JP2006202730A - Sheet shape forming material for fuel cell separator, its manufacturing method, and separator for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheet shape forming material for obtaining a fuel cell separator which has a superior conductivity is capable of thinning than the conventional one, and has a high thickness precision, and its manufacturing method, and a fuel cell separator made by forming the forming material. <P>SOLUTION: This is the sheet shape forming material having a conductive particle layer made of a particle containing a conductive particle on at least one side of a resin sheet, and the content of the conductive particle in the sheet shape forming material is 70-95 wt%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a sheet-shaped molding material for use in a fuel cell separator such as a phosphoric acid fuel cell, a direct methanol fuel cell, and a solid polymer fuel cell used for an automobile power source, a portable power source, an emergency power source, etc. The present invention also relates to a fuel cell separator using the same.

A so-called fuel cell that extracts energy obtained by an electrochemical reaction between hydrogen and oxygen as electric power is expected to be widely used in various applications such as portable devices and automobiles. In this fuel cell, a membrane / electrode assembly (hereinafter referred to as MEA) having electrodes and gas diffusion layers such as carbon paper on both surfaces of an electrolyte membrane, fuel (hydrogen gas, etc.) and oxidant (air or oxygen) on at least one surface. ) Or by putting several tens to hundreds of cells in series in a series of basic structural units (hereinafter referred to as single cells) sandwiched between two separators in which refrigerant flow paths for cooling the cells are formed. It is common to secure.
Therefore, separators used in these fuel cells are required to have “conductivity” in order to increase the power generation efficiency of the fuel cell. At the same time, the demand for miniaturization of the fuel cell has led to the “thinning” of the separator. The demand is high. In addition, as described above, since a fuel cell for obtaining practical power is usually used by laminating a plurality of separators in the thickness direction, the separator itself is provided with a high “thickness accuracy” and is separated. It is expected to reduce the contact resistance between the MEA and the MEA and between the fuel cells, and to ensure the airtightness or watertightness of the various gas or liquid seal packings and gaskets introduced into the fuel cell. From such a viewpoint, a molding material suitable for producing separators with high conductivity, thinness, and high thickness accuracy is desired. In addition, a method capable of producing a separator with high productivity and low cost from the economical aspect is also demanded.

  For this reason, after mixing the conductive agent and the thermoplastic resin, a sheet-shaped molding material is prepared by a conventional method such as extrusion molding or hot rolling, and then this sheet-shaped molding material is used as fuel and / or oxidation. There has been proposed a method of forming a predetermined separator using a mold having an agent flow path (see, for example, Patent Documents 1 and 2).

However, in these methods, a kneading step of a mixture of a thermoplastic resin and conductive particles such as graphite used as a conductive agent, and a strong shearing force on the thermoplastic resin and the conductive agent when the mixture is extruded. Pressure will be applied. As a result, since the conductive particles are crushed, the number of conductive particles increases, the contact resistance between the conductive particles increases, and the conductivity of the separator obtained by molding the sheet material decreases. is there.
Further, if the ratio of the conductive agent in the mixture is increased to 80% by weight or more for the purpose of improving the conductivity of the separator, a larger shearing force and pressure are required in the kneading process, sheeting process and molding process of the mixture. As a result, it is difficult to obtain the conductive performance desired for the separator, and since a high concentration of the conductive agent is included, it is difficult to obtain a thin sheet with poor workability. Furthermore, a separator obtained by molding such a sheet material has poor mold shape transferability, tends to cause dimensional accuracy defects, and thickness accuracy becomes a problem.

In Patent Document 3, as a method for obtaining a conductive thin sheet without applying a strong shearing force or pressure to a conductive agent, a so-called conductive coating material in which conductive fine particles such as graphite are uniformly dispersed in an epoxy resin is coated with a nonwoven fabric surface. There has been proposed a coating method.
However, according to this method, in order to uniformly apply the epoxy resin in which the conductive fine particles are dispersed on the nonwoven fabric, the addition amount of the conductive particles is reduced to about 35 to 60% by weight, and the fluidity is reduced. Therefore, it was inevitably impossible to obtain the conductivity of 200 mΩcm or less required for the fuel cell separator with the amount of the conductive particles.
Therefore, in conventional sheet stamping molding, sheet rolling molding, and punching molding, it is possible to produce a molding material that has high conductivity required for a fuel cell separator and is suitable for producing a thin and highly accurate separator. It was difficult.
Further, a separator for a fuel cell obtained by heating and softening a nonwoven fabric having thermoplastic resin fibers having a diameter of 0.1 to 20 μm and conductive powder particles uniformly distributed therein (for example, a patent) Document 4) has been proposed. However, with this method, a sheet-shaped molding material having a thickness of about 0.05 mm can be obtained, but since the conductive powder particles are distributed inside the nonwoven fabric, a sheet-shaped molding material thinner than this cannot be obtained. There was a problem that a mold separator could not be obtained. In addition, since a process for producing a nonwoven fabric once using thermoplastic resin fibers and conductive particles as a raw material is included, it is disadvantageous in terms of production efficiency, and the thickness accuracy of the resulting nonwoven fabric tends to be low. It was.
JP 2001-122777 A JP 2002-198062 A JP 2003-89969 A JP 2004-356091 A

  Accordingly, the present invention aims to solve the above-mentioned problems of the prior art. Specifically, the present invention has excellent conductivity, can be thinner than the conventional one, and has high thickness accuracy. It aims at providing the separator for fuel cells formed by shape | molding the sheet-like molding material for obtaining a fuel cell separator, its manufacturing method, and this molding material.

As a result of intensive studies to solve the above technical problems, the present inventors have produced a sheet-shaped molding material by depositing conductive particles in a layer form on the surface of the resin sheet, and molded the sheet-shaped molding material. This eliminates the kneading step between the resin and the conductive particles, enables the sheet to be produced under relatively mild conditions, and extremely reduces the crushing of the conductive particles. It has been discovered that a high fuel cell separator can be produced efficiently.
That is, the present invention is a sheet-shaped molding material having one conductive particle layer composed of particles containing conductive particles on at least one surface of a resin sheet, wherein the conductive particles in the sheet-shaped molding material A sheet-like molding material for a fuel cell separator, characterized in that the content is 70 to 95% by weight.
In the present invention, at least one side of the resin sheet
Step (1); Step (2) of uniformly dispersing conductive particles on the surface of the resin sheet; Step (3) of attaching a part of the conductive particles to the resin sheet; In the step (2) The present invention provides a method for producing a sheet-shaped molding material for a fuel cell separator, wherein the step of removing conductive particles not attached to a resin sheet is sequentially performed.
Furthermore, this invention provides the separator for fuel cells formed by shape | molding an above described sheet-like molding material.

