JP2009280437A - Method for producing porous carbon sheet - Google Patents

Abstract

A method for producing a porous carbon sheet capable of appropriately controlling the compressive deformation rate of the porous carbon sheet and the compressive residual strain of the surface when locally pressed is provided.
This is achieved by a method for producing a porous carbon sheet in which an epoxy resin composition 1 is coated on the surface of a short carbon fiber paper 2 impregnated with a phenol resin composition, heated and pressurized, and then carbonized. Is done. Properties required of porous carbon sheets as gas diffuser materials for fuel cells, specifically, high compressive deformation rate, low compressive residual strain on both surfaces, high electrical conductivity, mechanical properties It is possible to provide a porous carbon sheet that satisfies all high requirements simultaneously.
[Selection] Figure 1

Description

  The present invention relates to a method for producing a porous carbon sheet that is preferably used as a material for a gas diffuser of a polymer electrolyte fuel cell.

  A polymer electrolyte fuel cell is used as a fuel cell stack in which a plurality of cells made of a solid polymer electrolyte membrane, a catalyst, a gas diffuser, and a separator are stacked. In applications where high output is required, such as automobiles, 2 0 0 to 4 0 0 cells are stacked and used. Therefore, if the thickness of each constituent material is different from the designed thickness, a large deviation occurs in the entire stack. Therefore, high thickness accuracy is required for each constituent material. The gas diffuser of a polymer electrolyte fuel cell is generally surrounded by a material having a certain thickness called a sealing material, and the thickness is controlled by compressing it to the same thickness as the sealing material at the time of stacking. Therefore, the gas diffusion body is required to have a high compressive deformation rate (that is, excellent compressive deformability) so as to have the same thickness as the sealing material. In addition, the gas diffuser is required to have mechanical characteristics for conductivity and handling.

A material using a porous carbon sheet formed by binding carbon short fibers with resin carbide is known as a material for a gas diffuser of a polymer electrolyte fuel cell that requires the above characteristics.
In Patent Document 1, the porous carbon sheet was formed by laminating two precursor fiber sheets containing a thermosetting resin composition in the compression step so as to be symmetrical in the thickness direction, and was in contact with the short mesh plate during paper making. It is described that the layer having a relatively large amount of the thermosetting resin composition faces the surface by facing the surface outward, and therefore the compression deformation rate is relatively high.
In Patent Document 2, a layer having a large amount of thermosetting resin is obtained by sandwiching and compressing a precursor sheet having a low bulk density between precursor sheets having a high bulk density. It is described that it is higher.
However, although the bulk density gradient is given by changing the amount of the thermosetting resin composition, it is difficult to control the resin distribution during the heat and pressure treatment due to interlayer movement due to softening of the thermosetting resin. there were.
JP 2006-40885 A JP 2007-176750 A

  An object of this invention is to provide the manufacturing method of the porous carbon sheet which can control appropriately the compressive deformation rate of a porous carbon sheet and the compression residual distortion of the surface at the time of pushing locally.

The present invention is as follows.
(1) A porous carbon sheet that is coated with an epoxy resin composition on the surface of a short carbon fiber paper impregnated with a phenol resin composition, heated and pressurized to cure both resin compositions, and then carbonized. Manufacturing method.
(2) The method for producing a porous carbon sheet according to (1), wherein a laminate obtained by laminating two carbon short fiber papers impregnated with a phenol resin composition is used as the carbon short fiber paper impregnated with the phenol resin composition.
(3) As the carbon short fiber paper impregnated with the phenol resin composition, a laminate in which two carbon short fiber papers impregnated with the phenol resin composition are laminated with the surface having a large amount of impregnation of the phenol resin composition as the outer surface is used. (2) The manufacturing method of the porous carbon sheet.
(4) Instead of carbon short fiber paper impregnated with phenol resin composition, carbon short fiber paper impregnated with phenol resin composition, carbon short fiber paper, and carbon short fiber paper impregnated with phenol resin composition, The manufacturing method of the porous carbon sheet of (1) using the laminated body formed by laminating in order.
(5) A porous carbon sheet produced by the method for producing a porous carbon sheet according to any one of (1) to (4).

  Provided is a method for producing a porous carbon sheet capable of appropriately controlling the compressive deformation rate of the porous carbon sheet and the compressive residual strain of the surface when locally pressed.

  In the method for producing a porous carbon sheet of the present invention, an epoxy resin composition is applied to the surface of a short carbon fiber paper impregnated with a phenol resin composition, and both resin compositions are cured by heat and pressure treatment. , And carbonization treatment.

[Carbon short fiber paper]
The carbon short fiber paper that can be used in the present invention is a carbon short fiber produced by a wet method in which carbon fibers are dispersed in a liquid medium for paper making, or a dry method in which carbon fibers are dispersed in air and piled up. Although fiber paper can be applied, short carbon fiber paper produced by a wet method is preferred because of good fiber dispersibility.

