Prepreg manufacturing method and gas diffusion electrode substrate

Abstract

To suppress the fluctuation of weight in a longitudinal direction at the time of manufacturing a pre-preg used for manufacturing a gas diffusion electrode base material for a polymer electrolyte fuel cell.SOLUTION: A long carbon fiber base material is continuously impregnated with a resin liquid while conveying, and then dried to continuously manufacture pre-pregs, in a manufacturing method of pre-preg. The manufacturing method includes an excessive resin removal process in which, after impregnating the carbon fiber base material with the resin liquid, resin removal means is brought into contact with the fiber resin base material so as to remove an excessive resin liquid from the carbon fiber base material. In the excessive resin removal process, a cooling operation for continuously cooling the resin removal means to hold a surface temperature of the resin removal means at the temperature when impregnating with the resin liquid or below is performed, and a pre-cooling operation for cooling the resin removal means before the carbon fiber base material reaches the resin removal means is performed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for producing a prepreg used mainly in the production of a gas diffusion electrode substrate for a polymer electrolyte fuel cell, and to a gas diffusion electrode substrate. [Background technology]

[0002] The electrodes used in polymer electrolyte fuel cells have a structure consisting of catalyst layers arranged in contact with both sides of a polymer electrolyte membrane and gas diffusion layers formed on the outside of the catalyst layers. The material for forming the gas diffusion layers is generally called a gas diffusion electrode substrate.

[0003] The properties required for a gas diffusion electrode substrate include, for example, gas diffusivity, conductivity for conducting electrons that react in the catalyst layer, drainage properties for efficiently removing moisture generated in the catalyst layer, etc. To satisfy these properties, specific gas diffusion electrode substrates that are used include carbon felt, carbon paper, and carbon cloth made of carbon fiber, and among these, carbon paper is most widely used from the viewpoint of mechanical strength, etc.

[0004] In polymer electrolyte fuel cells, the component that integrates the polymer electrolyte membrane and electrodes is called a membrane electrode assembly (MEA). Multiple MEAs are further stacked via separators, which are components with gas flow paths, and the entire assembly is fastened together with bolts to form a fuel cell stack. At this time, the electrolyte membrane, catalyst layer, and gas diffusion layer that make up the MEA are pressed together with high pressure, but if the thickness of the gas diffusion layer varies, the catalyst layer and electrolyte membrane will become locally thin, which may lead to a decrease in the power generation performance and durability of the fuel cell.

[0005] To solve this problem, it is necessary to suppress the thickness variation of the gas diffusion layer, and to do so, it is necessary to minimize the variation in the basis weight of the gas diffusion electrode substrate. Patent Document 1 discloses, as conventional techniques for reducing the variation in basis weight of the gas diffusion electrode substrate, techniques such as slowing down the papermaking speed when papermaking carbon fibers, dividing dewatering during papermaking into multiple stages, and reducing the dewatering pressure. Patent Document 2 also discloses a technique for adjusting the basis weight of the carbon fiber paper, the short fiber concentration during papermaking, and the basis weight of the gas diffusion layer itself within specific ranges to minimize the variation in the basis weight of the resin to be impregnated when producing a prepreg by impregnating a carbon fiber paper, which is a precursor of the gas diffusion electrode substrate, with a resin. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-157314 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-157653 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in both technologies, the means for reducing the variation in basis weight is only performed in the papermaking process, and it is not possible to improve the variation in basis weight caused by the resin carbonized material, which accounts for approximately half of the weight of the gas diffusion electrode substrate, in the resin impregnation process.