  By using the sheet-shaped molding material of the present invention, it is possible to efficiently produce a fuel cell separator that is superior in conductivity, thin, and has high thickness accuracy, and such separators are portable power supplies, automobile power supplies, and emergency power supplies. It can be effectively used for a fuel cell.

The present invention will be described in more detail below.
The sheet-shaped molding material for a fuel cell separator of the present invention has one conductive particle layer on at least one surface of a resin sheet, and the content of conductive particles in the sheet-shaped molding material is 70 to 95. It is characterized by weight percent. As long as the content of the conductive particles is within the above range, the particle layer may be formed only on one side of the sheet-shaped molding material or on both sides.
The sheet-like molding material of the present invention is characterized in that conductive particles are present on the surface (one side or both sides) of the sheet and are unevenly distributed in the thickness direction of the sheet to form one layer. To do. FIG. 7 schematically shows a cross section of the sheet-shaped molding material for a fuel cell separator according to the present invention.

  The resin sheet of the present invention may or may not have voids. However, if the voids are present, the ratio of conductive particles is increased, and a separator having excellent conductivity can be obtained. Even when the true specific gravity of the resin sheet is large (the thickness of the resin sheet is the thinnest), a sheet having a large thickness can be applied to the present invention, and the handleability of the obtained sheet-like molding material is improved. This is preferable.

The position of the voids in the resin sheet used in the present invention and the shape of the voids are not particularly limited, and may be present inside the resin sheet or on the surface of the resin sheet. In order to facilitate the adhesion of the conductive particles to be used, the voids are preferably present in an open state on the surface of the resin sheet, and the opening area of the voids is large on the surface of the resin sheet. It is more preferable that the opening area is smaller inside because the conductive particles adhere more reliably to the resin sheet.
Moreover, it is preferable to select the shape of the conductive material used that is similar to the shape of the gap.

The preferred resin sheet porosity is that a large amount of conductive particles can be inserted into the resin sheet, that the conductive particles can be easily fixed to the resin sheet, and the resin sheet. And from the handleability etc. of sheet-like molding material, 30 to 90% is preferable, More preferably, it is 50 to 85%.
Here, the porosity of the resin sheet can be calculated by the formula (I).
Porosity of resin sheet (%) = [1- (true volume of resin sheet) / (apparent volume of resin sheet)] × 100 (I)
The true volume of the resin sheet can be calculated by measuring the weight of the resin sheet and dividing the value by the specific gravity of the sheet. The apparent volume of the resin sheet can be calculated from the measured values of the apparent thickness, width, and length of the sheet. In the resin sheet of the present invention, when a void is opened on the surface, the apparent thickness is the thickness between the upper and lower planes of the resin sheet.

The size of the void in the resin sheet is determined in consideration of the size of the conductive particles to be used. That is, when using large conductive particles, the resin sheet gap is increased, and when using small conductive particles, the resin sheet gap is reduced.
In the present invention, the average pore diameter of the voids is preferably 10 to 800 μm, particularly preferably 50 to 500 μm, from the range of the average particle diameter of the conductive particles described later.
If the average pore diameter of the voids is within this range, the conductive particles can be uniformly dispersed on the resin sheet, and the homogeneous sheet is less likely to fall out of the voids of the resin sheet in which the conductive particles are inserted. A shaped molding material can be obtained.
Here, the average pore diameter of the voids is a weighted average value of the average pore diameters of voids existing in a 10 mm square sheet, which is a circumscribed circle diameter of an enlarged image of the sheet surface obtained using a stereomicroscope or the like. In this case, when the space | gap has penetrated in the thickness direction of the sheet | seat, the shortest diameter of the inscribed circle of a penetration part is employ | adopted.

Basis weight of the resin sheet used in the present invention is preferably 5~300g / ^{m 2,} and particularly preferably 5 to 200 g / ^{m 2.} If the basis weight of the resin sheet is in the range of 5 to 300 g / m ^2, a sheet-shaped molding material in which the ratio of the weight of conductive particles to be described later and the weight of the resin sheet is suitable is obtained. By using this, a thin fuel cell separator with small thickness variation can be formed.
Moreover, it is preferable that the thickness of a resin sheet is 5-300 micrometers, and it is especially preferable that it is 50-200 micrometers. If the thickness of the resin sheet is in the range of 5 to 300 μm, it is preferable in terms of easily maintaining the thickness accuracy of the separator obtained by molding and securing the conductivity of the separator finally obtained. If a thicker resin sheet is used, when a plurality of sheets are stacked and formed into a separator shape, sufficient contact between the conductive particles cannot be secured, and the conductivity of the separator is reduced. become.

Examples of the resin of the resin sheet used in the present invention include a thermosetting resin and a thermoplastic resin. Examples of such thermosetting resins include phenol resins, epoxy resins, vinyl ester resins, urea resins, melamine resins, unsaturated polyester resins, silicone resins, diallyl phthalate resins, maleimide resins, polyimide resins, and the like.
The thermosetting resin is not limited to one composed of one type of resin, and even if two or more types of resins are mixed, a composite sheet in which two or more types of resins are formed in layers can be used (see FIG. 1). . A sheet made of a thermosetting resin is prepared by preparing a resin solution in which a thermosetting resin and a curing catalyst are diluted with a solvent, and applying this solution onto a release paper, etc. It can be obtained by removing the solvent. However, it goes without saying that this resin sheet is used in an uncured state, an uncured state or a so-called B-stage state in order to be finally cured in a separator molding step.

