product, a punching member having a cylindrical tip portion, a columnar tip portion, a conical tip portion, or other shape in the mold The hole may be formed in the material by allowing the tip of the punching member to enter the material during the mold clamping or after the mold clamping is completed and before the material is completely cured.

Molding conditions vary depending on the resin used.
For example, when an epoxy resin is used as a base, the molding pressure is 10 MPa to 80 MPa, more preferably 20 MPa to 60 MPa. When the molding pressure is lower than 10 MPa, filling failure occurs. On the other hand, if the molding pressure is higher than 80 MPa, the molding machine becomes large and the molding cost increases. The molding temperature is 120 ° C. to 250 ° C., more preferably 130 ° C. to 210 ° C. in terms of the mold surface temperature. When the molding temperature is lower than 120 ° C., it takes time to cure. On the other hand, when the molding temperature exceeds 250 ° C., curing is likely to proceed while the tablet material is filled in the mold and molding is started, and it is necessary not only to start molding in a very short time, but also at the time of mold release. If the thickness is not lowered, the strength of the molded product is low and it is difficult to take out. The molding time is 0.5 to 20 minutes, preferably 1 to 15 minutes. If it is within 0.5 minutes, it will not cure. If it exceeds 20 minutes, the molding efficiency is poor. After molding is completed, the mold is opened to obtain a separator. Further, aftercuring may be performed. In addition, warping may be corrected by applying a load to the separator during after-curing.

  Further, an external release agent may be used to facilitate release of the manufactured separator. As the type of the external release agent, known ones such as silicon-based, fluorine-based, waxes, metal soaps, and stearic acids can be used. As a method for applying the external release agent, an appropriate method such as a method of directly applying a solid, powder or granular material or a method of spray coating can be used.

  The flash generated in the separator taken out from the mold is subjected to flash processing by a usual method such as cutter processing, punching, drill processing, sand blasting or shot peening.

According to the manufacturing method according to the present embodiment, when manufacturing a fuel cell separator, even a separator material having poor fluidity does not require a tablet having a special shape, and a normal tablet can be used.
In this case, if the spiral flow is less than 3 cm, even if a high molding pressure is applied, filling will be poor, and even if it can be filled, there is a risk that the separator will crack when it is released from the mold, If the spiral flow is 3 cm or more, the risk is small. When the spiral flow exceeds 100 cm, a burr problem or a mold breakage problem may occur.
Therefore, according to the manufacturing method according to the present embodiment, by using a tablet manufactured by a general-purpose tablet manufacturing apparatus, material is charged and filled in a short time, and can be molded at a constant mold temperature. Production efficiency can be increased.
Further, when molding, a fuel cell separator excellent in conductivity can be obtained without requiring a large compression molding machine. For example, it has physical properties of a bulk density of 1.80 g / cm ² or more, a specific resistance of 100 mΩcm or less, a bending strength of 30 MPa or more, a gas permeability of 1 × 10 ⁻¹⁴ cm ² or less, and an extremely excellent thickness accuracy (variation) of 100 μm or less. A separator exhibiting physical properties can be obtained.

It is a schematic side view of the metal mold | die used by this invention. It is a schematic side view of the jig | tool used by this invention. It is a figure for demonstrating the method of charging and filling a tablet with a metal mold | die using the jig | tool of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Mold 12 Upper mold 14 Middle mold 16 Lower mold 20 Jig 24 Tablet set part 26 Slide plate W Tablet

Claims (2)

  A fuel cell comprising carbon and a resin as main components, a material having a spiral flow of 3 cm to 100 cm formed into a tablet shape, and a plurality of the tablet-shaped materials are charged into a mold and compression-molded. Separator manufacturing method. 2. The method for producing a fuel cell separator according to claim 1, wherein the resin is a thermosetting resin.