JP6813056B2 - How to wind up the porous carbon fiber sheet - Google Patents

Description

The present invention relates to a method for winding a porous carbon fiber sheet used in a polymer electrolyte fuel cell.

The sheet-like material used as the porous carbon electrode base material used in the polymer electrolyte fuel cell is required to have characteristics such as diffusivity and high conductivity of substances involved in the electrode reaction. Further, in addition to these functions, a long roll-shaped porous carbon fiber sheet is required in order to improve the post-workability of the electrode member and to increase the productivity of the member itself and reduce the cost. However, since such a porous carbon fiber sheet is a brittle material, if the handling at the manufacturing stage, especially the unwinding to winding process, is not optimized, cracks, unwinding, and carbon powder generated from the sheet are not appropriate. In some cases, the roll quality was significantly deteriorated due to the adhesion of lumps.

As a method of winding a long sheet-like object for the purpose of improving battery productivity, a method of winding with a winding shaft and a device having a pressure roll arranged parallel to the winding shaft, an initial winding tension, and a final winding A method of defining a tension and winding while gradually reducing the winding tension (Patent Document 1) is disclosed. Further, in order to improve winding misalignment, a method of detecting a sheet-like object edge before a nip roll to control a sheet-like object end face (Patent Documents 2 and 3) is disclosed. However, in these documents, the sheet path is not clear, and the above-mentioned problems such as cracking of the base material when passing through the process before winding have not been solved.

JP-A-2002-302557 Japanese Unexamined Patent Publication No. 2008-247610 Japanese Unexamined Patent Publication No. 2010-70334

There has been a demand for a method for winding a porous carbon fiber sheet for a polymer electrolyte fuel cell, which does not have problems such as cracking, miswinding, and adhesion of carbon powder lumps generated from the sheet.

As a result of diligent studies to solve the above problems, the present inventors have focused on the curvature r and the holding angle θ of the seat path, and as a result, the above problems can be solved by arranging the rolls so as to satisfy certain specific conditions. We have found that it can be solved and have completed the present invention. That is, the gist of the present invention lies in the following [1] to [6].

[1] A shaft for unwinding the porous carbon fiber sheet, a winding shaft for winding in a roll shape, a nip roll for nipating the porous carbon fiber sheet-like material on the upstream side of the winding shaft, and a porous carbon fiber. In the step of arranging the end position detection device of the sheet-like object and moving the take-up shaft in the axial direction of the take-up shaft by the detection signal, at least 1 between the take-up shaft and the take-up shaft. Each nip roll and guide roll include more than one guide roll, and when the curvature of the sheet path of the nip roll and guide roll is r (mm ^-1 ) and the holding angle formed by the nip roll and guide roll is θ (degree). A method for winding a porous carbon fiber sheet for a polymer electrolyte fuel cell, wherein the following formula (1) is satisfied.
0 <r ・ θ <1.5 ・ ・ ・ Equation (1)

[2] The method for winding a porous carbon fiber sheet for a polymer electrolyte fuel cell according to the above [1], wherein each nip roll and guide roll satisfy the following formula (2).
0 <r · θ <1.2 ... Equation (2)

[3] The method for winding a porous carbon fiber sheet for a polymer electrolyte fuel cell according to the above [1] or [2], wherein the guide roll is a free roll or a driving roll.

[4] The method for winding a porous carbon fiber sheet for a polymer electrolyte fuel cell according to the above [3], wherein the rotation torque of the free roll is 0.5 Nm or less.

[5] In the step of winding the porous carbon fiber sheet, the roll diameter at the start of winding is D ₁ (mm), the winding tension at that time is T ₁ (N / m), and the roll diameter at the end of winding is D ₂ . When the take-up tension at that time is T ₂ (N / m), the take-up tension satisfies the following equation (3), and the take-up tension gradually decreases from the start to the end of the winding [1]. The method for winding a porous carbon fiber sheet for a solid polymer fuel cell according to any one of [4].
T ₁ ≧ 100 and T ₁ ≧ T ₂ ≧ 0.8 × (D ₁ / D ₂ ) × T ₁ ... Equation (3)

[6] The method for winding a porous carbon fiber sheet for a polymer electrolyte fuel cell according to any one of [1] to [5] above, wherein the end detection device is arranged downstream of the nip roll. ..

It is possible to provide a method for winding a porous carbon fiber sheet for a polymer electrolyte fuel cell, which does not have problems such as cracking, miswinding, and adhesion of carbon powder lumps generated from the sheet.

It is explanatory drawing of the holding angle θ in this invention. It is a figure of the position detection means of the ear end portion of a non-contact type sheet-like object. It is a figure which shows the winding deviation. It is a figure of the apparatus used in an Example. It is a process diagram of a carbon powder mass inspection.

In the present invention, a shaft for unwinding the porous carbon fiber sheet, a winding shaft for winding in a roll shape, a nip roll for nipating the porous carbon fiber sheet-like material on the upstream side of the winding shaft, and porous carbon. In the step of arranging the end position detection device of the fiber sheet-like material and moving the take-up shaft in the axial direction of the take-up shaft by the detection signal, at least between the take-up shaft and the take-up shaft. When one or more guide rolls are included, the curvature of the seat path of the nip roll and the guide roll is r (mm ^-1 ), and the holding angle formed by the nip roll and the guide roll is θ (degree) (see FIG. 1). It is essential that the following equation (1) is satisfied in each nip roll and guide roll.
0 <r ・ θ <1.5 ・ ・ ・ Equation (1)

FIG. 4 shows a specific example of equipment arrangement of the winding method. 7: The winding shaft is set with the porous carbon fiber sheet, and 13: the winding shaft is set with the porous carbon fiber sheet. A 9: nip roll is arranged upstream of the take-up shaft, and 11 which is a sheet-like object end position detecting device is arranged downstream of the nip roll. Based on the detection signal of this EPC, the winder moves in the A direction or the B direction along the winding shaft so as not to cause a winding deviation.

In addition, the porous carbon fiber sheet, which is a brittle material, is used for measurement, processing, and inspection while being transported from the unwinding shaft to the winding shaft, or from the viewpoint of preventing the sheet from slipping, such as a guide roll. The seat path is often bent with a certain curvature. For example, in FIG. 4, guide rolls 8 and 10 are arranged immediately after unwinding and before winding. In the above step, it is indispensable to satisfy the formula (1) in order to wind the roll as a high quality roll. In the present invention, the number of guide rolls arranged on the line is not limited, but it is necessary to satisfy the above formula (1) for all the guide rolls.

In the formula (1), r · θ is 1.5 or less, more preferably 1.2 or less, and particularly preferably 1.0 or less. If r · θ is too large, it means that the curvature is large, the hugging angle is large, or both are large, and the stress on the surface layer of the sheet increases and the possibility of cracking increases, which is not preferable.

Further, in the present invention, since it is premised that the sheet path between the unwinding shaft and the winding shaft is bent with a certain curvature, r · θ takes a value larger than 0, preferably 0.1 or more. is there. If r · θ is less than 0.1, the seat path cannot be substantially changed, which is not preferable.

In the present invention, a measuring device such as a thickness gauge and a basis weight meter, a processing device such as a slitter, an impregnating device, a drying device and a coating device, and an appearance inspection are performed between the unwinding shaft and the nip roll or between the nip roll and the winding shaft. It is possible to install equipment and perform measurement, processing, and inspection of sheet-like objects during transportation.

Further, from the viewpoint of adhesion of the carbon powder mass to the sheet, the guide roll is preferably a free roll or a driving roll. If the guide roll is a fixed type that does not rotate according to the running of the sheet, there is a problem that carbon powder is generated due to rubbing between the roll and the porous carbon fiber sheet, is deposited on the roll, and is reattached to the porous carbon fiber sheet. Therefore, it is not preferable.

Further, when the guide roll is a free roll, the rotational torque is preferably 0.5 N · m or less. More preferably, it is 0.3 N · m or less. If the rotational torque is too high, the porous carbon fiber sheet slips on the roll and carbon powder is generated as described above, which is not preferable.

The nip roll is composed of upper and lower rolls, but at least one of them is preferably a rubber roll. Further, the width of the nip roll is larger than the width of the porous carbon fiber sheet, and it is preferable to nip over the entire width of the sheet. When the width of the nip roll is smaller than the width of the porous carbon fiber sheet, there are places where the nip roll is nipped in the width direction and places where the nip roll is not made, which adversely affects the final thickness variation, which is not preferable.

In the step of winding the porous carbon fiber sheet, the roll diameter at the start of winding is D ₁ (mm), the winding tension at that time is T ₁ (N / m), the roll diameter at the end of winding is D ₂ , and the winding at that time. When the take-up tension is T ₂ (N / m), it is preferable that the take-up tension satisfies the following formula (3) and the take-up tension gradually decreases from the start to the end of winding.

T ₁ ≧ 100 and T ₁ ≧ T ₂ ≧ 0.8 × (D ₁ / D ₂ ) × T ₁ ... Equation (3)
More preferably, the following formula (4) is satisfied, and the winding tension gradually decreases from the beginning to the end of winding.

T ₁ ≥ 200 N / m and T ₁ ≥ T ₂ ≥ (D ₁ / D ₂ ) x T ₁ ... Equation (4)
If the take-up tension (T ₂ ) is too low to satisfy the above equation (3), meandering occurs and winding shift occurs after winding, which is not preferable. Further, if the take-up tension (T ₂ ) is too high to satisfy the above formula (4), the sheet-like material may be cracked, which is not preferable.

As shown in FIG. 2, the end position detecting device for the porous carbon fiber sheet-like material is installed so as to be able to detect the position of either one of the left and right ends or both ends of the sheet-like material 3 in the traveling direction. Is preferable. A non-contact type sheet-like end position detecting means generally called EPC (edge position control: Nireco Corporation registered trademark) is used for the sheet-like end position detection device (4 in FIG. 2). Is preferable. The sensor unit of the position detection device 4 at the end of the sheet-like object includes a photoelectric sensor using an infrared light emitting diode as a light source, an ultrasonic sensor, a detection method using air pressure, and the like, but there are no particular restrictions.

Further, it is preferable that the sheet-like object end detection device is arranged downstream of the nip roll. More preferably, they are arranged downstream of the nip roll and downstream of the unwinding shaft, respectively.

In the present invention, a measuring device such as a thickness gauge and a scale meter, a processing device such as a slitter, an impregnating device, a drying device, a coating device, and a visual inspection device are provided between the unwinding shaft and the nip roll or between the nip roll and the winding shaft. It can be installed and measured, processed, and inspected during transportation. Among them, in the slit process of dividing the porous carbon fiber sheet into a plurality of pieces in the longitudinal direction, the end of the divided sheet-like material is used. The end detection device arrangement is preferable because each detection device can be arranged to suppress winding deviation and wind up.

In the present invention, the winding deviation of the wound roll is preferably 5 mm or less, more preferably 3 mm or less. As shown in FIG. 3, the winding deviation in the present invention corresponds to a number obtained by subtracting the sheet width (Wa) from the total width (Wb) including the winding deviation. If the winding deviation exceeds 5 mm, the unwinding in the post-processing process is not stable and the process passability deteriorates, which is not preferable.

The porous carbon fiber sheet in the present invention is produced by the following steps.
(A) The process of obtaining carbon fiber paper from carbon short fibers and
(B) A step of impregnating the carbon fiber paper with a thermosetting resin to obtain a resin-impregnated paper.
(C) A step of obtaining a resin-cured sheet by heat-press molding the resin-impregnated paper.
(D) A step of running the resin-cured sheet in a firing furnace in an inert atmosphere to perform heat treatment.

((A) Step of obtaining carbon fiber paper from carbon short fibers (step (a))
As a method for producing carbon fiber paper in the step (a), a wet method in which carbon short fibers are dispersed in a liquid medium to make a paper machine and a dry method in which carbon short fibers are dispersed in air and deposited are applied. Although it can be done, the wet method is preferable. Step (a) is performed continuously.

The short carbon fibers contained in the carbon fiber paper may be any of polyacrylonitrile-based carbon fibers, pitch-based carbon fibers, rayon-based carbon fibers and the like, but polyacrylonitrile-based carbon fibers having relatively high mechanical strength are preferable. The polyacrylonitrile-based carbon fiber is produced by using a polymer containing acrylonitrile as a main component as a raw material. Specifically, a spinning step of spinning acrylonitrile fibers; a flameproofing step of heating and firing acrylonitrile fibers in an air atmosphere of 200 to 400 ° C. to convert them into oxide fibers; an inert atmosphere such as nitrogen, argon, and helium. It is a carbon fiber obtained through a carbonization step of further heating to 300 to 2500 ° C. and carbonizing; and can be suitably used as a composite material reinforcing fiber. Therefore, it is possible to form carbon fiber paper having higher strength and mechanical strength than other carbon fibers.

Further, in the present invention, short carbon fibers obtained from recycled carbon fibers are preferable. Carbon fiber is generally used as a composite material with a thermosetting resin or a thermoplastic resin. The scraps generated when the composite material is processed and the retired waste material after being used for a certain purpose are used as raw materials for recycled carbon fibers. As a method for extracting only the carbon fibers from the composite material, a method that does not damage the carbon fibers as much as possible is preferable, and for example, a combustion method, a semiconductor thermoactive decomposition method, a normal pressure dissolution method, a supercritical fluid method, or the like can be used. .. In order to obtain recycled carbon short fibers, they may be crushed before separation or chopped to a predetermined length after separation.

The polyacrylonitrile-based carbon fiber is preferably contained in the carbon 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 porous carbon electrode base material. In particular, it is preferable that the carbon monofiber used is only polyacrylonitrile-based carbon fiber.

The average fiber length of the carbon short fibers is preferably 2 to 18 mm, more preferably 2 to 10 mm, and 3 to 6 mm from the viewpoint of the strength and uniform dispersibility of the porous carbon electrode base material. Is even more preferable. If the fiber length is less than 2 mm, the entanglement between the fibers is reduced, and the strength of the porous carbon electrode base material is weakened. On the other hand, if it exceeds 18 mm, the dispersibility of the fibers in the dispersion medium is lowered, and the carbon fiber paper has dispersion spots. By setting the average fiber length of the short carbon fibers to 2 mm or more, the short carbon fibers are entangled with each other, and the strength of the porous carbon electrode base material is increased. Further, by setting the average fiber length of the carbon short fibers to 18 mm or less, the dispersibility of the carbon short fibers in the dispersion medium is improved, and the dispersion unevenness in the carbon fiber paper is reduced.

As the liquid medium for dispersing the short carbon fibers, water that can be used industrially at low cost is preferable.

The carbon fiber paper produced by making short carbon fibers preferably contains an organic polymer compound as a binder. Examples of the organic polymer compound include thermoplastic resins such as polyvinyl alcohol (PVA), polyvinyl acetate, polyester, polypropylene, polyethylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, acrylic resin, and polyurethane resin, phenol resins, and epoxy resins. Thermoplastic resins, butadiene / styrene copolymers (SBR), butadiene / acrylonitrile copolymers (NBR), as well as thermocurable resins such as melamine resin, urea resin, alkyd resin, unsaturated polyester resin, acrylic resin, and polyurethane resin. Such as elastomer, rubber, cellulose and the like can be used. One type of organic polymer compound may be used alone, or two or more types may be used in combination.

Pulp-like substances and short fibers are suitable as the form of the organic polymer compound. The pulp-like material referred to here has 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 sheet-like material using this pulp-like material efficiently forms entanglements between fibers. It has a feature that even a thin sheet-like material is excellent in handling. Further, the short fiber is obtained by cutting a fiber thread or a fiber toe to a predetermined length. The length of the short fibers is preferably 2 to 12 mm from the viewpoint of binding property and dispersibility as a binder.

As the organic polymer compound, polyvinyl alcohol, polyethylene, polyacrylonitrile, cellulose or polyvinyl acetate pulp or short fibers are preferable. Since these organic polymer compounds have excellent binding force in the papermaking process, the use of these organic polymer compounds reduces the loss of short carbon fibers. In addition, most of these organic polymer compounds are decomposed and volatilized in the carbonization process at the final stage of manufacturing the porous carbon electrode base material, and pores are formed. The presence of these vacancies improves the permeability of water and gas.

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

((B) Step of impregnating the carbon fiber paper with a thermosetting resin to obtain a resin-impregnated paper (step (b))
The thermosetting resin to be impregnated in the carbon fiber paper is preferably a resin that exhibits adhesiveness or fluidity at room temperature and remains as a conductive substance even after carbonization, and a phenol resin, furan resin, or the like may be used. it can. As the phenol resin, a resol type phenol resin obtained by the reaction of phenols and aldehydes in the presence of an alkali catalyst can be used. It is also possible to dissolve and mix a novolak-type phenol resin, which is produced by the reaction of phenols and aldehydes under an acidic catalyst, into a resole-type fluid phenol resin, which exhibits heat-sealing properties, by a known method. .. However, in this case, it is preferable to use a self-crosslinking type containing, for example, hexamethylenediamine as a curing agent. It is also possible to use a commercially available product as the phenol resin. As the phenols, for example, phenol, resorcin, cresol, xylene and the like are used. As the aldehydes, formalin, paraformaldehyde, furfural and the like are used, for example. Moreover, these can be used as a mixture.

The content of the thermosetting resin in the resin-impregnated paper obtained by impregnating the carbon fiber paper with the thermosetting resin is preferably 30 to 70% by mass. By setting the content of the thermosetting resin to 30% by mass or more, the structure of the obtained porous carbon electrode base material becomes dense and the strength becomes high. Further, by setting the content of the thermosetting resin to 70% by mass or less, the porosity and gas permeability of the obtained porous carbon electrode base material can be kept good. The resin-impregnated paper refers to a carbon fiber paper impregnated with a thermosetting resin before heating and pressurization, but when a solvent is used for resin impregnation, the solvent is removed.

The carbon fiber paper may be impregnated with a mixture of a thermosetting resin and a conductive substance. Examples of the conductive substance include carbonaceous milled fiber, carbon black, acetylene black, and isotropic graphite powder. The mixing amount of the conductive substance is preferably 1 to 10% by mass with respect to the thermosetting resin. If the amount mixed is less than 1% by mass, the effect of improving the conductivity is small, which is disadvantageous, and if it exceeds 10% by mass, the effect of improving the conductivity tends to be saturated, and it becomes a factor of cost increase. It is disadvantageous in that. By setting the mixing amount of the conductive substance to 1% by mass or more, the effect of improving the conductivity becomes sufficient. Further, even if the mixed amount of the conductive substance exceeds 10% by mass, the effect of improving the conductivity tends to be saturated. Therefore, the cost increase can be suppressed by setting the mixed amount of the conductive substance to 10% by mass or less. Can be done.

As a method of impregnating the carbon fiber paper with a solution containing a thermosetting resin and optionally a conductive substance, a method using a drawing device or a method of laminating a separately prepared thermosetting resin film on the carbon fiber paper is preferable. In the method using a drawing device, the impregnated solution is impregnated with carbon fiber paper so that the intake liquid is uniformly applied to the entire carbon fiber paper by the drawing device, and the amount of the liquid is adjusted by changing the roll interval of the drawing device. The method. If the viscosity of the solution is relatively low, a spray method or the like can also be used. In the method of laminating a thermosetting resin film on carbon fiber paper, first, a solution containing a thermosetting resin and, in some cases, a conductive substance is coated on a release paper to obtain a thermosetting resin film. After that, a thermosetting resin film is laminated on the carbon fiber paper and heat-pressurized to impregnate the carbon fiber paper with the thermosetting resin.

((C) A step (step (c)) of obtaining a resin-cured sheet by heat-press molding the resin-impregnated paper.
The step (c) is an important step of curing the thermosetting resin in the resin-impregnated paper to control the sheet thickness. Step (c) is performed continuously from the viewpoint of productivity.

As the press device to be used, it is preferable to use a continuous heating roll press device or a continuous heating press device (double belt press device) provided with a pair of endless belts. In the heating roll press apparatus, one set or two or more sets of multi-stage presses can be adopted. In the double belt press device, when the thermosetting resin is softened in the preheating stage, it can be conveyed by the belt with almost no tension applied to the resin-impregnated paper, so that the resin-cured sheet during manufacturing is less likely to be broken and the process passes. Excellent in sex. Therefore, it is more preferable to use a double belt press device.

It is preferable to perform preheat treatment before the heating press. By applying heat to the resin-impregnated paper before the heat pressing to soften the thermosetting resin once, the thermosetting resin can be well blended with the carbon fiber paper. When the heat press is performed on the carbon short fibers, the carbon short fibers are effectively bonded to each other, and a porous carbon electrode base material having excellent mechanical properties and high handleability can be produced. The heating means adopted in the preheat treatment may be any of heat transfer heating such as a heating roll, convection heating provided with a heating region, radiant heating such as far infrared rays, or a combination thereof, but from the viewpoint of reducing heat loss. , It is preferable to perform heat transfer heating using a heating roll or the like.

It is preferable to heat-press mold a resin-impregnated paper laminate in which two or more resin-impregnated papers are laminated. As the number of resin-impregnated papers to be laminated increases, the basis weight of one carbon fiber paper can be reduced, and the surface condition of the carbon fiber paper becomes better. However, when three or more sheets of resin-impregnated paper are laminated, not only the productivity of the carbon fiber paper is lowered, but also press mistakes may increase.

Further, by laminating two or more sheets, a laminating interface is formed. When stress is applied to the sheet obtained by this manufacturing method, there is a problem that fracture at the interface is likely to occur. However, by applying the winding method of the present invention, high quality rolls can be obtained without causing fracture at the interface.

((D) A step (step (d)) of running the cured resin sheet in a firing furnace in an inert atmosphere to perform heat treatment.
In the step (d), the resin cured sheet is fired. Specifically, the resin cured sheet is run in a firing furnace in an inert atmosphere. Step (d) is performed continuously.

From the viewpoint of mechanical properties and conductivity of the finally obtained porous carbon electrode base material, step (d) is a step of heat treatment (preliminary carbonization) in which the maximum temperature is at least 600 ° C. or higher (preferably 700 ° C. or higher). Step) and a heat treatment step (carbonization step) in which the maximum temperature is at least 1500 ° C. or higher (preferably 1600 ° C. or higher).

The porous carbon fiber sheet obtained from the above step is a measuring device such as a thickness gauge and a basis weight meter, a slitter, an impregnating device, a drying device, and a coating device between the unwinding shaft and the nip roll or between the nip roll and the winding shaft. It is possible to measure, process, and inspect the sheet-like material during transportation by installing processing equipment such as, and appearance inspection equipment.

For example, when slitting to a desired width, it is preferable to slit the resin cured sheet after the heat press molding step or the porous carbon fiber sheet after the firing step to the desired width. Examples of the slit method at this time include rectangular blade shear cutting, round blade shear cutting, laser cutting, score cutting and the like. The type adopted in the present invention is not limited, but in order to smooth the edge of the base material, a method of cutting the sheet in cooperation with a disk-shaped slit blade is preferable. Further, it is preferable to suck and remove the chips generated immediately after the slit.

(Physical characteristics of porous carbon fiber sheet)
The thickness of the porous carbon fiber sheet of the present invention is preferably 0.05 to 0.4 mm, more preferably 0.1 to 0.3 mm, from the viewpoint of the resistance value. If the thickness is less than 0.05 mm, the strength in the thickness direction becomes weak, and it becomes impossible to withstand the handling when the cell stack is assembled. Further, if it exceeds 0.5 mm, the electric resistance becomes high, and the total thickness becomes large when the stacks are laminated. By setting the thickness of the porous carbon fiber sheet to 0.05 mm or more, the strength in the thickness direction becomes high, and it becomes possible to withstand the handling when the cell stack is assembled. Further, by setting the thickness of the porous carbon fiber sheet to 0.4 mm or less, the electric resistance thereof is lowered, and the total thickness when the stacks are laminated is reduced.

The bulk density of the porous carbon fiber sheet of the present invention is preferably from 0.3 to 0.8 g / cm ^3, more preferably 0.4 to 0.7 g / cm ^3. When the bulk density is less than 0.3 g / cm ³ , the electrical resistance becomes high and satisfactory flexibility cannot be obtained. Further, if the value exceeds 0.8 g / cm ³ , the gas permeability deteriorates and the performance of the fuel cell deteriorates. By setting the bulk density of the porous carbon fiber sheet to 0.3 g / cm ³ or more, the electrical resistance is lowered and satisfactory flexibility can be obtained. Further, by setting the bulk density of the porous carbon fiber sheet to 0.8 g / cm ³ or less, the gas permeability is improved and the performance of the fuel cell is improved.

The bending deflection of the porous carbon fiber sheet of the present invention is preferably 1.5 mm or more, preferably 2.0 mm or more, under the conditions of a strain rate of 10 mm / min, a distance between fulcrums of 2 cm, and a test piece width of 1 cm. More preferred. When the bending deflection is less than 1.5 mm, it is easily cracked when continuously wound on a roll, and it becomes difficult to prepare and handle a long porous carbon fiber sheet. By setting the bending deflection of the porous carbon fiber sheet to 1.5 mm or more, it becomes difficult to crack when continuously winding the porous carbon fiber sheet on a roll, and it becomes easy to prepare and handle a long porous carbon fiber sheet. The bending deflection of the porous carbon fiber sheet is preferably 1.5 mm or more, and more preferably 2.0 mm or more, from the viewpoint of handleability.

(About the content of carbides derived from thermosetting resin)
The porous carbon fiber sheet of the present invention is composed of carbon short fibers and carbides derived from a thermosetting resin, and has a structure in which the carbon short fibers are bound to each other by the carbides derived from a thermosetting resin. Is preferable. The carbide is derived from a thermosetting resin, but the proportion of the carbide that finally remains as a carbide on the porous carbon fiber sheet differs depending on the type of the thermosetting resin and the amount of impregnation on the carbon fiber paper. When the porous carbon fiber sheet is 100% by mass, the content of carbon dioxide derived from the thermosetting resin excluding the carbon short fiber content is the binding of carbon short fibers in the porous carbon fiber sheet and the porous carbon fiber. From the viewpoint of developing sheet flexibility, it is preferably 20 to 60% by mass.

The porous carbon fiber sheet in the present invention also includes a sheet having a coating layer coated on one surface of the sheet-like material obtained in the above step. As a step of forming the coating layer, a coating layer made of carbon powder and a water repellent is provided on the porous carbon fiber sheet between the unwinding shaft and the nip roll of the present invention or between the nip roll and the winding shaft. It is preferable to manufacture by the above process. The specific process is as follows.

(E) A step of forming a uniform coating film on a porous carbon fiber sheet by applying a coating liquid consisting of carbon powder, a water repellent, a surfactant and water.

(F) The porous carbon fiber sheet on which the coating film obtained in the step (e) is formed is dried in an environment of 150 ° C. to 300 ° C. to remove water in the coating film, and the porous carbon fiber sheet is removed. The process of forming a coating layer on top.

(G) A step of heating the dried sheet obtained in step (f) to 200 ° C. to 400 ° C.

The details of each process are shown below.

<Step (e)>
As the carbon powder to be used, for example, graphite powder, carbon black or the like can be used. For example, as carbon black, acetylene black (for example, Denka black manufactured by Denki Kagaku Kogyo Co., Ltd.), Ketjen black (for example, Ketjen Black EC manufactured by Lion Corporation), furnace black (for example, Balkan XC72 manufactured by CABOT), etc. Can be used. It is preferable to use carbon black from the viewpoint of exhibiting higher conductivity.

Examples of the water repellent agent include fluororesin and the like. Examples of the fluororesin include tetrafluoroethylene-hexafluoropropylene copolymer, polytetrafluoroethylene (PTFE), tetrafluoroethylene-ethylene copolymer and the like, and polytetrafluoroethylene (PTFE) is particularly preferable. The PTFE may be dispersed in water with a surfactant, or a pre-dispersed dispersion may be used.
Known surfactants can be used. Examples thereof include nonionic surfactants such as polyoxyethylene (10) octylphenyl ether (for example, Triton X-100 manufactured by ACROS ORGANICS), alkyl ethers and alkyl phenyl ethers. It is preferable to use polyoxyethylene (10) octylphenyl ether from the viewpoint of handleability and decomposition temperature.

As a method for preparing a coating liquid from carbon powder, a water repellent, a surfactant and water, a known method can be used. It is obtained by preparing and mixing a dispersion of carbon powder and a dispersion of a water repellent, respectively. In order to obtain a carbon dispersion liquid, water is mixed with the carbon powder. At this time, it is preferable to add an organic solvent or a surfactant in order to improve the wettability of the carbon powder and improve the dispersibility. As such an organic solvent, lower alcohols, acetone and the like are preferable. The amount of the surfactant added may be 0.1 wt% or more with respect to the entire coating liquid in order to improve the dispersibility of the carbon powder, and if the amount added is too large, foaming will occur, so 5 wt%. The following is preferable. A thickener or the like can also be added depending on the desired viscosity. As an apparatus used for stirring, a general stirrer, for example, a dispenser, a homogenizer, a sand mill, a jet mill, a ball mill, a bead mill or the like can be used. From the viewpoint of simple operation and shortening of processing time, it is preferable to use a disper or a homogenizer. In order to make the water repellent into fibers, the stirring temperature of the coating liquid in which the carbon powder and the water repellent are dispersed is kept at 30 ° C. or higher, and the stirring speed when using the disper is 5,000 rpm or higher. It is preferable to mix and stir for at least a minute.

<Step (f)>
<Coating treatment of porous carbon fiber sheet>
For the water-repellent treatment performed to impart water repellency to the porous carbon fiber sheet, a dispersion liquid in which particles of a water-repellent agent such as fluororesin are dispersed in a solvent is used. When water is used as the solvent, the water repellent does not disperse in water as it is, so it is dispersed in water with an appropriate surfactant. Further, as the dispersion liquid, a dispersion or the like in which a water repellent agent is dispersed in advance can also be used.

<Formation of coating film>
As a coating method for forming a coating film on the porous carbon fiber sheet, a conventionally known method can be used, for example, a bar coating method, a blade method, a screen printing method, a spray method, a curtain. Examples include a coating method and a roll coating method. By these methods, the thickness of the coating film capable of forming a uniform coating film on the porous carbon electrode base material is preferably 50 to 2000 μm. If the thickness of the coating film is less than 50 μm, it becomes difficult to obtain a film having a uniform thickness, and if it is larger than 2000 μm, unintended large cracks are likely to occur in the coating layer after drying, which is not preferable. A more preferable coating film thickness range is 50 to 1000 μm.

<Process (g)>
In the present invention, the coating film is dried by placing the porous carbon fiber sheet on which the coating film is formed in an environment of 150 ° C. to 300 ° C. For example, an environment of 150 ° C. to 300 ° C. can be created by using a plate heater, a heating roll, a hot air dryer, an IR heater, or the like.

<Step (h)>
In this step, the dried "porous carbon fiber sheet on which the coating film is formed" is fired in an environment of 300 to 400 ° C. In this firing step, first, the dispersant such as the surfactant contained in the porous carbon electrode base material and the coating film is eliminated, and in addition, the water repellent is heated to near the melting point to make it water repellent. By melting the agent particles and controlling their shape, the pore structure of the coating layer is controlled and the binding of carbon powder is strengthened. Therefore, the temperature is preferably in the range of 300 to 400 ° C, more preferably 340 to 400 ° C.

Further, according to the winding method of the present invention, a porous carbon fiber sheet provided with a coating layer can be brought out. That is, it is also possible that the unwinding porous carbon fiber sheet has a coating layer composed of carbon powder and a water repellent on at least one surface.

Further, if necessary, after the step [4], a processing step such as a slit of the porous carbon sheet and an inspection step such as an appearance inspection device can be introduced in-line.

Hereinafter, the present invention will be described in more detail with reference to Examples. The evaluation / inspection method performed in the examples is as follows. In addition, Example 5 is a reference example.

1) Thickness The thickness of the porous carbon fiber sheet was measured at 5 points in the width direction with a micrometer (manufactured by Mitutoyo Co., Ltd., trade name: MDC-25MJ), and the average thickness was calculated.

2) Bulk Density Five samples having a size of 200 mm × 300 mm were cut out from the porous carbon fiber sheet and weighed with an electronic balance. Then, the bulk density was calculated using the average thickness measured in 1).

3) Bending deflection of the porous carbon electrode base material A load is applied to a sample with a width of 10 mm at a distance of 2 cm between fulcrums and a strain rate of 10 mm / min, and a pressure wedge when the test piece breaks from the point where the load begins to be applied. The value obtained by measuring the moving distance of the above was taken as the bending deflection.

4) Content of carbides derived from thermosetting resin When the porous carbon electrode base material is 100% by mass, the content of carbides derived from thermosetting resin excluding carbon fibers is the following formula (5). ).
C = {Gw- (Pw × F / 100)} / Gw × 100 ... Equation (5)
C: Content of carbides derived from thermosetting resin of porous carbon fiber sheet (mass%)
Gw: Metsuke of porous carbon fiber sheet (g / m ² )
Pw: Carbon fiber paper basis weight (g / m ² )
F: Ratio of carbon fibers in carbon fiber paper (mass%)

5) Equipment used The equipment used in the examples is shown in FIG. Among them, the guide roll 8 and the guide roll 10 are mobile free rolls, and the holding angle is changed by moving the guide roll 8 in the direction of the seat path, and the holding angle and the guide roll 10 always formed by the guide roll 8 are formed. The hugging angles formed in the above were the same. In addition, data with different roll diameters were acquired by exchanging rolls.

6) Calculation of r · θ The curvature of each roll is calculated from the radii of the guide rolls and nip rolls arranged between the unwinding shaft and the winding shaft. Furthermore, the holding angle (θ) of the guide roll or the nip roll is measured. However, the hugging angle refers to the angle (θ) shown in FIG. From the above, r and θ are calculated for each bend of the seat road, and the maximum value thereof is used as a representative value.

7) Guide roll rotation torque A rope was attached to the guide roll (free roll) shown in FIG. 4, and a spring scale was attached to the tip of the rope and pulled to measure the minimum stress required for the roll to rotate. The rotational torque ( _Tr (Nm)) was calculated from the measured stress (F (N)) and the guide roll diameter (d (m)) by the following formula (6).
_Tr = (d × F) / 2 ... Equation (6)

The rotational torque of each of the guide roll 8 and the guide roll 10 was measured, and a high number was used as a representative value.

8) Winding tension The value obtained by dividing the tensile stress (N) of the winder by the sheet width (m).

9) Crack inspection Using the device shown in Fig. 4, the porous carbon fiber sheet with a length of 1000 m was unwound and wound, and the cracked parts were visually counted using transmitted light at the position immediately before winding. ..

10) Measurement of winding deviation The number calculated from the following formula (7) based on the total width (Wb) including the winding deviation and the length of the sheet width (Wa) shown in FIG. 3 was defined as the winding deviation (Wg).
Wg = Wb-Wa ... Equation (7)

11) Number inspection of carbon powder lumps The porous carbon fiber sheet roll wound by the device shown in FIG. 4 is unwound using the device shown in FIG. 5, so that the back surface of the sheet can be confirmed, and then the long side at the unwinding position. The number of carbon powder lumps having a size of 1 mm or more was counted.

(Example 1)
Polyacrylonitrile-based carbon short fibers cut to an average fiber length of 3 mm (manufactured by Mitsubishi Rayon Co., Ltd., trade name: Pyrofil TR50S, average single fiber diameter: 7 μm), polyvinyl alcohol (PVA) short fibers (manufactured by Claret Co., Ltd., trade name:) VBP105-1, fiber length 3 mm) and polyethylene pulp (manufactured by Mitsui Kagaku Co., Ltd., trade name: SWP) were prepared. 50 parts by mass of polyacrylonitrile-based carbon short fibers were uniformly dispersed and defibrated in water in a slurry tank of a wet short net continuous papermaking machine, and 10 parts by mass of PVA short fibers and 40 parts by mass of polyethylene pulp were uniformly dispersed in a sufficiently dispersed place. Dispersed and sent out. The sent out web was passed through a short net plate, dried with a dryer, and then a roll-shaped carbon fiber paper having a width of 1000 mm and a basis weight of 43 g / m ² was obtained.

Next, the carbon fiber paper was immersed in a methanol solution of phenol resin (manufactured by DIC Co., Ltd., trade name: Phenolite J-325), 53 parts by mass was attached to 100 parts by mass of carbon fiber paper, and the phenol resin was attached. A resin-impregnated paper was obtained. Two sheets of this resin-impregnated paper were laminated and press-molded using a double belt press device. At that time, the preheating conditions were hot air temperature 150 ° C, preheating roll temperature 230 ° C, press roll temperature 260 ° C, and linear pressure 8 × 10 ⁴
A resin cured sheet was obtained under processing conditions of N / m.

The obtained resin cured sheet was run in a firing furnace in a nitrogen gas atmosphere, and heat-treated at a maximum temperature of 800 ° C. under a heating rate condition of 140 ° C./min. Then, it was further run in a firing furnace in a nitrogen gas atmosphere and heat-treated at a maximum temperature of 2000 ° C. to obtain a porous carbon fiber sheet having a length of 1000 m. Regarding the physical characteristics of the obtained porous carbon fiber sheet, the thickness was 0.201 mm, the bulk density was 0.31 g / cm ³ , the bending deflection was 2.4 mm, and the content of carbides derived from the thermosetting resin was 31%. It was.

The porous carbon fiber sheet having a width of 300 mm and a length of 1000 m was unwound and subjected to a winding test using the apparatus shown in FIG. The details of the winding conditions are as shown in Table 1, but the results are as shown in Table 2. The number of cracks is 0, the winding deviation is 3 mm, and the carbon powder mass is 0, which is a high-quality roll-shaped porous carbon fiber. I was able to get a sheet.

For Examples 2 to 7, the same porous carbon fiber sheet as in Example 1 was used, and the winding test was performed by unwinding and using the apparatus shown in FIG. However, in each of the examples, the guide rolls 8 and 10 were replaced with rolls having different diameters shown in Table 1, and the guide roll positions were further moved to adjust the holding angles shown in Table 1. In Table 1, the curvature represents the curvature of the guide roll, the maximum hugging angle represents the maximum hugging angle of the guide roll, and rθ represents the r · θ of the guide roll. The results obtained are also summarized in Table 2.

(Example 8)
Using the same porous carbon fiber sheet as in Example 1, the apparatus shown in FIG. 4 is used under the sheet path conditions of Example 4, and 8: a coating layer coating device and a drying device between the guide rolls 1 and 9: nip rolls. Was installed and wound up.

(Adjustment of coating liquid 1)
Denka Black (manufactured by Denki Kagaku Kogyo Co., Ltd.), ion-exchanged water, and isopropyl alcohol are mixed at a ratio of 5: 100: 80, respectively, and using Homomixer MARK-II (manufactured by Primix Corporation), 30 at 15000 rpm while cooling. Stirring was performed for 1 minute to obtain coating liquid 1.

(Preparation of coating liquid 2)
Polytetrafluoroethylene (PTFE) dispersion was added to the coating liquid 1 at a ratio of 0.3 to carbon black 1, and the mixture was stirred with the dispersion at 5000 rpm for 15 minutes to obtain the coating liquid 2.

(Adjustment of water repellent treatment liquid)
To prepare a water-repellent treatment liquid for a porous electrode base material, PTFE dispersion (31-JR, manufactured by Mitsui DuPont Fluorochemical), a surfactant (polyoxyethylene (10) octylphenyl ether) and distilled water are used. There was. After adjusting the solid content concentration in the water repellent treatment liquid to 1 wt% for PTFE and 2 wt% for the surfactant, distilled water is added and the mixture is stirred at 1000 rpm for 10 minutes using a disper to repel water. A treatment liquid was prepared.

(Water repellent treatment on porous carbon fiber sheet and formation of coating layer)
The porous electrode base material is impregnated by immersing it in the above water-repellent treatment liquid, and the impregnated porous electrode base material is dried by removing excess water-repellent treatment liquid adhering to the porous electrode base material by a nip roll. The sheet was dried in a machine at 200 ° C. Further, the coating liquid 2 was applied to a water-repellent treated porous carbon fiber sheet by a bar coating method, and dried using a hot air drying furnace set at 100 ° C. Further, after drying, a sintering treatment was performed at 360 ° C. in a sintering furnace to obtain a porous carbon electrode base material on which a coating layer was formed.

At this time, the porous carbon fiber sheet had 0 cracks, the winding deviation was 2 mm, and the carbon powder lump adhesion was 0, which were good results.

(Comparison example)
Using the same porous carbon fiber sheet as in Example 1, unwinding and winding test were performed using the apparatus shown in FIG. However, the device shown in FIG. 4 was adjusted, and the device with r · θ of 2.3 was used. As a result of inspecting the number of cracks, two cracks were found.

1: Porous carbon fiber sheet 2: Guide roll or nip roll 3: Porous carbon fiber sheet 4: Position detection device at the end of the sheet-like material 5: Porous carbon fiber sheet 6: Core bobbin 7: Porous carbon fiber sheet 8: Guide roll 1
9: Nip roll 10: Guide roll 2
11: Sheet-like object end position detection device 12: Light source 13: Porous carbon fiber sheet

Claims (7)

A shaft for winding the porous carbon fiber sheet, a winding shaft for winding in a roll shape, a nip roll for nipating the porous carbon fiber sheet on the upstream side of the winding shaft, and an end position of the porous carbon fiber sheet. In the process of arranging a detection device and moving the take-up shaft in the axial direction of the take-up shaft according to the detection signal, at least one free fiber having a diameter of 200 mm or less between the unwinding shaft and the nip roll is free. Including rolls , including at least one free roll having a diameter of 200 mm or less between the nip roll and the take-up shaft, the curvature of the sheet path of the free roll is r (mm ^-1 ), and the hugging angle formed by the free roll. the when the theta (degrees), the following equation (1) is satisfied in each of the free roll, a porous carbon fiber sheet rotation torque of the free roll, characterized in der Rukoto below 0.5 N · m Winding method.
0 <r ・ θ <1.5 ・ ・ ・ Equation (1) The method for winding a porous carbon fiber sheet according to claim 1, wherein each free roll satisfies the following formula (2).
0 <r · θ <1.2 ... Equation (2) The method for winding a porous carbon fiber sheet according to claim 1 or 2 , wherein the end position detecting device is arranged downstream of the nip roll. The method for winding a porous carbon fiber sheet according to any one of claims 1 to 3 , wherein the bulk density of the porous carbon fiber sheet is 0.3 to 0.8 g / cm ³ . The bending deflection of the porous carbon fiber sheet is 1.5 mm or more under the conditions of a strain rate of 10 mm / min, a distance between fulcrums of 2 cm, and a width of a test piece of 1 cm, according to any one of claims 1 to 4 . How to wind a porous carbon fiber sheet. The method for winding a porous carbon fiber sheet according to any one of claims 1 to 5 , wherein the porous carbon fiber sheet contains carbon fibers having an average fiber length of 2 to 10 mm. The method for winding a porous carbon fiber sheet according to any one of claims 1 to 6 , wherein the width of the nip roll is larger than the width of the porous carbon fiber sheet.