JP7393933B2 - Manufacturing method of polymer electrolyte membrane - Google Patents

Description

The present invention relates to a method for manufacturing a polymer electrolyte membrane.

A fuel cell directly converts the chemical energy of fuel into electrical energy and extracts it by electrochemically oxidizing hydrogen, methanol, or the like within the cell. Therefore, fuel cells are attracting attention as a clean electrical energy supply source. In particular, solid polymer electrolyte fuel cells operate at lower temperatures than other fuel cells, and are therefore expected to be used as an alternative power source for automobiles, home cogeneration systems, portable generators, and the like.

Such a solid polymer electrolyte fuel cell includes at least a membrane electrode assembly in which a gas diffusion electrode in which an electrode catalyst layer and a gas diffusion layer are laminated is joined to both sides of an electrolyte membrane. The electrolyte membrane referred to herein is a material that has a strong acidic group such as a sulfonic acid group or a carboxylic acid group in its polymer chain, and has the property of selectively permeating protons.

Polymer electrolyte membranes for use in fuel cell vehicles are used in environments where the water content changes significantly and is heated to about 80° C. due to accelerator work during acceleration and deceleration. At this time, the polymer electrolyte membrane undergoes very large dimensional changes due to water swelling and drying shrinkage, and there is room for improvement in terms of durability and reliability. Therefore, in order to reduce the dimensional change, various methods have been proposed for embedding reinforcing materials in the electrolyte.

In recent years, the use of fuel cell vehicles has required chemical durability, physical durability, and power generation performance in a harsher fuel cell driving environment of around 120°C. The effects of operating in this high-temperature environment are expected to be that the capacity of the radiator can be halved, making it possible to install it in small cars, reducing catalyst poisoning by CO in the fuel gas, and expanding heat utilization. Further, when used as a fuel cell, the electrolyte membrane itself needs to have low membrane resistance. For this purpose, it is desirable that the thickness of the electrolyte membrane be as thin as possible. Furthermore, thinner films and improved productivity are highly desirable from the cost perspective, which is one of the reasons for the negative effects of the widespread use of fuel cell vehicles. However, non-PTFE porous materials suitable for electrolyte reinforcing materials have a low basis weight and high porosity in order to reduce resistance during power generation, but they have low strength and are extremely difficult to handle. difficult to obtain. Furthermore, if the thickness of the electrolyte membrane is made excessively thin, there are problems in that physical strength decreases such as pinholes during film formation and tearing of the membrane during electrode molding, and short circuits between electrodes are likely to occur.

Unlike the driving environment temperature of 80° C. for conventional fuel cells, in a harsh environment of 120° C., extremely large repeated stress of water swelling and drying contraction is applied to the electrolyte membrane. Therefore, an electrolyte membrane used in such an environment needs to have improved durability against both humidification, swelling and drying and thermal deformation stress. In particular, when an electrolyte membrane is heated and some external stress is applied, stress strain accumulates, and the stress causes permanent deformation, promoting thinning of the membrane and deterioration of the polymer. In order to suppress these problems, it is effective not only to improve the thermal deformation resistance of the electrolyte membrane itself but also to include a reinforcing material having a high glass transition temperature. However, increasing the reinforcing material content causes problems such as hindering proton conductivity and increasing membrane resistance. Therefore, it is required not only to rely on reinforcing materials with a high glass transition temperature, but also to improve the heat resistance of the electrolyte membrane itself, thereby achieving both durability and high proton conductivity of the electrolyte membrane.

For example, U.S. Pat. No. 5,000,302 includes an electrolyte membrane having a first proton-conducting polymer reinforced by a nanofiber sheet, the nanofiber sheet being made of nanofibers comprising a fibrous material selected from polymers and polymer blends. It is described that the fabricated and fibrous materials can include highly fluorinated polymers, perfluorinated polymers, hydrocarbon polymers, and blends and combinations thereof. In the embodiment disclosed in Patent Document 1, the nanofiber sheet is calendered at 140°C. This has the effect of improving the strength of the nanofiber sheet, but on the other hand, a region where the nanofiber fibers partially overlap each other forms a binding portion and the porosity decreases. If such areas are scattered in a nanofiber sheet, the nanofiber sheet will bend and wrinkle when it is brought into contact with a solution containing an electrolyte to evaporate the solvent and dry, and even if tension is applied to the nanofiber sheet, the nanofiber sheet will not wrinkle. It becomes difficult to resolve. In addition, in areas where nanofibers overlap and settle, when filling the voids between nanofibers with electrolyte while vaporizing the solvent, the nanofibers cannot follow the deformation in the film thickness direction, resulting in void defects. etc., are not suitable for electrolyte membranes for fuel cells.

Patent Document 2 describes a method of applying tension in the direction of movement of a porous material to compose it with a polymer electrolyte, but the porous material is a biaxially oriented porous polypropylene film and has a structure different from that of nanofibers. Therefore, the impregnation behavior when composited with a proton-conducting polymer solution is different, and the design philosophy is completely different, such as making the porous material wider than the width of the base material.

In addition to Patent Document 1, there are also Patent Documents 3 to 6 as prior art techniques for combining nanofibers and electrolyte membranes. However, all of the prior art techniques are limited to the preparation of small-sized samples at the laboratory level, and have not yet reached the point of producing a continuous large-area polymer electrolyte membrane that is free from wrinkle defects and has excellent uniformity.

Patent No. 5798186 Japanese Patent Application Publication No. 2011-222499 International Publication No. 2017/141878 Patent No. 5830654 Special Publication No. 2014-525115 Special table 2017-532716 publication

The present invention provides a method for fabricating large-area polymer electrolyte membranes whose dimensions change uniformly in a fuel cell operating environment (e.g., 120°C, 100% relative humidity) without causing wrinkle defects and without rupturing the membrane. Intended for continuous production.

As a result of extensive studies, the present inventors have found a manufacturing method that can achieve the above object, and have completed the present invention. That is, the present invention is as follows.

[1]
A method for continuously manufacturing a polymer electrolyte membrane, the method comprising:
A step of unwinding the base sheet,
a coating step of continuously coating the first proton conductive polymer solution on the base sheet;
A process of applying tension to the nanofiber sheet while bringing it into contact with a non-mirrored roll,
A first treatment step of continuously bringing the first surface of the nanofiber sheet into contact with the applied first proton-conducting polymer solution to obtain a first surface-treated nanofiber sheet;
a first drying step of drying the first surface-treated nanofiber sheet;
including;
The average fiber diameter of the nanofibers contained in the nanofiber sheet is 100 nm to 600 nm,
The load required to deform the nanofiber sheet by 8% in the longitudinal direction is 0.2 N/10 mm or more,
The tension for feeding out the nanofiber sheet is such that the length of the nanofiber sheet in the short direction changes by -3.0% to 0.5%,
The nanofiber sheet has a first end and a second end in the short direction, and in the first treatment step, at least one of the first end and the second end is brought into contact with the first proton conductive polymer solution. Said method.
[2]
The method according to [1], wherein the length of the nanofiber sheet in the short direction is 270 mm or more.
[3]
The method according to [1] or [2], wherein the first end and the second end of the nanofiber sheet are brought into contact with the first proton conductive polymer solution.
[4]
The method according to any one of [1] to [3], wherein the nanofiber sheet contains polyether sulfone.
[5]
The method according to any one of [1] to [4], wherein the nanofiber sheet has a basis weight of 1.5 to 4.0 g/m ² .
[6]
The method according to any one of [1] to [5], wherein the nanofiber sheet has a porosity of 75% to 88%.
[7]
A second treatment step of continuously bringing a second proton-conducting polymer solution into contact with the second surface of the first surface-treated nanofiber sheet that has undergone the first drying step to obtain a double-surface-treated nanofiber sheet;
a second drying step of drying the both surface-treated nanofiber sheets;
The method according to any one of [1] to [6], further comprising:

According to the present invention, it is possible to rupture a large-area polymer electrolyte membrane whose dimensions change uniformly in a fuel cell operating environment (e.g., 120° C., 100% RH) without causing wrinkle defects. It can be manufactured continuously.