On the other hand, examples of the thermoplastic resin include polyethylene, polypropylene, cycloolefin polymer, polystyrene, syndiotactic polystyrene, polyvinyl chloride, ABS resin, polyamide resin, polyacetal, polycarbonate, polyphenylene ether, modified polyphenylene ether, polyethylene terephthalate, polytrimethylene. Terephthalate, polybutylene terephthalate, polycyclohexylene terephthalate, polyphenylene sulfide, polythioethersulfone, polyetheretherketone, polyarylate, polysulfone, polyethersulfone, polyetherimide, polyamideimide, thermoplastic polyimide, liquid crystal polymer, polytetra Fluoroethylene copolymer, polyvinylidene fluoride, etc. Resin, wholly aromatic polyester, semi aromatic polyester, polylactic acid, polyester polyester elastomer include thermoplastic elastomers such as polyester-polyether elastomer.
Also, as with thermosetting resins, thermoplastic resins are not only composed of one type of resin, but even if two or more types of resins are mixed, a composite sheet in which two or more types of resins are formed in layers is also used. (See FIG. 2).
A sheet made of a thermoplastic resin can be usually obtained by extruding a resin melted in an extruder through a slit-shaped die having a predetermined thickness.

  In addition, the resin sheet of the present invention can be a sheet in which a thermosetting resin and a thermoplastic resin are mixed, or a composite sheet in which two or more kinds of resins are formed in a layer shape (see FIG. 3). When the thermosetting resin is liquid, it can be used as an adhesive between the resin sheet and the conductive particles.

  Furthermore, reinforcing materials such as fibers can be added to the resin sheets. Examples of the fiber that can be used as the reinforcing material include glass fiber, carbon fiber, metal fiber, and fiber made of resin.

The thermoplastic resin can be appropriately selected and used according to the heat resistance and durability with respect to the operating temperature of each fuel cell.
For example, when used in a phosphoric acid fuel cell, a polyphenylene sulfide resin (hereinafter referred to as PPS) is preferable from the viewpoint of corrosion resistance and heat resistance. In addition, a solid polymer fuel cell and a so-called direct methanol fuel cell using methanol as a fuel. When used, PPS and polypropylene are preferable from the viewpoint of corrosion resistance and mechanical strength. PPS is particularly preferable because it has a low melt viscosity and a high affinity with conductive particles, and can increase the conductivity and mechanical strength of the molded product.

In order to achieve a volume resistivity of several hundred mΩ · cm or less required for a separator for a fuel cell based on the results of investigations by the inventors so far, using conductive particles and a resin that is an insulator, It has been found that it is necessary to use 70% by weight or more of particles.
Theoretically, in order to increase the weight ratio of the conductive particles using a resin sheet having a small conductive particle diameter and a large true specific gravity, it is necessary to reduce the thickness of the resin sheet.
In view of such points, the resin of the resin sheet used in the present invention is generally superior in mechanical strength of thermoplastic resin to that of uncured thermosetting resin. Considering the ease of handling of the sheet-like molding material of the invention, a thermoplastic resin is preferable.

Specific examples of the resin sheet used in the present invention include, for example, a synthetic resin sheet, a synthetic fiber fabric, and a nonwoven fabric. Of these, non-woven fabrics are preferred because of their excellent handleability and high porosity.
The basis weight and thickness variation of the nonwoven fabric are affected by the thickness and porosity, but are generally said to be ± 5 to 10%. Within the range of the thickness and porosity of the resin sheet of the present invention, even in the case where there is some variation in the thickness of the nonwoven fabric itself, the sheet-shaped molding material is manufactured and the separator is manufactured using the same. In addition, the thickness accuracy of the final separator can be sufficiently ensured.

In general, a nonwoven fabric refers to a structure in which fibers are bonded or entangled by a chemical method, a mechanical method, or a combination thereof.
The non-woven fabric may be any type of non-woven fabric, for example, any one bonded by an adhesive, one mechanically bonded by a needle punch or the like, or one bonded by direct melting such as spunbond can be used. . From the viewpoint of good thickness accuracy of the nonwoven fabric, a nonwoven fabric joined by direct melting such as spunbond is preferable.

Although the kind of fiber which comprises a nonwoven fabric is not restrict | limited in particular, A thermoplastic resin fiber is preferable at the point which can be fiberized easily. As the thermoplastic resin of the thermoplastic resin fiber, those exemplified as the thermoplastic resin of the resin sheet can be used.
A plurality of fibers having different compositions may be used in combination. In this case, it is preferable to combine fibers having different melting points of 10 ° C. or more, preferably 30 ° C. or more, and in particular, a nonwoven fabric using fibers composed of fibers having a high melting point in the core and a low melting point in the sheath. Preferably there is. With such a non-woven fabric, when the conductive particles spread on the surface are adhered to the non-woven fabric, the low-melting fiber is simply melted while the shape of the high-melting fiber in the core is maintained, and the non-woven fiber surface is electrically conductive. Particles can be easily attached.

Moreover, the nonwoven fabric containing carbon fiber can be used as a sheet-like molding material of this invention. By using carbon fibers, thermal expansion during molding can be suppressed, and the strength of the molded product can be improved. Examples of such carbon fibers include pitch-based carbon fibers, rayon-based carbon fibers, and polyacrylonitrile-based carbon fibers. These can be used alone or as a mixture of two or more.
Furthermore, the carbon fiber surface in the nonwoven fabric can be used after being surface-treated with the above-mentioned thermosetting resin without departing from the weight range of the conductive particles in the sheet-shaped molding material. In this case, the thermosetting resin not only acts as a binder between the nonwoven fabric and the carbon fiber in the sheet-shaped molding material, but also when the sheet-shaped molding material described later is molded into a separator shape. Is effective as a binder for the carbon material in the separator. For example, after the nonwoven fabric is immersed in a resin solution in which an epoxy resin and a curing agent are diluted in a solvent, or after the resin solution is applied to the nonwoven fabric by a method such as spraying, the nonwoven fabric is surface-treated by removing the solvent. be able to.

Next, the electroconductive particle layer which consists of particle | grains containing the electroconductive particle which comprises the sheet-like molding material of this invention is demonstrated.
The present invention is characterized in that the conductive particle layer is a single layer, and is specifically exemplified in FIG.
In addition, the particle layer preferably contains 75% by weight or more of conductive particles in terms of conductivity, and most preferably 100% by weight.
The particle layer only needs to be formed in layers on the surface of the resin sheet. Even if the particle layer adheres to the resin sheet and is formed on the surface of the sheet, the particles fit into the open voids on the surface of the resin sheet. And may be formed on the surface layer of the resin sheet.
When the particles are present in the open voids without adhering to the surface of the resin sheet, the average pore diameter of the voids of the resin sheet and the average particle size of the conductive particles may have a certain relationship. is necessary. About this relationship, it is as having demonstrated the magnitude | size of above-mentioned space | gap.