[0008] The present invention aims to provide a fuel cell with stable power generation performance by reducing fluctuations in the basis weight of a prepreg used as an intermediate substrate for producing a gas diffusion electrode substrate in the longitudinal direction, thereby suppressing fluctuations in the basis weight of the gas diffusion electrode substrate and ensuring uniform contact between the gas diffusion layer and the microporous layer or catalyst layer. Another object of the present invention is to suppress fluctuations in the basis weight in the longitudinal direction of not only the intermediate substrate for a gas diffusion electrode substrate but also prepregs used as intermediate substrates for fiber-reinforced composite materials used as various structural materials. Another object of the present invention is to suppress fluctuations in the basis weight in the width direction. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention employs the following means. (1) A method for producing a prepreg, which comprises continuously impregnating a long carbon fiber substrate with a resin liquid while transporting the same, and then drying the same to continuously produce a prepreg, and includes an excess resin removing step of removing excess resin liquid from the carbon fiber substrate by bringing a resin removing means into contact with the carbon fiber substrate after the carbon fiber substrate has been impregnated with the resin liquid, and in the excess resin removing step, a cooling operation is performed in which the resin removing means is continuously cooled to maintain the surface temperature of the resin removing means at or below the temperature at which the resin liquid was impregnated, and a pre-cooling operation is performed in which the resin removing means is cooled before the carbon fiber substrate reaches the resin removing means. (2) The method for producing a prepreg according to (1), wherein the cooling operation and the pre-cooling operation are operations in which a cooling liquid is brought into contact with the resin removing means. (3) The method for producing a prepreg according to (2), wherein the coolant is brought into contact with the resin removal means by dropping the coolant onto the resin removal means. (4) The method for producing a prepreg according to (2) or (3), wherein a solvent for the resin liquid is used as the coolant. (5) The method for producing a prepreg according to (4), wherein methanol is used as a solvent for the coolant and the resin liquid. (6) The method for producing a prepreg according to any one of (1) to (5), wherein the resin removing means is a squeeze roll that squeezes the carbon fiber base material. (7) The method for producing a prepreg according to any one of (1) to (6), wherein in the pre-cooling operation, the surface temperature of the resin removal means is cooled to a temperature at the time of impregnation with the resin liquid or lower. (8) The method for producing a prepreg according to (7), wherein in the pre-cooling operation, cooling is carried out so that the surface temperature of the resin removal means satisfies the following formula: -2.0 ≦ Surface temperature of resin removal means -0.84 × Temperature at time of resin liquid impregnation ≦ 2.0 (9) The method for producing a prepreg according to (7) or (8), wherein the pre-cooling operation is controlled so that the difference in surface temperature in the width direction of the resin removal means is ±1.0°C or less. (10) The method for producing a prepreg according to (9), wherein the pre-cooling operation is an operation of bringing a cooling liquid into contact with the resin removal means, and the pre-cooling operation is carried out by varying the amount of the cooling liquid that comes into contact with the resin removal means in the width direction. (11) The method for producing a prepreg according to (10), wherein the pre-cooling operation is carried out by increasing the amount of the cooling liquid contacting both ends of the resin removal means compared to the central portion of the resin removal means. (12) The method for producing a prepreg according to any one of (1) to (11), wherein the carbon fiber substrate is a carbon fiber paper sheet. (13) The method for producing a prepreg according to any one of (1) to (12), wherein the density of the resin liquid is continuously monitored and the density of the resin liquid is controlled to be constant by intermittently replenishing the solvent into the resin liquid according to changes in density. (14) A method for producing a gas diffusion electrode substrate, comprising firing a prepreg molded article produced by the production method according to any one of (1) to (13). (15) A gas diffusion electrode substrate having a longitudinal variation in basis weight of 2.0% / 1400 m or less. (16) The gas diffusion electrode substrate according to (15), wherein the variation in basis weight in the width direction is 1% / m or less. [Effects of the Invention]

[0010] By using the gas diffusion electrode substrate manufactured by the manufacturing method of the present invention for the gas diffusion layer, it is possible to reduce thickness fluctuations of the catalyst layer and pressure fluctuations on the catalyst layer and electrolyte membrane in the fuel cell stack, and to manufacture a fuel cell with stable power generation performance. Furthermore, when applied to prepregs of fiber-reinforced composite materials, thickness fluctuations of the prepregs are suppressed, so that the dimensions of the structure are stable and a structural material with stable mechanical strength can be manufactured. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram showing an example of a production facility for carrying out a prepreg production method according to the present invention. [Figure 2] 2 is a view of the periphery of the squeeze roll 1 of FIG. 1 as seen from the arrow. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention relates to a method for continuously impregnating a long carbon fiber substrate with a resin liquid while transporting the same, and then drying the same to continuously produce a prepreg. The method for producing a prepreg according to the present invention will be described with reference to the drawings, but the present invention is not limited by these drawings. Furthermore, the description of the specific embodiments shown in the drawings can also be understood as a description of the present invention as a generic concept.

[0013] Fig. 1 is a schematic diagram showing an example of a production facility for carrying out the prepreg production method according to the present invention. As shown in Fig. 1, an impregnation tank 6 is provided with a rotatable in-tank roll 7 therein. The carbon fiber substrate 4 is continuously immersed in the resin liquid 5a while being transported along the arrow from diagonally above the impregnation tank 6. Thereafter, the carbon fiber substrate 4 is changed in direction along the in-tank roll 7 and pulled out from the top of the impregnation tank 6. In this way, the carbon fiber substrate 4 is continuously impregnated with the resin liquid 5a.

[0014] Next, the carbon fiber base material 4 is passed through a pair of squeeze rolls 1 arranged in parallel with the gap adjusted to a constant width, thereby removing excess resin contained in the carbon fiber base material 4. Then, although not shown, if the resin liquid 5a impregnated into the carbon fiber base material 4 contains a solvent, the solvent is volatilized and removed in a drying furnace, and then cooled and wound up to produce a prepreg.

[0015] From the viewpoint of reducing unevenness in impregnation with the resin liquid 5a and drying of the solvent, it is preferable that the liquid level of the resin liquid 5a in the impregnation tank does not fluctuate as much as possible. Therefore, it is preferable that the in-tank roll 7 is positioned so that it is completely immersed in the resin liquid 5a. In this embodiment, a level gauge 8 is installed in the impregnation tank 6, and the resin liquid 5a is supplied from the blending tank 12 to the impregnation tank 6 as needed so that the liquid level is always approximately constant.

[0016] As the carbon fiber substrate, in the case of a prepreg for a gas diffusion electrode substrate, a carbon fiber woven fabric, a carbon fiber paper sheet, or a carbon fiber nonwoven fabric is preferably used, and in the case of a prepreg for a fiber-reinforced composite material, in addition to these, unidirectionally aligned carbon fibers are preferably used. The present invention is particularly useful as a method for producing a prepreg for a gas diffusion electrode substrate, and in this case, a carbon fiber paper sheet is most preferably used as the carbon fiber substrate.

[0017] Carbon fiber paper sheets are generally produced by dispersing carbon fibers cut to lengths of 3 mm to 20 mm in a solution of a dispersant together with a binder such as polyvinyl alcohol, and then papering and drying the paper in a normal papermaking process.

[0018] The resin contained in the resin solution may be any resin that can be carbonized to function as a binder or conductive agent for carbon fibers. Thermosetting resins such as phenolic resins, epoxy resins, melamine resins, and furan resins are preferred, with phenolic resins being particularly preferred due to their high carbonization yield. The resin solution may also contain a carbon-based filler as an additive to improve the mechanical properties, electrical conductivity, thermal conductivity, and other properties of the final gas diffusion electrode substrate. Examples of carbon-based fillers that can be used include carbon black, carbon nanotubes, carbon nanofibers, milled carbon fiber, and graphite.

[0019] The resin liquid may be the resin component obtained by the above-mentioned configuration as it is, but in order to improve the impregnation into the carbon fiber substrate, various solvents may be used to use the above-mentioned resin solution or dispersion. Here, as the solvent, a volatile solvent that is easily removed by drying after impregnation with the resin liquid is preferred, and methanol, ethanol, isopropyl alcohol, acetone, methyl ethyl ketone, etc. are preferably used. Among them, it is particularly preferred to use methanol, which is inexpensive and has an excellent balance of drying property and flammability resistance.

[0020] When the resin liquid contains a solvent, the solvent volatilizes during processing, gradually increasing the density of the resin liquid, which in turn tends to gradually increase the basis weight of the carbon fiber substrate after resin impregnation. Therefore, it is preferable to continuously monitor the density of the resin liquid and control the density of the resin liquid to a constant value by intermittently replenishing the solvent into the resin liquid according to density changes. In this embodiment, the density of the resin liquid is monitored by a density meter 10 installed in the resin circulation line 9a, and the solvent is replenished into the resin liquid over time to offset the increase in density of the resin liquid. It is preferable to control the density of the resin liquid to ±0.01 kg / L, preferably ±0.005 kg / L, and more preferably ±0.001 kg / L. At this time, in order to suppress local density fluctuations of the resin liquid due to replenishment of the solvent, in this embodiment, the solvent is introduced into the blending tank 12 from the solvent dropping pipe 13, the resin liquid 5b is stirred and homogenized, and then the resin liquid (5a, 5b) is constantly circulated between the blending tank 12 and the resin bath 6 that impregnates the carbon fiber substrate with the resin through the resin circulation lines 9a and 9b.