1 is a schematic diagram of a cross section of a polymer electrolyte membrane of Example 1. FIG. 3 is a schematic diagram of a cross section of a polymer electrolyte membrane of Example 3. FIG. 3 is a schematic cross-sectional view of a polymer electrolyte membrane of Comparative Example 1. FIG. This is measurement data from a tensile test of nanofiber sheets used in Examples. 2 is a SEM photograph showing a cross section of the polymer electrolyte membrane of Example 1. This is an example of an apparatus for manufacturing a polymer electrolyte membrane according to the present embodiment. 3 is an SEM photograph showing a cross section of a wrinkle defective part of a polymer electrolyte membrane of Comparative Example 3.

Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail with reference to the drawings as necessary, but the present invention is limited to the following present embodiment. It's not a thing. The present invention can be modified in various ways without departing from the gist thereof.

One aspect of the manufacturing method of this embodiment is a method of continuously manufacturing a polymer electrolyte membrane, comprising:
A step of unwinding the base sheet,
a coating step of continuously coating the first proton conductive polymer solution on the base sheet;
A process of applying tension to the nanofiber sheet while bringing it into contact with a non-mirrored roll,
A first treatment step of continuously bringing the first surface of the nanofiber sheet into contact with the applied first proton-conducting polymer solution to obtain a first surface-treated nanofiber sheet;
a first drying step of drying the first surface-treated nanofiber sheet;
including;
The average fiber diameter of the nanofibers contained in the nanofiber sheet is 100 nm to 600 nm,
The load required to deform the nanofiber sheet by 8% in the longitudinal direction is 0.2 N/10 mm or more,
The tension for unwinding the nanofiber sheet is such that the length of the nanofibers in the short direction changes by -3.0% to 0.5%,
A method in which the nanofiber sheet has a first end and a second end in the short direction, and in the first treatment step, at least one of the first end and the second end is brought into contact with the first proton conductive polymer solution. It is.

The method includes continuously contacting the second surface of the first surface-treated nanofiber sheet that has undergone the first drying step with a second proton-conducting polymer solution to obtain a double-surface-treated nanofiber sheet. processing step;
a second drying step of drying the both surface-treated nanofiber sheets;
may further include.

By the method described above, it is possible to obtain a sheet shape in which a nanofiber sheet and a proton conductive polymer are combined.

In the manufacturing method of this embodiment, it is preferable to continuously manufacture the polymer electrolyte membrane for 50 m or more, more preferably for 300 m or more, and even more preferably for 800 m or more.

After the electrolyte membrane of this embodiment is manufactured as described above, it is preferable that the electrolyte membrane is further subjected to heat treatment. This heat treatment may be performed multiple times, and the heat treatment advances the crystallization of, for example, the perfluoroalkyl skeleton of the proton conductive polymer, and as a result, the mechanical strength of the electrolyte membrane can be further stabilized. The temperature of this heat treatment is preferably 100°C or more and 230°C or less, more preferably 120°C or more and 220°C or less, and even more preferably 140°C or more and 200°C or less. By adjusting the temperature of the heat treatment within the above range, crystallization progresses sufficiently and the mechanical strength of the electrolyte membrane improves. Further, the above temperature range is suitable from the viewpoint of maintaining a higher mechanical strength while appropriately maintaining the water content of the electrolyte membrane. The time for the heat treatment depends on the temperature of the heat treatment, but from the viewpoint of obtaining an electrolyte membrane with higher durability, it is preferably 5 minutes to 3 hours, more preferably 10 minutes to 2 hours. During this heat treatment, it is also possible to include a step in which the film is immersed in a water bath containing water or an organic solvent to remove foreign substances on the surface and unnecessary components in the film.

Hereinafter, the manufacturing method of this embodiment will be described with reference to FIG. 6 as appropriate, but FIG. 6 is only an example showing a part of the manufacturing method, and the manufacturing method of this embodiment is not limited thereby. do not have.

<Coating process>
In the coating step, the first proton conductive polymer solution 14 is continuously coated on the base sheet 13 that is being fed out. The area to be applied (that is, the length in the direction (TD) perpendicular to the flow direction (MD)) may be appropriately determined based on the length of the nanofiber sheet 11 in the short direction.
The method of applying the first proton conductive polymer solution to the base sheet is not particularly limited, but for example, in addition to slot die, gravure coater, bar coater, roll coater, doctor coater, PDN coater, blade coater, impregnation coater can be used. There are various methods such as These methods can be appropriately selected in consideration of the thickness of the coating liquid layer to be produced, the physical properties of materials such as the coating liquid, and coating conditions.

<Nanofiber sheet feeding process>
In parallel with the coating process, the nanofiber sheet 11 is fed out while being brought into contact with the non-mirrored roll 18 while applying tension. The roll that feeds out the nanofiber sheet 11 has a unit that detects and controls the tension of the nanofiber sheet 11, so that the tension can be controlled.

The tension for feeding out the nanofiber sheet is preferably such that the length of the nanofiber sheet in the short direction changes by -3.0% to 0.5%, and the tension changes by -3.0% to 0.0%. More preferably, the tension changes by -2.5% to 0.0%. By adjusting the tension within the above range, it is possible to suppress the occurrence of wrinkles in the polymer electrolyte membrane and to continuously produce a stable and homogeneous polymer electrolyte membrane.

Mirror rolls, which reflect light specularly like a mirror when irradiated with light, have strong nanofiber sheet adhesion and poor slipperiness, making it difficult to control the length in the short direction and prone to wrinkle defects. . On the other hand, non-specular rolls that diffusely reflect the reflected light when irradiated with light have good sliding properties with the nanofiber sheet, can easily control the rate of change in the length of the nanofiber sheet in the short direction, and are free from wrinkles. Defects can be suppressed. As non-mirror-finished rolls, satin-finished rolls that have been blasted and have a finely textured roll surface are suitably used. Mirror-finished rolls can also be coated with highly slippery PTFE or silicone resin tapes, or rolls laminated with these resins. It can be used suitably. The degree of fine irregularities on the roll surface is preferably in the range of 0.5 to 10.0 μm in arithmetic mean roughness (Ra), more preferably in the range of 0.6 to 5.0 μm, and in the range of 0.7 to 3.0 μm. The range is more preferred.

When Ra is 0.5 μm or more, the nanofiber sheet has good sliding properties, and the length in the short direction can be easily controlled to change by -3.0 to 0.5%. When Ra is 10.0 μm or less, local friction such as nanofiber fibers being caught in convex portions of fine irregularities is less likely to occur, and damage such as unraveling of nanofiber sheet fibers is reduced.

The arithmetic mean roughness (Ra) of the fine irregularities on the roll surface can be measured using an optical microscope type with a confocal optical system. For example, the OPTELICS S130 device manufactured by Lasertec Corporation is suitable. In addition, Ra of the non-specular roll described in the following examples was measured under the following conditions. After acquiring the unevenness data on the roll surface with an objective lens magnification of 20x and wavelength selection of 546 nm, select the processing range (line ROI button) so that the Z Image data has a processing range of approximately 100 μm in the direction parallel to the roll. , the arithmetic mean roughness (Ra) was determined in LM measurement mode. The Ra value of the example was measured at five arbitrary positions where the nanofiber sheet came into contact, and the average value thereof was adopted.

It is preferable to remove static electricity from the nanofiber sheet using an ionizer or the like during transport from when the nanofiber sheet is unrolled to when it is brought into contact with the first proton conductive polymer solution. This lowers the resistance of the roll that comes into contact with the nanofiber sheet, making it possible to remove foreign matter adhering to the surface of the nanofiber sheet.

<First treatment step>
In the first treatment step, after the nanofiber sheet 11 contacts the non-specular roll 18, the first surface 11A of the nanofiber sheet 11 contacts the first proton conductive polymer solution 14 applied to the base sheet 13. Thus, a first surface-treated nanofiber sheet is obtained.

It is preferable that the nanofiber sheet has a first end and a second end in the short direction, and at least one of the first end and the second end contacts the first proton conductive polymer solution. By bringing at least one of the first end and the second end into contact with the first proton conductive polymer solution, generation of wrinkles in the polymer electrolyte membrane can be suppressed. Only one of the first end and the second end may be in contact with the first proton conductive polymer solution, but both the first end and the second end may be in contact with the first proton conductive polymer solution. It is more preferable to be present.

<First drying step>
The first drying step is a step of drying the nanofiber sheet (first surface-treated nanofiber sheet) impregnated with the first proton conductive polymer solution to obtain a polymer electrolyte membrane. In the first drying step, it is preferable to gradually heat and dry the material from the entrance of the dryer 16. Note that "gradual heating" refers to heating at a temperature increase rate in the range of 2.5 to 150° C./min. The above drying is preferably carried out by heating at, for example, 50 to 350°C. The drying method is not particularly limited, but for example, a hot air oven and a heater oven are generally used. The winding speed (drying speed) by the winder 17 depends on the thickness of the coating liquid layer and the volatility of the solvent used, but is usually preferably about 10.0±5.0 m/min, and 5.0±2.5 m/min. /min is more preferable.

<Second treatment step>
In the second treatment step, the second surface 11B of the first surface-treated nanofiber sheet that has undergone the first drying step is continuously contacted (overcoated) with a second proton conductive polymer solution (not shown), Obtain a double-surface treated nanofiber sheet.

Preferably, the first and second ends of the first surface-treated nanofiber sheet contact the second proton-conducting polymer solution. By bringing the first and second ends into contact with the second proton-conducting polymer solution, exposure of the nanofiber sheet, which is easily charged and has low strength, can be eliminated, making it possible to stably process long rolled rolls. .
<Second drying process>
The second drying step is a step of drying both surface-treated nanofiber sheets to obtain a polymer electrolyte membrane. The second drying step can be carried out under the conditions described in the section <First Drying Step>.

<Nanofiber sheet>
The nanofiber sheet in this embodiment functions as a reinforcing material that strengthens the electrolyte membrane.

The porosity (%) of the nanofiber sheet before composite of the present embodiment is preferably 75% or more and 88% or less, more preferably 79% or more and 84% or less. In addition, the nanofiber sheet (nonwoven fabric) of this embodiment is different from the one before being composited with a proton-conducting polymer (fluoropolymer electrolyte), that is, the nanofiber sheet (nonwoven fabric) is composited with a fluoropolymer electrolyte and the proton-conducting polymer solution It is preferable that the film thickness shrinks within a range of 40% or more and 75% or less when the solvent evaporates. Furthermore, in the electrolyte membrane of this embodiment, the ratio of the thickness of the nanofiber sheet to the thickness of the electrolyte membrane is preferably 25% or more and less than 60%. As a result, the electrolyte has excellent embedding properties, that is, the ability to fill the voids of the nonwoven fabric with the fluoropolymer electrolyte, and has lower membrane resistance, higher proton conductivity, and even better suppression of dimensional changes in the planar direction. can be realized. When the porosity is 75% or more, poor embedding of the fluoropolymer electrolyte into the nonwoven fabric can be further suppressed. On the other hand, when the porosity is 88% or less, more preferably 86% or less, the self-supporting nature of the nanofiber sheet improves, making it easier to handle, and the reinforcing effect of the nonwoven fabric tends to be more sufficient. The porosity is derived from the following formula.
P=[1-Mn/(t×SG)]×100
Here, P is the porosity (%) of the nanofiber sheet, Mn is the basis weight (g/m ² ) of the nonwoven fabric, t is the thickness (μm) of the nonwoven fabric, and SG is the specific gravity (g/cm ³ ) respectively.

The basis weight of the nanofiber sheet before composite in this embodiment is preferably 1.5 g/m ² or more and 4.0 g/m ² or less, and preferably 2.0 g/m ² or more and 3.5 g/m ² or less. More preferably, it is 2.5 g/m ² or more and 3.1 g/m ² or less. When the basis weight is 1.5 g/m ² or more, the membrane is self-supporting, does not rupture during compounding, is easy to handle, and stabilizes the process. Furthermore, since the number of fibers per unit area is sufficient, swelling and contraction of the electrolyte membrane in the planar direction is suppressed. On the other hand, when the basis weight is 4.0 g/m ² or less, the polymer has excellent filling properties and proton conductivity, and it becomes possible to suppress swelling and shrinkage of the electrolyte membrane.

The basis weight of a nanofiber sheet is a value obtained by measuring the area and mass of the largest surface that can be collected, and converting it into mass per 1 m ² .
The thickness of the nonwoven fabric is derived as follows. That is, using a film thickness meter (for example, ABS Digimatic Indicator ID-F125 (product name) manufactured by Mitutoyo Co., Ltd.), measure the thickness at five arbitrary points within the same nanofaber sheet, and calculate the arithmetic average of the thickness. Let be the thickness of the nonwoven fabric.

It is preferable that the load required to deform the nanofiber sheet before composite in the present embodiment by 8% in the longitudinal direction is 0.2 N/10 mm or more. Hereinafter, the load when deforming by 8% in the longitudinal direction is also referred to as "8% deformation load." By having an 8% deformation load of 0.2 N/10 mm or more, it is possible to obtain a large-area polymer electrolyte with uniform properties without wrinkles without breaking when tension is applied to the nanofiber sheet. can. The 8% deformation load is more preferably 0.3 N/10 mm or more, still more preferably 0.4 N/10 mm or more. Although the upper limit of the 8% deformation load is not particularly limited, examples thereof include 0.6 N/10 mm, 0.8 N/10 mm, and the like. The 8% deformation load can be determined according to the method described in the Examples.

In this embodiment, the average fiber diameter of the nanofibers contained in the nanofiber sheet before composite is preferably 100 nm to 600 nm. As a result, even if the electrolyte membrane is thin (for example, 25 μm or less in thickness), the embeddability of the fluoropolymer electrolyte is better, and dimensional changes in the planar direction of the electrolyte membrane can be suppressed more effectively and reliably. I can do it. When comparing the fiber diameters of the fibers in the nanofiber sheet at the same basis weight, the smaller the fiber diameter, the smaller the pore diameter surrounded by the nanofiber fibers. Thereby, the closest distance between adjacent nanofibers in the polymer electrolyte membrane can be shortened, and a uniform dimensional change in the planar direction of the electrolyte membrane can be achieved in the fuel cell operating environment. When the fiber diameter is less than 100 nm, productivity decreases, costs increase and processing difficulty increases, and it tends to be difficult to ensure uniformity of nanofiber sheet fibers (dispersion in fiber diameter, basis weight, porosity). On the other hand, if the fiber diameter exceeds 600 nm, when composited with a proton-conducting polymer, the film thickness tends to be insufficiently contracted at the overlapped portion of the fibers, and the embeddability of the proton-conducting polymer, which is an electrolyte, tends to be insufficient. Due to the long distance between adjacent nanofibers in the polymer electrolyte membrane, it is difficult to achieve uniform dimensional changes in the plane of the electrolyte membrane in the fuel cell operating environment. Become. The average fiber diameter is more preferably 200 nm to 500 nm, and still more preferably 350 nm to 450 nm. The average fiber diameter can be determined according to the method described in the Examples.

