Wet nonwoven fabric, electrolyte-reinforced membrane, and method for producing wet nonwoven fabric

Abstract

Provided is a wet nonwoven fabric having a thin thickness, high strength and air permeability, and high pore diameter uniformity. The wet nonwoven fabric contains stretched polyarylene sulfide fibers having an average fiber diameter of 0.3 [mu] m or more and 3.0 [mu] m or less, has an average pore diameter of 0.5 [mu] m or more and 50.0 [mu] m or less, and has a basis weight of 1.0 g / m2 or more and less than 8.0 g / m2.

Description

TECHNICAL FIELD

[0001] The present application relates to a wet nonwoven fabric, an electrolyte-reinforced film, and a method for manufacturing a wet nonwoven fabric. BACKGROUND

[0002] Polyarylene sulfides have high heat resistance, chemical resistance, electrical insulation, flame retardancy, and in addition, excellent mechanical properties or molding processability, and thus are widely used as a metal substitute material or a material that can withstand extreme environments. Polyarylene sulfide fibers also effectively utilize these properties and are used for applications such as bag filters, papermaking cloths, electrical insulation paper, battery separators, and various separators. In particular, in view of electrolyte membrane reinforcement materials that are attracting attention as clean energy, the combination of the heat resistance or chemical resistance of polyarylene sulfides and the ion permeability or gas separation properties of nonwoven materials has been studied.

[0003] In order to improve the efficiency of electrolyte membranes, it is required to reduce the thickness of the film, and at the same time, mechanical strength needs to be taken into account. For this reason, a structure in which an electrolyte film is formed on an electrolyte film reinforcement material has been proposed. As the electrolyte film reinforcement material, in order not to reduce the ion permeability of the electrolyte film reinforcement film, it is required to be thin, have high air permeability, have high mechanical strength, and have high uniformity of the pore size of the wet nonwoven fabric.

[0004] For the problem, for example, a wet nonwoven fabric for a solid polymer electrolyte reinforcement material mainly composed of polyphenylene sulfide fibers, which is one type of polyarylene sulfide, has been proposed (Patent Literature 1). It is described that, compared to stretched polyphenylene sulfide fibers, unstretched polyphenylene sulfide fibers are plasticized at low temperatures, and thus become a wet nonwoven fabric having excellent mechanical strength by functioning as a bonding fiber.

[0005] In addition, a wet nonwoven fabric that has excellent gas blocking properties and ion permeability by being composed of thermoplastic fibers having an average single fiber fineness of 0.1 dtex to 10 dtex and containing a specific number of crimps has been proposed (Patent Literature 2). Furthermore, it is described that polyphenylene sulfide (PPS) fibers are included as the thermoplastic fibers.

[0006] On the other hand, polyphenylene sulfide fibers have the problem of low moisture retention and easy paper breakage in the papermaking process. Therefore, a polyphenylene sulfide wet nonwoven fabric mixed with aramid fibers having higher water retention than polyphenylene sulfide fibers has been proposed (Patent Literature 3). It is described that the specific surface area of the fibers is increased by including fibrillated aramid fibers, and the bonding points between the fibers are increased, thereby becoming a wet nonwoven fabric with strong paper strength.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2003-77494

[0010] Patent Document 2: Japanese Patent Application Publication No. 2016-89197

[0011] Patent Document 3: Japanese Patent Application Publication No. 2020-76174 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] The technology disclosed in Patent Document 1 can produce polyphenylene sulfide wet nonwoven fabrics with excellent mechanical strength. However, the skeleton fibers constituting the wet nonwoven fabric are substantially coarse, thus making it impossible to thin the wet nonwoven fabric. For example, if the wet nonwoven fabric described in the examples contains stretched PPS fibers with a fineness of 1.1 dtex (i.e., a fiber diameter of 10 μm in polyphenylene sulfide fibers) and a fineness of 2.2 dtex (i.e., a fiber diameter of 14 μm in polyphenylene sulfide fibers), it is impossible to obtain a wet nonwoven fabric with a thickness of less than 14 μm. In addition, if coarse fibers are used to produce wet nonwoven fabrics with low weight per unit area, there is a problem of extremely reduced strength.

[0014] Furthermore, the technology disclosed in Patent Document 2 uses coarse thermoplastic fibers with a fineness of 0.1 dtex or more (i.e., a fiber diameter of 3.03 μm or more in polyphenylene sulfide fibers), and the nonwoven fabric has a high unit area weight, resulting in low air permeability. Therefore, when the nonwoven fabric is used to make an electrolyte reinforcing membrane, the power generation efficiency sometimes decreases. On the other hand, if the thickness of the nonwoven fabric is reduced, the air permeability increases, but the number of constituent fibers in the wet nonwoven fabric decreases, leading to a reduction in strength.

[0015] Furthermore, in Patent Document 3, a wet nonwoven fabric with high wet paper strength is obtained by mixing fibrillated polyaramid fibers into a polyphenylene sulfide wet nonwoven fabric. However, the wet nonwoven fabric has low air permeability due to the presence of fibrillated fibers, and its chemical resistance is also reduced due to the presence of polyaramid fibers with low acid resistance. Therefore, the following problem arises: the strength of the wet nonwoven fabric is reduced, making it unsuitable as a reinforcing material for electrolyte membranes.

[0016] The purpose of this invention is to improve upon the problems of the prior art and provide a wet nonwoven fabric that is thin, has high tensile strength and air permeability, and is highly uniform.

[0017] Technical means to solve the problem

[0018] As a result of studies conducted by the present inventors, it was found that, in order to reduce the thickness of a wet nonwoven fabric containing polyarylene sulfide fibers and improve the air permeability and tensile strength, it is effective to make the weight per unit area of the wet nonwoven fabric low and make the fibers constituting the fabric finer. On the other hand, in the case of using very fine fibers, when the wet nonwoven fabric is manufactured, the dispersibility of the fibers in the fiber dispersion liquid decreases due to aggregation between the fibers and the like, and particularly in a wet nonwoven fabric having a low weight per unit area, unevenness is easily generated in a wet nonwoven fabric produced using the dispersion liquid, and it is difficult to obtain a wet nonwoven fabric having high uniformity of pore size.

[0019] Therefore, in order to solve the problem, the present inventors conducted intensive studies, and as a result, it was found that even if the weight per unit area is low, by setting the average fiber diameter of the polyarylene sulfide fibers to a specific range, a wet nonwoven fabric having both high air permeability and tensile strength and high uniformity of pore size can be obtained, and the present invention was completed.

[0020] The present invention is an invention for solving the problem, and employs the following means.

[0021] (1) A wet nonwoven fabric containing stretched polyarylene sulfide fibers having an average fiber diameter of 0.3 μm or more and 3.0 μm or less, and having an average pore size of 0.5 μm or more and 50.0 μm or less, and a weight per unit area of 1.0 g / m 2 or more and less than 8.0 g / m 2 .

[0022] (2) The wet nonwoven fabric according to (1), containing unstretched polyarylene sulfide fibers having an average fiber diameter of 0.8 μm or more and 6.0 μm or less.

[0023] (3) The wet nonwoven fabric according to (1) or (2), wherein the aspect ratio (average fiber length / average fiber diameter) of the stretched polyarylene sulfide fibers is 800 or more and 2000 or less,

[0024] and the aspect ratio (average fiber length / average fiber diameter) of the unstretched polyarylene sulfide fibers is 400 or more and 1800 or less.

[0025] (4) The wet nonwoven fabric according to any one of (1) to (3), wherein, in a pore size distribution curve, when the pore size of the largest peak indicating the pore size distribution is set as Dp (nm), pores of 0.9 Dp or more and 1.1 Dp or less are 50% or more of the entire pores.

[0026] (5) The wet nonwoven fabric according to any one of (1) to (4), wherein the shrinkage rate after standing in an atmosphere at a temperature of 160°C for 24 hours is 8.0% or less.

[0027] (6) The wet-type nonwoven fabric according to any one of (2) to (5), wherein the average fiber diameter of the unstretched polyarylene sulfide fiber is thinner than the average fiber diameter of the stretched polyarylene sulfide fiber.

[0028] (7) An electrolyte-enhancing film comprising the wet-type nonwoven fabric according to any one of (1) to (6).

[0029] (8) A method for producing a wet-type nonwoven fabric according to any one of (2) to (7), the method comprising a step of dispersing the stretched polyarylene sulfide fiber and the unstretched polyarylene sulfide fiber in an aqueous medium to obtain a dispersion liquid, the fiber concentration in the dispersion liquid being 1.0 mass ppm or more and 80.0 mass ppm or less.

[0030] (9) The method for producing a wet-type nonwoven fabric according to (8), wherein a dispersant is contained in the dispersion liquid, the concentration of the dispersant with respect to the dispersion liquid being 0.0010 mass% or more and 8.0 mass% or less.

[0031] Effects of the Invention

[0032] According to the present application, a wet-type nonwoven fabric having a small thickness, a high strength, a high air permeability, and a high uniformity of pore diameter can be obtained. DETAILED DESCRIPTION

[0033] The wet-type nonwoven fabric of the present application satisfies the following necessary conditions.

[0034] contains the stretched polyarylene sulfide fiber having an average fiber diameter of 0.3 μm or more and 3.0 μm or less, has an average pore diameter of 0.5 μm or more and 50.0 μm or less, and has a weight per unit area of 1.0 g / m 2 or less than 8.0 g / m 2 .

[0035] Hereinafter, the present application will be described in detail, but the present application is not limited in any way by the following description as long as the gist of the present application is not deviated from.

[0036] < Polyarylene sulfide fiber >

[0037] The polyarylene sulfide used in the polyarylene sulfide fiber is a homopolymer or a copolymer having a repeating unit of -(Ar-S)-. As Ar, a constitutional unit represented by the following formula (1) to formula (12), or the like can be exemplified.

[0038] [Chemical Formula 1]

[0039]

[0040] [Chemical Formula 2]

[0041]

[0042] [Chemical Formula 3]

[0043]

[0044] [Chemical Formula 4]

[0045]

[0046] [Chemical Formula 5]

[0047]

[0048] [Chemical Formula 6]

[0049]

[0050] [Chemical Formula 7]

[0051]

[0052] [Chemical Formula 8]

[0053]

[0054] [Chemical Formula 9]

[0055]

[0056] [Chemical Formula 10]

[0057]

[0058] [Chemical Formula 11]

[0059]

[0060] [Chemical Formula 12]

[0061]

[0062] (In formulae (1) to (10), R 1 , R 2 are each a substituent selected from a hydrogen atom, an alkyl group, an alkoxy group, a halogen group, and R 1 and R 2 may be the same or different.)

[0063] As a representative example of the polyarylene sulfide, polyphenylene sulfide (PPS), polyphenylene sulfide sulfone, polyphenylene sulfide ketone, and the like can be given. As a repeating unit of the polyarylene sulfide, a para-arylene sulfide unit in which the formula (1) is set as Ar is preferred.

[0064] Further, by making a resin containing, as a main constitutional unit of the polymer, a para-phenylene unit represented by the following formula (13) preferably 60 mol% or more, more preferably 70 mol% or more, and further preferably 80 mol% or more, a resin having excellent heat resistance can be obtained. Further, when processed into a fiber and a wet nonwoven fabric, excellent strength is obtained.

[0065] [Chem. 13]

[0066]

[0067] Further, a copolymerization unit can also be contained within a range not impairing the effects of the present application, and the copolymerization unit is preferably 20 mol% or less relative to the polyarylene sulfide polymer.

[0068] In the polyarylene sulfide fiber, various additives such as titanium oxide, silica, barium oxide, calcium carbonate, coloring agents such as carbon black, dyes or pigments, flame retardants, optical brighteners, antioxidants, or ultraviolet absorbers can also be contained within a range not impairing the effects of the present application.

[0069] The polyarylene sulfide fiber can be not only a single component fiber but also a composite fiber in which two or more resins are compounded. In the case where the polyarylene sulfide fiber is a composite fiber, the composite form is not particularly limited as long as the effects of the present application are not impaired, and can be appropriately selected from a core-sheath type or an island-in-sea type, a side-by-side type, an eccentric core-sheath type, a blend type, and the like. The polyarylene sulfide contained in the polyarylene sulfide fiber is preferably 70% by mass or more relative to the total mass of the polymer in the fiber.

[0070] The cross-sectional shape of the polyarylene sulfide fiber is not particularly limited, and can be not only a round cross-section but also any irregular cross-sectional shape such as a Y-shaped cross-section or a triangular cross-section, a flat cross-section, an S-shaped cross-section, a cross-shaped cross-section, a hollow cross-section, and the like.

[0071] <Stretching the Polyarylene Sulfide Fiber>

[0072] The wet nonwoven fabric of the present application contains a drawn polyarylene sulfide fiber having an average fiber diameter of 0.3 μm or more and 3.0 μm or less. Here, the "drawn polyarylene sulfide fiber" means a fiber having an orientation parameter of the polyarylene sulfide molecular chain of 3.0 or more. The orientation parameter is a value indicating the orientation of the polyarylene sulfide molecular chain, and the larger the orientation parameter, the higher the orientation of the molecular chain. Here, the orientation parameter is measured using a laser Raman device. The orientation parameter of the drawn polyarylene sulfide fiber is preferably 3.0 or more, more preferably 5.0 or more, and further preferably 7.0 or more. By setting the orientation parameter to the above range, a fiber having high heat resistance and excellent tensile strength is obtained. The orientation parameter of the drawn polyarylene sulfide fiber is preferably 40 or less, more preferably 30 or less, and further preferably 25 or less. By setting the orientation parameter to the above range, a fiber having a large elongation of the fiber is obtained.

[0073] Here, the "orientation parameter" in the present application means an orientation parameter obtained by the method described in the examples. In addition, as a method of setting the orientation parameter of the drawn polyarylene sulfide fiber to the above range, the draw ratio in the drawing step of the fiber can be set to 2.5 times or more, or other methods can be used within a range not impairing the object of the present application.

[0074] The average fiber diameter of the drawn polyarylene sulfide fiber is 0.3 μm or more and 3.0 μm or less. If the average fiber diameter of the drawn polyarylene sulfide fiber is more than 3.0 μm, the number of fibers per unit weight decreases, and thus the tensile strength of the wet nonwoven fabric decreases, and in addition, the thickness of the wet nonwoven fabric increases. In addition, if the average fiber diameter is large, the variation in the pore diameter increases, and the uniformity of the pore diameter decreases. The average fiber diameter of the drawn polyarylene sulfide fiber is preferably 2.8 μm or less, and more preferably 2.7 μm or less. On the other hand, if the average fiber diameter is less than 0.3 μm, the number of fibers per unit weight increases, and thus the wet nonwoven fabric becomes a structure in which the fibers are densely packed, and thus the air permeability of the obtained wet nonwoven fabric decreases. In addition, the aspect ratio increases, and thus the dispersibility decreases, and the uniformity of the pore diameter of the wet nonwoven fabric decreases. The average fiber diameter of the drawn polyarylene sulfide fiber is preferably 0.5 μm or more, and more preferably 1.0 μm or more. The average fiber diameter (μm) of the fiber described herein can be obtained by the method described in the examples.

[0075] As a method of setting the average fiber diameter of the drawn polyarylene sulfide fiber to the above range, a method of adjusting the discharge amount of the spinning and the draw ratio can be used, or other methods can be used within a range not impairing the object of the present application.

[0076] The aspect ratio (average fiber length / average fiber diameter) of the stretched polyarylene sulfide fibers is preferably 800 or more and 2000 or less. By setting the aspect ratio of the stretched polyarylene sulfide fibers to 2000 or less, stretched polyarylene sulfide fibers with excellent dispersibility can be obtained, and wet nonwoven fabrics with higher pore size uniformity can be obtained. The aspect ratio of the stretched polyarylene sulfide fibers is more preferably 1800 or less, and even more preferably 1500 or less. On the other hand, by setting the aspect ratio of the stretched polyarylene sulfide fibers to 800 or more, the fibers are less likely to fall off during the processing process, and the tensile strength of the wet nonwoven fabric is further improved by the entanglement between the fibers. The aspect ratio of the stretched polyarylene sulfide fibers is more preferably 900 or more, and even more preferably 1000 or more.

[0077] Here, the average fiber length can be determined based on "8.4.1. Direct method (C method) for average fiber length" of Japanese Industrial Standards (JIS) L1015:2010 "Test method for short fiber length of chemical fibers". In addition, the aspect ratio is the value obtained by dividing the average fiber diameter by the average fiber length.

[0078] <Unstretched polyarylether sulfide fiber>

[0079] The wet nonwoven fabric of the present invention preferably comprises unstretched polyarylene sulfide fibers with a diameter of 0.8 μm or more and 6.0 μm or less. Here, "unstretched polyarylene sulfide fibers" refers to fibers with an orientation parameter of less than 3.0 for the unoriented molecular chains. The orientation parameter of the unstretched polyarylene sulfide fibers is preferably less than 3.0, more preferably 2.5 or less, and even more preferably 2.0 or less. By setting the orientation parameter to the aforementioned range, fibers with a large number of amorphous portions are formed, resulting in fibers with high adhesive strength when used as adhesive fibers.

[0080] As a method for setting the orientation parameters of unstretched polyarylether sulfide fibers to the aforementioned range, it can be achieved by setting the spinning speed to 1500 m / min or less, or other methods can be used within the scope of the present invention.

[0081] The average fiber diameter of the unstretched polyarylene sulfide fiber is preferably 0.8 μm or more and 6.0 μm or less. If the average fiber diameter of the unstretched polyarylene sulfide fiber is more than 6.0 μm, the number of fibers per unit weight decreases, and the number of bonding points decreases, so that the tensile strength of the wet nonwoven fabric decreases, and in addition, the wet nonwoven fabric becomes thick. In addition, if the average fiber diameter is large, the variation in the pore diameter increases, and the uniformity of the pore diameter decreases. The average fiber diameter of the unstretched polyarylene sulfide fiber is preferably 4.0 μm or less, and further preferably 2.5 μm or less. On the other hand, if the average fiber diameter of the unstretched polyarylene sulfide fiber is less than 0.8 μm, the number of fibers per unit weight increases, and the structure in which the fibers are densely packed is formed, so that the air permeability of the obtained wet nonwoven fabric decreases. In addition, the aspect ratio increases, and the dispersibility decreases, so that the uniformity of the pore diameter of the wet nonwoven fabric decreases. The average fiber diameter of the unstretched polyarylene sulfide fiber is preferably 0.9 μm or more, and further preferably 1.0 μm or more.

[0082] As a method of setting the average fiber diameter of the unstretched polyarylene sulfide fiber to the above range, the method of adjusting the discharge amount of the spinning and the draw ratio can be used, and other methods can be used within a range not impairing the object of the present application.

[0083] The aspect ratio (average fiber length / average fiber diameter) of the unstretched polyarylene sulfide fiber is preferably 400 or more and 1800 or less. By setting the aspect ratio of the unstretched polyarylene sulfide fiber to more preferably 1600 or less, further preferably 1400 or less, and most preferably 1300 or less, an unstretched polyarylene sulfide fiber having excellent dispersibility can be obtained, the adhesive bonding points are uniformized, and a wet nonwoven fabric having high tensile strength can be obtained. In addition, by setting the aspect ratio to preferably 500 or more, and further preferably 700 or more, the fibers are less likely to be detached in the process, and in addition, the fibers are easily entangled with each other to form a wet nonwoven fabric having excellent tensile strength.

[0084] Wet Nonwoven Fabric

[0085] The wet nonwoven fabric of the present application preferably contains the stretched polyarylene sulfide fiber and the unstretched polyarylene sulfide fiber. The stretched polyarylene sulfide fiber functions as a main fiber, and the unstretched polyarylene sulfide fiber functions as an adhesive fiber. Most of the unstretched polyarylene sulfide fiber is in an amorphous structure, and is melted by heating to function as an adhesive. The stretched polyarylene sulfide fiber is stretched in the fiber manufacturing process, and thus has high single fiber strength and excellent dimensional stability. In the present application, by using the stretched polyarylene sulfide fiber and the unstretched polyarylene sulfide fiber together, a wet nonwoven fabric having excellent chemical resistance and heat resistance can be provided. In addition, by forming a wet nonwoven fabric, a nonwoven fabric having low weight per unit area and high uniformity of the pore diameter can be obtained.

[0086] The wet nonwoven fabric of the present application preferably contains 20 mass% or more and 80 mass% or less of the drawn polyarylene sulfide fiber with respect to the total mass of the wet nonwoven fabric. More preferably, it is 30 mass% or more and 70 mass% or less. By making the main fiber of the wet nonwoven fabric, that is, the drawn polyarylene sulfide fiber 20 mass% or more, a wet nonwoven fabric having higher tensile strength is obtained. On the other hand, by making the drawn polyarylene sulfide fiber 80 mass% or less, the proportion of the binder fiber can be increased, and the adhesion points of the main fibers to each other are increased, thereby obtaining a wet nonwoven fabric having higher tensile strength.

[0087] In addition, it is preferable to contain 20 mass% or more and 80 mass% or less of the undrawn polyarylene sulfide fiber with respect to the total mass of the wet nonwoven fabric. Further preferably, it is 30 mass% or more and 70 mass% or less. By making the binder fiber of the wet nonwoven fabric, that is, the undrawn polyarylene sulfide fiber 20 mass% or more, the adhesion points are increased, thereby obtaining a wet nonwoven fabric having higher tensile strength. On the other hand, by making the undrawn polyarylene sulfide fiber 80 mass% or less, the proportion of the main fiber component can be increased, thereby obtaining a wet nonwoven fabric having higher tensile strength.

[0088] In addition, other fibers can be mixed within a range not impairing the effects of the present application, and the total of the drawn polyarylene sulfide fiber and the undrawn polyarylene sulfide fiber is preferably 80 mass% or more with respect to the total mass of the wet nonwoven fabric.

[0089] The mixing ratio of the mass of the drawn polyarylene sulfide fiber and the undrawn polyarylene sulfide fiber is preferably (drawn polyarylene sulfide fiber) : (undrawn polyarylene sulfide fiber) = 10 : 90 to 90 : 10, and more preferably (drawn polyarylene sulfide fiber) : (undrawn polyarylene sulfide fiber) = 20 : 80 to 80 : 20. By setting the drawn polyarylene sulfide fiber and the undrawn polyarylene sulfide fiber to the above-mentioned proportions, the number of adhesion points with respect to the main fiber becomes appropriate, and a wet nonwoven fabric having higher tensile strength can be obtained.

[0090] The average fiber diameter of the unstretched polyarylene sulfide fiber constituting the wet nonwoven fabric of the present application is preferably finer than the average fiber diameter of the stretched polyarylene sulfide fiber. The wet nonwoven fabric of the present application exhibits high stress at the time of stretching by the main fibers (i.e., the stretched polyarylene sulfide fibers) being bonded to each other via the binder fibers (i.e., the unstretched polyarylene sulfide fibers). In the case where the binder fibers are made finer than the main fibers, the structure becomes one in which the bonding portions are multipointized / homogenized, stress is dispersed at the time of stretching without easily being plastically deformed, and the strength of the wet nonwoven fabric becomes higher. The ratio of the average fiber diameter of the unstretched polyarylene sulfide fiber to the average fiber diameter of the stretched polyarylene sulfide fiber (average fiber diameter of unstretched polyarylene sulfide fiber / average fiber diameter of stretched polyarylene sulfide fiber) is preferably 0.05 or greater and 0.90 or less, and more preferably 0.10 or greater and 0.80 or less. By being set to the range, the bonding portions become a structure that is multipointized / homogenized, stress is dispersed at the time of stretching without easily being plastically deformed, and the tensile strength of the wet nonwoven fabric becomes higher.

[0091] The wet nonwoven fabric of the present application has through-holes. Here, the through-holes can be formed by the gaps between the fibers. It is important that the average pore diameter thereof is 0.5 μm or greater and 50.0 μm or less. In the case of the previous wet nonwoven fabric, when it is desired to obtain a wet nonwoven fabric having a low weight per unit area by making only the diameters of the constituting fibers fine, there is a problem in that a wet nonwoven fabric having high uniformity of pore diameter cannot be obtained, and the tensile strength decreases. Therefore, the present inventors have found that these problems can be solved by appropriately adjusting the average pore diameter. If the average pore diameter is less than 0.5 μm, the wet nonwoven fabric becomes like a film, and it is difficult to maintain the porosity characteristic of a nonwoven fabric, and the air permeability decreases. The average pore diameter is preferably 1.0 μm or greater, and more preferably 3.0 μm or greater. On the other hand, if the average pore diameter is excessively large and greater than 50.0 μm, there is a tendency that the texture of the wet nonwoven fabric deteriorates, the uniformity of the pore diameter is impaired, and the tensile strength decreases. The average pore diameter is preferably 30.0 μm or less, and more preferably 20.0 μm or less.

[0092] The average pore diameter described herein refers to a value calculated by the bubble point method. As the bubble point method, for example, a Porous Material Automatic Fine Pore Measuring System Perm-Porometer (manufactured by PMI Co., Ltd.) can be used. In the measurement based on the Perm-Porometer, a wet nonwoven fabric sheet is immersed in a liquid having a known surface tension value, a gas pressure is increased from the upper side of the sheet while the gas is supplied, and the average pore diameter is measured based on the relationship between the pressure and the liquid surface tension on the surface of the wet nonwoven fabric sheet.

[0093] As a method of setting the average pore diameter of the polyarylene sulfide wet nonwoven fabric to the range, the average fiber diameter of the constituting fibers and the weight per unit area can be adjusted.

[0094] The wet nonwoven fabric of the present application has a weight per unit area of 1.0 g / m 2 8.0 g / m 2 If the weight per unit area is 8.0 g / m 2 or more, the wet nonwoven fabric becomes thick, and in addition, the number of constituent fibers is excessive, so there is a tendency that the pore diameter becomes extremely small, the air permeability decreases, and the ion conduction properties of the electrolyte-reinforcing film sometimes decrease. The weight per unit area is preferably 6.0 g / m 2 or less, more preferably 5.0 g / m 2 or less, and further preferably 3.0 g / m 2 or less. On the other hand, if the weight per unit area is 1.0 g / m 2 or less, the number of constituent fibers is insufficient, so the tensile strength decreases. In addition, the pore diameter distribution deviates, and the uniformity of the pore diameter of the nonwoven fabric decreases. The weight per unit area is preferably 1.5 g / m 2 or more, and more preferably 2.0 g / m 2 or more.

[0095] As a method of setting the weight per unit area of the wet nonwoven fabric to the above range, the amount of fibers charged to the fiber dispersion liquid for papermaking can be adjusted.

[0096] The thickness of the wet nonwoven fabric of the present application is preferably 15.0 μm or less. By setting the thickness to preferably 12.0 μm or less, more preferably 10.0 μm or less, and further preferably 8.0 μm or less, the ion permeability of the electrolyte-reinforcing film using the present wet nonwoven fabric is sometimes improved and is preferred. In addition, when the wet nonwoven fabric is installed in a device in the form of an electrolyte membrane reinforcing material, the occupied volume of the wet nonwoven fabric becomes small, so the miniaturization / lightweight of the device can be achieved.

[0097] As a method of setting the thickness of the wet nonwoven fabric to the above range, the weight per unit area, the average fiber diameter of the constituent fibers, and the calendering conditions can be adjusted.

[0098] The wet nonwoven fabric of the present application is preferably such that, in a pore size distribution curve, pores of 0.9 Dp or more and 1.1 Dp or less, when the pore size of the largest peak of the pore size distribution is taken as Dp (nm), are 50% or more of the total number of pores. Here, the pore size distribution curve is determined from the pressure change (in the range of 0 kPa to 3000 kPa) of the air flow under dry and wet conditions. Pores of 0.9 Dp or more and 1.1 Dp or less are more preferably 55% or more of the total number of pores, and further preferably 60% or more. The higher the proportion of pores of 0.9 Dp or more and 1.1 Dp or less, the more uniform the pores are, and the less the variation in the tensile strength or air permeability of the wet nonwoven fabric. The higher the value, the more desirable.

[0099] To set the proportion of pores of 0.9 Dp or more and 1.1 Dp or less to the above range, the aspect ratio of the fibers, the concentration of the fiber dispersion liquid for papermaking, the concentration of the dispersant, and the concentration of the thickener can be adjusted.

[0100] The pore size distribution curve of the wet nonwoven fabric of the present application can be measured using a Perm-Porometer and according to the bubble point method (American Society of Testing Materials (ASTM) F316-86).

[0101] The shrinkage of the wet nonwoven fabric of the present application, after being kept at a temperature of 160°C for 24 hours and cooled to room temperature, is preferably 8.0% or less. The shrinkage is more preferably 7.0% or less, and further preferably 6.0% or less. The lower the value of the shrinkage, the higher the dimensional stability with respect to heat, and when used as an electrolyte membrane reinforcement material that operates at high temperatures for a long time, deterioration or rupture of the membrane due to shrinkage is less likely to occur. When the shrinkage is negative and the fabric expands, deterioration or rupture of the membrane also occurs, so this is not preferred. Therefore, the shrinkage is preferably 0% or more.

[0102] To set the shrinkage to the above range, it is effective to perform heat crystallization on the shape of the wet nonwoven fabric. As a method of heat crystallization, the method described later can be used, or other methods can be used within a range that does not interfere with the purpose of the present application.

[0103] The wet nonwoven fabric of the present application preferably has a tensile strength of 0.50 N / 15 mm or more. The tensile strength is more preferably 0.55 N / 15 mm or more, further preferably 0.60 N / 15 mm or more, and most preferably 0.80 N / 15 mm or more, whereby breakage during the manufacturing process is less likely to occur. In addition, a wet nonwoven fabric that is less likely to break when a tensile stress is applied during a subsequent process or use is obtained. The tensile strength can be increased because the stretched polyarylene sulfide fibers, which have high fiber strength, are firmly bonded by the non-stretched polyarylene sulfide fiber fusion portions. That is, by having stretched polyarylene sulfide fiber fusion portions with non-stretched polyarylene sulfide fibers, fiber shedding is less likely to occur, and a wet nonwoven fabric having high tensile strength is obtained by the stretched polyarylene sulfide fibers bearing stress and the like. Furthermore, the tensile strength of the wet nonwoven fabric in the present application refers to a value measured using the method described in the examples.

[0104] The wet nonwoven fabric of the present application preferably has an air permeability of 3.0 cm 3 / (cm 2 · s) or more. Further preferably, the air permeability is 10.0 cm 3 / (cm 2 · s) or more, and particularly preferably 15.0 cm 3 / (cm 2 · s) or more. In order to ensure the properties of the nonwoven fabric, the air permeability is also required. If the air permeability is high, when used as an electrolyte membrane reinforcement material, ion conduction is less likely to be hindered, and there is a tendency for the ion conductivity to increase. On the other hand, if the air permeability of the wet nonwoven fabric is too high, the dimensional stability decreases, and thus the air permeability is preferably 300 cm 3 / (cm 2 · s) or less.

[0105] < electrolyte reinforcement membrane >

[0106] The wet nonwoven fabric of the present application can be preferably used as an electrolyte membrane reinforcement material. At this time, the wet nonwoven fabric can be used as is, or can be subjected to a hydrophilization treatment within a range that does not hinder the effects of the present application. By subjecting the wet nonwoven fabric to a hydrophilization treatment, the permeability of the electrolyte membrane is improved. The wet nonwoven fabric is thin and has a low weight per unit area, and has excellent tensile strength and air permeability, and thus is an electrolyte membrane reinforcement material that has excellent ion permeation efficiency and is less likely to break during installation and use.

[0107] As the electrolyte-enhanced membrane of the present application, the wet nonwoven fabric of the present application can be used in combination with an electrolyte membrane, and can be preferably used for fuel cell applications. As the electrolyte membrane, for example, fluorine-based electrolytes, hydrocarbon-based electrolytes, and the like can be listed. As the fluorine-based electrolytes, perfluorosulfonic acid-based polymers, polytrifluorostyrene sulfonic acid-based polymers, perfluorocarbon sulfonic acid-based polymers, and the like can be listed. In particular, a cation exchange membrane containing a perfluorosulfonic acid having a sulfonic acid group represented by "Nafion" (registered trademark, Du Pont) has excellent basic properties, and thus can be preferably used.

[0108] <Method for manufacturing wet nonwoven fabric>

[0109] Hereinafter, the method for manufacturing the wet nonwoven fabric of the present application will be described.

[0110] [Method for manufacturing stretched polyarylene sulfide fiber]

[0111] The polyarylene sulfide fiber can use various fibers, and is preferably obtained by removing a polymer of a sea component having easy solubility of an island-type composite fiber having an island component disposed with a polyarylene sulfide in the island component.

[0112] In the manufacturing method at this time, first, the polyarylene sulfide and the polymer having easy solubility are separately melted individually, and are measured via a polymer pipe and a known measuring device such as a gear pump. Thereafter, after passing through a filter for removing foreign matter in the polymer, the polymer is made to flow to a spinning nozzle. Each of the polymers flowing to the spinning nozzle can be shape-limited to an arbitrary composite shape in the spinning nozzle and merged to be discharged from a nozzle hole in the form of an island-type composite fiber.

[0113] The cross-sectional area of the island component in the island-type composite fiber can be adjusted by adjusting the discharge amount of the polymer. For example, by making the polyarylene sulfide as the island component into a circular shape having a diameter of 2.0 μm, a circular cross-sectional fiber having an average fiber diameter of 2.0 μm can be manufactured.

[0114] The discharged unstretched fiber can be drawn by a roller (godet) rotating at a certain speed. In order to improve linear uniformity and productivity, the drawing speed is preferably 300 m / minute or more, and in order not to advance the orientation of the molecular chain, the drawing speed is preferably 1500 m / minute or less.

[0115] The unstretched fiber obtained in the above-described manner can be subjected to a stretching process. The stretching can be performed by traveling on a heated first roller or a heating device provided between the first roller and a second roller. The stretching conditions can be determined depending on the mechanical properties of the obtained unstretched fiber, and the stretching ratio can be determined depending on the ratio of the circumferential speeds of the first roller and the second roller.

[0116] The temperature of the heated first roller or heating device in the stretching step is preferably set to 80°C or higher and 130°C or lower. By being set to 80°C or higher, the stretching point can be fixed, enabling stable stretching, and by being set to 130°C or lower, the occurrence of breakage can be suppressed, improving the processability. In terms of the fixation of the stretching point, the temperature of the second roller is preferably set to the temperature of the heated first roller or heating device + 20°C or lower.

[0117] Further, heat setting can also be performed by heating the stretched fiber with a heated third roller or a heating device provided between the second roller and the third roller after passing through the second roller. Furthermore, the heat setting temperature at the time of heat setting is preferably set to 150°C to 240°C. By setting the heat setting temperature to 150°C or higher, the shrinkage can be reduced by heat crystallization. Thus, the width of the nonwoven fabric product in the wet nonwoven fabric production process can be prevented from becoming uneven, and a wet nonwoven fabric having excellent dimensional stability can be obtained.

[0118] Subsequently, the obtained fiber is cut into a length of 0.3 mm to 10 mm with a cutting machine, whereby a cut fiber can be obtained.

[0119] [Method for producing unstretched polyarylene sulfide fiber]

[0120] Except that stretching and heat setting are not performed, the same as in the method for producing stretched polyarylene sulfide fiber, a cut fiber of unstretched fiber can be obtained.

[0121] [Method for producing wet nonwoven fabric]

[0122] With respect to the two kinds of cut fibers obtained by the method, the sea components are eluted with sodium hydroxide, and then dispersed in an aqueous medium, respectively. Here, the aqueous medium means a liquid in which water is the main component. The dispersions are mixed in a desired ratio to prepare a dispersion for papermaking. The fiber concentration in the dispersion is preferably 1.0 mass ppm or higher and 80.0 mass ppm or lower. By setting the fiber concentration to 1.0 mass ppm or higher, more preferably 1.5 mass ppm or higher, the production efficiency is improved, and the load of the dehydration process can be reduced. On the other hand, by setting the fiber concentration to 80.0 mass ppm or lower, more preferably 60.0 mass ppm or lower, further preferably 10.0 mass ppm or lower, the dispersion state is improved, a uniform wet nonwoven fabric can be obtained, and the tensile strength of the wet nonwoven fabric becomes high.

[0123] The dispersion liquid contains a dispersant, and the concentration of the dispersant in the dispersion liquid is preferably 0.0010% by mass or more and 8.0% by mass or less. By setting the dispersant concentration to 0.0010% by mass or more, more preferably 0.0075% by mass or more, and further preferably 0.010% by mass or more, the fibers are uniformly dispersed in the dispersion liquid, the uniformity of the pore size of the obtained wet nonwoven fabric is improved, and a wet nonwoven fabric having a higher tensile strength is obtained. In addition, by setting the concentration of the dispersant to 8.0% by mass or less, more preferably 6.0% by mass or less, more preferably 3.0% by mass or less, and further preferably 0.80% by mass or less, the fibers are uniformly dispersed in the dispersion liquid, the uniformity of the pore size of the obtained wet nonwoven fabric is further improved, and a wet nonwoven fabric having a higher tensile strength is obtained.

[0124] As the dispersant, a surfactant or the like can be used, and as the surfactant, cationic, anionic, nonionic, or the like can be exemplified.

[0125] In the fiber dispersion liquid for papermaking, a water-soluble polymer or the like as a thickening agent or a defoaming agent or the like to suppress the generation of bubbles can be added.

[0126] The dispersion liquid prepared as described above is subjected to papermaking using a cylinder type, a fourdrinier type, an inclined wire type, or the like, and is dried using a yankee dryer or a rotary dryer or the like, and a dry fiber web is produced. Subsequently, a heating / pressurizing treatment is performed, and a wet nonwoven fabric is obtained. In the present application, a case where heating and pressurizing are simultaneously performed is referred to as a heating / pressurizing treatment, and is distinguished from a treatment where only heating is performed using drying or the like without pressurizing. The dry fiber web refers to a nonwoven fabric in which the heating / pressurizing treatment is not performed among the wet nonwoven fabrics.

[0127] In the preferred production method of the wet nonwoven fabric of the present application, in order to improve the adhesion between the fibers, it is preferable to produce by performing a heating / pressurizing treatment or the like on the unstretched polyarylene sulfide fibers. In this case, it is preferable to suppress crystallization in the production process of the dry fiber web as much as possible. For this purpose, it is preferable to set the drying temperature in the papermaking process to 80°C to 150°C, and more preferably to 90°C to 140°C. In addition, it is also preferable to suppress crystallization by shortening the through time of the drying process. If the drying is insufficient, the paper strength of the dry fiber web is reduced, and in addition, a sharp heat shrinkage occurs at the heating / pressurizing treatment in the next process, and paper breakage is easily generated. On the contrary, if the drying is excessive, crystallization of the dry fiber web proceeds, and the unstretched polyarylene sulfide fibers are not easily plastically deformed at the heating / pressurizing treatment in the next process. As a result, the mechanical properties of the obtained wet nonwoven fabric are reduced.

[0128] In the production of the wet-type nonwoven fabric of the present application, a dry-type fiber web in which two kinds of cut fibers are mixed is subjected to a heating / pressurizing treatment. By performing the heating / pressurizing treatment, as described above, the unstretched polyarylene sulfide fibers are caused to melt and soften to form polyarylene sulfide fusion portions. As the heating / pressurizing means, any means can be used, for example, a hot press using a flat plate or the like, a hot calender, or the like can be used. Among them, a hot calender which allows continuous processing is preferred. As the roll of the hot calender, a metal-metal roll, a metal-paper roll, a metal-rubber roll, or the like can be used.

[0129] The temperature condition of the heating / pressurizing treatment is preferably a temperature of 150°C or higher and a temperature of 240°C or lower. By setting the heating temperature to 150°C or higher, the unstretched polyarylene sulfide fibers are caused to melt and soften, whereby polyarylene sulfide fusion portions are formed, and a wet-type nonwoven fabric having excellent mechanical properties is obtained. By setting the heating temperature to 240°C or lower, the polyarylene sulfide fibers are completely fused, and the shape of the fibers can be prevented from being damaged.

[0130] When a calendering operation is used as the heating / pressurizing treatment, the pressure is preferably 98 N / cm or more and 7000 N / cm or less. By setting the pressure to 98 N / cm or more, polyarylene sulfide fusion portions are formed, and a wet-type nonwoven fabric having excellent mechanical properties is obtained. On the other hand, by setting the pressure to 7000 N / cm or less, the wet-type nonwoven fabric can be prevented from being broken or the like during the heating / pressurizing treatment process, and the treatment can be stably performed. As the process speed, 1 m / min or more and 30 m / min or less are preferred. By setting to 1 m / min or more, and more preferably 2 m / min or more, good work efficiency can be obtained. On the other hand, by setting to 30 m / min or less, and more preferably 20 m / min or less, heat can also be conducted to the fibers in the inside of the wet-type nonwoven fabric, and the adhesive fibers can be heat-fused.

[0131] Example

[0132] Hereinafter, the wet-type nonwoven fabric of the present application will be described more specifically by way of examples. The present application is not limited to these examples. Various modifications or changes can be made within the technical scope of the present application. Further, each of the characteristic values in the examples is obtained by the following method.

[0133] [Measurement / Evaluation Method]

[0134] (1) Average Fiber Diameter

[0135] The measurement was performed using a scanning electron microscope "S-5500" manufactured by Hitachi High-technologies, Inc. as a scanning electron microscope, and "WinROOF2015" manufactured by Shimadzu Corporation as an image analysis software, as follows.

[0136] Process 1: An image was taken with a scanning electron microscope for the cross section of the fiber. The observation magnification was as follows. In the case where the fiber diameter of the fiber was 5 μm or more and 14 μm or less, the observation magnification was set to 1000 times, in the case where the fiber diameter was 1 μm or more and less than 5 μm, the observation magnification was set to 3000 times, and in the case where the fiber diameter was less than 1 μm, the observation magnification was set to 5000 times.

[0137] Process 2: The taken image was used, and the area Af (μm 2 ) formed by the cross-sectional profile of the single fiber was measured using the image analysis software, and the diameter of a true circle having the same area as the area Af was calculated.

[0138] Process 3: The diameter was measured for 100 fibers arbitrarily extracted, the simple number average was calculated, and the average fiber diameter (μm) was calculated, and the second decimal place was rounded off.

[0139] (2) Average fiber length

[0140] The measurement was performed based on "8.4.1. Average fiber length direct method (C method)" of JIS L1015:2010 "Chemical fiber staple length test method", and the average value of 200 was calculated, and the second decimal place was rounded off.

[0141] (3) Weight per unit area

[0142] The measurement was performed based on JIS L1913:2010 "General nonwoven fabric test method", and 3 pieces of 10 cm x 10 cm sample pieces per unit area were taken, the respective masses (g) in the standard state were weighed, and the average value was expressed by the mass (g / m 2 ) per 1 m 2 .

[0143] (4) Thickness

[0144] The measurement was performed according to "9.3.1 Measurement of thickness" of JIS P8118:2014 "Paper and paperboard - Test methods for thickness, density and specific volume", 20 pieces of 10 cm x 10 cm sample pieces were taken, a micrometer (manufactured by Mitutoyo Corporation) was used, the thickness of 20 sample pieces was measured in units of 1 piece, and the arithmetic average value was set as the thickness (μm).

[0145] (5) Tensile strength

[0146] The tensile strength was measured in accordance with "6.3.1 Standard time" of "6.3 Tensile strength and elongation (International Standards Organization (ISO) method)" of JIS L1913:2010 "Chemical fiber staple length test method". Using Tensilon ("UTM-III-100" manufactured by Orientec Corporation), the maximum point load was measured under the conditions of a sample width of 15 mm, an initial length of 20 mm, and a tensile speed of 20 mm / minute. The measurement was performed 5 times per 1 level, and the arithmetic mean value was calculated and set as the tensile strength (N / 15 mm).

[0147] (6) Average pore diameter

[0148] A porous material automatic fine pore measuring system Perm-Porometer (manufactured by PMI Corporation) was used, and the pore size was calculated based on the bubble point method (based on ASTM F-316-86). The measurement sample diameter was set to 25 mm, and the average pore diameter was obtained by using the average flow rate obtained by automatic calculation using Galwick (surface tension: 16 mN / m) as a measurement liquid whose surface tension was known, as the average flow rate diameter, and using the value rounded off to the first decimal place of the second decimal place.

[0149] (7) Pore size distribution

[0150] A porous material automatic fine pore measuring system Perm-Porometer (manufactured by PMI Corporation) was used, and a wet nonwoven fabric sheet was immersed in a liquid whose surface tension value was known, gas was supplied from the upper side of the sheet while increasing the pressure, and the measurement was performed in the order of Dry-up and Wey-up based on the relationship between the pressure and the liquid surface tension of the wet nonwoven fabric sheet surface, and a pore size distribution curve was obtained. In the obtained pore size distribution curve, the proportion of pores of 0.9 Dp to 1.1 Dp when the pore diameter representing the maximum peak of the pore size distribution was set to Dp (nm) was calculated and obtained in all the pores detected in the range of 0 kPa to 3000 kPa.

[0151] (8) Air permeability

[0152] According to "6.8.1 Fragile method" of "6.8 Air permeability (JIS method)" of JIS L1913:2010 "Test method for staple fiber length of chemical fibers", 3 pieces of 15 cm x 15 cm test pieces were taken, and the air permeability of the 3 pieces of test pieces was measured using an air permeability tester ("FX3300" manufactured by TEXTEST AG) at a test pressure of 125 Pa, and the arithmetic average value thereof was set as the air permeability (cm 3 / (cm 2 ·s).

[0153] (9) Shrinkage

[0154] A 15 cm x 15 cm wet-type nonwoven fabric in a free state was kept in a dryer at a temperature of 160°C for 24 hours, and the shrinkage (%) was calculated from the change in size before and after heat treatment using the following formula.

[0155] Shrinkage = (1 - area of wet-type nonwoven fabric after heat treatment / area of wet-type nonwoven fabric before heat treatment) x 100.

[0156] (10) Orientation parameter

[0157] The measurement was performed using a laser Raman device (manufactured by Photon Design, Inc.) as follows. First, a spectrum was obtained by passing through a polarizer disposed in a polarization direction parallel to the polarization direction of the laser light. Next, the sample was rotated, and spectra were obtained in the polarization direction parallel to the polarization direction of the laser light and in the perpendicular polarization direction. Thereafter, the orientation parameter was calculated by the following formula.

[0158] (Orientation parameter) = (I 1080 / I 740 ) (parallel) / (I 1080 / I 740 ) (perpendicular)

[0159] I 1080 / I 740 (parallel): In the Raman spectrum measured in the polarization direction parallel to the fiber axial direction, the Raman band near 1080 cm -1 was divided by the Raman band intensity near 740 cm -1 .

[0160] I 1080 / I 740 (perpendicular): In the Raman spectrum measured in the polarization direction perpendicular to the fiber axial direction, the Raman band near 1080 cm -1 was divided by the Raman band intensity near 740 cm -1 .

[0161] [Production Example 1]

[0162] <Production of Stretched Polyarylene Sulfide Fiber>

[0163] A polyphenylene sulfide containing only a p-phenylene sulfide unit was set as an island component, and a polyethylene terephthalate copolymerized with 5.0 mol% of sodium 5-sulfoisophthalate was set as a sea component. A sea / island composite die (island number 1000) in which the island component had a circular shape was used, the sea / island component composite ratio was set to 40 / 60, and after cooling and solidifying the melt-blown filaments, an oil agent was applied, and winding was performed at a spinning speed of 1000 m / min, whereby an unstretched fiber having a sea-island composite profile was obtained (single-hole discharge amount: 2.6 g / min).

[0164] The obtained unstretched fiber was subjected to heat stretching by winding it around a first roller and a second roller heated to 90°C and 100°C, respectively, for 6 turns. Further, heat setting was performed by winding it around a third roller heated to 180°C for 6 turns. The stretching ratio was 3.85 times, and after the third roller, drawing was performed using a non-heated roller at a circumferential speed of 400 m / min, whereby a stretched polyphenylene sulfide fiber was obtained.

[0165] Subsequently, the obtained stretched polyphenylene sulfide fiber was cut using a cutter, whereby a cut fiber was obtained. The orientation parameter of the obtained stretched polyphenylene sulfide fiber was measured, and the result was 11.

[0166] [Production Example 2]

[0167] <Production of Unstretched Polyarylene Sulfide Fiber>

[0168] After obtaining an unstretched fiber by the method described in <Production of Stretched Polyarylene Sulfide Fiber>, the obtained unstretched fiber was cut using a cutter, whereby a cut fiber was obtained. The orientation parameter of the obtained unstretched polyphenylene sulfide fiber was measured, and the result was 2.5.

[0169] [Example 1]

[0170] To the drawn polyphenylene sulfide fibers and the undrawn polyphenylene sulfide fibers having the average fiber diameters and aspect ratios described in Table 1, sea components were subjected to elution treatment with a 3 mass% sodium hydroxide aqueous solution heated to 90°C and 65°C (bath ratio 1 / 100), respectively, whereby fiber dispersions were obtained. Then, the obtained fiber dispersions were measured in such a manner that the weight per unit area / mixing ratio described in Table 1 would be obtained, and the fibers were dispersed in such a manner that the fiber concentration in the dispersion would be 2.0 mass ppm, whereby papermaking fiber dispersions were obtained. To the papermaking fiber dispersions, a dispersant ("Y-258" (anionic surfactant) manufactured by Yuki Chemical Co., Ltd.) was added in such a manner that the concentration of the dispersant would be 0.020 mass%, and a thickening agent ("Meipam" (registered trademark) manufactured by Meisei Chemical Industry Co., Ltd.) was added in such a manner that the concentration would be 0.00030 mass% and was sufficiently stirred. Using the papermaking fiber dispersions, a square sheet machine (250 mm square) manufactured by Kumagai Riki Kogyo Co., Ltd. was used for papermaking, and after drying was performed using a rotary-type dryer with the roller temperature set to 120°C to obtain a dry fiber web, then, heat calendering was performed at an iron roll surface temperature of 220°C, a line pressure of 490 N / cm, and a roller rotation speed of 3 m / minute, a wet nonwoven fabric was obtained, and physical property evaluations thereof were performed. The evaluation results are shown in Table 1.

[0171] [Examples 2 to 22, Comparative Examples 1 to 8]

[0172] A wet nonwoven fabric was obtained in the same manner as in Example 1 except that the various conditions were changed as described in Tables 1 to 3.

[0173] As is apparent from the tables, the wet nonwoven fabrics of Examples 1 to 22 had high tensile strength and air permeability and high uniformity of the pore diameter, although the thickness was thin. In contrast, any of the thickness, strength, air permeability, or uniformity of the pore diameter of the wet nonwoven fabrics of Comparative Examples 1 to 8 was low.

[0174] [Table 1]

[0175] [Table 1]

[0176]

[0177] [Table 2]

[0178] [Table 2]

[0179]

[0180] [Table 3]

[0181] [Table 3]

[0182]

Claims

1. A wet nonwoven fabric comprising stretched polyarylene sulfide fibers with an average fiber diameter of 0.3 μm or more and 3.0 μm or less, an average pore size of 0.5 μm or more and 50.0 μm or less, and a basis weight of 1.0 g / m². 2 Above but less than 8.0 g / m 2 .

2. The wet nonwoven fabric according to claim 1, comprising the unstretched polyarylene sulfide fiber having an average fiber diameter of 0.8 μm or more and 6.0 μm or less.

3. The wet laid nonwoven fabric according to claim 1 or 2, wherein The aspect ratio of the stretched polyarylene sulfide fiber is 800 or more and 2000 or less, the aspect ratio being average fiber length / average fiber diameter. The aspect ratio of the unstretched polyarylene sulfide fiber is 400 or more and 1800 or less, the aspect ratio being average fiber length / average fiber diameter.

4. The wet nonwoven fabric according to claim 1 or 2, wherein In the pore size distribution curve, when a pore diameter representing a maximum peak of the pore size distribution is set as Dp (nm), pores of 0.9 Dp or more and 1.1 Dp or less account for 50% or more of the entire pores.

5. The wet nonwoven fabric according to claim 1 or 2, wherein The shrinkage rate after standing in an atmosphere at a temperature of 160°C for 24 hours is 8.0% or less.

6. The wet laid nonwoven fabric of claim 2, wherein, The average fiber diameter of the unstretched polyarylene sulfide fiber is finer than the average fiber diameter of the stretched polyarylene sulfide fiber.

7. An electrolyte-reinforced membrane comprising the wet nonwoven fabric according to claim 1 or 2.

8. A method for producing a wet nonwoven fabric, the wet nonwoven fabric being the wet nonwoven fabric according to claim 2, the method comprising a step of dispersing the stretched polyarylene sulfide fiber and the unstretched polyarylene sulfide fiber in an aqueous medium to obtain a dispersion liquid, the concentration of the fibers in the dispersion liquid being 1.0 mass ppm or more and 80.0 mass ppm or less.

9. The method for producing a wet nonwoven fabric according to claim 8, wherein A dispersant is contained in the dispersion liquid, the concentration of the dispersant with respect to the dispersion liquid being 0.0010 mass% or more and 8.0 mass% or less. A dispersant is contained in the dispersion liquid, the concentration of the dispersant with respect to the dispersion liquid being 0.0010 mass% or more and 8.0 mass% or less.

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