  Examples of the conductive particles include powder particles such as carbon particles, metals, metal compounds, and the like, and one or more of these conductive particles can be used in combination. In the present invention, the conductive particles can be used by mixing nonconductive particles or semiconductive particles.

Examples of non-conductive particles include calcium carbonate, silica, kaolin, clay, talc, mica, glass flakes, glass beads, glass powder, hydrotalcite, wollastonite, and the like.
Examples of the semiconductive particles include zinc oxide, tin oxide, and titanium oxide.

  Examples of the carbon particles include artificial graphite, natural graphite, glassy carbon, carbon black, acetylene black, and ketjen black. These carbon particles can be used alone or in combination of two or more. There is no restriction | limiting in particular in the shape of these carbon particles, Any of foil shape, scale shape, plate shape, needle shape, spherical shape, an amorphous shape, etc. may be sufficient. In addition, expanded graphite obtained by chemically treating graphite can also be used. Considering the conductivity, artificial graphite, natural graphite, and expanded graphite are preferable in that a separator having a high degree of conductivity can be obtained in a smaller amount.

  Examples of the metal and metal compound include aluminum, zinc, iron, copper, gold, stainless steel, palladium, titanium, and borides such as titanium, zirconium, and hafnium. These metals and metal compounds can be used alone or in combination of two or more. There are no particular restrictions on the shape of the powder of these metals and metal compounds, and any shape such as foil, scale, plate, needle, sphere, and amorphous may be used. Furthermore, it is also possible to use a metal or metal compound coated on the surface of a non-conductive or semiconductive material powder.

The size of the conductive particles is not particularly limited as long as it can be uniformly distributed on the resin sheet. However, from the viewpoint of the conductivity and mechanical properties of the fuel cell separator obtained by molding, the average particle size is The thing of the range of 1-800 micrometers is preferable, and 50-600 micrometers is especially preferable.
Examples of the method for measuring the particle diameter of the conductive particles include a laser beam diffraction method and a sieving method.
The laser light diffraction method utilizes the fact that the intensity distribution of the diffracted light of a particle is a function of the particle diameter. Specifically, a suspension in which carbon powder is dispersed is caused to flow through the laser light path, one after another. The diffracted light of the particles passing through is converted into a plane wave by a lens, and the intensity distribution in the radial direction is detected by projecting it onto a photodetector with a rotary slit.

In addition, carbon fibers can be used in combination as long as the uniformity of distribution and distribution uniformity of the conductive particles on the sheet surface are not impaired. By using this carbon fiber in combination, the elastic modulus of the separator can be improved.
As the carbon fiber, the fiber length of the carbon fiber is 3 mm or less, preferably 1 mm or less, from the viewpoint of homogenizing the conductive particles and the carbon fiber distribution on the surface of the sheet-shaped molding material.
In order to reduce the thickness variation of the molded product, the apparent average thickness of the sheet-shaped molding material of the present invention is preferably 0.1 to 0.6 mm in relation to the average particle diameter of the conductive particles. It is preferable that it is 0.1-0.4 mm.

Next, the manufacturing method of the sheet-like molding material for fuel cell separators of this invention is demonstrated.
As a method for producing a sheet-shaped molding material for a fuel cell separator of the present invention, for example, a) a method in which conductive particles are adhered to a resin sheet without using an adhesive, and b) an adhesive is applied to a resin sheet. For example, a method of adhering conductive particles through the substrate can be used. Among these methods, the method a) is preferable in that the content of conductive particles can be increased and high conductivity can be obtained.
Next, the method for producing a sheet-shaped molding material for a fuel cell separator according to the present invention, which is the method a), will be described in more detail.
That is, this manufacturing method is performed by sequentially performing the following step (1), step (2) and step (3) on one side of the resin sheet.
Step (1) is a step of uniformly dispersing conductive particles on the surface of the resin sheet.

As a spraying method, it is preferable to spray the resin sheet so that the entire surface of the resin sheet is covered with the conductive particles, and to spread the contact area between the conductive particles and the resin sheet as much as possible.
There are no particular restrictions on the method of spraying the conductive particles. For example, a) a method of spraying the required amount of conductive particles evenly on a resin sheet using a spraying device having a large number of nozzles; There is a method in which the conductive particles are placed on one end of the surface of the resin sheet and uniformly spread over the entire surface of the resin sheet with a squeegee plate. The method b) is preferred in that a more uniform and uneven conductive particle layer can be obtained. In this case, it is preferable that the amount of the conductive particles is sprayed in an amount that is twice or more the amount that is expected to adhere.

FIG. 4 is a conceptual diagram showing the step (1) of spreading the conductive particles 7 on one side of the resin sheet 6.
The method b) will be described with reference to FIG. Conductive particles are placed on the resin sheet 6, and then the conductive particles are spread over the entire surface of the resin sheet 6. There are various methods for spreading the conductive particles. For example, spacers 8 having a height of 3 to 10 times the average diameter of the conductive particles are placed on both sides (up and down or left and right) of the resin sheet 6, and the other side of the spacer The conductive particles are uniformly spread over the entire surface of the resin sheet 6 by the squeegee plate 9 along one side. By spreading over the entire surface of the sheet 6 with the squeegee plate 9, a uniform layer of conductive particles having a certain thickness is formed on the resin sheet 6.
In the method of b) using an adhesive, an adhesive is applied in advance before the conductive particles are dispersed on the surface of the resin sheet.

The compound that can be used as the adhesive is not particularly limited, and may be any of an aqueous type, a solvent type, and a solventless type.
The solventless type needs to be liquid at room temperature, and in this case, it is preferably a liquid thermosetting resin. In the case of using a water-based or solvent-type adhesive, after applying them on a resin sheet, the conductive particles can be dispersed and then heated or decompressed to be adhered. In any type of adhesive, it is necessary to use an adhesive that is thermally stable at the melting point temperature of the resin sheet.
As an adhesive having excellent adhesion to both resin sheets and conductive particles, a compound containing a single functional group or two or more functional groups such as carboxyl group, hydroxyl group, amino group, sulfonic acid group, and phosphoric acid group Is preferable.
In the method using an adhesive, a molding material having an adhesive layer and a conductive particle layer on the surface of the resin sheet is obtained.

Step (2) is a step of attaching a part of the conductive particles to the resin sheet.
As a method for adhering the conductive particles to the resin sheet, after spreading the conductive particles on the surface of the resin sheet, 1) Press the conductive particles against the resin sheet using a pressure roll or press, 2) Method of adhering particles to resin sheet, 2) When resin sheet is composed of fibers such as non-woven fabric, the conductive particles are pressed against the resin sheet to entangle the conductive particles and fibers. 3) When the resin sheet is softened or melted by heating, heat is applied to the resin sheet and / or conductive particles to melt all or part of the resin sheet. And a method of cooling and thermally fusing the conductive particles to the resin sheet. Further, the above methods 1) to 3) may be combined.

  Examples of the heat fusion method in the method 3) include a calender roll, a hot air heater, an infrared heater, and heating with water vapor. In the present invention, from the viewpoint of preventing scattering of conductive particles, Heating by a laser or infrared heater is preferred.

The calender roll heating method will be specifically described with reference to FIG. First, the calender roll 10 is heated to a temperature 5 to 20 ° C. higher than the heat softening temperature of the resin sheet 6, and the conductive particles are formed on the laminate of the resin sheet 6 and the conductive particles 7 prepared in the step (1). The heat is transferred to the conductive particles 7 while being brought into contact with the conductive particles 7, and the local portions of the resin sheet 6 that are in contact with the conductive particles 7 are melted by the heat stored in the conductive particles 7. Next, the molten resin sheet 6 is naturally cooled, and the conductive particles 7 in contact with the resin sheet 6 are fused to the resin sheet 6.
In this calendar heating method, the entire resin sheet 6 is not heated, only the local portion of the resin sheet 6 that contacts the conductive particles 7 is heated, and heat is not transmitted to other portions. This is preferable in that a more uniform sheet-shaped molding material can be obtained. At this time, if the pressing pressure of the calendar roll is 5 kgf / cm or less, the conductive particles can be adhered to the resin sheet without breaking. When the step (2) is completed, the conductive particles are attached to the resin sheet, and the conductive particles not attached to the resin sheet are placed on the resin sheet. A sheet-like molding material precursor can be obtained.
In the method of b) in which an adhesive is previously applied to the resin sheet in step (1), in this step (2), for example, when a liquid thermosetting resin is used as the adhesive, the resin sheet is in contact with the resin sheet. A part of the conductive particles can be attached to the resin sheet by adhering the conductive particles to the resin sheet using a calender roll heating method or the like.

Step (3) is a step of removing conductive particles not attached to the resin sheet in the step (2). The conductive particles that are not in direct contact with the resin sheet 6 are not fused, and by removing these non-fused conductive particles, a sheet-shaped molding material having the conductive particle layer of the present invention can be obtained. it can.
As a method for removing conductive particles not adhered to the resin sheet, a) Conductivity not adhered to the resin sheet by turning over the top of the sheet-shaped molding material precursor for the fuel cell separator. A method of dropping the conductive particles from above the resin sheet, a) a method of sucking and removing conductive particles not attached to the resin sheet from above the precursor using a suction nozzle, and c) the precursor of the precursor There is a method in which gas is blown from above and conductive particles that are not attached to the resin sheet are blown away and removed.
When the apparatus shown in FIG. 6 is used for the sheet-shaped molding material precursor for a fuel cell separator, the conductive particles not continuously adhered can be removed from the precursor. The removed conductive particles can be recovered and reused.
Reference numeral 11 in FIG. 7 denotes a heat-sealed portion between the thermoplastic resin sheet 6 and the conductive particles 7.

A sheet-shaped molding material for a fuel cell separator in which conductive particles are adhered in a layered manner on one surface of a resin sheet by sequentially performing the above-described steps (1), (2) and (3). Can be manufactured.
When the conductive particle layer is formed on the other surface of the resin sheet, the sheet-like molding material obtained in the above step is turned upside down, and the steps (1), (2) and ( 3) may be performed sequentially.

The method for producing a sheet-shaped molding material of the present invention employs a method of molding a sheet-shaped molding material by adhering conductive particles to a resin sheet by penetration, heat fusion or adhesion, and thus used as a raw material in each step. There is a feature that the conductive particles are hardly crushed and the particle diameter is easily maintained.
According to the method of the present invention, the amount of conductive particles adhering to the resin sheet can be designed by appropriately selecting the size and shape of the conductive particles and the surface area of the resin sheet. Since the amount of conductive particles adhering to the resin sheet per unit area is defined by the surface area of the resin sheet and the size and shape of the conductive particles, the resin sheet and conductive material that are usually used are used. By using the conductive particles, it is possible to manufacture a sheet-shaped molding material for a fuel cell separator with extremely small variations in the thickness of the sheet-shaped molding material and the amount of conductive particles attached.

The fuel cell separator of the present invention can be obtained by molding one or a plurality of laminated sheet-like molding materials obtained through the above-described steps.
Examples of such molding methods include conventionally performed press molding and stampable molding. The sheet-shaped molding material will be described in detail below by dividing it into a case of being made of a thermoplastic resin and a case of being made of a thermosetting resin.

When the sheet-shaped molding material is made of a thermoplastic resin, at least one sheet-shaped molding material is placed in a cavity mold having a separator shape. In this case, the mold temperature is preferably not higher than the melting point of the resin sheet. When the mold temperature is equal to or higher than the melting point of the resin sheet, when the sheet-shaped molding material is placed in the mold, the sheet undergoes deformation such as shrinkage in a short time, and the resin and the conductive particles This is not preferable because the partial distribution tends to be non-uniform.
Next, the core mold is placed on the sheet-shaped molding material, and the sheet-shaped molding material is pressed with the core mold and the cavity mold at a pressure of 0.05 MPa to 10 MPa while being heated. After heating to a temperature not lower than the melting point of the resin sheet using, etc., the mold temperature is cooled to a temperature not higher than the melting point of the resin sheet, preferably not higher than the melting point to 50 ° C. using a cooling press or the like. However, a pressure of 0.5 MPa to 100 MPa is applied to the sheet-shaped molding material. After the mold is cooled, the pressure is released and the separator is removed from the mold.

  When the sheet-shaped molding material is made of a thermosetting resin, the sheet-shaped molding material is separated by a compression molding method using a separator mold heated to the curing temperature of the thermosetting resin. Make the data. The molding pressure in this case is appropriately selected within the range of 0.5 MPa to 100 MPa.