  The carbon fiber contained in the carbon short fiber paper may be any carbon fiber such as polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, rayon-based carbon fiber, etc., but polyacrylonitrile-based carbon having relatively high mechanical strength. Fiber is preferred. In particular, it is preferable that the carbon fiber to be used consists only of polyacrylonitrile-based carbon fiber.

  The polyacrylonitrile-based carbon fiber here is produced using a polymer containing acrylonitrile as a main component as a raw material. Specifically, a spinning process for spinning acrylonitrile fibers, a flameproofing process for heating and firing the fibers in an air atmosphere at 200 to 400 ° C. to convert them into oxidized fibers, and in an inert atmosphere such as nitrogen, argon, helium, etc. And carbon fiber obtained through a carbonization step of carbonizing by heating to 300 to 2500 ° C. The carbon fiber can be suitably used as a composite material reinforcing fiber. Therefore, it is possible to form a carbon short fiber paper having a higher strength and a higher mechanical strength than other carbon fibers.

  The polyacrylonitrile-based carbon fiber is preferably contained in the carbon short fiber paper in an amount of 50% by mass or more, more preferably 70% by mass or more, from the viewpoint of maintaining the mechanical properties of the electrode substrate.

  The average fiber length of the carbon fibers is preferably 2 to 18 mm, more preferably 2 to 10 mm, and further preferably 3 to 6 mm from the viewpoint of the strength of the base material and uniform dispersibility. When the fiber length is less than 2 mm, the entanglement between the fibers decreases, and the strength of the substrate may be weakened. Moreover, when it exceeds 18 mm, the dispersibility in the dispersion medium of a fiber will fall and it may become a carbon short fiber paper with a dispersion spot.

The short carbon fiber paper of the present invention may contain an organic polymer compound as a binder.
Examples of the organic polymer compound include polyvinyl alcohol (PVA), polyvinyl acetate, polyester, polypropylene, polyethylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, acrylic resin, polyurethane resin, and other thermoplastic resins, phenol resins, epoxy resins, Thermosetting resins such as melamine resin, urea resin, alkyd resin, unsaturated polyester resin, acrylic resin, polyurethane resin, thermoplastic elastomer, butadiene / styrene copolymer (SBR), butadiene / acrylonitrile copolymer (NBR) Elastomer such as rubber, rubber, cellulose and the like can be used. Further, as the form, pulp-like materials and short fibers are suitable.

  The pulp-like material here is a structure in which a large number of fibrils having a diameter of several μm or less are branched from a fibrous trunk, and the carbon short fiber paper using this pulp-like material is entangled with each other efficiently and thin carbon short fiber. Even fiber paper has the characteristics of excellent handling.

  Short fibers are obtained by cutting fiber yarns or fiber tows into a predetermined length. The length of the short fibers is preferably 2 to 12 mm from the viewpoint of binding properties and dispersibility as a binder.

  In particular, the organic polymer compound is preferably polyvinyl alcohol (PVA), polyethylene, polyacrylonitrile, cellulose, polyvinyl acetate pulp or short fibers.

  Since these organic polymer compounds are excellent in binding power in the paper making process, they are preferable as a binder with less carbon fiber falling off. These may be used as a single component, or two or more types may be used. In addition, most of these organic polymer compounds are decomposed and volatilized in the final carbonization process for producing the electrode substrate to form pores. The presence of these pores is preferable because the permeability of water and gas is improved.

  The content of the organic polymer compound in the short carbon fiber paper is preferably in the range of 5 to 60% by mass. More preferably, it is the range of 10-50 mass%. In order to reduce the electric resistance of the electrode base material obtained by impregnating a short carbon fiber paper with a thermosetting resin, which will be described later, and firing, it is better that the content of the organic polymer compound is small, and the content is 60 The mass% or less is preferable. From the viewpoint of maintaining the strength and shape of the short carbon fiber paper, the content is preferably 5% by mass or more.

It is preferred that the basis weight of the short carbon fiber paper is 10~70g / m ² from the viewpoint of achieving both mechanical strength and gas permeability, more preferably from 15 to 60 g / m ^2.

  In the present invention, it is necessary to use a phenol resin composition that exhibits adhesiveness or fluidity at room temperature and remains as a conductive substance even after carbonization.

  As the phenol resin composition, a resol type phenol resin obtained by reaction of phenols and aldehydes in the presence of an alkali catalyst can be used. In addition, a novolac type phenol resin having a solid heat fusion property, which is produced by a reaction of phenols and aldehydes under an acidic catalyst, can be dissolved and mixed in the resol type flowable phenol resin by a known method. In this case, a self-crosslinking type containing a curing agent such as hexamethylenediamine is preferred.

