JP7365885B2 - Fiber sheet and its manufacturing method - Google Patents

Description

The present invention relates to a fiber sheet and a method for manufacturing the same.

Fiber sheets containing fibers containing a sulfo group-containing fluororesin having ion exchange ability such as Nafion can be used as ion exchange membranes, fuel cell electrolyte membranes, catalyst support materials, metal recovery materials, desalination materials, It is used for a variety of industrial materials such as decolorizing and dehydrating materials.
However, a fluororesin having a sulfo group tends to have poor spinnability when used alone, and, for example, it is difficult to produce a fiber sheet by electrostatic spinning. Therefore, as exemplified in JP-A No. 2006-233355 (Patent Document 1), a spinning method using a spinning solution containing a mixture of a fluorine-based resin having a sulfo group and a fiber-forming organic polymer has been considered. has been done.
Note that Patent Document 1 lists polyethylene oxide, polyvinyl alcohol, polyvinyl ester, polyvinyl ether, polyvinylpyridine, polyacrylamide, ether cellulose, pectin, etc. as specific examples of fiber-forming organic polymers, and The example discloses that a fiber structure was produced by electrostatically spinning a spinning solution containing Nafion and polyethylene oxide.

JP2006-233355A (Claims, 0020, 0023, 0025, Examples)

In order to further provide a fiber sheet that can be widely used in industrial material applications, the applicant has proposed a fiber sheet containing fibers (for example, fibers containing Nafion and polyethylene oxide) according to the above-mentioned prior art. Attempted to manufacture. However, it was thought that it would be difficult to realize a fiber sheet that can achieve both a thin fiber diameter and an ion exchange ability by simply referring to the prior art.

For example, if the proportion of fiber-forming organic polymers contained in a spinning solution is increased in order to realize a fiber sheet with a small fiber diameter, The content ratio of the fluororesin having a sulfo group becomes low, and the ion exchange ability of the fiber sheet is greatly reduced.
On the other hand, when the ratio of fiber-forming organic polymers contained in the spinning solution is reduced in order to prevent the ion exchange ability of the fiber sheet from being significantly reduced, the fiber sheet prepared using the spinning solution is The content ratio of fluororesin having a sulfo group in the constituent fibers becomes high, the spinnability decreases, and it is difficult to realize a fiber sheet with a small fiber diameter.

Therefore, there is a limit to providing a fiber sheet that can be widely used in industrial material applications just by referring to the prior art.

The present invention
“(Claim 1) A fiber sheet containing fibers containing a fluororesin having a sulfo group and a maleic anhydride copolymer and/or a maleic acid copolymer.
(Claim 2) (1) A step of preparing a spinning solution containing a fluororesin having a sulfo group and a maleic anhydride copolymer and/or a maleic acid copolymer;
(2) a step of preparing fibers by reducing the diameter of the spinning solution;
(3) collecting the fibers to prepare a fiber sheet;
A method for manufacturing a fiber sheet, comprising: ”
It is.

As a result of studies, the applicant of the present application has found that by satisfying the configuration of the present invention, it is possible to realize a fiber sheet that can achieve both a thin fiber diameter and ion exchange ability.
Although the reason for this is not completely clear, the applicant of this application believes that it is because the following effects are being achieved.

・Maleic anhydride copolymer is an acidic organic polymer that has a chemical structure in which a divalent carboxylic acid is dehydrated and condensed in its repeating unit; Since it is an acidic organic polymer containing a carboxylic acid, it has excellent ion exchange ability (especially, it has a superior ion exchange ability than an organic polymer having a monovalent carboxylic acid in its repeating unit). ). Even if the content ratio of maleic anhydride copolymer and/or maleic acid copolymer to the content ratio of fluororesin having a sulfo group is increased for the purpose of reducing the fiber diameter, both of the above-mentioned copolymers are ion-exchangeable. Therefore, it is possible to realize a fiber sheet with high ion exchange ability, which is prevented from greatly decreasing in ion exchange ability.