The nanofiber sheet before composite in this embodiment preferably has 3 or less pinhole defects with a diameter of 1 mm or more and less than 2 mm in the width of the sheet in the short direction and the length in the long direction of 100 mm, and 0 It is more preferable that the number of In this specification, the term "pin-pole defect" includes areas where no fibers are present in the thickness direction of the nanofiber sheet, and areas where some fibers are bound and dissolved to form a thin film. This pinhole defect has higher transmittance than the normal part, and there is a difference in brightness from the outer periphery of the pinhole. When a tensile force is applied to a region containing a pinhole defect, membrane rupture tends to occur starting from the pinhole defect. By using nanofiber sheets that do not have pinhole defects, it is possible to composite the nanofiber sheets continuously without breaking them, allowing for large areas where the membrane dimensions change uniformly in the operating environment of the fuel cell. becomes a polymer electrolyte membrane. When a pinhole defect has an irregular shape, the diameter is defined as the longest range of the defect. A nanofiber sheet with few pinhole defects can be continuously composited without breaking when brought into contact with a proton-conducting polymer solution, even at a low basis weight of 1.5 g/ ^m2 , for example. This results in a large-area polymer electrolyte membrane whose dimensions change uniformly in the operating environment of the fuel cell. If the pinhole defect is 2 mm or more, the probability that the nanofiber sheet will break when the nanofiber sheet is brought into contact with a proton-conducting polymer solution increases. To detect pinhole defects, a light projector irradiates the nanofiber sheet with inspection light, and the light that passes through the sheet is received by a light receiver and converted into an electrical signal. This converted electrical signal is preferably processed by a dedicated detection circuit/judgment circuit such as a plurality of image processing filters and detected as a pinhole defect. Although it is difficult to determine the shape of pinhole defects smaller than 1 mm, it is possible to determine the distribution and frequency of pinhole defects by illuminating the back of the nanofiber sheet and visually observing it through the nanofiber sheet. You can get an overview of the

It is preferable that the nanofiber sheet before composite in this embodiment has a length of 50 m or more in the longitudinal direction. Note that the longitudinal direction corresponds to the direction (MD) in which the nanofiber sheet fed out when manufacturing the polymer electrolyte membrane flows. By having a length of 50 mm or more in the longitudinal direction, a large-area polymer electrolyte membrane without wrinkles and whose dimensions change uniformly in the fuel cell operating environment can be provided at low cost. The length in the longitudinal direction is more preferably 300 m or more, still more preferably 800 m or more.

It is preferable that the nanofiber sheet before composite in this embodiment has a length of 270 mm or more in the short direction. Note that the short direction corresponds to the direction (TD) perpendicular to the MD. By having a length of 270 mm or more in the short direction, it is possible to keep the tension constant when the nanofiber sheet is fed out when compounding the proton conductive polymer solution and the nanofiber sheet, and the in-plane tension of the nanofiber sheet can be maintained constant. It is possible to provide a large-area polymer electrolyte membrane at a low cost, which can disperse the stress of , and has no wrinkles and whose dimensions change uniformly. The length in the short direction is more preferably 270 mm to 1000 mm, still more preferably 600 mm to 1000 mm.

The nanofiber sheet in this embodiment includes, for example, polyolefin resins (e.g., polyethylene, polypropylene, and polymethylpentene), styrene resins (e.g., polystyrene), polyester resins (e.g., polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polycarbonate, polyarylate and fully aromatic polyester resins), acrylic resins (e.g. polyacrylonitrile, polymethacrylic acid, polyacrylic acid and polymethyl methacrylate), polyamide resins (e.g. nylon 6) , 66 nylon and aromatic polyamide resins), polyether resins (e.g. polyether ether ketone, polyacetal, polyphenylene ether, modified polyphenylene ether and aromatic polyether ketone), urethane resins, chlorine resins (e.g. polyvinyl chloride) and polyvinylidene chloride), fluorine resins (e.g. polytetrafluoroethylene and polyvinylidene fluoride (PVDF)), polyphenylene sulfide (PPS), polyamideimide resins, polyimide resins (PI), polyetherimide resins, aromatic Group polyetheramide resins, polysulfone resins (e.g. polysulfone and polyethersulfone (PES)), polyazole resins (e.g. polybenzimidazole (PBI), polybenzoxazole, polybenzothiazole and polypyrrole), cellulose resins, and Contains one or more selected from the group consisting of polyvinyl alcohol resins.

Among them, nanofiber sheets containing one or more selected from the group consisting of polyethersulfone (PES), polybenzimidazole (PBI), polyimide (PI), and polyphenylene sulfide (PPS) are easy to form into nanofibers. It has excellent chemical resistance and heat resistance, and is preferred for its high strength even at a low basis weight. From the same viewpoint, nanofiber sheets containing one or more selected from the group consisting of PES, PBI, and PI are particularly preferred. Such a nanofiber sheet has excellent chemical resistance and heat resistance, and is more stable when composited with a proton-conducting polymer.

Such a nanofiber sheet can be manufactured by, for example, an electrospinning method, a melt blow method, a spunbond method, or the like. Among these, the electrospinning method can prepare nanofiber sheets with an average fiber diameter of 1 μm or less, which has high uniformity of fiber diameter, consists of substantially continuous fibers, and has a porosity of more than 70%. It is also possible to continuously produce wide nanofibers with a large diameter of over 1000 mm, so it is suitably used. Examples of mass-production equipment for manufacturing nanofiber sheets include NS8S1600U (model name, wire electrode method) of "Nanospider" (trade name) manufactured by Elmarco Co., Ltd., and EDEN (NF-1001S) (model name, wire electrode method) manufactured by MEC Co., Ltd. Product name: Nozzle discharge electrode method), Esplayer mass production machine manufactured by Fuence Co., Ltd. (nozzle discharge electrode method) can be suitably used. PPS nanofibers to which electrospinning is difficult to apply can be processed, for example, with reference to JP-A-2013-79486.

The fibers of the nanofiber sheet produced by the electrospinning method are produced to the desired nanofiber fiber diameter by a combination of multiple conditions such as the applied voltage of the above device, the distance between the electrodes, temperature, humidity, the solvent type of the spinning solution, and the concentration of the spinning solution. Can be processed.

It is preferable that the nanofiber sheet of this embodiment is subjected to heat treatment before being composited. Examples of the heat treatment method include heating by hot air drying using an infrared heater or an oven. According to this heat treatment method, while maintaining the high porosity of the nanofiber sheet, it is possible to partially fuse the fibers at points where they are in moderate contact with each other, thereby further suppressing fuzz on the surface of the nonwoven fabric and increasing the sheet strength. Enables further improvement.

<Proton conductive polymer>
The proton conductive polymer in this embodiment is a polyelectrolyte. The proton-conducting polymer is not particularly limited, but includes, for example, a perfluorocarbon polymer compound having an ion exchange group, and a hydrocarbon polymer compound having an aromatic ring in the molecule into which an ion exchange group is introduced. These may be used alone or in combination of two or more. Among these, perfluorocarbon polymer compounds having ion exchange groups are preferred from the viewpoint of superior chemical stability.

The ion exchange capacity of the proton conductive polymer is preferably 0.5 meq/g or more and 3.0 meq/g or less, and preferably 0.65 meq/g or more and 2.0 meq/g or less. More preferably, it is 0.8 meq/g or more and 1.5 meq/g or less. When the ion exchange equivalent is 3.0 milliequivalents/g or less, when used as an electrolyte membrane, swelling of the electrolyte membrane under high temperature and high humidity during fuel cell operation tends to be further reduced. By reducing swelling in this way, problems such as a decrease in the strength of the electrolyte membrane, wrinkles and peeling from the electrode, and problems such as a decrease in gas barrier properties tend to be reduced. . Furthermore, when the ion exchange capacity is 0.5 meq/g or more, the power generation capacity of a fuel cell equipped with the obtained electrolyte membrane tends to be further improved.

Ion exchange capacity can be determined by the following method. That is, an electrolyte membrane (approximately 2 cm ² or more and 20 cm ² or less in sheet area) in which the counter ions of the ion exchange groups are in the state of protons is immersed in 30 mL of a saturated NaCl aqueous solution at 25°C and left for 30 minutes while stirring. . Next, protons in the saturated NaCl aqueous solution are neutralized and titrated using a 0.01N aqueous sodium hydroxide solution using phenolphthalein as an indicator. The electrolyte membrane obtained after neutralization, in which the counter ions of the ion exchange groups are sodium ions, is rinsed with pure water, dried in vacuum, and weighed. The amount of sodium hydroxide required for neutralization is M (mmol), the weight of the electrolyte membrane in which the counter ion of the ion exchange group is sodium ion is W (mg), and the equivalent weight EW (g) is calculated using the following formula (C). /eq).
EW=(W/M)-22 (C)
Furthermore, the ion exchange capacity (milliequivalents/g) is calculated by taking the reciprocal of the obtained EW value and multiplying it by 1000 times.

Ion exchange groups include, but are not particularly limited to, sulfonic acid groups, sulfonimide groups, sulfonamide groups, carboxylic acid groups, and phosphoric acid groups, with sulfonic acid groups being preferred. One type of ion exchange group may be used alone or two or more types may be used in combination.

Hydrocarbon polymer compounds having an aromatic ring in the molecule are not particularly limited, but include, for example, polyphenylene sulfide, polyphenylene ether, polysulfone, polyether sulfone, polyether ether sulfone, polyether ketone, polyether ether ketone, and polyether sulfone. Thioetherethersulfone, polythioetherketone, polythioetheretherketone, polybenzimidazole, polybenzoxazole, polyoxadiazole, polybenzoxazinone, polyxylylene, polyphenylene, polythiophene, polypyrrole, polyaniline, polyacene, polycyanogen, polynaphthyridine, polyphenylene sulfide Examples include sulfone, polyphenylene sulfone, polyimide, polyetherimide, polyesterimide, polyamideimide, polyarylate, aromatic polyamide, polystyrene, polyester, and polycarbonate. These may be used alone or in combination of two or more.

In addition, perfluorocarbon polymer compounds having ion exchange groups that have even better chemical stability include, but are not particularly limited to, perfluorocarbon sulfonic acid resins, perfluorocarbon carboxylic acid resins, perfluorocarbon sulfonimide resins, perfluorocarbon sulfones, etc. Examples include amide resins, perfluorocarbon phosphate resins, and amine salts and metal salts of these resins. These may be used alone or in combination of two or more.

The perfluorocarbon polymer compound is not particularly limited, but more specifically, a polymer represented by the following formula [1] may be mentioned.
_- [CF ₂ CX ¹ X ² _{] a -} [ ^CF ₂ -CF(-O-(CF _{2 -CF (} ^{CF 2} CF ₂ ) _f −X ⁴ )] _g − [1]
Here, in the formula, X ¹ , X ² and X ³ each independently represent a halogen atom or a perfluoroalkyl group having 1 to 3 carbon atoms. a and g satisfy 0≦a<1, 0<g≦1, and a+g=1. b is an integer from 0 to 8. c is 0 or 1. d and e are integers of 0 or more and 6 or less, independently of each other. f is an integer from 0 to 10. However, d+e+f is not equal to 0. R ¹ and R ² each independently represent a halogen atom, a perfluoroalkyl group having 1 to 10 carbon atoms, or a fluorochloroalkyl group. X ⁴ represents COOZ, SO ₃ Z, PO ₃ Z ₂ or PO ₃ HZ. Here, Z is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or an amine (NH ₄ , NH ₃ R ³ , NH ₂ R ³ R ⁴ , NHR ³ R ⁴ R ⁵ , or NR ³ R ⁴ R ⁵ R ⁶ ). Further, R ³ , R ⁴ , R ⁵ and R ⁶ each independently represent an alkyl group or an arene group.

Among these, perfluorocarbon sulfonic acid resins represented by the following formula [2] or formula [3] or metal salts thereof are preferred.
-[CF ₂ CF ₂ ] _a - [CF ₂ -CF(-O-(CF ₂ -CF(CF ₃ )) _b -O-(CF ₂ ) _c -SO ₃ X)] _d - [2]
Here, in the formula, a and d satisfy 0≦a<1, 0≦d<1, and a+d=1. b is an integer from 1 to 8. c is an integer from 0 to 10. X represents a hydrogen atom or an alkali metal atom.
-[CF ₂ CF ₂ ] _e - [CF ₂ -CF(-O-(CF ₂ ) _f -SO ₃ Y)] _g - [3]
Here, in the formula, e and g satisfy 0≦e<1, 0≦g<1, and e+g=1. f is an integer from 0 to 10. Y represents a hydrogen atom or an alkali metal atom.

Among the above perfluorocarbon polymer compounds, the perfluorocarbon polymer compound represented by the above formula [3] is preferable because it has even better heat resistance and can further increase the amount of ion exchange groups introduced.

The perfluorocarbon polymer compound having an ion exchange group that can be used in this embodiment is not particularly limited, but for example, after polymerizing a precursor polymer represented by the following formula [4], alkaline hydrolysis, acid treatment, etc. can be manufactured by
_- [CF ₂ CX ¹ X ² _{] a -} [ ^CF ₂ -CF(-O-(CF _{2 -CF (} ^{CF 2} CF ₂ ) _f −X ⁵ )] _g − [4]
Here, in the formula, X ¹ , X ² and X ³ each independently represent a halogen atom or a perfluoroalkyl group having 1 to 3 carbon atoms. a and g satisfy 0≦a<1, 0<g≦1, and a+g=1. b is an integer from 0 to 8. c is 0 or 1. d and e are integers of 0 or more and 6 or less, independently of each other. f is an integer from 0 to 10. However, d+e+f is not equal to 0. R ¹ and R ² each independently represent a halogen atom, a perfluoroalkyl group having 1 to 10 carbon atoms, or a fluorochloroalkyl group. X ⁵ represents COOR ⁷ , COR ⁸ or SO ₂ R ⁸ . Here, R ⁷ represents an alkyl group having 1 to 3 carbon atoms. R ⁸ represents a halogen element.

The precursor polymer is not particularly limited, but can be produced, for example, by copolymerizing a fluorinated olefin compound and a fluorinated vinyl compound.

Here, the fluorinated olefin compound is not particularly limited, but includes, for example, a compound represented by the following formula [5].
CF ₂ =CFZ [5]
Here, in the formula, Z represents a hydrogen atom, a chlorine atom, a fluorine atom, a perfluoroalkyl group having 1 to 3 carbon atoms, or a cyclic perfluoroalkyl group which may contain oxygen.

Further, the vinyl fluoride compound is not particularly limited, but examples thereof include the compounds shown below.
CF ₂ =CFO(CF ₂ ) _z −SO ₂ F,
CF ₂ =CFOCF ₂ CF(CF ₃ )O(CF ₂ ) _z −SO ₂ F,
CF ₂ =CF(CF ₂ ) _z -SO ₂ F,
CF ₂ = CF (OCF ₂ CF (CF ₃ )) _z - (CF ₂ ) _z - SO ₂ F,
CF ₂ =CFO(CF ₂ ) _z -CO ₂ R,
CF ₂ =CFOCF ₂ CF(CF ₃ )O(CF ₂ ) _z −CO ₂ R,
CF ₂ =CF(CF ₂ ) _z -CO ₂ R,
CF ₂ =CF(OCF ₂ CF(CF ₃ )) _z −(CF ₂ ) ₂ −CO ₂ R
Here, in the formula, Z is an integer of 1 to 8, and R represents an alkyl group having 1 to 3 carbon atoms.

<Proton conductive polymer solution>
The first proton conductive polymer solution and the second proton conductive polymer solution may be the same or different. Hereinafter, these will be collectively referred to as a proton-conducting polymer solution, and this will be specifically explained.

The proton conductive polymer solution contains the above proton conductive polymer, a solvent, and other additives as necessary. This proton conductive polymer solution is used as it is, or after passing through steps such as filtration or concentration, to be combined with a nanofiber sheet. Alternatively, this solution can be used alone or mixed with other electrolyte solutions.

Next, a method for producing a proton-conducting polymer solution will be explained in more detail. The method for producing this proton-conducting polymer solution is not particularly limited. For example, after obtaining a solution in which a proton-conducting polymer is dissolved or dispersed in a solvent, additives are dispersed in the solution as necessary. Alternatively, first, the proton conductive polymer and the additive are mixed by melt-extruding the proton conductive polymer, stretching or the like, and the mixture is dissolved or dispersed in a solvent. A proton-conducting polymer solution is thus obtained.

More specifically, first, a molded article made of a precursor polymer of a proton conductive polymer is immersed in a basic reaction liquid and hydrolyzed. Through this hydrolysis treatment, the precursor polymer of the proton conductive polymer is converted into a proton conductive polymer. Next, the hydrolyzed molded product is sufficiently washed with warm water, and then the molded product is subjected to an acid treatment. The acid used in the acid treatment is not particularly limited, but mineral acids such as hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as oxalic acid, acetic acid, formic acid, and trifluoroacetic acid are preferable. By this acid treatment, the precursor polymer of the proton-conducting polymer is protonated and a proton-conducting polymer, such as a perfluorocarbon sulfonic acid resin, is obtained.

The molded article (molded article containing the proton conductive polymer) that has been acid-treated as described above can be dissolved or suspended in a solvent that can dissolve or suspend the proton conductive polymer (a solvent that has good affinity with the polymer). suspended. Examples of such solvents include water, protic organic solvents such as ethanol, methanol, n-propanol, isopropyl alcohol, butanol, and glycerin, N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl Examples include aprotic organic solvents such as pyrrolidone. These may be used alone or in combination of two or more. In particular, when one type of solvent is used, it is preferable that the solvent is water. Moreover, when using two or more types in combination, a mixed solvent of water and a protic organic solvent is preferable.

The method of dissolving or dispersing (suspending) the proton conductive polymer in a solvent is not particularly limited. For example, the proton conductive polymer may be directly dissolved or dispersed in the above solvent. However, it is preferable to dissolve or disperse the proton conductive polymer in a solvent at a temperature range of 0 to 250° C. under atmospheric pressure or under sealed and pressurized conditions such as in an autoclave. In particular, when using water and a protic organic solvent as a solvent, the mixing ratio of water and protic organic solvent is determined by the dissolution method, dissolution conditions, type of proton conductive polymer, total solid concentration, dissolution temperature, stirring speed, etc. It can be selected as appropriate. However, the mass ratio of the protic organic solvent to water is preferably 0.1 to 10 of the protic organic solvent to 1 of water, more preferably 0.1 to 5 of the protic organic solvent to 1 of water. It is.

Note that the proton conductive polymer solution may contain one or more of emulsions, suspensions, colloidal liquids, and micellar liquids. Here, an emulsion has a milky state in which liquid particles are dispersed in a liquid as colloidal particles or coarser particles. Further, a suspension is a liquid in which solid particles are dispersed as colloidal particles or microscopic particles. Further, a colloidal liquid is a state in which macromolecules are dispersed, and a micellar liquid is a lyophilic colloid dispersion system formed by a large number of small molecules associating with each other due to intermolecular forces.

Furthermore, depending on the method of forming the electrolyte membrane and the intended use, the proton-conducting polymer solution can be concentrated or filtered. The concentration method is not particularly limited, but examples include a method of heating the proton conductive polymer solution to evaporate the solvent, and a method of concentration under reduced pressure. When using a proton conductive polymer solution as a coating solution, the solid content of the proton conductive polymer solution should be 0. The content is preferably .5% by mass or more and 50% by mass or less.

The method of filtering the proton-conducting polymer solution is not particularly limited, but a representative example is a method of filtering under pressure using a filter. It is preferable to use a filter medium in which the 90% collection particle size is 10 to 100 times the average particle size of the solid particles contained in the proton-conducting polymer solution. Examples of the material of this filter medium include paper and metal. In particular, when the filter medium is paper, it is preferable that the 90% collection particle size is 10 to 50 times the average particle size of the solid particles. When using a metal filter, it is preferable that the 90% collection particle size is 50 to 100 times the average particle size of the solid particles. Setting the 90% collection particle size to 10 times or more the average particle size prevents the pressure required when pumping liquid from becoming too high and prevents the filter from clogging in a short period of time. It is effective in suppressing. On the other hand, it is preferable to set the 90% collection particle size to 100 times or less the average particle size from the viewpoint of effectively removing particle aggregates and undissolved resin particles that may cause foreign substances in the film.

<Polymer electrolyte membrane>
The polymer electrolyte membrane of this embodiment has a sheet shape in which a nanofiber sheet and a proton conductive polymer are combined. The composite sheet is formed by the proton-conducting polymer entering the voids of the nanofiber sheet.

In the polymer electrolyte membrane of this embodiment, the nanofiber sheet has a first end and a second end in the short direction, and at least one of the first end and the second end is complexed with a proton conductive polymer. It is preferable that Note that the term "the ends of the nanofiber sheet are composited with the proton-conducting polymer" means that the proton-conducting polymer has penetrated into the voids at the ends of the nanofiber sheet. Since at least one of the first end and the second end is composited with a proton conductive polymer, it is possible to obtain a polymer electrolyte membrane that is free from wrinkle defects and whose dimensions change uniformly. The nanofiber sheet maintains a high porosity through appropriate heat treatment, and the fibers are slightly bonded. Most of the fibers come into contact with each other while intertwining, creating a large amount of frictional resistance that makes the nanofiber sheet self-supporting. When this nanofiber sheet comes into contact with a proton-conducting polymer solution, the solvent in the solution wets the nanofiber fiber surface and greatly reduces the friction between the fibers, expanding the sheet area as if it were swollen. . At this time, if both ends of the first end and the second end are not composited with the proton conductive polymer, wrinkles are generated in the longitudinal direction (MD) in the polymer electrolyte. Wrinkles are nanofiber sheets composited with a proton-conducting polymer in a folded or curved form, with a thickness difference of 4 μm or more from the normal film thickness, and extending over 100 mm in length in the longitudinal direction. Refers to existing defects. This wrinkle defect can be roughly classified into two types. One type of defect is a "fold wrinkle" defect in which the nanofiber is greatly curved or bent, as shown in FIG. 7, and has a length of 100 mm or more in the longitudinal direction. The second type is, for example, wrinkles, which are not as severe as the "fold wrinkle" defect, but which cause periodic curvature in the short direction at intervals of 2 mm to 6 mm in the polymer electrolyte membrane, making the electrolyte thickness layer non-uniform. This is called "equal pitch wrinkles." Wrinkle defects can be created by compositing only one of the first and second ends with a proton-conducting polymer (for example, see Figure 2) and applying appropriate tension in the longitudinal direction of the nanofiber sheet. This can be suppressed by changing the length in the short direction from -3% to 0.5%. The first and second ends of the nanofiber sheet are both composited with a proton-conducting polymer, so a stable tension balance can be maintained on the nanofiber sheet surface, and the nanofiber sheet is not exposed. This is more preferable for obtaining a homogeneous large-area polymer electrolyte membrane since the nanofiber sheet does not break during handling (see, for example, FIG. 1).

The polymer electrolyte membrane of this embodiment preferably has a length of 50 m or more, more preferably 300 m or more, and even more preferably 800 m or more in the longitudinal direction.

The nanofiber sheet included in the polymer electrolyte membrane of this embodiment preferably has a length of 270 mm or more in the short direction, more preferably a length of 270 mm to 1000 mm, and a length of 600 mm to 1000 mm. It is more preferable to have the following.

The length of the nanofiber sheet included in the polymer electrolyte membrane of this embodiment in the short direction is -3.0% based on the length of the nanofiber sheet in the short direction before being composited with the proton conductive polymer. Preferably, the change is 0.5%. Hereinafter, the rate of change in the length in the short direction based on the length in the short direction before compounding is also referred to as "compounding change rate." By having a compounding change rate of -3.0% or more, it is possible to obtain a homogeneous large-area polymer electrolyte membrane without uniform pitch wrinkle defects when compounding a proton-conducting polymer solution and a nanofiber sheet. I can do it. When the composite change rate is 0.5% or less, it is possible to obtain a homogeneous large-area polymer electrolyte membrane without folding and wrinkle defects. The compounding change rate is more preferably -3.0% to 0.0%, still more preferably -2.5% to 0.0%. The rate of compound change can be determined according to the method described in the Examples.

In the nanofiber sheet included in the polymer electrolyte membrane of this embodiment, the closest distance between adjacent nanofibers is preferably 0 μm to 3 μm. In this specification, "the closest distance between adjacent nanofibers" is measured using a cross-sectional SEM image of the polymer electrolyte membrane at a magnification of 3000 to 5000 times in the film thickness direction. Using contrast differences in cross-sectional SEM images, the distance between any given nanofiber and another nanofiber located closest to it is measured. By having a closest distance of 0 μm or more and 3 μm or less, a large-area polymer with no wrinkle defects, whose dimensions change uniformly in the fuel cell operating environment (e.g., 120°C, 100% RH), and whose power generation performance is homogeneous. An electrolyte membrane can be obtained. The closest distance is more preferably 0 μm to 2 μm.

The polymer electrolyte membrane of this embodiment preferably changes uniformly in the short direction when exposed to an environment of 120° C. and 100% relative humidity (RH) for 2 hours. Specifically, we measured the length of multiple points in the short direction from one end to the other end before and after exposure to the above environment, and measured the length of the point where the change in length was the largest. It is preferable that the difference obtained by subtracting the change rate at the smallest point from the change rate is small. As an example, if there is a 10% change in the short direction from 20 mm to 22 mm at the point where the change in length is the largest, and a 5% change from 20 mm to 21 mm in the short direction at the point where the change in length is the smallest, then the difference is 5%. Hereinafter, the difference in the rate of change described above will also be referred to as a "difference in rate of change in the short direction." The difference in change rate in the short direction is preferably 0% to 4%, more preferably 0% to 3%, and still more preferably 0% to 2%. The difference in rate of change in the short direction can be determined according to the method described in Examples.

Hereinafter, the present invention will be explained in more detail using Examples and Comparative Examples. The present invention is not limited in any way by the following examples.

<Composite change rate>
The rate of change in the length of the nanofiber sheet (after composite) included in the polymer electrolyte membrane in the short direction was measured as follows, based on the length of the nanofiber sheet before composite in the short direction.
The length A of the nanofiber sheet in the short direction before being composited was measured using a 1000 mm steel gauge according to the JIS Class 1 standard. The length B in the short direction of the nanofiber sheet after composite was measured in the same manner, and the composite change rate was calculated by B/A x 100-100.

<8% deformation load>
The load when the nanofiber sheet before composite was deformed by 8% in the longitudinal direction was measured as follows.
Five points were sampled at approximately equal intervals across the width of the nanofiber sheet in the short direction. The sample was cut into a size of 70 mm in the longitudinal direction (MD) and 10 mm in the transverse direction (TD). The five cut samples were subjected to a tensile test in the MD direction in accordance with JIS K-7127, and the arithmetic mean load value at 8% elongation at the five points obtained was taken as the 8% deformation load. The measurement was carried out using a tensile tester equipped with a 50N load cell (manufactured by A&D, product name: ``Tensilon Universal Material Tester RTG-1210''). The distance between the chucks was 50 mm, the crosshead speed was 300 mm/min, and the testing was carried out in an environment of 24° C. and 45% relative humidity.

<Average fiber diameter of nanofibers>
The average fiber diameter of the nanofibers contained in the nanofiber sheet before composite was measured as follows.
The arithmetic mean value of the fiber diameters of 50 fibers was used as the average fiber diameter of the fibers in the nonwoven fabric. Here, the "fiber diameter" refers to the length in the direction perpendicular to the length direction of the fiber, as measured based on an electron micrograph of the fiber taken at a magnification of 5000 times. In addition, if the fiber diameter is too small to be measured, it can be measured based on an electron micrograph at a magnification higher than 5000 times. In addition, when the cross-sectional shape of the fiber was non-circular, the diameter of a circle having the same area as the cross-sectional area was regarded as the fiber diameter.

<Wrinkles on polymer electrolyte membrane>
The presence or absence of wrinkles in the polymer electrolyte membrane was determined based on the following criteria.
If there is a film thickness difference of 4 μm or more with respect to the normal part of the polymer electrolyte membrane and there is a defect extending in the longitudinal direction with a length of 100 mm or more, it is considered to be wrinkled. Wrinkles were determined by visually observing the polymer electrolyte membrane through illumination, extracting areas with contrast differences and differences in color, and measuring the thickness and length. The thickness was measured using a contact type film thickness meter (manufactured by Mitutoyo, product name: "ABS Digimatic Indicator ID-F125"). The length was measured using a 1000 mm steel ruler according to the JIS Class 1 standard.
To determine wrinkles with subtle differences in thickness (uniform pitch wrinkles), cut a cross section of the polymer electrolyte membrane in the film thickness direction with a microtome, magnify it with a measuring microscope (manufactured by OLYMPUS, model "STM6"), and measure the length. Good too.

<Long length stable processability>
Whether or not a polymer electrolyte membrane with a length of 50 m or more could be stably processed was determined based on the following criteria.
○: When the nanofiber sheet could be composited with the proton conductive polymer for 50 m or more without breaking in the first treatment step.
×: When the nanofiber sheet was broken at less than 50 m in the first treatment step.

<Difference in change rate in short direction>
The difference between the maximum rate of change and the minimum rate of change in length in the short direction at multiple locations from one end to the other end in the short direction of the polymer electrolyte membrane was measured as follows.
Five points were sampled at approximately equal intervals with respect to the width of the polymer electrolyte membrane in the short direction. The sample was cut into a size of 30 mm in the longitudinal direction (MD) and 40 mm in the transverse direction (TD). Draw a rectangular frame of approximately 15 mm x 20 mm (MD: 15 mm, TD: 20 mm) in the center of the five cut out polymer electrolyte membranes using a lab marker (2017 AS ONE catalog product number 2-5674-02). The length of the TD at 20° C. and 65% RH was measured using a measuring microscope (manufactured by OLYMPUS, model “STM6”). Next, the electrolyte membrane was placed in a highly accelerated life tester (manufactured by HAST, model "EHS-211") and exposed to an environment of 120°C and 100% RH for 2 hours, and then maintained in a hydrated state. The length of the TD was promptly measured. The rate of change in the TD dimension on two sides of one polymer electrolyte membrane before and after the accelerated test in the highly accelerated life test device is calculated, and the average value is used as the rate of change in the dimension in the short direction TD at each position. did. The difference obtained by subtracting the change rate at the smallest point from the change rate at the largest point among the five samples was defined as the difference in change rate in the short direction.

[Example 1]
<Manufacture of polymer electrolyte membrane>
First, a precursor polymer of a perfluorosulfonic acid resin obtained from tetrafluoroethylene and CF ₂ =CFO (CF ₂ ) ₂ -SO ₂ F (after hydrolysis and acid treatment), which is a precursor polymer of a proton-conducting polymer, is used. Ion exchange capacity: 1.4 meq/g) A pellet was prepared. Next, the precursor pellets were brought into contact with an aqueous solution containing potassium hydroxide (15% by mass) and methyl alcohol (50% by mass) at 80° C. for 20 hours to perform a hydrolysis treatment. Thereafter, the pellets were immersed in water at 60°C for 5 hours. Next, the pellets that had been immersed in water were immersed in a 2N aqueous hydrochloric acid solution at 60°C for 1 hour, and the process was repeated five times, replacing the aqueous hydrochloric acid solution with a new one each time. Then, the pellets that had been repeatedly immersed in an aqueous hydrochloric acid solution were washed with ion-exchanged water and dried. As a result, a perfluorocarbon sulfonic acid resin (-[CF ₂ CF ₂ ]-[CF ₂ -CF(-O-(CF ₂ ) ₂ -SO ₃ H)]-; PFSA), which is a proton-conducting polymer, was obtained. .