Considering the state in which the resin of the sheet-shaped molding material is melted and pressurized, the pressure applied from the press is transmitted to the molten resin through the conductive particles that are solid, and the conductivity in the pressure load direction The molten resin interposed between the particles is extruded in a direction perpendicular to the pressure load direction by pressure.
That is, the resin in the sheet-shaped molding material that existed as an insulating layer before pressurization is pushed out into the void portion formed between the conductive particles in the pressurization process, thereby causing the separator in the thickness direction of the separator. Conductivity can be secured. (See Figure 8)

In the prior art, it was difficult to mold a separator having a thickness of 1 mm or less, but the apparent thickness range of the sheet-shaped molding material of the present invention is 0.1 to 0.6 mm. By laminating, a thin separator of 1 mm or less with small thickness variation can be easily obtained.
The thickness variation of the separator obtained by molding the sheet-shaped molding material of the present invention is preferably 15 μm or less.

The separator for a fuel cell molded using the sheet-shaped molding material of the present invention can uniformly distribute conductive particles particularly in a thermoplastic resin matrix at high density, and as a result, obtains a separator having excellent conductivity. Can do.
In general, when forming a fuel cell separator, the fuel cell separator in which the average particle diameter of the conductive particles used as a raw material is finally obtained is preferably maintained as much as possible. From the viewpoint of From this viewpoint, the average particle size of the conductive particles contained in the finally obtained fuel cell separator is preferably 60% or more of the average particle size before molding the resin sheet, and is 70% or more. More preferably, it is more preferably 80% or more.

The fuel cell separator can be used for a fuel cell composed of only a single cell as a basic unit of a fuel cell, that is, a fuel cell stack in which a plurality of such single cells are stacked. it can.
A fuel cell is a power generation device that uses hydrogen obtained by reforming fossil fuel as a main fuel and extracts energy generated by an electrochemical reaction between the hydrogen and oxygen as electric power. Usually, this is formed by stacking a plurality of single cells that generate power in series and collecting current with current collecting plates provided at both ends of the stack.
Although there is no restriction | limiting in particular in the shape of the separator for fuel cells obtained by this invention, For example, the separator 12 for fuel cells shown by FIG. 9 is mentioned. In FIG. 9, a separator having a shape having gas or liquid flow passages 13 on one side or both sides is shown.
The sheet-shaped molding material for a fuel cell separator of the present invention is particularly suitable for producing a fuel cell separator having such a structure and a so-called ribbed shape.
Specifically, the separator for a fuel cell of the present invention can be used as a separator for various types of fuel cells such as a hydrazine type, a direct methanol type, an alkali type, a solid polymer type, and a phosphoric acid type.
Since the fuel cell obtained by using the fuel cell separator of the present invention is strong against impact and can be downsized, for example, an electric vehicle power source, a portable power source, an emergency power source, an artificial satellite, an airplane, etc. It can be used as a power source for various mobile objects such as spacecraft.

Next, embodiments of the present invention will be described with reference to examples. In Examples and Comparative Examples, parts and% represent parts by weight and% by weight unless otherwise specified.
Example 1
On a PPS fiber nonwoven fabric having a size of 150 mm × 150 mm (weight is 15 g / m ² , thickness is 60 μm, average pore diameter is 38 μm, porosity is 85%), artificial graphite (amorphous, average particle diameter is 88 μm) ) Disperse 5g of particles, then place a spacer with a height of 0.8mm on both ends of the nonwoven fabric, move the squeegee plate from one side of the spacer to the other side, so that the artificial graphite particles are placed on the entire surface of the nonwoven fabric Spread out.
Next, the calender roll previously heated to 265-280 degreeC was moved to the other side from one side, pressing the graphite side of the nonwoven fabric. Next, after natural cooling, air blown at 5 kgf / cm ² to remove graphite that is not fused with the nonwoven fabric fiber, so that the apparent thickness is 0.15 mm, the basis weight is 75 g / m ² , and the porosity is about A sheet-shaped molding material of 73% was obtained.
A stack of 20 sheets of the sheet-shaped molding material is heated to 300 ° C. in a heating furnace to melt the PPS fiber, and immediately supplied to a mold heated to 150 ° C. mounted on a press molding machine and applied at 40 MPa. The product was shaped by cooling and cooled and solidified to obtain a molded product with ribs having a shape shown in FIG. The molding cycle was 30 seconds.
The same operation as described above was performed to form a flat molded product having a width of 15 cm, a thickness of about 1 mm, and a length of 15 cm.
The molded product had a volume resistivity of 6 mΩ · cm, a bending strength of 53 MPa, a thickness variation of 0.009 mm, and an average particle size of graphite in the molded product of 81 μm.

Example 2
Using a PPS fiber nonwoven fabric (weight is 20 g / m ² , thickness is 80 μm, average pore diameter is 38 μm, porosity is 85%), operation is performed with the same raw materials, methods and conditions as in Example 1, and apparent A sheet-shaped molding material having a thickness of 0.16 mm, a basis weight of 80 g / m ² , and a porosity of about 75% was obtained.
Using this sheet-shaped molding material, the same operation as in Example 1 was performed to obtain a molded product with ribs having a shape shown in FIG. 10 having a width of 15 cm, an average thickness of 1.1 mm, and a length of 15 cm. The molding cycle was 30 seconds.
Using the obtained sheet-shaped molding material, the same operation as described above was performed to mold a flat molded product having a width of 15 cm, a thickness of about 1 mm, and a length of 15 cm.
The volume resistivity of the molded product was 16 mΩ · cm, the bending strength was 60 MPa, the thickness variation was 0.007 mm, and the average particle size of graphite in the molded product was 83 μm.

Example 3
Using a PPS fiber nonwoven fabric (weight is 25 g / m ² , thickness is 100 μm, average pore diameter is 38 μm, porosity is 85%), the same raw materials, methods and conditions as in Example 1 are used. A sheet-shaped molding material having a thickness of 0.17 mm, a basis weight of 85 g / m ² , and a porosity of about 77% was obtained.
Using this sheet-shaped molding material, the same operation as in Example 1 was performed to obtain a molded product with ribs having a shape shown in FIG. 10 having a width of 15 cm, an average thickness of 1.1 mm, and a length of 15 cm. The molding cycle was 30 seconds.
Using the obtained sheet-shaped molding material, the same operation as described above was performed to mold a flat molded product having a width of 15 cm, a thickness of about 1 mm, and a length of 15 cm.
The volume resistivity of the molded product was 17 mΩ · cm, the bending strength was 64 MPa, the thickness variation was 0.007 mm, and the average particle size of graphite in the molded product was 83 μm.

Example 4
Instead of PPS fiber nonwoven fabric, PP / PE fiber nonwoven fabric (weight is 10 g / m ² , thickness is 45 μm, average pore diameter is 37 μm, porosity is 85%), and calender roll temperature is heated to 140 ° C. The sheet-like molding material is operated in the same manner and under the same conditions as in Example 1 except that the apparent thickness is 0.15 mm, the basis weight is 70 g / m ² , and the porosity is about 75%. Got.
A stack of 22 sheets of this sheet-shaped molding material was heated to 185 ° C. in a heating furnace, the polyolefin resin fibers were melted, and immediately supplied to a mold heated to 80 ° C. mounted on a press molding machine at 40 MPa. Molding was performed by pressurization and cooling and solidification was performed to obtain a molded product with a rib having a shape shown in FIG. 10 having a width of 15 cm, an average thickness of 0.97 mm, and a length of 15 cm. The molding cycle was 30 seconds.
Using the obtained sheet-shaped molding material, the same operation as described above was performed to mold a flat molded product having a width of 15 cm, a thickness of about 1 mm, and a length of 15 cm.
The volume resistivity of the molded product was 8 mΩ · cm, the bending strength was 40 MPa, the thickness variation was 0.01 mm, and the average particle size of graphite in the molded product was 81 μm.

Example 5
Using PP / PE non-woven fabric (weight is 15 g / m ² , thickness is 68 μm, void average pore diameter is 37 μm, void ratio is 85%), operation is performed in the same manner and conditions as in Example 1, and apparent A sheet-shaped molding material having a thickness of 0.16 mm, a basis weight of 75 g / m ² , and a porosity of about 77% was obtained.
A stack of 22 sheets of this sheet-shaped molding material was heated to 185 ° C. in a heating furnace, the polyolefin resin fibers were melted, and immediately supplied to a mold heated to 80 ° C. mounted on a press molding machine at 40 MPa. Molding was performed by pressurization and cooling and solidification was performed to obtain a molded product with a rib having a shape shown in FIG. 10 having a width of 15 cm, an average thickness of 0.99 mm, and a length of 15 cm. The molding cycle was 30 seconds.
Using the obtained sheet-shaped molding material, the same operation as described above was performed to mold a flat molded product having a width of 15 cm, a thickness of about 1 mm, and a length of 15 cm.
The volume resistivity of the molded product was 10 mΩ · cm, the bending strength was 43 MPa, the thickness variation was 0.009 mm, and the average particle size of graphite in the molded product was 80 μm.

Example 6
B) PP / PE non-woven fabric having a size of 150 mm × 150 mm (weight is 5 g / m ² ), based on b) a method for producing conductive sheet material by bonding an adhesive particle to a resin sheet via an adhesive. , Epiklon 830 (epoxy resin with a viscosity of 4000 mPa.s, registered trademark of Dainippon Ink & Chemicals, Inc.) on an environment having an ambient temperature of 40 ° C. on a thickness of 20 μm, an average pore diameter of 37 μm, and a porosity of 80%. Below, the epoxy resin is applied so as to be 15 g / m ^2, and 5 g of artificial graphite (amorphous, average particle diameter is 88 μm) particles are sprayed thereon, and then the height of the non-woven fabric is 0. Place an 8mm spacer, move the squeegee plate from one side of the spacer to the other, spread it so that the artificial graphite is placed on the entire surface of the nonwoven fabric coated with epoxy resin, and then the nonwoven fabric. By removing the graphite particles that are not adhered to obtain a nonwoven fabric, a composite sheet made of an epoxy resin and graphite particles.
The composite sheet was semi-cured in a drying oven at 60 ° C. for 2 hours, and then the graphite not adhered to the nonwoven fabric fiber was removed, whereby the apparent thickness was 0.15 mm and the basis weight was 75 g / m ² . A certain sheet-shaped molding material was obtained.
20 sheets of this sheet (150 mm x 150 mm) are stacked, filled in a preheated 150 ° C mold and pressed at 40 MPa to obtain a molded product with ribs having a width of 15 cm, an average thickness of 1.06 mm, and a length of 15 cm. It was. The molding cycle was 45 minutes.
The same operation as described above was performed to form a flat molded product having a width of 15 cm, a thickness of about 1 mm, and a length of 15 cm. The volume resistivity of the molded products was 22 mΩ · cm, the bending strength was 44 MPa, the thickness variation was 0.011 mm, and the average particle size of graphite in the molded products was 80 μm.

Comparative Example 1
70 parts of artificial graphite similar to the artificial graphite used in Example 1 and 30 parts of PPS were dry-mixed for 10 minutes using a mixer. This mixture was roll press molded under conditions of a molding pressure of 20 MPa and 320 ° C. to obtain a stampable sheet having a thickness of 4 mm.
The stampable sheet obtained was cut into a predetermined size (120 mm x 120 mm), heated in a heating furnace at 320 ° C for 10 minutes to melt PPS, and immediately heated to 150 ° C mounted on a press molding machine And then solidified by cooling at 40 MPa to obtain a molded product with ribs having a width of 15 cm, an average thickness of 1.1 mm, and a length of 15 cm. The molding cycle was 30 seconds. Similarly, a flat molded product having a width of 15 cm, a thickness of about 1 mm, and a length of 15 cm was also formed. The volume resistivity of the molded products was 116 mΩ · cm, the bending strength was 61 MPa, the thickness variation was 0.110 mm, and the average particle size of graphite in the molded products was 14 μm.

Comparative Example 2
60 parts of artificial graphite similar to the artificial graphite used in Example 1 and 40 parts of Epicron 830 were sufficiently mixed and stirred for 2 minutes in an atmosphere at an ambient temperature of 40 ° C. to prepare a uniform dispersion. A squeegee plate is used on one side of the resulting dispersion of the PP / PE fiber nonwoven fabric used in Example 3 (weight is 10 g / m ² , thickness is 45 μm, average pore diameter is 37 μm, porosity is 85%). The resin sheet (graphite content: 54%) was obtained by coating so as to be 90 g / m ² . This resin sheet was semi-cured in a drying oven at 60 ° C. for 2 hours. 20 sheets of such sheets (150mm x 150mm) are stacked, filled in a pre-heated 150 ° C mold, and pressed at 40MPa to form a ribbed molded product with a width of 15cm, an average thickness of 1.27mm, and a length of 15cm Got. The molding cycle was 45 minutes. Similarly, a flat molded product having a width of 15 cm, a thickness of about 1 mm, and a length of 15 cm was also formed. The volume resistivity of the molded products was 466 mΩ · cm, the bending strength was 46 MPa, the thickness variation was 0.165 mm, and the average particle size of graphite in the molded products was 80 μm.
Comparative Example 3
40 parts of artificial graphite similar to the artificial graphite used in Example 1 and a viscosity of 4000 mPa.s. 60 parts of Epicron 830 of s was sufficiently mixed and stirred for 2 minutes in an environment with an ambient temperature of 40 ° C. to prepare a uniform dispersion. A squeegee plate is used on one side of the resulting dispersion of the PP / PE fiber nonwoven fabric used in Example 3 (weight is 10 g / m ² , thickness is 45 μm, average pore diameter is 37 μm, porosity is 85%). The resin sheet (graphite content: 36% by weight) was obtained by coating so as to be 90 g / m ² . This resin sheet was semi-cured in a drying oven at 60 ° C. for 2 hours. 20 sheets of such sheets (150mm x 150mm) are stacked, filled in a preheated 150 ° C mold, and pressed at 40MPa to form a ribbed product with a width of 15cm, an average thickness of 1.25mm, and a length of 15cm Got. The molding cycle was 45 minutes. Similarly, a flat molded product having a width of 15 cm, a thickness of about 1 mm, and a length of 15 cm was also formed. The volume resistivity of the molded products was 783 mΩ · cm, the bending strength was 49 MPa, the thickness variation was 0.143 mm, and the average particle size of graphite in the molded products was 80 μm.

  As described above, by using the sheet-shaped molding material for a fuel cell separator of the present invention, a thin fuel cell separator having excellent conductivity and high thickness accuracy can be easily produced.

It is a conceptual diagram of the composite sheet of two types of thermosetting resins. It is a conceptual diagram of the composite sheet of two types of thermoplastic resins. It is a conceptual diagram of the composite sheet of a thermosetting resin and a thermoplastic resin. It is the top view and sectional drawing (AA) of a resin sheet showing the state which spread | dispersed the graphite particle | grains on one side and spread | expanded to the whole surface with the squeegee board concerning one Embodiment of this invention. It is a conceptual diagram showing the state which adheres a part of said graphite particle to a resin sheet. It is a conceptual diagram of an apparatus for removing non-adhering graphite particles from a sheet-shaped molding material precursor for molding a fuel cell separator. It is a schematic cross section of the sheet-shaped molding material for fuel cell separator molding. It is a conceptual diagram of each stage when the laminated sheet-like molding material is press-pressed in the molten state of resin. It is a fragmentary perspective view which shows the separator for fuel cells of this invention. It is the top view (a) of the separator for fuel cells which filled in the thickness measurement point, and its sectional drawing (b).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Thermosetting resin layer 2 Thermosetting resin layer 3 other than 1 Thermosetting resin composite sheet 4 Thermoplastic resin layer 5 Thermoplastic resin layer 3 other than 4 'Thermoplastic resin composite sheet 3 " Composite sheet 6 with thermoplastic resin Resin sheet 7 Graphite particle 8 Spacer 9 Squeegee plate 10 Calender roll 7 'Adhered graphite particle 7 "Non-adherent graphite particle 11 Thermal fusion part 12 between resin sheet and graphite particle Separator 13 Gas or liquid Channel 14 of the rib of the separator

Claims (16)

A sheet-shaped molding material having one conductive particle layer composed of particles containing conductive particles on at least one surface of a resin sheet, wherein the content of conductive particles in the sheet-shaped molding material is 70 to A sheet-shaped molding material for a fuel cell separator, characterized by being 95% by weight. The sheet-shaped molding material for a fuel cell separator according to claim 1, wherein the content of the conductive particles in the particle layer is 75% by weight or more. The sheet-shaped molding material for a fuel cell separator according to claim 1, wherein the resin sheet has voids. The sheet-shaped molding material for a fuel cell separator according to claim 1, wherein the resin sheet has a porosity of 30 to 90%. 2. The sheet-shaped molding material for a fuel cell separator according to claim 1, wherein the resin sheet has an average pore diameter of 10 to 800 μm. The sheet-shaped molding material for a fuel cell separator according to claim 1, wherein the resin of the resin sheet is a thermoplastic resin. The sheet-shaped molding material for a fuel cell separator according to claim 1, wherein the resin sheet is a nonwoven fabric. The sheet-shaped molding material for a fuel cell separator according to claim 1, wherein the conductive particles are graphite. The molding material for a fuel cell separator according to claim 1, wherein the average thickness is 0.1 to 0.6 mm. For at least one side of the resin sheet,
Step (1); Step (2) of uniformly dispersing conductive particles on the surface of the resin sheet; Step (3) of attaching a part of the conductive particles to the resin sheet; In the step (2) A method for producing a sheet-shaped molding material for a fuel cell separator, comprising sequentially performing a step of removing conductive particles not attached to a resin sheet. The sheet-shaped molding material for a fuel cell separator according to claim 10, wherein the step (1) is a step of spreading conductive particles on the surface of the resin sheet and then spreading the spread conductive particles uniformly over the entire surface of the resin sheet. Manufacturing method. The resin of the resin sheet is a thermoplastic resin, and in the step (2), by heating the resin sheet on which the conductive particles obtained in the step (1) are dispersed, the conductive particles are applied to the resin sheet. The manufacturing method of the sheet-like molding material for fuel cell separators of Claim 10 which heat-seals a part of. The manufacturing method of the sheet-shaped molding material for fuel cell separators of Claim 10 with which the said resin sheet has a space | gap. The method for producing a sheet-shaped molding material for a fuel cell separator according to claim 10, wherein the conductive particles are graphite. The separator for fuel cells formed by shape | molding the sheet-like molding material of any one of Claims 1-9. The fuel cell separator according to claim 15, wherein the thickness variation is 15 μm or less.

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