・Maleic anhydride copolymers and maleic acid copolymers are organic polymers that exhibit acidity (in particular, they can exhibit stronger acidity than acidic organic polymers that have monovalent carboxylic acids in their repeating units), and they also exhibit acidity. Easily miscible with fluororesins having sulfo groups. Even when the content ratio of maleic anhydride copolymer and/or maleic acid copolymer is lowered to the content ratio of fluororesin having a sulfo group for the purpose of realizing a fiber sheet with high ion exchange ability, the above-mentioned Since both copolymers easily mix well with the fluororesin having a sulfo group, the spinnability is unlikely to deteriorate and a fiber sheet with a small fiber diameter can be realized.

By exerting the above effects, even if the content ratio of maleic anhydride copolymer and/or maleic acid copolymer to the content ratio of fluororesin having a sulfo group is low or high, the fiber It is possible to provide a fiber sheet that has both a small diameter and ion exchange ability and can be widely used in industrial material applications.

By adopting the method for producing a fiber sheet according to the present invention, the content ratio of maleic anhydride copolymer and/or maleic acid copolymer to the content ratio of fluororesin having a sulfo group can be high even when it is low. Even in such cases, it is possible to produce a fiber sheet that can be used in a wide range of industrial material applications, having both a thin fiber diameter and ion exchange ability.

In the present invention, various configurations can be selected as appropriate, for example, the following configurations.
The various measurements described in the present invention were performed under normal pressure and 25° C. unless otherwise specified. Unless otherwise specified or specified, various measurement results described in the present invention were obtained by measurement to a value one digit smaller than the desired value, and the obtained value was calculated by rounding off the value. As a specific example, if the desired value is to the first decimal place, the value to the second decimal place is determined by measurement, and the value to the first decimal place is calculated by rounding the obtained value to the second decimal place. This value was used as the value to be determined.
Further, each upper limit value and each lower limit value illustrated in the present invention can be arbitrarily combined.

The fiber sheet according to the present invention includes fibers containing a fluororesin having a sulfo group and a maleic anhydride copolymer and/or a maleic acid copolymer.

The fluororesin referred to in the present invention is an organic resin having the following chemical structural formula in its skeleton, and has a sulfo group at its terminal portion and/or side chain portion.

In addition, x and m in this chemical structural formula are integers of 0 or more, and y and n are integers of 1 or more.

The type of fluororesin having such a sulfo group can be selected as appropriate so as to provide the fiber sheet according to the present invention. ), Solvay's Aquivion (registered trademark), Asahi Kasei Corporation's Aciplex (registered trademark), etc. can be adopted.

The molecular weight of the fluororesin having a sulfo group can be appropriately selected as long as the above-mentioned problems can be solved. Note that the molecular weight can be calculated by gel permeation chromatography measurement or NMR measurement, but if the molecular weight is described in the catalog, the stated value is regarded as the molecular weight. Alternatively, when the molecular weight cannot be obtained by the method described above, the product of the molecular weight of the repeating unit and the number of repeating units can be regarded as the molecular weight.

The mass percentage of the sulfo group-containing fluororesin to the organic resin mass contained in the constituent fibers of the fiber sheet can be adjusted as appropriate depending on the application and required physical properties of the industrial material, but the higher the mass percentage, the better the ion exchange It becomes easier to provide a fiber sheet with excellent performance. Therefore, the mass percentage is more than 0 mass%, preferably 1 mass% or more, preferably 10 mass% or more, preferably 30 mass% or more, and preferably 50 mass% or more. It is preferably 70% by mass or more, and preferably 80% by mass or more. Although the upper limit value is also adjusted appropriately, it is less than 100% by mass, can be 95% by mass or less, and can be 90% by mass or less.
Moreover, the type of fluororesin having a sulfo group contained in the constituent fibers of the fiber sheet may be one type or multiple types.

The maleic anhydride copolymer referred to in the present invention is an organic resin having a repeating unit represented by the following chemical structural formula in its skeleton.

In addition, R ₁ to R ₄ in this chemical structural formula are any of H, (CH ₂ ) _x CH ₃ (x≧0), O(CH ₂ ) _x CH ₃ (x≧0), and C ₆ H ₅ . or can be. Further, n is an integer of 1 or more.