  Examples of phenols include phenol, resorcin, cresol, xylenol, and the like. As aldehydes, for example, formalin, paraformaldehyde, furfural and the like are used. Moreover, these can be used as a mixture. These can also use a commercial item as a phenol resin.

  The proportion of the phenol resin composition that remains as a carbide on the electrode base material varies depending on the type and the amount of impregnation into the short carbon fiber paper. When the electrode substrate is 100% by mass, the content of the carbide derived from the phenol resin composition excluding the carbon fiber content is 10% by mass or more from the viewpoint of binding of the carbon fibers in the electrode substrate. preferable. More preferably, it is 20 mass% or more. In addition, when the amount of the phenol resin composition is large, the amount of shrinkage at the time of pressing is increased, and wrinkles are more easily formed. It is preferable. More preferably, it is 40 mass% or less.

  The method for impregnating the carbon short fiber paper with the phenol resin composition is not particularly limited, but a method of uniformly coating the resin on the carbon short fiber paper surface using a coater, a dip nip using a squeezing device The method, or the method of superposing carbon short fiber paper and a resin film and transferring the resin to the carbon short fiber paper can be impregnated with the resin continuously, and is preferable in terms of productivity and production of a long product. .

In the present invention, it is essential to apply the epoxy resin composition to the surface of the short carbon fiber paper impregnated with the phenol resin composition.
The epoxy resin composition has low handleability and low carbonization yield and is easy to control curing. The carbonization yield is preferably 30% or less, and more preferably 25% or less. By using a resin composition having a low carbonization yield, the gas permeability required for the gas diffuser can be ensured. In addition, once the heat and pressure treatment is performed at a temperature at which only the epoxy resin composition is cured, it is only necessary to perform the heat treatment when curing the phenol resin composition. .

The basis weight of the epoxy resin composition is preferably ² to 70 g / m ^{2 and} particularly preferably ²⁰ to 50 g / m ² . Within this range, the compressive deformation rate is high, the compressive residual strain on both surfaces is small, the conductivity is high, the mechanical properties are high, and damage prevention of peripheral members is all satisfied at the same time. . When heated and pressurized, the phenolic resin composition is more compatible with the epoxy resin composition than the short carbon fiber, so the phenolic resin composition moves to the surface of the short carbon fiber paper where the epoxy resin composition is located and becomes porous. A structure capable of appropriately controlling the compressive deformation rate of the carbon sheet and the compressive residual strain of the surface when pressed locally is formed.

As a laminating method, since it is necessary to adhere the laminated carbon short fiber papers in the heat and pressure treatment, it is preferable to laminate two or more carbon short fiber papers impregnated with the phenol resin composition.
In this case, carbon short fiber paper not impregnated with the phenol resin composition may be laminated between carbon short fiber paper impregnated with the phenol resin composition.
The carbon short fiber paper impregnated with the phenol resin composition can satisfy the fact that the compression deformation rate is higher and the compression residual strain on both surfaces is smaller when the surface with a large amount of impregnation of the phenol resin composition is the outer surface. This is preferable.
In the case of using a release paper, a method of laminating the lower release paper, the carbon short fiber paper laminate, the upper release paper in this order, and a method of simultaneously sandwiching the carbon short fiber paper laminate with the release paper may be mentioned.
In order to be subjected to the heat and pressure treatment, the lamination direction of the carbon short fiber paper and / or the carbon short fiber paper so that the bulk density of both surfaces of the carbon short fiber paper after being cured and bonded by heat and pressure is higher than the internal bulk density, and / or It is necessary to set the stacking order.

[Heat and pressure treatment]
As a heating press apparatus used in the heating and pressurizing process, a continuous heating double belt press apparatus (hereinafter referred to as a double belt apparatus) provided with a pair of endless belts or a continuous heating roll press apparatus (hereinafter referred to as a roll press apparatus). Is preferred).

  The epoxy resin composition is coated on the surface of short carbon fiber paper impregnated with the phenol resin composition, sandwiched between release papers, and conveyed by a belt into a double belt device. After the release paper and the short carbon fiber paper are overlapped by the press roll, pre-heat treatment is performed by the hot air in the hot air generator and by the pre-heating roll. It is preferable to preheat the carbon short fiber paper before the heat and pressure treatment. By preheating the carbon short fiber paper before the heating and pressurizing treatment, the epoxy resin composition can be once softened and well adapted to the carbon short fiber paper. Then, by performing the heat and pressure treatment, the carbon fibers are effectively bound to each other, and a porous carbon sheet having excellent mechanical properties and high handling properties can be produced. The heating means employed in the preheat treatment may be any one of heat transfer heating such as a heating roll, convection heating provided with a heating region, radiation heating such as far infrared rays, or a combination thereof, but from the viewpoint of reducing heat loss, the heating roll It is preferable that the heat transfer heating is used.

  A release paper may be used to transfer the epoxy resin composition uniformly and smoothly to the carbon short fiber paper impregnated with the phenol resin composition. Specifically, it is preferable that the heat resistant temperature is 200 ° C. or higher, the tensile strength is 50 N / cm or higher, and the resin composition can be easily removed in a cured state. There are no particular restrictions on the method of applying the epoxy resin composition to the release paper. However, the amount of resin applied can be determined by the method of applying a certain amount of resin through a fixed gap with a doctor blade or the roll interval of the kiss coater. Examples thereof include a control method and a method using a device such as a reverse roll coater. A method using a kiss coater or a reverse roll coater is preferable in that clearance can be achieved and productivity and a long product can be produced.

As temperature of the hot air in a hot air generator, 100 degreeC or more and 250 degrees C or less are preferable. Moreover, as a temperature of a preheating roll, 150 degreeC or more and 300 degrees C or less are preferable.
After the pre-heat treatment, heating and pressing are performed by a press roll. The temperature of the press roll is preferably 200 ° C. or higher and 400 ° C. or lower from the viewpoint of promoting the curing of the resin composition.

Moreover, as the linear pressure of the press roll, it may be adjusted so as to have a desired thickness of the porous carbon sheet, from the viewpoint of promoting the binding between the carbon fibers in order to improve the mechanical properties of the porous carbon sheet, It is preferable to pressurize at 1 × 10 ² N / m or more and 1 × 10 ⁶ N / m or less.

The obtained resin-cured carbon short fiber paper laminate is wound up by a winder. When the release paper is used, the release paper is removed from the resin-cured carbon short fiber paper laminate. The method of winding by the winding machine different from the winding machine which winds up the laminated body of the resin short carbon fiber paper is mentioned.
Moreover, although the laminated body of carbon short fiber paper which hardened | cured resin was once wound up with the winder, you may perform the carbonization process mentioned later continuously as it is, without winding up.

[Carbonization treatment]
In the present invention, after the heat and pressure treatment, the resin-cured carbon short fiber paper laminate is fired. The firing is performed while a resin-cured carbon short fiber paper laminate is introduced into a heating furnace maintained in an inert atmosphere and continuously running in the heating furnace. From the viewpoint of mechanical properties and conductivity of the electrode substrate finally obtained, the firing is performed by a heat treatment at a maximum temperature of 600 ° C. or more, preferably 700 ° C. or more (preliminary carbonization step), and a maximum temperature of 1500. It is preferable to be composed of a step of heat treatment (carbonization step) at a temperature of at least 1 ° C, preferably at least 1600 ° C.

The heating rate of the preliminary carbonization treatment is preferably 40 to 300 ° C./min. Moreover, as for the temperature increase rate of a carbonization process, 50-400 degreeC / min is preferable.
A temperature increase rate of less than 40 ° C./min in the preliminary carbonization treatment or less than 50 ° C./min in the carbonization treatment is not preferable because productivity is extremely low. In addition, a heating rate exceeding 300 ° C./min in the preliminary carbonization treatment step or a heating rate exceeding 400 ° C./min in the carbonization step is not preferable because conductivity and mechanical properties are deteriorated.
When the rate of temperature increase is too slow, the productivity of the porous carbon sheet is lowered. When it is too early, cracks occur in the resin carbide due to rapid carbonization shrinkage of the resin composition, and wrinkles occur in the porous carbon sheet.

FIG. 1 is an example showing a laminate. For example, they are integrated by heating and pressing according to the stacking order shown in the figure.
FIG. 2 is a schematic view showing an embodiment of the heat and pressure treatment of the method for producing a porous carbon sheet of the present invention. 5 is, for example, carbon short fiber paper impregnated with the laminated phenol resin composition shown in FIG. 1, and this is compressed and integrated between the upper hot plate 7 and the lower hot plate 8 by the hot press 6. At this time, it is also preferable to regulate the thickness with a 4: spacer.

  In the present invention, as the porous carbon sheet, the short carbon fibers do not have a remarkable orientation in the sheet surface and are present in a generally random direction, and the short carbon fibers are bound with resin carbide. preferable.

  In the porous carbon sheet, if the amount of resin carbide in the unit volume is reduced in order to reduce the bulk density, the binding point of the carbon fiber by the resin carbide decreases due to the decrease in the amount of resin carbide. The amount of deformation at the time increases. Further, when the amount of short carbon fibers in a unit volume is reduced in order to reduce the bulk density, the number of deformations when compressed by pressurization increases because the number of short carbon fibers contacts decreases. However, when the bulk density is reduced, the number of binding points due to the resin carbide and the contact points between the short carbon fibers are reduced, so that the portion compressed by pressure is broken and permanent set is increased. In the present invention, as a characteristic corresponding to the permanent strain accompanying the fracture of the compressed portion, the compression residual strain whose measurement method was previously shown was used as an index.

  In the porous carbon sheet obtained by the production method of the present invention, the compression deformation rate at the time of pressurization of the sheet is controlled in the range of 16 to 30%, and the compressive residual strain on both surfaces is controlled in the range of 3 to 10 μm. Therefore, it has been difficult to satisfy all of the conventional requirements at the same time, the characteristics required of a porous carbon sheet as a gas diffuser of a fuel cell, a large compressive deformation rate, a small compressive residual strain on the surface, and an electrical conductivity Satisfy both high and high mechanical strength at the same time.

  When the compressive deformation rate during pressurization is less than 16%, when it is used as a gas diffuser of a polymer electrolyte fuel cell, it is not compressed to the thickness of the sealing material designed to a certain thickness, and as a stack A large deviation occurs in the overall size, or it becomes thicker than a sealing material for gas sealing, so that a sufficient sealing performance cannot be obtained and the performance as a battery is lowered, which is not preferable. When the compression deformation rate is more than 30%, the compressive residual strain becomes large, or the mechanical strength is low and the handling property is problematic.

The compressive deformation rate of the sheet is preferably in the range of 16 to 25%, and more preferably in the range of 16 to 20%.
If the compressive residual strain on both surfaces is greater than 10 μm, when used as a gas diffuser of a polymer electrolyte fuel cell, it will fall into the groove provided in the separator and close the gas flow path, thereby improving the performance as a battery. It is not preferable because it lowers. The porous carbon sheet obtained by the production method of the present invention is a porous material, and even if the compressive residual strain on both surfaces can be reduced, 3 μm is the limit.
The compressive residual strain on both surfaces of the sheet is more preferably 3 to 7 μm, and further preferably 3 to 5 μm.

  The porous carbon sheet obtained by the production method of the present invention preferably has a different surface and internal structure in order to have a suitable compressive deformation rate and compressive residual strain. That is, by increasing the bulk density of the surface of the porous carbon sheet as described above, the gas at the time of stacking when used as a gas diffuser of a polymer electrolyte fuel cell is reduced by reducing the compressive residual strain on the surface. The battery performance can be prevented from being deteriorated due to the diffuser falling into the groove provided in the separator and closing the gas flow path. And by reducing the internal bulk density, the compression deformation rate of the entire porous carbon sheet can be increased, and the gas diffuser can be prevented from being greatly compressed as a stack without being compressed to the thickness of the sealing material. Therefore, it is preferable.

  The porous carbon sheet obtained by the production method of the present invention has a bulk density of 0.5 μm from the surface to 50 μm. 40 to 0. Preferably it is in the range of 60 g / cm 3, 0. 4 5-0. More preferably, it is in the range of 5 5 g / cm 3. The bulk density is 0. If it is less than 40 g / cm 3, the mechanical strength of the porous carbon sheet, specifically, the bending strength is lowered, and it becomes difficult to handle, which is not preferable. The bulk density is 0. If it exceeds 60 g / cm 3, it may be used as a gas diffuser of a polymer electrolyte fuel cell, and when the fuel cell is operated at a high power density, it may cause a decrease in cell performance due to clogging with purified water. It is not preferable.

  When the bulk density D A having a thickness of up to 50 μm from the surface of the porous carbon sheet obtained by the production method of the present invention and the bulk density D B in the region of 20 μm in the center in the thickness direction are 2 < It is preferable that D A / D B <6, more preferably 2 <D A / D B <4, and further preferably 2 <D A / D B <2.5. When D A / D B exceeds 6, D B, which is the bulk density of the region of 20 μm in the thickness direction, becomes too small, which is not preferable because the conductivity is lowered. In addition, since the porous carbon sheet obtained by the production method of the present invention preferably has a DA higher than the bulk density DB of the region of 20 μm in the thickness direction, DA / DB is less than 1. There is no.

The porous carbon sheet obtained by the production method of the present invention preferably has an electric resistance value in the thickness direction in the range of 1 to 8 Ω cm ² . When the electrical resistance value is 8 Ω cm ² or less, it is possible to suppress a decrease in battery performance due to ohmic loss due to the resistance of the gas diffuser itself when the fuel cell is formed. Although the ohmic loss can be reduced as the electrical resistance value in the thickness direction is smaller, as long as it takes the form of carbon paper, carbon fiber woven fabric, or carbon fiber nonwoven fabric, about 1 Ω cm ² is the limit.

  The porous carbon sheet obtained by the production method of the present invention preferably has a bending strength of 10 to 100 MPa, more preferably 15 to 80 MPa, and more preferably 20 to 60. More preferably, it is MPa. When the bending strength is less than 10 M Pa, the porous carbon sheet is cracked or chipped when transported or handled, causing problems in handling properties, which is not preferable. Further, if the bending strength is 100 M Pa or more, the rigidity of the porous carbon sheet becomes too high, and when handled in a roll shape, it can only be wound around a large diameter paper tube, It is not preferable because it requires a very large space and is difficult to handle.

  In general, a gas diffuser using a porous carbon sheet as a base material constitutes a membrane-electrode assembly by bonding them to a solid polymer electrolyte membrane having a catalyst layer on both sides. In addition, a solid polymer fuel cell is constructed by laminating a plurality of materials sandwiched by separators provided with grooves serving as gas flow paths necessary for reaction on both sides of the membrane-electrode assembly via a sealing material. ing. Therefore, the surface where the gas diffuser contacts the separator is only one side, and the compression residual strain on the one side surface only needs to be small in order to prevent the drop into the groove. However, porous carbon sheets with high bulk density on one side and low bulk density on the other side have different bulk densities on both surfaces. Therefore, there is a problem that warpage is likely to occur. For the same reason, the porous carbon sheet is likely to warp unless it has a symmetrical structure centered in the middle of the thickness direction.

  The thickness of the porous carbon sheet obtained by the production method of the present invention is preferably in the range of 120 to 400 μm, and preferably in the range of 130 to 300 μm. More preferably, it is still more preferably in the range of 14 0 to 2 20 μm. If the thickness is less than 120 μm, it is not preferable because sufficient mechanical strength cannot be obtained. On the other hand, if the thickness exceeds 400 μm, the flexibility of the porous carbon sheet is greatly reduced, and it becomes difficult to wind it on a roll described later.

  It is preferable that at least a part of the porous carbon sheet obtained by the production method of the present invention is in the form of the carbon short fiber paper. That is, it is preferable that the carbon short fiber and the resin carbide are dispersed, and at least a part of the carbon short fiber has a structure bound with the resin carbide. Since the carbon short fiber paper is laminated and compressed and bonded in the heat and pressure treatment of the method for producing the porous carbon sheet, it is desirable that the carbon short fiber paper contains a phenol resin composition, and also after the carbonization step. It is preferable to bind the carbon fiber as a resin carbide.

The measuring method of various characteristic values related to the porous carbon sheet is as follows.
The compressive deformation rate and the compressive residual strain on both surfaces of the porous carbon sheet obtained by the production method of the present invention were measured using a micrometer having a circular cross section having a diameter of 5 mm. In the thickness direction of 0. The thickness when a surface pressure of 3 3 M Pa is applied is d 1, and then 1. After applying and releasing the surface pressure of 6 MPa twice, 0. The thickness when a surface pressure of 3 3 M Pa is applied is defined as d2. The thickness when a surface pressure of 6 MPa is applied can be determined from the following equations (I) and (II), where d3 is the thickness. The number of measurements shall be 3 and calculated from the average value. The compressive residual strain is measured from both surfaces of the porous carbon sheet.
Compressive residual strain = d 1 −d 2 (I) equation Compression deformation rate = (d 2 −d 3) / d 2 (II) equation

For the measurement of the electrical resistance of the porous carbon sheet obtained by the production method of the present invention, two gold-plated stainless steel blocks provided with terminals for current and voltage are prepared. A porous carbon plate cut at 20 mm × 25 mm is sandwiched between two gold-plated stainless steel blocks, and the sample is pressurized so that a pressure of 1 M Pa is applied. At this time, the voltage terminal is placed near the surface sandwiching the sample, and the current terminal is placed near the surface opposite to the surface sandwiching the sample. 1 A is passed between the current terminals, the voltage V (V) is measured between the voltage terminals, and the resistance value is calculated by the following equation (III).
Electrical resistance (mΩ · cm 2) = V × 2 × 2. 5 × 1 0 0 0 (III) Formula

  The bending strength of the porous carbon sheet obtained by the production method of the present invention is measured by a three-point bending test based on JISK 6 9 1 1. However, the width (W) of the test piece is 15 mm and the distance between supporting points (Lv) is 15 mm. Also, the R of the fulcrum and the pressure wedge is 3 mm, and the load speed is 2 mm / min. The number of measurements is 5 and is calculated from the average value.

  The thickness of the porous carbon sheet was set to 0. 0 mm in the thickness direction of the sheet using the micrometer described above. It is measured by applying a surface pressure of 15 MPa. The measurement points are 1. The number of measurements is 20 times or more with a grid of 5 cm intervals, and the average value is the thickness.

The basis weight (weight per unit area) of the porous carbon sheet is calculated from an average value obtained by measuring the weight of the 10 cm × 10 cm square porous carbon sheet 10 times.
The bulk density DT of the porous carbon sheet is calculated from the thickness and basis weight of the porous carbon sheet described above.
The bulk density D A up to 50 μm from both surfaces and the bulk density DB of the region in the thickness direction central part 20 μm are measured by first measuring both the thickness T T and the porous carbon sheet of bulk density D T. The thickness of the remaining porous carbon sheet is scraped off from the surface by a certain thickness T A (50 to 60 μm), and the bulk density D B in the region of 20 μm in the center in the thickness direction from the basis weight is determined. calculate. From these, D A is calculated by the following equation (IV).
Bulk density D A (g / cm 3) of both surfaces =
(TTDT- (TT-2TA) DB) / 2TA (IV) Formula

Example 1
Polyacrylonitrile-based carbon fibers cut to an average fiber length of 3 mm (trade name: “Pyrofil TR50S”, manufactured by Mitsubishi Rayon Co., Ltd. (average single fiber diameter: 7 μm)), polyvinyl alcohol (PVA) short fibers (trade name: “VBP105- 1 ", manufactured by Kuraray Co., Ltd. (fiber length 3 mm).
Carbon fiber is continuously made using water as a paper making medium, further immersed in a 10% by weight aqueous solution of polyvinyl alcohol and dried, and the short carbon fiber having a basis weight of about 20 g / m ² is obtained. Paper was obtained and wound into a roll. The amount of polyvinyl alcohol attached corresponds to 20 parts by weight per 100 parts by weight of carbon short fiber paper.

  Next, a methanol solution (phenol resin: 23% by mass) of a phenol resin composition (trade name: “Phenolite J-325”, manufactured by DIC Corporation) was prepared. Carbon short fiber paper was continuously impregnated with a phenol resin composition, and 150 parts by weight of the phenol resin composition was adhered to 100 parts by weight of the carbon short fiber paper. Then, carbon short fiber paper impregnated with the phenol resin composition was obtained by drying at 90 ° C. for 3 minutes, and wound into a roll.

  The hot plates 7 and 8 were set on the press so that they were parallel to each other. Two spacers 9 were placed on the hot plate 8 next to the short carbon fiber paper impregnated with the phenol resin composition. At this time, the effective pressurization length L P of the hot plate was 1 2 0 0 mm, and the spacer length L S was 1 2 0 0 mm. The width W P of the short carbon fiber paper impregnated with the phenol resin was 60 mm, and the width of the spacer was 100 mm. After stacking two short carbon fiber papers impregnated with a phenol resin composition so that the surface with a large amount of impregnation is the outer surface, a 40 g / m 2 epoxy resin composition (trade name: “# 830”, Mitsubishi Rayon ( Coated surface is directed to the carbon short fiber paper laminate side impregnated with phenol resin composition with two release papers (trade name: “WBE90R”, manufactured by Lintec Co., Ltd.) The hot plate temperature is 160 ° C., the surface pressure is 0. At 8 MPa, the same part is heated and pressurized for a total of 6 minutes while intermittently transporting the carbon short fiber paper laminate and release paper with a width of 60 mm while repeating opening and closing of the press. It processed as follows. At this time, the effective pressurization length L P of the hot plate was 1 2 0 0 mm, and the feed amount L F of the precursor fiber sheet when intermittently transported was 1 0 0 mm. That is, the process is repeated by heating and pressurizing for 30 seconds, opening the mold, feeding the carbon short fiber paper laminate and the release paper (10 0 mm), removing the release paper, and removing the 600 mm. A laminate of carbon short fiber paper cured with resin at a width of was rolled up into a roll.

  The above-mentioned laminate of resin-cured short carbon fiber paper subjected to heat and pressure treatment was introduced into a heating furnace maintained at a nitrogen gas atmosphere and having a maximum temperature of 2,000 ° C. While running, it is fired at a heating rate of about 500 ° C./min (40 ° C./min up to 650 ° C., 55 ° C./min at temperatures exceeding 65 ° C.) and rolled into a roll Winded up. The obtained porous carbon sheet had a length of 100 m. The evaluation results of the obtained porous carbon sheet are shown in Table 1 below.

(Example 2)
A porous carbon sheet was obtained in the same manner as in Example 1 except that the basis weight of the coated epoxy resin composition was changed to 57 g / m2. The evaluation results of the obtained porous carbon sheet are shown in Table 1 below.

(Comparative Example 1)
Polyacrylonitrile-based carbon fibers cut to an average fiber length of 3 mm (trade name: “Pyrofil TR50S”, manufactured by Mitsubishi Rayon Co., Ltd. (average single fiber diameter: 7 μm)), polyvinyl alcohol (PVA) short fibers (trade name: “VBP105- 1 ", manufactured by Kuraray Co., Ltd. (fiber length 3 mm). Carbon fiber is continuously made using water as a paper making medium, dipped in a 10% by weight aqueous solution of polyvinyl alcohol, dried, and a short carbon fiber having a basis weight of about 13 g / m 2 is obtained. A fiber paper was obtained and wound into a roll. The amount of polyvinyl alcohol attached corresponds to 20 parts by weight with respect to 10 parts by weight of carbon short fiber paper.

  Next, a methanol solution of phenol resin composition trade name: “Phenolite J-325” (manufactured by DIC Corporation) was prepared. The carbon short fiber paper was continuously impregnated, and 90 parts by weight of the phenol resin composition was adhered to 100 parts by weight of the carbon short fiber paper. Thereafter, carbon short fiber paper having a low bulk density was obtained by drying at 90 ° C. for 3 minutes, and wound into a roll. Moreover, the high bulk density carbon short fiber paper impregnated so that the phenol resin composition would be 200 parts by weight with respect to 100 parts by weight of the carbon short fiber paper was also wound up in a roll shape.

  One carbon short fiber paper having a low bulk density is sandwiched between two carbon short fiber papers having a high bulk density, and a laminate of carbon short fiber papers is sandwiched by a release paper not coated with an epoxy resin composition. . Moreover, the heating-pressing process was performed by the method similar to Example 1 except having set the hot plate temperature as 180 degreeC, and it wound up in roll shape with the width | variety of 60 mm. The carbon short fiber paper subjected to the heating and pressurizing treatment was introduced into a heating furnace having a maximum temperature of 2,000 ° C. maintained in a nitrogen gas atmosphere and continuously running in the heating furnace. It was fired at a heating rate of 0 ° C./minute (40 ° C./minute up to 650 ° C., and 55 ° C./minute at temperatures exceeding 65 ° C.) and wound into a roll. The obtained porous carbon sheet had a length of 100 m. The evaluation results of the obtained porous carbon sheet substrate are shown in Table 1 below.

(Comparative Example 2)
The carbon short fiber paper impregnated so that the phenol resin composition is 90 parts by weight with respect to 100 parts by weight of carbon short fiber paper having a basis weight of 20 g / m 2 in papermaking A porous carbon sheet was obtained in the same manner as in Example 1 except that low carbon short fiber paper was used. The evaluation results of the obtained porous carbon sheet substrate are shown in Table 1 below.

  Since the porous carbon sheet of Example 1 is manufactured by being laminated in the compression process so that the bulk density of both surfaces is higher than the internal bulk density, the compression deformation rate is 16 to 30%, The compressive residual strain on the surface is controlled within an appropriate range of 3 to 10 μm. Therefore, the porous carbon sheets of Examples 1 and 2 are excellent in compressive deformation rate and compressive residual strain on both surfaces, and show sufficient values in both evaluation results of electrical resistance in the thickness direction and bending strength. All the characteristics required for the porous carbon sheet as a material for the gas diffuser of the fuel cell are satisfied simultaneously.

  On the other hand, Comparative Examples 1 and 2 are manufactured by laminating short carbon fiber papers having different bulk densities and heat-pressing, but the thermosetting resin moves from a resin-rich layer to a less-heated layer by heating. There is no significant difference in the amount of resin between the surface layer and the central part. Therefore, the compression deformation rate is lowered.

  As described above, according to the method for producing a porous carbon sheet of the present invention, characteristics required for a porous carbon sheet as a material for a gas diffuser of a fuel cell, specifically, a high compressive deformation rate, It is possible to provide a porous carbon sheet that satisfies all the requirements that the surface compressive residual strain is small, the conductivity is high, and the mechanical properties are high.

It is an example which shows the laminated body in this invention. It is the schematic which shows the heating-pressing process of the manufacturing process of the porous carbon sheet of this invention.

Explanation of symbols

1: Epoxy resin composition coated 2: Carbon short fiber paper impregnated with phenol resin composition 3: Carbon short fiber paper 4: Spacer 5: Carbon short fiber paper laminate coated with epoxy resin composition 6: Hot Press 7: Upper heating plate 8: Lower heating plate

Claims (5)

  A method for producing a porous carbon sheet in which an epoxy resin composition is applied to the surface of a short carbon fiber paper impregnated with a phenol resin composition, both the resin compositions are cured by heating and pressing, and then carbonized. .   The manufacturing method of the porous carbon sheet of Claim 1 using the laminated body which laminated | stacked two carbon short fiber papers impregnated with the phenol resin composition as carbon short fiber papers impregnated with the phenol resin composition.   The carbon short fiber paper impregnated with the phenol resin composition is a laminate in which two carbon short fiber papers impregnated with the phenol resin composition are laminated with the surface of the phenol resin composition impregnated on the outer surface. 2. The method for producing a porous carbon sheet according to 2. Instead of carbon short fiber paper impregnated with phenol resin composition, carbon short fiber paper impregnated with phenol resin composition, carbon short fiber paper and carbon short fiber paper impregnated with phenol resin composition are laminated in that order. The manufacturing method of the porous carbon sheet of Claim 1 using the laminated body formed by.   The porous carbon sheet manufactured with the manufacturing method of the porous carbon sheet in any one of Claims 1-4.

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