[0021] In the manufacturing method of the present invention, as described above, after impregnating the carbon fiber substrate 4 with the resin liquid 5a, there is an excess resin removing step in which the resin removing means 1 is brought into contact with the carbon fiber substrate 4 to remove excess resin liquid from the carbon fiber substrate 4. Examples of the resin removing means include squeeze rolls that squeeze the carbon fiber substrate by passing it between rolls, rolls with a substantially circular cross section in which one or both are fixed, and mechanisms that squeeze the carbon fiber substrate 4 while passing it through a gap formed by members such as a blade-shaped doctor knife, and among these, it is preferable to use a squeeze roll because it enables stable resin removal.

[0022] In the present invention, the resin removal means used in the resin removal step is continuously cooled to perform a cooling operation to maintain the surface temperature of the resin removal means 1 at or below the temperature at which the resin liquid 5a is impregnated. The cooling operation is preferably an operation of bringing the resin removal means into contact with a cooling liquid, and more specifically, a preferred embodiment is an operation of dropping the cooling liquid onto the resin removal means.

[0023] Fig. 2 is a view of the periphery of the squeeze roll 1 in Fig. 1 as seen from the arrow. In this embodiment, the cooling operation is an operation of dripping a liquid coolant 2 onto the squeeze roll 1. In this case, it is preferable to provide a plurality of liquid coolant discharge ports 3 across the width above the squeeze roll 1 so that the liquid coolant 2 is dripped across the entire width of the squeeze roll 1. In other words, it is preferable that the cooling operation in the present invention is carried out so as to cool the entire width of the resin removal means.

[0024] There are no particular limitations on the coolant 2, but when the resin liquid described above contains a solvent, it is preferable to use the solvent of the resin liquid in terms of quality stability and ease of raw material management. A particularly preferred embodiment is one in which methanol is used as the solvent for the coolant 2 and the resin liquid.

[0025] In the manufacturing method of the present invention, in addition to the above-mentioned cooling operation, a pre-cooling operation is performed to cool the resin removing means before the carbon fiber substrate reaches the resin removing means. By performing the pre-cooling operation, it is possible to suppress fluctuations in basis weight over the entire length in the longitudinal direction of the long carbon fiber substrate. That is, in the above embodiment, the pre-cooling operation can be performed by starting the dripping of the cooling liquid 2 onto the squeeze roll 1 before the tip end of the long carbon fiber substrate 4 reaches the squeeze roll 1. At this time, it is preferable that the surface temperature of the resin removing means is cooled to a temperature equal to or lower than the temperature at the time of impregnation with the resin liquid in the pre-cooling operation.

[0026] In the pre-cooling operation, it is more preferable to control the surface temperature of the resin removal means so that "(surface temperature of the resin removal means) - 0.84 x (temperature at the time of impregnation with the resin liquid)" is preferably -2.0 to 2.0°C, and more preferably -1.0 to 1.0°C. If this range is exceeded, the amount of heat transferred between the resin and the resin removal means during processing increases, causing fluctuations in the temperature of the resin removal means, which in turn tends to increase fluctuations in the amount of resin removed.

[0027] In the pre-cooling operation, it is preferable to control the surface temperature difference in the width direction of the resin removing means to be ±1.0°C or less, more preferably ±0.5°C or less. The surface temperature difference in the width direction here means the surface temperature difference when including not only the central part (1b) that contacts the carbon fiber substrate but also both end parts (1a) that do not contact the carbon fiber substrate. The width of both end parts (1a) that do not contact the carbon fiber substrate is preferably at least 10% or more of the width of the central part (1b) that contacts the carbon fiber substrate.

[0028] When there is a large temperature difference between the central portion 1b in contact with the carbon fiber substrate and the end portions 1a not in contact with the carbon fiber substrate, the surface temperature of the central portion 1b, especially at the end portions, tends to change over time. This causes the amount of resin removed to fluctuate due to changes in the surface pressure applied to the carbon fiber substrate, which may result in unevenness in the longitudinal basis weight of the resulting gas diffusion electrode substrate. Furthermore, this temperature difference increases the temperature difference within the central portion (1b) of the squeeze nip roll where the carbon fiber substrate is in contact, widening the gap between the squeeze nip rolls. This changes the surface pressure when squeezing the carbon fiber substrate, resulting in unevenness in the basis weight in the width direction.

[0029] The surface temperature of the resin removal means in the width direction during such a pre-cooling operation is preferably adjusted by varying the amount of coolant that comes into contact with the resin removal means in the width direction, and more preferably by increasing the amount of coolant that comes into contact with both end portions 1a of the resin removal means compared to the central portion 1b. That is, in the above embodiment, it is preferable to increase the amount of coolant 2 dripped onto the squeeze roll 1 at both end portions 1a compared to the central portion 1b.

[0030] The prepreg thus obtained is pressed to a desired thickness while being heated to a temperature at which the resin melts and hardens, and is then formed into a molded article. This molded article is then fired at a temperature at which the resin carbonizes, to obtain carbon paper or the like that will serve as the gas diffusion electrode substrate.

[0031] The present invention stabilizes the solid content of a resin solution, such as a phenolic resin, which is the cause of longitudinal variations in basis weight. This stabilizes the longitudinal variation in basis weight of a long gas diffusion electrode substrate to 2.0% / 1400 m or less, preferably 1.5% / 1400 m or less. The lower limit of the basis weight variation is not particularly limited as long as it is 2.0% / 1400 m or less, and 0.1% / 1400 m or less is particularly preferred. By limiting the basis weight variation to 2.0% / 1400 m or less, the variation in catalyst layer coating thickness is reduced, resulting in an electrode substrate with stable power generation performance and durability. This effect is particularly pronounced when producing a long gas diffusion electrode substrate with a length of 600 m or more. The variation in basis weight over a substrate length of L (m) was determined by taking a 10 x 10 cm square test piece from the gas diffusion electrode substrate at two points in the width direction and four points at 5 cm intervals in the longitudinal direction, and weighing a total of eight masses on an electronic balance. The average of these eight masses was taken as the basis weight at that location. This was measured in the same way every 200 m in the longitudinal direction, and the average basis weight of a total of M locations sampled in an Lm section was calculated. In this case, M was calculated as (L + 200) / 200 (decimals rounded down). The deviation rate from the average basis weight at the location with the largest deviation from the average basis weight among the M locations was taken as the longitudinal basis weight variation.

[0032] Furthermore, according to one aspect of the present invention, it is possible to suppress the change in surface pressure when squeezing a carbon fiber substrate due to the difference in the gap between squeeze nip rolls, which is the cause of variation in basis weight in the width direction, and to suppress variation in basis weight in the width direction of a long gas diffusion electrode substrate to 1.0% / m or less. Such an effect is particularly pronounced when producing a long gas diffusion electrode substrate with a width of 0.42 m or more. The variation in basis weight in the width direction when the width of the gas diffusion electrode substrate is W (m) can be determined as follows: First, 10 × 10 cm square test pieces are taken from the gas diffusion electrode substrate at N points at approximately equal intervals in the width direction, and the mass of the total N points is weighed using an electronic balance and divided by the area to determine the basis weight. In this case, N is calculated as (W + 0.055) / 0.155 (decimals are rounded down). The deviation rate of the basis weight with the largest deviation from the average basis weight among the basis weights of these N points is determined as the variation in basis weight in the width direction. [Example]

[0033] The present invention will be described in more detail below with reference to examples.

[0034] <Variation in basis weight in the longitudinal direction> Two 10 x 10 cm square test pieces were taken from the gas diffusion electrode substrate in the width direction and four at 5 cm intervals in the longitudinal direction of the sheet, and the masses of a total of eight test pieces were weighed on an electronic balance, and the average value of these eight masses was taken as the basis weight at that location. This was measured in the same way every 200 m in the longitudinal direction, and the average value of the basis weight at a total of eight locations taken over a 1,400 m section was calculated. Of these eight basis weights, the deviation rate from the average basis weight at the location with the largest deviation from the average basis weight was taken as the basis weight variation in the longitudinal direction.

[0035] <Balance weight fluctuation in width direction> Six 10 × 10 cm square test pieces were taken out at approximately equal intervals in the width direction from a 1 m wide gas diffusion electrode substrate, and the mass of all six pieces was weighed on an electronic balance and divided by the area to obtain the basis weight. The deviation rate of the basis weight with the largest deviation from the average basis weight of these six pieces was taken as the basis weight variation in the width direction.

[0036] <Resin liquid density> The resin in the impregnation bath was constantly circulated with the resin in the blending tank using a pump, and a Coriolis mass flow meter manufactured by Endress+Hauser was installed in the extraction piping from the resin bath to the blending tank, and density fluctuations were calculated by converting the mass flow rates immediately after the start of processing and immediately after processing into density.

[0037] [Example 1] Toray Industries, Inc.'s polyacrylonitrile carbon fiber "TORAYCA" (registered trademark) T300 was cut into 12 mm lengths, dispersed in water, and formed into a paper sheet on a mesh. An aqueous solution of polyvinyl alcohol (PVA) was applied to the paper sheet, which was then dried to obtain a carbon fiber paper sheet with approximately 20 parts by mass of PVA as a binder attached to 100 parts by mass of short carbon fibers. At this time, the weight of the carbon fiber was 31 g / m. 2 It was decided.

[0038] Next, the carbon fiber web was impregnated with resin using an apparatus equipped with a resin bath 6 containing a resin liquid 5a and a squeeze roll 1, as shown in Figure 1. The resin bath 6 contained a 15 mass% methanol solution of a mixed resin containing the same mass parts of resol phenolic resin and novolac phenolic resin as the resin liquid. The temperature of the resin liquid was 20°C.

[0039] Methanol 2 was dripped from a cooling liquid outlet 3 onto a squeeze roll 1, a resin removal means installed above a resin bath 6, to cool the squeeze roll surface. Methanol was dripped onto both end portions 1a of the squeeze roll for 40 minutes, and then onto the contact positions 1b between both end portions 1a. The "squeeze roll surface temperature - 0.84 × temperature at the time of resin liquid impregnation" was 0.2°C, and the temperature difference across the squeeze roll was 0.4°C. The paper sheet was then continuously immersed in a resin bath for 30 minutes while roughly maintaining the temperature difference across the width, and the excess resin liquid was removed by passing it through a squeeze roll whose temperature had been adjusted as described above. The paper sheet was then heated in a drying furnace to evaporate the solvent methanol, yielding a prepreg with 100 parts by mass of mixed resin adhering to 100 parts by mass of the paper sheet.

[0040] Next, the prepreg was set in a press molding machine with the upper and lower plates parallel to each other, and the press was repeatedly opened and closed to heat and pressurize the prepreg while intermittently transporting it, thereby obtaining a molded product.

[0041] The molded article was then heated in an inert atmosphere high-temperature furnace to a maximum temperature of 1200°C for firing (carbonizing the resin-containing molded article) to obtain carbon paper (gas diffusion electrode substrate). The variation in basis weight in the longitudinal direction of the obtained carbon paper was 0.4% / 1400m. The variation in basis weight in the width direction was 0.4% / m.

[0042] [Example 2] Methanol was dripped onto only both end portions 1a of the squeeze roll for 30 minutes, and then dripped onto the position where both end portions 1a and contact position 1b were in contact. Carbon paper was obtained in the same manner as in Example 1, except that "surface temperature of the resin removal means - 0.84 x temperature at the time of impregnation with the resin liquid" was set to -1.9°C and the temperature difference in the width direction of the squeeze roll was set to 0.8°C.

[0043] [Example 3] Methanol was dripped onto only both end portions 1a of the squeeze roll for 20 minutes, and then dripped onto the contact positions 1b of both end portions 1a. Carbon paper was obtained in the same manner as in Example 1, except that "surface temperature of the resin removal means - 0.84 x temperature at the time of impregnation with the resin liquid" was set to 1.0°C and the temperature difference in the width direction of the squeeze roll was set to 0.6°C.

[0044] [Example 4] Methanol was dripped onto only both end portions 1a of the squeeze roll for 15 minutes, and then dripped onto the positions of both end portions 1a and contact positions 1b, and carbon paper was obtained in the same manner as in Example 1, except that "surface temperature of the resin removal means - 0.84 x temperature at the time of impregnation with the resin liquid" was set to 1.0°C, and the temperature difference in the width direction of the squeeze roll was set to 1.0°C.

[0045] [Example 5] Carbon paper was obtained in the same manner as in Example 1, except that the time for dropping methanol onto both end portions 1a of the squeeze roll in the width direction was the same as that at the resin-impregnated substrate contact position 1b, the "surface temperature of the resin removal means - 0.84 x temperature during resin liquid impregnation" was set to -1.7°C, and the temperature difference in the width direction of the squeeze roll was set to 5.0°C.

[0046] [Comparative Example 1] Carbon paper was obtained in the same manner as in Example 1, except that the squeeze roll surface was not cooled before impregnation, the "surface temperature of the resin removal means - 0.84 x temperature during resin liquid impregnation" was 5.9°C, and the temperature difference in the width direction of the squeeze roll was 3.0°C. The variation in basis weight in the longitudinal direction was 9.0% / 1400 m. The variation in basis weight in the width direction was 3.5% / m.

[0047] Table 1 summarizes the manufacturing methods of each example and comparative example and the variations in basis weight of the resulting carbon paper.

[0048] [Table 1] [Explanation of symbols]

[0049] 1 Resin removal means (squeeze roll) 1a Both ends of the resin removal means (squeeze roll) 1b Center of resin removal means (squeeze roll) 2 Coolant (methanol) 3 Coolant outlet 4. Carbon fiber substrate 6 resin solutions in 5a resin bath 5b Resin liquid in blending tank 12 6 Resin Bath 7. In-tank roll 8 Level gauge 9a Circulation piping (return liquid) 9b Circulation piping (liquid supply) 10 Density meter 11 Stirring blade 12 Mixing Tank 13 Solvent drip piping 14 Coolant piping

Claims

1. A method for producing a prepreg, which continuously impregnates a long carbon fiber base material with a resin liquid while transporting the long carbon fiber base material, and then dries the same to continuously produce a prepreg, and which includes an excess resin removing step of removing excess resin liquid from the carbon fiber base material by bringing a resin removing means into contact with the carbon fiber base material after the carbon fiber base material has been impregnated with the resin liquid, and in the excess resin removing step, a cooling operation is performed in which the resin removing means is continuously cooled to maintain a surface temperature of the resin removing means at or below a temperature during impregnation with the resin liquid, and a pre-cooling operation is performed in which the resin removing means is cooled before the carbon fiber base material reaches the resin removing means, and wherein the cooling operation and the pre-cooling operation are operations in which a solvent for the resin liquid is brought into contact with the resin removal means as a coolant.

2. The method for producing a prepreg according to claim 1 , wherein the coolant is brought into contact with the resin removing means by dropping the coolant onto the resin removing means.

3. The method for producing a prepreg according to claim 1 , wherein methanol is used as a solvent for the coolant and the resin liquid.

4. The method for producing a prepreg according to any one of claims 1 to 3, wherein the resin removing means is a squeeze roll that squeezes the carbon fiber base material.

5. The method for producing a prepreg according to any one of claims 1 to 4, wherein in the pre-cooling operation, the surface temperature of the resin removal means is cooled to a temperature equal to or lower than the temperature at the time of impregnation with the resin liquid.

6. The method for producing a prepreg according to claim 5, wherein in the pre-cooling operation, cooling is performed so that the surface temperature of the resin removal means satisfies the following formula: −2.0≦surface temperature of resin removal means−0.84×temperature at the time of impregnation with resin liquid≦2.0

7. The method for producing a prepreg according to claim 5 or 6, wherein the pre-cooling operation is controlled so that the surface temperature difference in the width direction of the resin removing means is ±1.0°C or less.

8. 8. The method for producing a prepreg according to claim 7, wherein the pre-cooling operation is an operation of bringing a cooling liquid into contact with the resin removal means, and the pre-cooling operation is carried out by varying the amount of the cooling liquid that comes into contact with the resin removal means in the width direction.

9. The method for producing a prepreg according to claim 8, wherein the pre-cooling operation is carried out by increasing the amount of the coolant that comes into contact with both ends of the resin removal means compared to a central portion of the resin removal means.

10. The method for producing a prepreg according to any one of claims 1 to 9, wherein the carbon fiber base material is a carbon fiber paper body.

11. The method for producing a prepreg according to any one of claims 1 to 10, wherein the density of the resin liquid is continuously monitored and the density of the resin liquid is controlled to be constant by intermittently replenishing the solvent into the resin liquid according to changes in density.

12. A method for producing a gas diffusion electrode substrate, comprising firing a prepreg molded article produced by the method according to any one of claims 1 to 11.

13. A gas diffusion electrode substrate whose constituent material is carbon paper and whose variation in basis weight in the longitudinal direction is 2.0% / 1,400 m or less.

14. 14. The gas diffusion electrode substrate according to claim 13, wherein the variation in basis weight in the width direction is 1.0% / m or less.

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