The type of maleic anhydride copolymer can be selected as appropriate so as to provide the fiber sheet according to the present invention. AN-169, AN-903, etc.), Kuraray's Isoban (registered trademark, product number: Isoban-600, 04, 06, 10, 18, etc.), Cray Valley HSC Asia Limited's SMA (registered trademark, product number: SMA1000, 2000, 3000, etc.) can be adopted.

Furthermore, the maleic acid copolymer referred to in the present invention is an organic resin having a repeating unit represented by the following chemical structural formula in its skeleton.

In addition, R ₁ to R ₄ in this chemical structural formula are any of H, (CH ₂ ) _x CH ₃ (x≧0), O(CH ₂ ) _x CH ₃ (x≧0), and C ₆ H ₅ . or can be. Further, n is an integer of 1 or more.

The type of maleic acid copolymer can be selected as appropriate so as to provide the fiber sheet according to the present invention. , product number: S-97BF, etc.) can be adopted.

The molecular weight of the maleic anhydride copolymer and the maleic acid copolymer can be appropriately selected as long as the above-mentioned problems can be solved. The molecular weight can be calculated by gel permeation chromatography measurement or NMR measurement, but if the molecular weight is listed in the catalog, the stated value is considered to be the molecular weight. Alternatively, when the molecular weight cannot be obtained by the method described above, the product of the molecular weight of the repeating unit and the number of repeating units can be regarded as the molecular weight.

The mass percentage of the maleic anhydride copolymer and/or maleic acid copolymer in the mass of the organic resin contained in the constituent fibers of the fiber sheet can be adjusted as appropriate depending on the use of the industrial material and the required physical properties, but the mass percentage is large. The more the spinnability is improved, the more it is possible to provide a fiber sheet with a thinner fiber diameter. Therefore, the mass percentage is more than 0 mass%, preferably 1 mass% or more, preferably 10 mass% or more, preferably 30 mass% or more, and preferably 50 mass% or more. It is preferably 70% by mass or more, and preferably 80% by mass or more. Although the upper limit value is also adjusted appropriately, it is less than 100% by mass, can be 95% by mass or less, and can be 90% by mass or less.
Further, the type of maleic anhydride copolymer and/or maleic acid copolymer contained in the constituent fibers of the fiber sheet may be one type or multiple types.

The ratio of the sulfo group-containing fluororesin to the maleic anhydride copolymer and/or maleic acid copolymer in the constituent fibers of the fiber sheet is determined by adjusting the fineness of the fiber diameter and ion exchange capacity according to the application and required physical properties of the industrial material. Adjust as appropriate to provide a compatible fiber sheet.

The mass ratio of the organic resin can be adjusted such that, for example, the mass of the fluororesin having a sulfo group: the mass of the maleic anhydride copolymer and/or the maleic acid copolymer is in the range of 1:99 to 99:1, and 5 : Can be adjusted to be in the range of 95 to 95:5, can be adjusted to be in the range of 10:90 to 90:10, and can be adjusted to be in the range of 20:80 to 80:20 It can be adjusted to be in the range of 30:70 to 70:30, and it can be adjusted to be in the range of 40:60 to 60:40.

Similarly, the molar equivalent ratio of the organic resin is, for example, molar equivalent of fluororesin having a sulfo group: molar equivalent of maleic anhydride copolymer and/or maleic acid copolymer = 95:5 to 0.1:99.9. It can be adjusted to fall within a range of 63:37 to 1:99, and it can be adjusted to fall within a range of 31:69 to 5:95.

The molar equivalent of the fluororesin having a sulfo group here refers to the number of repeating units in the fluororesin having a sulfo group, and the molar equivalent of the maleic anhydride copolymer and/or the maleic acid copolymer refers to the number of repeating units in the fluororesin having a sulfo group. Refers to the maleic acid copolymer and/or the number of repeating units in the maleic acid copolymer. The molar equivalent ratio refers to the ratio of the molar equivalent of the fluororesin having a sulfo group to the molar equivalent of the maleic anhydride copolymer and/or the maleic acid copolymer.

In addition, the mass ratio of the mass of the fluororesin having a sulfo group to the mass of the maleic anhydride copolymer and/or the maleic acid copolymer contained in the constituent fibers of the fiber sheet, and the number of repeating units in each organic resin. If the chemical structural formula is known, the molar equivalent ratio can be calculated from the mass ratio and the molecular weight of each repeating unit.
As a specific example, the mass ratio of the fluororesin having a sulfo group and the maleic anhydride copolymer contained in the constituent fibers of the fiber sheet is 90 parts by mass: 10 parts by mass, and the fluororesin having a sulfo group contains If the molecular weight of the repeating unit is 100 (M.W.), and if the molecular weight of the repeating unit in the maleic anhydride copolymer is 50 (M.W.), then the sulfo group-containing fluororesin: moles of the maleic anhydride copolymer The equivalent ratio can be calculated to be (90/100):(10/50), that is, 9:2.

The constituent fibers of the fiber sheet according to the present invention contain a fluororesin having a sulfo group and a maleic anhydride copolymer and/or a maleic acid copolymer, but may contain other resins and additives. .

Other resins include, for example, polyolefin resins (e.g., polyethylene, polypropylene, polymethylpentene, polyolefin resins with a structure in which part of the hydrocarbon is replaced with a cyano group or a halogen such as fluorine or chlorine), styrene resins, Polyvinyl alcohol resin, polyether resin (e.g. polyether ether ketone, polyacetal, modified polyphenylene ether, aromatic polyether ketone, etc.), polyester resin (e.g. polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene) naphthalate, polybutylene naphthalate, polycarbonate, polyarylate, fully aromatic polyester resin, etc.), polyimide resin, polyamideimide resin, polyamide resin (e.g. aromatic polyamide resin, aromatic polyetheramide resin, nylon resin, etc.) ), resins with nitrile groups (e.g., polyacrylonitrile, etc.), urethane resins, epoxy resins, polysulfone resins (e.g., polysulfone, polyethersulfone, etc.), fluorine resins (e.g., polytetrafluoroethylene, polyfluoroethylene, etc.). (vinylidene chloride, etc.), cellulose fibers, polybenzimidazole resins, acrylic resins (for example, polyacrylonitrile resins copolymerized with acrylic esters or methacrylic esters, modacrylic resins copolymerized with acrylonitrile and vinyl chloride or vinylidene chloride) etc.), etc.), etc.).

Note that there may be multiple types of other resins, and these resins may be made of either a linear polymer or a branched polymer, and the resin may be a block copolymer or a random copolymer. But that's fine. Further, the three-dimensional structure of the resin and the presence or absence of crystallinity may be arbitrary.

The type and content ratio of the resin (fluororesin having a sulfo group, maleic anhydride copolymer and/or maleic acid copolymer, and other resins) contained in the constituent fibers of the fiber sheet according to the present invention are as follows: By subjecting the constituent fibers to various analytical devices such as IR measurement, NMR measurement, thermogravimetry, differential scanning calorimetry, and elemental analysis, it is possible to qualitatively and/or quantitatively analyze and determine.

In addition, in the manufacturing process of the fiber sheet described below, materials forming the constituent fibers of the fiber sheet (for example, fluororesin having a sulfo group contained in the spinning solution, maleic anhydride copolymer and/or maleic acid copolymer, other resins) ), their purity, solid content concentration, and each mixing ratio in the spinning solution are known, the types of each resin contained in the spinning solution and their mixing ratio can be determined in the fiber sheet. It can be determined that it is the type of resin contained in the constituent fibers and their mixing ratio.

In addition, when a fiber sheet is prepared using a spinning solution containing a maleic anhydride copolymer, a chemical structure in which divalent carboxylic acids in the maleic anhydride copolymer are dehydrated and condensed during the spinning process and drying process. The maleic anhydride copolymer may be cleaved to convert the maleic anhydride copolymer into a copolymer (eg, a maleic acid copolymer) with a chemical structure having a divalent carboxylic acid moiety. Even in this case, the ratio of the molar equivalent of the fluororesin having a sulfo group contained in the spinning solution to the molar equivalent of the maleic anhydride copolymer and/or maleic acid copolymer (mixing ratio in molar equivalents) ) is caused by dehydration condensation of the molar equivalent of the fluororesin having a sulfo group contained in the constituent fibers of the fiber sheet and the maleic anhydride copolymer and/or the maleic acid copolymer and the divalent carboxylic acid in the maleic anhydride copolymer. It can be determined that it is the ratio of the molar equivalent of the copolymer formed by the cleavage of the chemical structure moiety (molar equivalent ratio contained in the constituent fibers).

The constituent fibers of the fiber sheet may contain additives as necessary depending on the use of the industrial material, required physical properties, etc. Examples of additives include flame retardants, fragrances, pigments (inorganic pigments and/or organic pigments), antibacterial agents, antifungal materials, photocatalyst particles, conductive particles, emulsifiers, dispersants, thickeners, and antifoaming agents. agent, crosslinking agent, curing accelerator, etc.

Moreover, the fiber sheet may contain fibers made of other resins mentioned above. The mass ratio of fibers containing a sulfo group-containing fluororesin and maleic anhydride copolymer and/or maleic acid copolymer to other fibers in the constituent fibers of the fiber sheet is determined by the use of the industrial material, required physical properties, etc. However, in order to provide a fiber sheet that can be widely used in industrial material applications, we have developed a fiber sheet that is made only of fibers containing a fluororesin having a sulfo group and a maleic anhydride copolymer and/or a maleic acid copolymer. It is preferable that the fiber sheet is made of fibers.

The average fiber diameter of the fibers contained in the fiber sheet and the average fiber length of the fibers contained in the fiber sheet can be adjusted as appropriate depending on the use of the industrial material, required physical properties, etc.

The thinner the average fiber diameter, the larger the surface area, which improves the ion exchange ability, and also improves various performances such as separation performance, liquid retention performance, wiping performance, hiding performance, insulation performance, and flexibility. We can provide fiber sheets with excellent properties. Therefore, the average fiber diameter is preferably 3 μm or less, preferably 2 μm or less, preferably 1 μm or less, and preferably 800 nm or less. Although the lower limit of the average fiber diameter is adjusted as appropriate, it is realistically 1 nm or more, and preferably 100 nm or more. The "average fiber diameter" herein refers to the arithmetic mean value of each fiber diameter of 50 fibers measured based on an electron micrograph taken at 5000 times magnification of a portion to be measured including fibers. When the cross-sectional shape of the fiber is non-circular, the diameter of a circle with the same area as the cross-sectional area is regarded as the fiber diameter.

The fiber length can be adjusted as appropriate, and specifically, the fibers can be short fibers, long fibers, or continuous fibers. In particular, it is preferable that the fibers constituting the fiber sheet include fibers having a continuous length, since the reduced number of fiber ends in the fiber sheet results in a smooth surface and can be widely used in industrial materials. Preferably, the fibers constituting the fiber sheet are only continuous fibers.

The fibrous sheet as used in the present invention refers to a sheet-like fibrous structure containing the above-mentioned fibers as constituent fibers, and can be, for example, a fibrous web, a nonwoven fabric, a woven fabric, a knitted fabric, or the like. In particular, fibrous sheets have excellent properties such as large surface area and porosity, and excellent flexibility, and their structure of randomly containing fibers efficiently exhibits rigidity and reinforcing properties. Most preferably, it is a fibrous web or non-woven fabric.

The fabric weight and thickness of the fiber sheet can be adjusted as appropriate depending on the use of the industrial material and the required physical properties. Its basis weight can be from 0.1 to 20 g/m ² , from 0.5 to 15 g/m ² , from 1 to 10 g/m ² . The thickness thereof is preferably 100 μm or less, preferably 75 μm or less, and preferably 50 μm or less. On the other hand, it is realistic that the thickness is 1 μm or more. In the present invention, the basis weight refers to the mass converted per 1 m ² on the main surface of the object to be measured, and the thickness refers to the thickness gauge (manufactured by Mitutoyo Co., Ltd., code No.: 547-401, measuring force 3). .5N or less).

Further, if necessary, a binder may be added to the fiber sheet of the present invention in order to bond fiber intersection points or to support additives. Note that the composition of the binder and the method of applying the binder can be adjusted as appropriate.

Next, a method for manufacturing a fiber sheet according to the present invention will be illustrated and explained. It should be noted that explanations of items having the same configuration as those already explained will be omitted.

The method for preparing the fiber sheet can be selected as appropriate, but examples include electrostatic spinning, a method of spinning by the action of gas as disclosed in JP-A No. 2009-287138, and a method of spinning by the action of gas as disclosed in JP-A No. 2011-32593. A method of spinning by applying shear force of a gas in addition to the action of an electric field, such as a centrifugal spinning method, etc. can be used. Then, by using these preparation methods to reduce the diameter of the spinning solution and turn it into fibers, the fiber web can be formed on the collecting body, for example, by collecting the spinning solution on a collecting body such as a net, a drum, or a belt conveyor.

Among these, it is easy to spin ultrafine fibers with an average fiber diameter of 3 μm or less by using an electrospinning method or a method of spinning using gas shearing action as disclosed in JP 2009-287138A. This is suitable because it is easy to prepare a fiber sheet consisting only of continuous ultrafine fibers with uniform fiber diameters.

As a preferred method for producing the fiber sheet according to the present invention, a spinning solution (solution, dispersion, or melting of the resin) containing a fluororesin having a sulfo group and a maleic anhydride copolymer and/or a maleic acid copolymer is used. Prepare the liquid. Then, the spinning solution is subjected to an electrostatic spinning method to reduce the diameter of the spinning solution to prepare fibers, and the fibers are collected to prepare a fiber sheet such as a fiber web.

When a fiber sheet is prepared using a spinning solution containing a solution or a dispersion liquid, the fiber sheet may be subjected to heat treatment in order to remove the remaining solvent or dispersion liquid from the prepared fiber sheet. The type of heat treatment can be selected as appropriate; for example, treatment using a device that heats with a roll or heats and presses, an oven dryer, a far infrared heater, a dry heat dryer, a hot air dryer, a device that can heat by irradiating infrared rays, etc. is adopted. can. The heating temperature by the heating device is selected appropriately, but it is adjusted appropriately so that the solution or dispersion can be removed by volatilization or decomposition, and the temperature will not unintentionally decompose or denature the constituent components such as constituent fibers. . As a specific example, the temperature can be in the range of 80 to 300°C.

Alternatively, the fiber sheet prepared as described above may be immersed in water or the like to elute and remove the solution or dispersion liquid remaining in the constituent fibers.

In addition, the physical properties of the fiber can be improved by improving the heat resistance of the constituent components of the fiber and/or making them insolubilized by the above-mentioned heat treatment or by reacting with an additive such as a crosslinking agent. Good too.
Furthermore, the fiber sheet prepared as described above may be subjected to a pressure treatment such as calender treatment in order to smooth the surface.
Alternatively, a fiber sheet may be prepared that has been subjected to surface modification treatment such as plasma treatment, sulfonation treatment, or fluorination treatment, or charging treatment.

The prepared fiber sheet may be used as it is for various industrial material applications, but it may also be necessary to use the process of preparing a composite membrane containing the fiber sheet in the membrane-constituting resin, or another porous body, film, foam, etc. After going through various secondary processes such as the process of laminating the component parts to prepare a laminate, and the process of processing such as molding and punching out shapes according to the purpose and usage, it can be used for various industrial materials. good.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but these are not intended to limit the scope of the present invention.

(Method for preparing spinning solution)
An alcohol dispersion of a fluororesin having a sulfo group (manufactured by Fuji Film Wako Chemical Co., Ltd., product number: 20% Nafion dispersion solution DE2020CS, solid content concentration: 20% by mass) was prepared.
Next, maleic anhydride copolymer (manufactured by ISP, GANTREZ (registered trademark), product number: AN139, molecular weight: Mw = 1,080,000) was dissolved in ion-exchanged water to obtain an aqueous maleic anhydride copolymer solution (solid content concentration: 20% by mass) was prepared.
The solid content ratio of the sulfo group-containing fluororesin and maleic anhydride copolymer and/or maleic acid copolymer contained in the constituent fibers of the finally prepared nonwoven fabric is the "mass ratio" in Table 1. By mixing the maleic anhydride copolymer aqueous solution prepared as described above and the Nafion dispersion solution so that the content ratios are as described in the column and the "Mole equivalent ratio" column, various spinning solutions with different mixing ratios can be obtained. was prepared.

(Electrospinning conditions and nonwoven fabric manufacturing method)
A grounded power supply was connected to a metal nozzle with an inner diameter of 0.33 mm. A grounded collector (metal plate) was provided so as to face the opening at the tip of the nozzle. At this time, the shortest distance between the nozzle tip and the collector was adjusted to 3 to 10 cm. A power supply of 15 to 27.5 kV was applied to the nozzle to form an electric field between the nozzle and the collector.
The amount of the spinning solution discharged from the opening of the nozzle was adjusted to be 1 cc/hour, and the spinning solution was guided to an electric field to fly the spinning solution from the opening at the tip of the nozzle to the collecting body and reduce the diameter. An attempt was made to prepare a fibrous web by converting the fibers into fibers and collecting them on a collector. The spinning environment in this step was adjusted to a temperature of 25° C. and a humidity of 40% RH.
Thereafter, the prepared fibrous web was peeled off from the collector and heat-treated at 180°C for 30 minutes to volatilize and remove the solvent and dispersion medium remaining in the constituent fibers ^. , thickness: 20 μm).

Regarding the Examples and Comparative Examples prepared as described above, the solid content mass (A) of the fluororesin having a sulfo group contained in the spinning solution and the solid content of the maleic anhydride copolymer and/or the maleic acid copolymer are shown. The mass ratio of mass (B) is listed in the "Mixed mass ratio" column in the table. In addition, the ratio of the molar equivalent (a) of the fluororesin having a sulfo group to the molar equivalent (b) of the maleic anhydride copolymer and/or maleic acid copolymer in the constituent fibers of the fiber sheet is determined by the "molar equivalent" in the table. It is stated in the "Ratio" column.

The average fiber diameter of the nonwoven fabrics of the Examples and Comparative Examples prepared as described above was measured and listed in the table. In addition, in Comparative Example 1, an attempt was made to manufacture a fiber sheet using only an alcohol dispersion of a fluororesin having a sulfo group as a spinning solution. ), and it was not possible to produce nonwoven fabric. Items that could not be measured because they could not be spun are marked with an "x" in the table.

Among the examples, the nonwoven fabric of Example 1 has a high content ratio of fluororesin having a sulfo group in its constituent fibers, so it has superior ion exchange ability than the other examples, and also has maleic anhydride. The nonwoven fabric contained a copolymer and/or a maleic acid copolymer and had a small average fiber diameter.
Furthermore, among the examples, the nonwoven fabric of Example 4 is considered to have a lower ion exchange ability than the other examples because the content ratio of the fluororesin having a sulfo group contained in the constituent fibers is low. However, since it contains a maleic anhydride copolymer and/or a maleic acid copolymer that has excellent ion exchange ability, it has an excellent ion exchange ability that prevents a large decrease in ion exchange ability compared to fiber sheets related to conventional technology. It was thought to be a non-woven fabric. The nonwoven fabric had a small average fiber diameter.

Based on the above results, according to the present invention, the fiber diameter can be adjusted regardless of whether the content ratio of maleic anhydride copolymer and/or maleic acid copolymer to the content ratio of fluororesin having a sulfo group is low or high. It has been found that it is possible to provide a fiber sheet that has both thinness and ion exchange ability and can be widely used in industrial material applications.

The fiber sheet of the present invention can be used for various industrial materials (e.g., liquid separation membranes such as water treatment membranes, gas separation membranes, medical materials, ion exchange membranes, dialysis membranes, polymer electrolyte membranes for fuel cells, etc.). As a support for composite membranes that can be used in industrial applications, separators for electrochemical devices such as capacitors and primary/secondary batteries, prepregs, gas filters and liquid filters, catalyst support materials, metal recovery materials, desalination materials, It can be used as a decolorizing agent, dehydrating agent, etc.).

Claims (2)

A fiber sheet containing fibers containing a fluororesin having a sulfo group and a maleic anhydride copolymer and/or a maleic acid copolymer. (1) A step of preparing a spinning solution containing a fluororesin having a sulfo group and a maleic anhydride copolymer and/or a maleic acid copolymer;
(2) a step of preparing fibers by reducing the diameter of the spinning solution;
(3) collecting the fibers to prepare a fiber sheet;
A method for manufacturing a fiber sheet, comprising: