JP2006236992A - Porous carbon base material and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a porous carbon base material high in power generation performance when it is formed into a gas diffusion body of a fuel cell and hardly damaging a membrane; and to provide its manufacturing method. <P>SOLUTION: This porous carbon base material is a sheet containing a carbon short fiber and a resin carbide dispersed in random directions; and a part of the carbon short fiber is bonded by the resin carbide; and the standard deviation of the thickness of the sheet is 1.0-5.0 μm. This manufacturing method comprises: a compression process for intermittently transporting a precursor fiber sheet containing a carbon fiber and a resin between heat plates positioned in parallel with each other to subject it to a heating and pressing process by the heat plates during the stop of the transportation; and a carbonization process for carbonizing the resin in the compressed precursor fiber sheet. In the compression process, two or more spacers are arranged beside the precursor sheet to be transported on the lower hot plate, and the precursor fiber sheet is transported between the spacers. The gas diffusion body is formed of the porous carbon base material and is used for a membrane-electrode assembly to constitute a fuel cell. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a porous carbon substrate preferably used as a material for a gas diffuser of a polymer electrolyte fuel cell and a method for producing the same.

Conventionally, a porous carbon base material obtained by binding carbon fibers with resin carbide has been used as a base material constituting a gas diffuser for a polymer electrolyte fuel cell. (For example, Patent Document 1)
The porous carbon base material disclosed here impregnates a sheet made of carbon fiber with a thermosetting resin, and heats and presses the sheet in batch mode to cure the thermosetting resin, and then fires in batch mode. Since it is obtained by performing, there existed a problem that productivity was low and cost was high.

  Also, even when post-treatment such as water repellent treatment of the porous carbon substrate, it takes time to process the single wafer, so a continuous roll-like porous carbon substrate that can be processed continuously is required. It had been.

  In order to solve the above problem, in Patent Document 2, a paper-made carbon fiber sheet is impregnated with a resin, cured, and continuously subjected to steps up to carbonization to obtain a roll-shaped porous carbon substrate. .

  Moreover, in patent document 3, the thermosetting resin is continuously heated and pressurized by a double belt press to cure and carbonize continuously to obtain a roll-shaped porous carbon substrate.

  When the resin is cured by the above method, there is a problem that a porous carbon substrate having a uniform thickness cannot be obtained. That is, if sufficient pressure molding is not performed at the time of molding or curing of the thermosetting resin, the thickness after molding or after curing will vary in thickness due to variations in the amount of carbon fiber and resin, and even after the carbonization step The variation remains. In addition, in the case of using a double belt press, it is necessary to increase the mold temperature in order to shorten the press time, so that the rapid thermosetting resin is cured, resulting in a large thickness variation. Even when batch-type heating and pressing are performed, the thickness variation can be reduced to some extent by stacking multiple sheets, but the thickness variation due to the inclination of the template to be heated and pressed occurs, and the variation is sufficiently low. There was a problem that could not be obtained.

In addition, when the porous carbon base material obtained by curing the resin by the above method is used as the material for the gas diffuser of the polymer electrolyte fuel cell, desired power generation performance cannot be obtained.
JP-A-7-220735 (first page) JP 2004-31326 A (page 3) International Publication No. 2002/006032 Pamphlet (9th page)

  In view of the above-described problems in the prior art, the present invention provides a porous carbon base material having high power generation performance as a battery when used as a gas diffuser of a fuel cell and a method for producing the same.

The inventors of the present invention have studied the reasons why the desired power generation performance cannot be obtained with the porous carbon substrate obtained by the conventional method. (A) The thickness of the gasket designed due to the large variation in thickness. The gas diffuser is thicker or thinner than the gas diffuser, and the thick part is not sufficiently sealed by the gasket, causing problems such as leakage of fuel gas. (B) When the fuel cell is used in the thin part It does not receive sufficient tightening pressure, the adhesion with the solid polymer membrane of the gas diffuser and the separator deteriorates and the electrical resistance increases, (c) damages the solid polymer membrane in the thick part of the gas diffuser, As a result of the development and application of a porous carbon base material and manufacturing method with reduced thickness variation, the solid-state battery has better power generation performance than the conventional one. It is those that began to see that the quality type fuel cell is obtained. That is,
(1) A sheet containing carbon short fibers and resin carbide dispersed in a random direction, wherein at least a part of the carbon short fibers are bound with the resin carbide, and are defined in the text. A porous carbon substrate characterized in that the standard deviation of the thickness of the sheet is 1.0 to 5.0 μm.

(2) The porous carbon substrate according to (1), wherein the thickness is in the range of 0.10 to 0.25 mm and the density is in the range of 0.3 to 0.7 g / cm ³ . Porous carbon substrate.

  (3) The porous carbon substrate according to (2), wherein the porous carbon substrate has a length of 50 to 500 m, a width of 100 to 1000 mm, and is wound into a roll. Wood.

  (4) In the above (3), the difference between the maximum value and the minimum value of the average value of the thickness when the porous carbon base material is sampled at 20 points every 10 m in the length direction is 15 μm or less. The porous carbon substrate as described.

  (5) The porous carbon substrate according to any one of (1) to (4), wherein the short carbon fibers constituting the porous carbon substrate have an average fiber diameter in the range of 5 to 20 μm. .

  (6) The porous carbon substrate according to any one of (1) to (5), wherein the porous carbon substrate includes a carbonaceous powder.

  (7) The porous carbon base material according to any one of (1) to (6), wherein the porous carbon base material is a sheet having a standard deviation in thickness within a range of 1.0 to 4.0 μm. .

  (8) A gas diffuser comprising a porous carbon substrate according to any one of (1) to (7) provided with a water-repellent substance.

  (9) A gas diffuser in which a conductive gas diffusion layer is disposed on at least one surface of the porous carbon substrate according to any one of (1) to (7).

  (10) Gas diffusion in which a water-repellent material is imparted to the porous carbon substrate according to any one of (1) to (7), and a conductive gas diffusion layer is disposed on at least one surface thereof. body.

  (11) In a membrane-electrode assembly comprising a solid polymer electrolyte membrane, a catalyst layer containing catalyst-supporting carbon provided on both surfaces thereof, and a gas diffuser provided in contact with the outside of both catalyst layers, At least one is comprised with the gas diffusion body in any one of said (8)-(10), The membrane-electrode assembly characterized by the above-mentioned.

  (12) A polymer electrolyte fuel cell comprising the membrane-electrode assembly according to (11).

  (13) A compression process in which a precursor fiber sheet containing carbon short fibers and a resin is intermittently conveyed between hot plates positioned parallel to each other, and heated and pressurized with the hot plate while the conveyance is stopped, And a carbonization process for carbonizing a resin in the precursor fiber sheet that has been subjected to compression treatment, and in the compression process, two or more spacers are conveyed on the lower hot plate A method for producing a porous carbon substrate, wherein the precursor fiber sheet is disposed beside a precursor fiber sheet to be conveyed, and the precursor fiber sheet is conveyed between the spacers.

  (14) The method for producing a porous carbon substrate according to (13), wherein a release sheet is disposed so as to sandwich the precursor fiber sheet, and the precursor sheet is conveyed and heated and pressurized.

(15) the thickness of the release sheet T _R, when the thickness of the precursor fiber sheet is compressed by the compression process and T _P, the thickness T _S of the spacer is porous as described in (13) satisfies the following equation Of producing a carbonaceous substrate.

T _S <T _R + T _P
(16) When the effective pressurization length in the conveying direction of the hot plates parallel to each other is L _P and the feed amount of the precursor fiber sheet when intermittently conveying is L _F , L _F / L _P is 0.1. The manufacturing method of the porous carbon base material in any one of said (13)-(15) which is -0.98.

  (17) The method for producing a porous carbon substrate according to any one of (13) to (16), wherein the temperature of the hot plates parallel to each other is 140 to 300 ° C. and the applied pressure is 0.1 to 4.0 MPa. .

  According to the present invention, there is no change in thickness continuously in the length direction, and the post-treatment process such as water repellent treatment can be performed continuously, so that the production efficiency is good and the gas diffuser of the fuel cell is used. A porous carbon base material having high power generation performance as a battery and having little damage to the membrane can be continuously supplied. Further, the porous carbon base material is a gas diffusion body of a polymer electrolyte fuel cell. Suitable as a material.

  The present invention, which is the subject, that is, a porous carbon base material having high power generation performance as a battery when used as a gas diffuser of a fuel cell and little damage to the membrane, has been intensively studied and specified a standard deviation of thickness. When a porous carbon substrate within the range was made, it was found that this problem could be solved all at once.

  As described above, the porous carbon base material of the present invention includes carbon short fibers and resin carbide, and at least a part of the carbon short fibers are bound by resin carbide, and the standard deviation of the thickness is 1.0 to 1.0. It is characterized by being 5.0 μm.

  When the standard deviation of the thickness is larger than 5.0 μm, when used as a gas diffuser for a polymer electrolyte fuel cell, a portion thicker or thinner than the designed thickness of the gasket used for gas sealing occurs. This is not preferable because the power generation performance as a battery is lowered or the solid polymer film is locally subjected to pressure due to the variation in the thickness of the porous carbon base material, thereby reducing the life of the solid polymer film. On the other hand, if the standard deviation of the thickness is made smaller than 1.0 μm, a highly accurate heating and pressurizing system is required in the manufacturing process, and the molding time becomes longer, which is not preferable in terms of productivity and cost.

The standard deviation measurement method of this thickness is that five porous carbon substrates are cut out at 100 mm × 100 mm, and the measurement points 2 are taken at intervals of 20 mm vertically and horizontally as shown in FIG. The thickness was measured at 25 points, a total of 125 points. The thickness is measured by applying a surface pressure of 0.15 MPa in the thickness direction of the substrate using a micrometer. The standard deviation of thickness is calculated from the thickness measured using the following formula. The thickness of the porous carbon base material is an average value of 125 points.
(Standard deviation of thickness) = [{nΣx ² − (Σx) ² } / n (n−1)] ^1/2
x: thickness of each measurement point
n: Number of measurement points In the present invention, the standard deviation of the thickness of the porous carbon base material is set to 1.0 to 5.0 μm, so that when used as a gas diffuser for a polymer electrolyte fuel cell, a solid Without damaging the polymer membrane due to variations in thickness, it is possible to suppress degradation of the power generation characteristics of the polymer electrolyte fuel cell due to membrane degradation and show high performance for a long time. The standard deviation of the thickness of the porous carbon substrate is more preferably 1.0 to 4.0 μm.

  The thickness of the porous carbon substrate is preferably in the range of 0.10 to 0.25 mm. If the thickness is less than 0.1 mm, the strength tends to decrease and it becomes difficult to handle. If the thickness is more than 0.25 mm, the electric resistance in the thickness direction increases, and the gas of the polymer electrolyte fuel cell increases. When used as a diffuser, the performance tends to be low, and the flexibility of the substrate tends to decrease, making it difficult to wind up the roll. The more preferable thickness of the porous carbon substrate is 0.11 to 0.22 mm, and the particularly preferable thickness is 0.12 to 0.16 mm.

The density of the porous carbon substrate is preferably 0.3 to 0.7 g / cm ³ , more preferably 0.32 to 0.60 g / cm ³ , and particularly preferably 0.34 to 0.60 g / cm ^3. It is. That is, when the density is lower than 0.3 g / cm ³ , the amount of the resin carbide is reduced, the thickness is not uniform, and the thickness variation tends to increase, and the density is reduced to 0.7 g / cm ³ . When exceeding, the drainage property of water when used as a gas diffuser of a polymer electrolyte fuel cell is deteriorated, causing water clogging and a tendency to deteriorate the cell performance.

  The basis weight and density are measured by measuring the weight of a 10 cm × 10 cm square porous carbon substrate and calculating the basis weight from the average value. The density is calculated from the thickness and basis weight of the substrate.

  Moreover, the porous carbon base material of this invention is 50-500 m in length, exists in the range of 100-1000 mm in width, and it is preferable that it is wound up by roll shape.

  By being wound up in a roll shape, post-treatment such as water repellent treatment can be continuously performed. When post-treatment such as water repellent treatment, the amount that can be processed at one time by one roll depends on the length and width of the roll. Therefore, when the length per roll is 50 m or less, the amount that can be processed is reduced and the productivity is reduced. descend. On the other hand, if the roll length exceeds 500 m, the weight per roll and the winding diameter become large, making it difficult to handle. In addition, when the width is 100 mm or less, the roll is likely to collapse during transportation and handling. When the width exceeds 1000 mm, the weight per roll becomes large and handling becomes difficult.

  The porous carbon substrate is preferably roll-shaped and has no change in thickness in the length direction. If the thickness greatly changes in the length direction in the roll, it is difficult to design the thickness of the sealing material when used as a gas diffuser of a polymer electrolyte fuel cell, and the base material is thicker than the sealing material. When it is used as a gas diffuser sufficiently, it may not be sealed by the seal material, or it may be thinner than the seal material and the adhesion between the gas diffuser and the film may deteriorate. If it is not sufficiently sealed, there is a problem that fuel gas leaks from an unsealed portion. Further, when the adhesion with the film is poor, peeling occurs at that portion, and the battery performance is lowered. Accordingly, the difference between the maximum value and the minimum value of the average value of the thickness of the porous carbon base material measured at 20 points at intervals of 10 m in the length direction of 50 to 500 m is preferably 15 μm or less. More preferably.

  The carbon fiber used for the porous carbon substrate of the present invention preferably has an average fiber diameter of 5 to 20 μm. When the average fiber diameter is 5 μm or less, although depending on the type of carbon fiber, the flexibility of the porous carbon substrate is lowered and it is difficult to form a roll. On the other hand, if the average fiber diameter exceeds 20 μm, the strength of the porous carbon substrate may be lowered. The average fiber diameter of the carbon fibers is more preferably 6 to 13 μm, and further preferably 6 to 10 μm.

  The average fiber diameter of the carbon fibers is determined as a simple average value by selecting arbitrary 10 carbon fibers from a cross-sectional photograph of the fibers with an electron microscope of 5,000 times that of the substrate and measuring the fiber diameter. When the cross-sectional shape is not circular, for example, an elliptical diameter, the average value of the major axis and the minor axis is taken as the fiber diameter. Moreover, the presence or absence of carbonaceous powder can be confirmed by confirming the resin carbide part of the electron micrograph.

  The porous carbon material of the present invention preferably contains carbonaceous powder in order to improve conductivity. Examples of the carbonaceous powder include carbon black, graphite, carbon nanotube, carbonaceous milled fiber, and expanded graphite. It is more preferable to use graphite for improving conductivity.

  3 and 4 are partial cross-sectional views showing an example of a polymer electrolyte fuel cell (FIG. 3 is a cross-sectional view in FIG. 4 for attaching reference numerals for explaining the structure of a membrane-electrode assembly part to be described later. (The gasket portion is omitted. In Fig. 4, the reference numerals other than the gasket portion are omitted, but the portions other than the gasket are the same as those in Fig. 3.) In FIG. 3, a catalyst layer 9 and a gas diffusion body 11 are arranged on both sides of the solid polymer electrolyte membrane 8, and these are integrated by heating and pressurizing to form a membrane-electrode assembly. In the example shown in FIG. 3, the gas diffuser 11 has a conductive gas diffusion layer 10 disposed on one surface of the porous carbon substrate 1. A unit cell is formed by sandwiching the membrane-electrode assembly between separators 12. Between the separator 12 and the gas diffuser 11, a gas flow path 13 for supplying hydrogen and oxygen used for the reaction of the polymer electrolyte fuel cell is formed. The porous carbon substrate 1 according to the present invention is preferably used as a material for the gas diffuser 11 of the polymer electrolyte fuel cell as in this example. 3 shows the gas diffuser 11 in which the gas diffusion layer 10 having conductivity is disposed on one surface of the porous carbon substrate 1, a configuration without the gas diffusion layer 10 is also possible.

  The gas diffuser 11 according to the present invention is a water-repellent substance on the porous carbon substrate 1 for the purpose of preventing water clogging when used in a fuel cell and for improving the water retention of the solid polymer electrolyte membrane. It is preferable that it is configured by adding. The water-repellent substance is not particularly limited, but for example, a fluorine-containing compound or a silicon-containing compound is preferably used.

  The gas diffuser 11 according to the present invention preferably has an electrically conductive gas diffusion layer 10 on at least one surface of the porous carbon material or the porous carbon material provided with the water-repellent substance. The conductive gas diffusion layer 10 preferably contains a fluororesin and carbon black. Here, the fluororesin includes tetrafluoroethylene resin (PTFE), perfluoroalkoxy resin (PFA), fluorinated ethylene propylene resin (FEP), fluorinated ethylene tetrafluoroethylene resin (ETFE), etc. A resin having water repellency containing atoms. By providing the gas diffusion layer 10 having conductivity on at least one surface of the gas diffuser 11, the surface of the gas diffuser 11 becomes smooth and it is easy to ensure electrical contact with the solid polymer electrolyte membrane 8. Has an effect. In addition, when creating a membrane-electrode assembly (portion consisting of 8, 9, and 11 in FIG. 3), it has an effect of preventing the convex portion of the gas diffuser from sticking into the solid polymer electrolyte membrane and causing a short circuit. .

  The membrane-electrode assembly according to the present invention uses the gas diffuser 11 on at least one side of both gas diffusers. The catalyst layer 9 is composed of a layer containing a solid polymer electrolyte and catalyst-supporting carbon. In general, the catalyst-supported carbon is one in which a solid polymer is used in a multi-fuel cell, and catalyst fine particles are supported on carbon in order to increase the effective area of electrode reaction. Platinum and ruthenium are preferably used as the catalyst.

  Since the membrane-electrode assembly according to the present invention has a small standard deviation in thickness as described above, there is little damage to the membrane when used as a gas diffuser, and there is little degradation in battery performance during long-time operation. Show properties.

  The polymer electrolyte fuel cell according to the present invention is obtained by superposing a plurality of cells sandwiched between separators via gaskets 14 on both sides of a membrane-electrode assembly. As described above, the fuel cell proposed in the present invention exhibits very high performance because of the use of the above-described membrane-electrode assembly that shows a small decrease in battery performance during long-time operation and exhibits high battery characteristics.

  Next, the manufacturing method of the porous carbon base material of this invention is demonstrated.

  The method for producing a porous carbon substrate according to the present invention intermittently conveys a precursor fiber sheet containing carbon short fibers and a resin between hot plates located in parallel with each other, and while the conveyance is stopped, The two steps are a basic step, including a compression step in which heat and pressure treatment is performed between parallel hot plates and a carbonization step in which the resin in the precursor fiber sheet subjected to the compression treatment is carbonized.

  In the compression step, two or more spacers are placed beside the precursor fiber sheet on a hot plate positioned parallel to each other, and the precursor fiber sheet is conveyed and heated and pressed between the two or more spacers. A method for producing a porous carbon substrate characterized by the following.

  The parallel hot plates are those having a parallelism of 1 mm or less in at least an area of 50% or more. The parallelism is defined as a difference between the maximum value and the minimum value of the thickness of the lead piece after the lead piece arranged on the hot plate is heated and pressed and deformed. Moreover, although the material of both hot plates may be the same, a different thing can also be used. For example, one hot plate may be made of stainless steel and the other hot plate may be made of silicon rubber.

  In this manufacturing method, as shown in FIG. 2, while the precursor fiber sheet 3 is conveyed between the hot plates 5 and 6, the conveyance is stopped by the hot plate 5 that repeatedly pressurizes and releases intermittently. The precursor fiber sheet 3 is continuously heated and pressed between the hot plates 5 and 6. The opposing surfaces of the hot plates 5 and 6 are arranged in parallel to each other, and the precursor fiber sheet is heated and pressurized while receiving a surface pressure. When the precursor fiber sheet 3 is conveyed, the hot plates 5 and 6 are separated from each other to allow the precursor fiber sheet 3 to move. At this time, the spacer 7 is disposed on the lower hot plate 6 next to the precursor fiber sheet 3, and the precursor fiber sheet 3 is conveyed between the spacers 7.

  As described above, the porous carbon plate used for the gas diffuser of the polymer electrolyte fuel cell is required to have a very high thickness uniformity. In general, in molded products made of fibers and thermosetting resins that are molded by heating and pressing with a press, the dimensional accuracy is determined by the parallelism of the hot plate and the accuracy of the mold. It is about μm to 1 mm, and the order is greatly different from the accuracy of the thickness required for the porous carbon plate used for the gas diffuser of the polymer electrolyte fuel cell. In the present invention, as will be described later, high thickness accuracy can be obtained by heating and pressing the precursor fiber sheet while intermittently conveying the precursor fiber sheet on a hot plate having spacers arranged on both sides. Further, by making the feed length fine, the precursor fiber sheet is heated and pressed on the hot plate a plurality of times, and the thickness is averaged to obtain higher thickness accuracy.

  In a conventional belt press used for forming a porous carbon plate, the precursor fiber sheet is subjected to a pressure treatment while continuously moving in the longitudinal direction. In order to form in a short time, it was necessary to increase the mold temperature. Therefore, rapid curing of the resin occurs, and the thickness variation of the precursor fiber sheet occurs.

  In order to solve this problem, the present invention adjusts the thickness between the hot plates by inserting a spacer, and continuously heats and presses the surface pressure while applying the surface pressure, so that the resin is cured and the precursor fiber sheet is molded. A porous carbon substrate with high thickness accuracy can be obtained because the pressure is sufficiently heated and pressurized.

L _S / L _P is 0.5 to 1.1 when the length of the precursor fiber sheet conveying direction of the spacer of the present invention is L _S , and the effective pressurization length L _P of the hot plate parallel to each other. It is preferable. When L _S / L _P is smaller than 0.5, that is, when a spacer having a sufficient length is not arranged with respect to the length of the hot plate, the thickness is increased when the precursor fiber sheet is heated and pressurized. However, there are few parts where the thickness is controlled, and it is not possible to obtain a film having sufficient thickness accuracy. When L _S / L _P exceeds 1.1, an extra spacer is present with respect to the pressurization length, and the spacer becomes longer, which makes it difficult to handle. In order to handle the spacer, the spacer may be shortened, and two or more spacers may be arranged side by side in the transport direction of the precursor fiber sheet. In that case, L _S is defined as a value obtained by adding two or more spacer length.

  Here, the effective pressurization length refers to the length of the portion where the precursor fiber sheet is in contact with the hot plate and heated and pressed.

When the spacer of the present invention has a width W _P of the precursor fiber sheet and a width W _{S of} the spacer, W _S / W _P is preferably 0.01 to 0.30. If W _S / W _P is less than 0.01, the width of the spacer is too thin to control the thickness between the hot plates, and the spacer is deformed by excessive pressure per unit area. There is a fear. When W _S / W _P is greater than 0.30, two or more spacers are used on both sides, so that there are 60% or more spacers relative to the width of the substrate, which is excessive for controlling the thickness. It uses a large spacer and is useless.

  Moreover, it is preferable that the spacer of the present invention does not deform when pressed, and the thickness does not change in the length direction. If the spacer is deformed during pressurization, it is difficult to obtain a thickness as designed. For this reason, the spacer is preferably made of metal, but is not particularly limited as long as it does not deform when pressed. Also, if the thickness changes in the length direction, it is difficult to make the thickness as designed, and it is not possible to obtain a uniform thickness because it is not uniformly pressed by the surface pressure. .

  In the compression process, since the precursor fiber sheet contains a resin, there is a possibility that when the resin is a thermoplastic resin, the precursor fiber sheet melts at the time of heating and adheres to the hot plate, and in the case of a thermosetting resin, Since the viscosity lowers during heating and cures, there is a possibility of bonding to the hot plate. Therefore, it is preferable to perform a release treatment so that the hot plate and the precursor fiber sheet are not bonded. As the mold release treatment, methods such as fluorination of the hot plate and placing a release sheet on the hot plate can be considered, but in the case of fluorination processing, if the compression process is performed, the fluorination treatment was performed. It is difficult to use for a long time because the releasability of the part disappears as it is used for a long time. Even when a release sheet is placed, it is difficult to use for a long time because the release property is lost by long-time use.

  Therefore, in this invention, it is preferable to arrange | position two or more release sheets so that a precursor sheet | seat may be pinched | interposed, and to convey and heat-press with a precursor sheet | seat. This prevents the precursor sheet from adhering to the hot plate, and the release sheet is conveyed together with the precursor sheet, heated and pressed together, and comes out of the press. There is no worry that the releasability is lost because the time required is the same as the precursor sheet and is short. Further, since the release sheet and the precursor sheet do not adhere even after the compression treatment, it is easy to separate the precursor fiber sheet and the release sheet after the compression step. As a result, the precursor fiber sheet can be continuously heated and pressed to be molded with high thickness accuracy.

  As the release sheet, a release film obtained by subjecting a film or paper to a release process, a release paper, or the like is used, but it is not particularly limited as long as it is a release sheet. When heating and pressurizing one precursor fiber sheet, it is sufficient that there are two upper and lower sheets. In that case, a release sheet on which at least one side coming to the precursor sheet side is subjected to release treatment may be used. In the case where a plurality of precursor fiber sheets are laminated and heated and pressurized at the same time, by using a double-sided release sheet in which both surfaces are released between the precursor fiber sheets, a multi-stage continuous heating and pressurizing process is performed. It becomes possible.

When using a release sheet, when the thickness of the release sheet T _R, the precursor fiber sheet thickness compressed by the compression process and T _P, the thickness T _S of the spacer, the following equation (1) T _S < T _R + T _P (1)
It is preferable to satisfy. Here, when heating and pressing simultaneously using a plurality of release sheet precursor fiber sheet, T _P, is T _R is the sum of the number of sheets of thickness used. That is, this requires that the precursor fiber sheet is thinner than the thickness after the compression step when the compression step is performed. In general, when a molded product made of fibers and resin or a molded product of resin is obtained by adjusting the thickness by press and heating and pressing, the following formula (1 ′): T _S = T _R + T _P ( 1 ')
As will be set spacer thickness T _S, i.e., the compressed thickness when being molded to design a spacer thickness T _S so that the thickness after the compression step. However, in the step of compressing the precursor fiber sheet for producing the porous carbon base material of the present invention, if the spacer thickness designed to satisfy the formula (1 ′) is used, the thickness after the compression step is compressed. In some cases, the thickness becomes thicker than the thickness when it is. The inventors have investigated the cause of this thickening, and the precursor fiber sheet of the present invention is porous, unlike a molded product made of generally used fibers and resins, so that the resin is cured by heating and pressing. Even after molding, it was found that when the pressure is released, a springback occurs in which the thickness of the sheet increases by a certain amount. Therefore, if the present invention in which the spring-back occurs be designed according spacer T _S a (1) taking into account the amount of deformation due to the spring back, set the precursor fiber sheet thickness after the compression step, Furthermore, it is preferable for designing the thickness after the carbonization step.

Since the thickness obtained by subtracting the release paper thickness T _R from the spacer thickness T _S is the thickness at the time of compression in the compression process, when spring back occurs, the following equation (2) R = (T _S −T _R ) _/ T P ··· (2)
In shown, the ratio R of the thickness after compressed thickness during compression it is preferable to set the spacer thickness T _S so as to satisfy 0.5 <R <0.98. More preferably, 0.6 <R <0.96, and even more preferably 0.7 <R <0.93. If R is less than 0.5, the amount of springback becomes too large, and it is difficult to reduce the standard deviation of thickness, which is not preferable. On the other hand, when R exceeds 0.98, the amount of resin contained in the precursor fiber sheet is too large, and it becomes difficult to obtain a porous carbon substrate having a suitable density, which is not preferable. .

The thickness T _P of the precursor sheet compressed by the compression process is determined by applying a surface pressure of 0.15MPa in the thickness direction of the substrate using a micrometer. The number of measurements is 20 times, and the average value is the thickness.

Spacer thickness T _S, the release sheet thickness T _R, measured over the same surface pressure and pressurizing time of surface pressure in the thickness direction to the compression step using a micrometer. The number of measurements is 20 times, and the average value is the thickness.

In the present invention, when the effective pressure圧長L _P of the heating plate in the conveying _direction, the precursor feed rate of the fiber sheet when intermittently transported L _F, L _{F /} L _P is 0.1 0.98 is preferable, and more preferably 0.15 to 0.45. If L _F / L _P is small, the number of times of pressurization increases and the thickness is also averaged, so that the variation in thickness is reduced, and the densification effect by heating and pressurization can be further averaged. In the processing time, the time ratio required for opening and closing the press and feeding the precursor fiber sheet increases, resulting in poor production efficiency. _Further, when L F / _{L P} exceeds 0.98, _L F / _{L P,} such as by feeding amount of error is a problem can pressurized portion not when exceeded 1. Here, the feed amount refers to the transport amount per time of the precursor fiber sheet that is sent out (or taken out) in the transport direction when the press is opened.

  The heating and pressurizing conditions with the hot plates parallel to each other are preferably heated and pressurized at a temperature of 140 to 300 ° C. and a surface pressure of 0.1 to 4.0 MPa for 0.2 to 15 minutes.

  Here, the surface pressure is a press load with respect to the pressurization area of the precursor fiber sheet, and the area of the spacer is not considered.

  More preferable processing temperature is 160-300 degreeC, More preferably, it is 170-230 degreeC. When the temperature is too low, the effect of densifying the precursor fiber sheet by heating and pressurization is insufficient, and a porous carbon substrate having a sufficient density cannot be obtained. In particular, when the temperature is less than 140 ° C., the densification effect may be reduced. When temperature exceeds 300 degreeC, since oxidation and decomposition reaction of resin in a precursor fiber sheet will occur in air, it is preferable to set it as 300 degrees C or less.

The surface pressure is preferably 0.2 to 2.5 MPa, more preferably 0.3 to 1.5 MPa. When the pressure is low, sufficient pressurization is not performed and the variation in thickness increases. When the pressure is high, a linear pattern is generated on the precursor fiber sheet, and the gas permeability of the carbon fiber sheet after firing is lowered, so that good characteristics as a gas diffuser of a fuel cell cannot be exhibited. In addition, problems such as adhesion to a pressing surface that is a pressing surface and a release sheet occur. Furthermore, in order to pressurize 1 m ² at 25 MPa, the press facility also requires a pressurizing force of 2550 tf, and it is necessary to use a large-scale press system or reduce the production efficiency and reduce the processing area per time.

  The measuring method of each characteristic value regarding the porous carbon base material in the following examples is as follows.

(Weight, density):
The basis weight is calculated from an average value obtained by measuring 10 weights of a 10 cm × 10 cm square porous carbon substrate.

  The density is calculated from the thickness and basis weight of the substrate.

(Average fiber diameter):
The average fiber diameter of the carbon fibers is determined as a simple average value by selecting arbitrary 10 carbon fibers from a cross-sectional photograph of the fibers with an electron microscope of 5,000 times that of the substrate and measuring the fiber diameter. When the cross-sectional shape is not circular, for example, an elliptical diameter, the average value of the major axis and the minor axis is taken as the fiber diameter. Moreover, the presence or absence of carbonaceous powder can be confirmed by confirming the resin carbide part of the electron micrograph.

Example 1
Polyacrylonitrile-based carbon fiber “Torayca (registered trademark)” T300-6K (average single fiber diameter: 7 μm, number of single fibers: 6,000 fibers) manufactured by Toray Industries, Inc. is cut to a length of 12 mm, and water is used as a papermaking medium. The paper was continuously made, further immersed in a 10% by weight aqueous solution of polyvinyl alcohol and dried to obtain a long carbon fiber paper having a carbon fiber basis weight of about 20 g / m ² and wound into a roll. The adhesion amount of polyvinyl alcohol corresponds to 20 parts by weight with respect to 100 parts by weight of the carbon fiber paper.

  A dispersion prepared by mixing scale-like graphite BF-5A (average particle size 5 μm), phenol resin, and methanol at a weight ratio of 1: 4: 16 manufactured by Chuetsu Graphite Industries Co., Ltd. was prepared. The carbon fiber paper is continuously impregnated with the dispersion so that the phenol resin becomes 110 parts by weight with respect to 100 parts by weight of the carbon fiber paper, and dried at 90 ° C. for 3 minutes, thereby impregnating the resin-impregnated carbon fiber paper. And rolled up into a roll. As the phenol resin, a resin in which a resol type phenol resin and a novolac type phenol resin were mixed at a weight ratio of 1: 1 was used.

The hot plates 5 and 6 were set so as to be parallel to each other on a 100 t press manufactured by Kawajiri Co., Ltd. Two spacers 7 were placed on the hot plate 6 beside the resin-impregnated fiber paper. At this time, the effective pressurization length L _P of the hot plate was 1200 mm, the spacer length L _S was 1200 mm, and L _S / L _P = 1.0. The width W _P of the precursor fiber sheet was 600 mm, the width of the spacer was 100 mm, and W _S / W _P = 0.17. Two release papers with release treatment on one side are sandwiched so that the release treatment surface faces the resin-impregnated carbon fiber paper side, the hot plate temperature is 170 ° C., the contact pressure is 0.8 MPa, and the press is repeatedly opened and closed and 600 mm While the resin-impregnated carbon fiber paper and release paper having a width of 5 mm were intermittently conveyed, the same portion was subjected to compression treatment so as to be heated and pressurized for a total of 6 minutes. At this time, the effective pressurization length L _P of the hot plate was 1200 mm, the feed amount L _F of the precursor fiber sheet when intermittently conveyed was 100 mm, and L _F / L _P = 0.08. That is, compression treatment was performed by repeating heating and pressurization for 30 seconds, mold opening, and feeding of carbon fiber paper (100 mm), and the product was wound up in a roll shape with a width of 600 mm.

  The carbon fiber paper subjected to resin heat treatment as a precursor fiber sheet, maintained in a nitrogen gas atmosphere, introduced into a heating furnace having a maximum temperature of 2,000 ° C., and continuously running in the heating furnace, It was fired at a heating rate of about 500 ° C./min (400 ° C./min up to 650 ° C., and 550 ° C./min at temperatures exceeding 650 ° C.) and wound up in a roll. The length of the obtained porous carbon substrate was 100 m.

  The specifications, production conditions and evaluation results of the obtained porous carbon substrate 1 are shown below.

Average fiber diameter of carbon fiber: 7 μm
Thickness: 0.14mm
Per unit weight: 64 g / m ²
Density: 0.45 g / cm ³
Standard deviation of thickness: 3.9 μm
Difference between maximum value and minimum value of thickness every 10m: 8μm
Spacer thickness T _S : 250 μm
Release paper thickness T _R (70 μm / sheet × 2 sheets): 140 μm
Base thickness after the compression step T _P: 170 [mu] m
Spacer length L _S : 1200mm
Spacer width _W S: 100mm

Example 2
In the compression step, the same procedure as in Example 1 was performed except that the same location was pressed for a total of 1.5 minutes at a hot plate temperature of 200 ° C., a surface pressure of 1.0 MPa, and a sheet feed amount L _F of 200 mm. A porous carbon substrate was obtained.

  The specifications, production conditions and evaluation results of the obtained porous carbon substrate 1 are shown below.

Average fiber diameter of carbon fiber: 7 μm
Thickness: 0.14mm
Per unit weight: 64 g / m ²
Density: 0.45 g / cm ³
Standard deviation of thickness: 4.0 μm
Difference between the maximum value and the minimum value of thickness every 10m: 9μm
Spacer thickness T _S : 250 μm
Release paper thickness T _R (70 μm / sheet × 2 sheets): 140 μm
Base thickness after the compression step T _P: 170 [mu] m
Spacer length L _S : 1200mm
Spacer width _W S: 100mm

Comparative Example 1
A porous carbon substrate was obtained in the same manner as in Example 1 except that no spacer was used in the compression step.

Average fiber diameter of carbon fiber: 7 μm
Thickness: 0.14mm
Per unit weight: 64 g / m ²
Density: 0.45 g / cm ³
Standard deviation of thickness: 5.3 μm
Difference between maximum value and minimum value of thickness every 10m: 15μm

Comparative Example 2
Polyacrylonitrile-based carbon fiber “Torayca (registered trademark)” T300-6K (average single fiber diameter: 7 μm, number of single fibers: 6,000 fibers) manufactured by Toray Industries, Inc. is cut to a length of 12 mm, and water is used as a papermaking medium. The paper was continuously made, further immersed in a 10% by weight aqueous solution of polyvinyl alcohol and dried to obtain a long carbon fiber paper having a carbon fiber basis weight of about 50 g / m ² and wound into a roll. The adhesion amount of polyvinyl alcohol corresponds to 20 parts by weight with respect to 100 parts by weight of the carbon fiber paper.

  A solution in which phenol resin and methanol were mixed at a weight ratio of 1: 4 was prepared. Resin-impregnated carbon fiber paper is obtained by continuously impregnating the above-mentioned liquid into the carbon fiber paper so that the phenol resin is 150 parts by weight with respect to 100 parts by weight of the carbon fiber paper and drying at 90 ° C. for 3 minutes. And rolled up into a roll. As the phenol resin, a resin in which a resol type phenol resin and a novolac type phenol resin were mixed at a weight ratio of 1: 1 was used.

  The roll of the resin-impregnated carbon fiber paper was cut and cut into a sheet shape. The sheet carbon fiber paper was set in a 100 t press manufactured by Kawajiri Co., Ltd. so that the hot plates were parallel to each other, and compressed to be heated and pressurized at a hot plate temperature of 150 ° C. and a surface pressure of 0.5 MPa for 30 minutes. .

  In a batch-type heating furnace in which a carbon fiber paper that has been compression-molded is used as a precursor fiber sheet and maintained in a nitrogen gas atmosphere, the maximum temperature is 2,000 ° C. and about 1.4 ° C./min (up to 800 ° C. is 1 ° C. / Min, at a temperature exceeding 800 ° C., it was fired at a temperature rising rate of 2 ° C./min).

Average fiber diameter of carbon fiber: 7 μm
Thickness: 0.20mm
Weight per unit: 85 g / m ²
Density: 0.45 g / cm ³
Standard deviation of thickness: 6.1 μm

About the above Examples and Comparative Examples, the main ones of the specifications of the porous carbon substrate, the production conditions, and the evaluation results are summarized in Table 1.

  The porous carbon substrates of Examples 1 and 2 have small thickness standard deviations of 3.9 μm and 4,0 μm, respectively. This is because in the compression step, a precursor is formed by placing a spacer in the form of a hot plate and intermittently heating and pressurizing, and pressurizing for a sufficient time to form with surface pressure while controlling the thickness. This is because the fiber sheet can be molded with small variations in thickness.

  On the other hand, in Comparative Example 1, since the spacer is not used, the thickness between the hot plates cannot be controlled, and the standard deviation of the thickness is large. This means that when used as a gas diffuser of a solid polymer type fuel cell, pressure is locally applied to the solid polymer membrane due to thickness variation, thereby reducing the life and performance of the fuel cell.

  In Comparative Example 2, since it is a batch-type heating and pressing, the surface accuracy of the hot plate itself directly affects the standard deviation of the thickness, and the standard deviation of the thickness of the porous carbon substrate is large.

The porous carbon substrate according to the present invention can be preferably used as a material for a gas diffuser of a polymer electrolyte fuel cell, but its application range is not limited thereto.

It is the schematic which shows the measuring method of the thickness of the porous carbon base material of this invention. It is the schematic which shows the one aspect | mode of the compression process in the manufacturing process of the porous carbon base material of this invention. It is a fragmentary sectional view showing an example of a polymer electrolyte fuel cell. It is a fragmentary sectional view showing an example of a polymer electrolyte fuel cell.

Explanation of symbols

1: Porous carbon substrate 2: Thickness measurement point 3: Precursor fiber sheet 4: Hot press 5: Upper heating plate 6: Lower heating plate 7: Spacer 8: Solid polymer electrolyte membrane 9: Catalyst layer 10: Gas diffusion Layer 11: Gas diffuser 12: Separator 13: Gas flow path 14: Gasket

Claims (17)

  A sheet comprising carbon short fibers and resin carbide dispersed in a random direction, wherein at least a part of the carbon short fibers are bound with the resin carbide, and the sheet is defined in the text. A standard deviation of the thickness of the porous carbon substrate is 1.0 to 5.0 μm. The porous carbon group according to claim 1, wherein the porous carbon substrate has a thickness in the range of 0.10 to 0.25 mm and a density in the range of 0.3 to 0.7 g / cm ^3. Wood.   The porous carbon substrate according to claim 2, wherein the porous carbon substrate has a length of 50 to 500 m and a width of 100 to 1000 mm, and is wound in a roll shape.   The porous carbon material according to claim 3, wherein the porous carbon substrate has a difference between a maximum value and a minimum value of an average value of 15 μm or less when 20 points are sampled every 10 m in the length direction. Carbon base material.   The porous carbon substrate according to any one of claims 1 to 4, wherein the short carbon fibers constituting the porous carbon substrate have an average fiber diameter in the range of 5 to 20 µm.   The porous carbon substrate according to any one of claims 1 to 5, wherein the porous carbon substrate includes a carbonaceous powder.   The porous carbon base material according to any one of claims 1 to 6, wherein the porous carbon base material is a sheet having a standard deviation in thickness within a range of 1.0 to 4.0 µm.   A gas diffuser comprising a porous carbon substrate according to any one of claims 1 to 7 and a water-repellent substance added thereto.   The gas diffusion body by which the gas diffusion layer which has electroconductivity is arrange | positioned at least on one side of the porous carbon base material in any one of Claims 1-7.   A gas diffuser in which a water-repellent substance is imparted to the porous carbon substrate according to claim 1 and a conductive gas diffusion layer is disposed on at least one surface thereof.   In a membrane-electrode assembly comprising a solid polymer electrolyte membrane, a catalyst layer containing catalyst-supporting carbon provided on both surfaces thereof, and a gas diffuser provided in contact with the outside of both catalyst layers, at least one of the gas diffusers is A membrane-electrode assembly comprising the gas diffuser according to any one of claims 8 to 10.   A polymer electrolyte fuel cell comprising the membrane-electrode assembly according to claim 11.   A compression process in which a precursor fiber sheet containing carbon short fibers and a resin is intermittently conveyed between hot plates positioned in parallel with each other, and heated and pressurized with the hot plate while the conveyance is stopped; And a carbonizing process for carbonizing a resin in the precursor fiber sheet, wherein the precursor transports two or more spacers on the lower hot plate in the compression process. A method for producing a porous carbon substrate, which is arranged beside a fiber sheet and transports a precursor fiber sheet between the spacers.   The manufacturing method of the porous carbon base material of Claim 13 which arrange | positions a release sheet so that a precursor fiber sheet may be pinched | interposed, conveys with a precursor sheet | seat, and heat-presses. The thickness of the release sheet T _R, when the precursor fiber sheet thickness compressed by the compression process and T _P, the thickness T _S of the spacer is porous carbon substrate of claim 13 which satisfies the following equation Manufacturing method.
T _S <T _R + T _P When the conveyance direction of the effective pressure圧長L _P of mutually parallel heat _plate, the precursor feed rate of the fiber sheet when intermittently transported L _F, L _{F /} L _P is 0.1 to 0. It is 98, The manufacturing method of the porous carbon base material in any one of Claims 13-15.   The method for producing a porous carbon substrate according to any one of claims 13 to 16, wherein the temperature of the hot plates parallel to each other is 140 to 300 ° C and the applied pressure is 0.1 to 4.0 MPa.

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