The pellets were placed in a 5L autoclave with an aqueous ethanol solution (water:ethanol = 50.0/50.0 (mass ratio)), sealed, and heated to 160°C while stirring with a stirring blade. It was held for 5 hours. Thereafter, the inside of the autoclave was naturally cooled to obtain a uniform perfluorocarbon sulfonic acid resin solution with a solid content concentration of 5% by mass. After concentrating this under reduced pressure at 80° C., it was diluted with water and ethanol to prepare a solution of ethanol:water=60:40 (mass ratio) with a solid content of 15.0% by mass.

First, a polyimide film (manufactured by DuPont-Toray, trade name "Kapton 300H") was run, and the ends of the long nanofiber sheets described in Example 1 in Table 1 were attached to the polyimide film with tape at a line speed of 1 m. /min to feed paper. Next, the line speed was set to 5 m/min, and the solution 1 was continuously coated onto the polyimide film with a coating width of 615 mm using a slit die coater at a discharge pressure of 0.17 MPa. The nanofiber sheet described in Example 1 in Table 1 was rolled out under a tension of 15 N, and a mirror-finished roll was coated with Nitoflon No. manufactured by Nitto Denko Corporation. After contacting a non-mirrored roll with arithmetic surface roughness (Ra) of 0.8 μm to which 903UL tape was attached, the nanofiber sheet was placed so that both ends in the short direction were impregnated with solution 1, and heated at 60°C, 100°C, It was transported to a five-zone drying oven set at 120°C, 140°C, and 140°C, dried, and then wound up. The composite rate of change in this first treatment step was -1.0%. Next, Solution 1 was again applied onto the dried film in the same manner as above, and it was continuously dried in a drying oven. The membrane thus obtained was annealed at 160° C. for 20 minutes to obtain a polymer electrolyte membrane with a thickness of 15 μm. The obtained polymer electrolyte membrane was evaluated for the presence or absence of wrinkles in the electrolyte membrane, the difference in rate of change in the short direction, and stable processability in long lengths of 50 m or more. The results are shown in Table 1.

[Example 2]
A polymer electrolyte membrane with a thickness of 15 μm was prepared and evaluated in the same manner as in Example 1, except that the tension for feeding out the nanofiber sheet was changed to 13N. The results are shown in Table 1.

[Example 3]
The same procedure as in Example 1 was carried out, except that the nanofiber sheet was placed so as to protrude by 5 mm from the end of the 615 mm coating width of solution 1 so that only one end of the nanofiber sheet in the short direction was impregnated with solution 1. A polymer electrolyte membrane with a thickness of 15 μm was prepared using the method and evaluated. The results are shown in Table 1.

[Example 4]
Using the nanofiber sheet described in Example 4 in Table 1, a polymer electrolyte membrane with a thickness of 15 μm was produced in the same manner as in Example 1, except that the feeding tension of the nanofiber sheet was changed to 14N. , conducted an evaluation. The results are shown in Table 1.

[Example 5]
Using the nanofiber sheet described in Example 5 in Table 1, a polymer electrolyte membrane with a thickness of 15 μm was produced in the same manner as in Example 1, except that the feeding tension of the nanofiber sheet was changed to 18N. , conducted an evaluation. The results are shown in Table 1.

[Example 6]
Using the nanofiber sheet described in Example 6 in Table 1, the thickness was A 15 μm polymer electrolyte membrane was prepared, and the portion where the nanofiber sheet was present was evaluated. The results are shown in Table 1.

[Comparative example 1]
In order to prevent both ends of the nanofiber sheet in the short direction from being impregnated with solution 1, the coating width of solution 1 was set to 590 mm, and the nanofiber sheet was placed so as to protrude by 5 mm from both ends of the coated part. A polymer electrolyte membrane having a thickness of 15 μm was prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[Comparative example 2]
A polymer electrolyte membrane with a thickness of 15 μm was produced and evaluated in the same manner as in Example 1, except that the tension for feeding out the nanofiber sheet was changed to 45 N. The results are shown in Table 1.

[Comparative example 3]
A polymer electrolyte membrane with a thickness of 15 μm was prepared and evaluated in the same manner as in Example 1, except that the tension for feeding out the nanofiber sheet was changed to 5N. The results are shown in Table 1.

[Comparative example 4]
Using the nanofiber sheet described in Comparative Example 4 in Table 1, a polymer electrolyte membrane with a thickness of 15 μm was prepared in the same manner as in Example 1, except that the feeding tension was 7 N and the coating width was 415 mm. It was manufactured and evaluated. The results are shown in Table 1. Stable long processing was not possible because the nanofibers were broken.

[Comparative example 5]
A polymer electrolyte membrane with a thickness of 15 μm was produced and evaluated in the same manner as in Example 1, except that the nanofiber sheet described in Comparative Example 5 in Table 1 was used. The results are shown in Table 1.
[Comparative example 6]
A polymer electrolyte membrane with a thickness of 15 μm was produced in the same manner as in Example 1, except that a mirror roll with an arithmetic surface roughness (Ra) of 0.07 μm was used instead of the non-mirror roll in the first treatment step. , conducted an evaluation. The results are shown in Table 1.

FIG. 4 shows the tensile test results (8% deformation load) of the nanofaber sheets used in Examples and Comparative Examples.

1, 11... Nanofiber sheet 1A... First end 1B... Second end 2... Proton conductive polymer 3, 13... Base sheet 11A... First surface 11B... Second surface 14... First proton conductive polymer solution 15 ...Slit die 16...Dryer 17...Winder 18...Non-mirror roll

Claims (7)

A method for continuously manufacturing a polymer electrolyte membrane, the method comprising:
A step of unwinding the base sheet,
a coating step of continuously coating the first proton conductive polymer solution on the base sheet;
A process of applying tension to the nanofiber sheet while bringing it into contact with a non-mirrored roll,
A first treatment step of continuously bringing the first surface of the nanofiber sheet into contact with the applied first proton-conducting polymer solution to obtain a first surface-treated nanofiber sheet;
a first drying step of drying the first surface-treated nanofiber sheet;
including;
The average fiber diameter of the nanofibers contained in the nanofiber sheet is 100 nm to 600 nm,
The load required to deform the nanofiber sheet by 8% in the longitudinal direction is 0.2 N/10 mm or more,
The tension for feeding out the nanofiber sheet is such that the length of the nanofiber sheet in the short direction changes by -3.0% to 0.5%,
The nanofiber sheet has a first end and a second end in the short direction, and in the first treatment step, at least one of the first end and the second end is brought into contact with the first proton conductive polymer solution. Said method. The method according to claim 1, wherein the length of the nanofiber sheet in the short direction is 270 mm or more. 3. The method of claim 1 or 2, wherein the first end and the second end of the nanofiber sheet are contacted with the first proton-conducting polymer solution. A method according to any one of claims 1 to 3, wherein the nanofiber sheet comprises polyethersulfone. The method according to any one of claims 1 to 4, wherein the nanofiber sheet has a basis weight of 1.5 to 4.0 g/m ² . The method according to any one of claims 1 to 5, wherein the nanofiber sheet has a porosity of 75% to 88%. A second treatment step of continuously bringing a second proton conductive polymer solution into contact with the second surface of the first surface-treated nanofiber sheet that has undergone the first drying step to obtain a double-surface-treated nanofiber sheet;
a second drying step of drying the both surface-treated nanofiber sheets;
The method according to any one of claims 1 to 6, further comprising: