Electrospun nonwoven fabric

Abstract

To achieve an electrospinning nonwoven fabric in which mass of iron contained in resin to be constituent fiber is small in order to provide an electrospinning nonwoven fabric available for a wide range of industrial use.SOLUTION: An electrospinning nonwoven fabric in which mass of iron contained in 1 gram of resin to be constituent fiber is less than 70.7 μg that is smaller than the content of iron in an electrospinning nonwoven fabric based on a prior art can be provided by preventing a spinning liquid from contacting with a member containing heavy metal during a period between contacting of the spinning liquid with a voltage applying member and discharging of the spinning liquid from a discharge member in an electrospinning producing method and producing device so that the electrospinning nonwoven fabric is available for a wide range of industrial use.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electrospun nonwoven fabric. [Background technology]

[0002] In recent years, nonwoven fabrics have been used in a variety of industrial applications, for example, as supports for composite membranes, such as liquid separation membranes for water treatment and gas separation membranes, medical materials, ion exchange membranes, dialysis membranes, water electrolysis membranes, and polymer electrolyte membranes for fuel cells; or as separators for electrochemical elements, such as capacitors and primary / secondary batteries, or separator support members, particle support materials forming sheets that support particles, prepregs, gas filters, liquid filters, medical applications, such as drug patch substrates and masks, cushioning materials, sealing materials, liquid-absorbent materials, interior skin materials, cell culture substrates and cell separation materials, conductive materials and insulating materials, heat dissipation materials and heat-retaining materials, interlinings and padding, etc.

[0003] In particular, it is expected that the fiber surface area of ​​the nonwoven fabric can be increased by narrowing the fiber diameter of the fibers constituting the nonwoven fabric, and the functionality in the above-mentioned applications can be improved. As a nonwoven fabric composed of such fibers with a narrow fiber diameter, the use of electrospun nonwoven fabric has been attracting attention in recent years. As is well known from being described in "Electrospinning Frontier (Non-Patent Document 1)", electrospun nonwoven fabric is a nonwoven fabric formed by applying a voltage to a spinning solution that passes through a liquid supply path and is supplied to a discharge member such as a nozzle by contacting a voltage application member, and discharging the spinning solution to which the voltage has been applied from the discharge member to turn the spinning solution into fibers and collect the spinning solution in a collector that is earthed or the like.

[0004] In addition, regarding a manufacturing method and a manufacturing apparatus for such an electrospun nonwoven fabric, JP 2011-102455 A (Patent Document 1) describes: A method can be adopted in which electrodes that serve as voltage application members are installed in the liquid delivery pipe, which is the liquid supply path. - The electrodes can be made of conductive materials such as metals and carbon. The material of the nozzle, which is the ejection member, is preferably, for example, engineering plastics such as Teflon (registered trademark) and Duracon (registered trademark), resins such as polyethylene, polypropylene, polysiloxane, polystyrene, polyamide, and polyvinyl chloride, metals such as stainless steel, iron, copper, nickel, platinum, gold, and silver, and conductive materials such as carbon. In the examples of Patent Document 1, it is disclosed that an electrospun nonwoven fabric is produced by using a metallic pipe electrode as a voltage application member that comes into contact with the spinning solution, and a nozzle made of stainless steel, which is an iron alloy, or a resin as a discharge member. [Prior art documents] [Patent documents]

[0005] [Non-Patent Document 1] The Frontline of Electrospinning (Author: Yoshihiro Yamashita, Publisher: Sen-i-sha Co., Ltd., Publication Year: 1st Edition January 20, 2007) [Patent Document 1] JP 2011-102455 A (claims, 0023, 0088, table 12, etc.) Summary of the Invention [Problem to be solved by the invention]

[0006] The applicant of the present application has attempted to provide an electrospun nonwoven fabric based on the findings disclosed in the prior art as described above. However, the electrospun nonwoven fabric according to the prior art has limitations in its use in various industrial applications. For example, when the electrospun nonwoven fabric according to the prior art is used in an industrial application in which it comes into contact with a liquid, the concentration of iron, a type of heavy metal, in the liquid may increase. In addition, when the electrospun nonwoven fabric according to the prior art is used as a component of an electrochemical element, problems such as an unintended decrease in the power generation performance of the electrochemical element may occur.

[0007] The applicant of the present application has investigated the cause and found that in the electrospun nonwoven fabric according to the conventional technology, the mass of iron contained in the resin constituting the constituent fibers is greater than the mass of iron contained in the resin constituting the spinning solution used to manufacture the electrospun nonwoven fabric. In other words, as long as the electrospun nonwoven fabric is based on the conventional technology, it has been impossible to provide an electrospun nonwoven fabric with a small mass of iron contained in the resin constituting the constituent fibers.

[0008] Based on these new findings, it was deemed necessary to develop an electrospun nonwoven fabric with a low iron mass contained in the resin that makes up the constituent fibers in order to provide an electrospun nonwoven fabric that can be used for a wider variety of industrial applications.

[0009] Furthermore, in order to investigate the cause of the above-mentioned problems, the applicant of the present application conducted detailed observations using a microscope and disassembled each component of the electrospun nonwoven fabric manufacturing apparatus according to the conventional technology after the electrospun nonwoven fabric had been produced. As a result, traces of melting and deposition of scale-like substances thought to be metal salts were found on heavy metal-containing components that contain heavy metals such as iron and that come into contact with the spinning solution to which voltage was applied (for example, a stainless steel pipe electrode and a stainless steel nozzle, which are an alloy containing at least iron and chromium).

[0010] From the results of this analysis, the applicant of the present application speculated that, in the manufacturing apparatus for electrospun nonwoven fabric according to the prior art, when the spinning solution to which a voltage is applied comes into contact with a heavy metal-containing member (for example, a stainless steel pipe electrode or a stainless steel nozzle, which is an alloy containing at least iron and chromium), the heavy metal-containing member is electrolyzed, and the heavy metal contained in the metal-containing member is dissolved into the spinning solution. Specifically, the applicant speculated that, when the spinning solution to which a voltage is applied comes into contact with a stainless steel pipe electrode or a stainless steel nozzle, the pipe electrode or nozzle is electrolyzed, and the iron contained in the pipe electrode or nozzle is dissolved into the spinning solution. [Means for solving the problem]

[0011] The present invention relates to " (Claim 1) Constituent fiber Polyethersulfone The mass of iron contained in 1g 10μg or less This is an electrospun nonwoven fabric. (Claim 2) A method for producing an electrospun nonwoven fabric, comprising: (1) preparing a spinning solution containing a resin that forms the constituent fibers of the electrospun nonwoven fabric; (2) preparing a liquid storage section for storing the spinning solution; (3) supplying the spinning solution from the storage section to a discharge member that discharges the spinning solution through a liquid supply path; (4) applying a voltage to the spinning liquid passing through the liquid supply path by a voltage application member constituting the liquid supply path, the voltage application member being in contact with the spinning liquid passing through the liquid supply path and capable of applying a voltage to the spinning liquid; (5) a step of collecting the spinning solution discharged from the discharge member and turned into fibers in a collector; The spinning solution does not come into contact with a heavy metal-containing member during the period from when the spinning solution comes into contact with the voltage application member until when the spinning solution is discharged from the discharge member. A method for producing electrospun nonwoven fabric. " It is. Effect of the Invention

[0012] As a result of extensive investigations, the applicant has now come to provide an electrospun nonwoven fabric that has a lower iron content than electrospun nonwoven fabrics made using conventional technology, with the mass of iron contained being less than 70.7 μg per gram of resin constituting the constituent fibers, and that can be used for a variety of industrial applications. [Brief description of the drawings]

[0013] [Figure 1] FIG. 2 is a schematic side view showing a manufacturing apparatus for electrospun nonwoven fabric. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] In the present invention, various configurations, such as the following configurations, can be appropriately selected. In addition, unless otherwise specified, various measurements described in the present invention were performed under normal pressure and at 25°C (room temperature) temperature conditions. In addition, unless otherwise specified, various measurement results described in the present invention were measured to a value one digit smaller than the desired value, and the desired value was calculated by rounding off the value. As a specific example, when the desired value is to the first decimal place, the value was measured to the second decimal place, and the obtained value to the first decimal place was rounded off to calculate the value to the first decimal place, and this value was used as the desired value. In addition, each upper limit value and each lower limit value exemplified in the present invention can be arbitrarily combined.

[0015] The basis weight, thickness, and porosity of the electrospun nonwoven fabric according to the present invention can be appropriately adjusted depending on the application and required properties. 2 and the thickness can be 0.05 to 50 g / m 2 and 0.1 to 25 g / m 2 It is possible to use a thickness of 1 μm or more. The term "basis weight" refers to the mass converted per square meter on the main surface of the object to be measured. The thickness is preferably 100 μm or less, more preferably 75 μm or less, and even more preferably 50 μm or less. On the other hand, it is practical for the thickness to be 1 μm or more. The term "thickness" refers to the length measured using a thickness gauge (manufactured by Mitutoyo Corporation, code No. 547-401, measuring force 3.5 N or less) in a direction perpendicular to the main surface of the object to be measured.

[0016] The porosity may be 70 to 99%, 80 to 95%, or 85 to 90%. The term "porosity" refers to the percentage of the volume of the components constituting the object relative to the apparent volume of the object.

[0017] The average fiber diameter of the fibers constituting the electrospun nonwoven fabric can be appropriately adjusted depending on the application, required physical properties, etc. The average fiber diameter can be 0.01 to 10 μm, 0.02 to 5 μm, 0.05 to 3 μm, or 0.1 to 1 μm. The term "average fiber diameter" refers to the arithmetic average value of the fiber diameters of 50 points of the fibers measured based on an electron microscope photograph of a measurement target part containing the fibers at a magnification of 5000 times. In addition, when the cross-sectional shape of the fiber is noncircular, the diameter of a circle having the same area as the cross-sectional area is regarded as the fiber diameter.

[0018] The cross-sectional shape of the fibers constituting the electrospun nonwoven fabric can be adjusted appropriately depending on the application, required physical properties, etc. In addition to circular, nearly circular, or elliptical fibers, irregular cross-sectional fibers may also be used. The irregular cross-sectional fibers may have a fiber cross-section having a hollow shape, a polygonal shape such as a triangular shape, an alphabet character shape such as a Y-shape, an irregular shape, a multi-lobed shape, a symbol shape such as an asterisk shape, or a shape in which multiple of these shapes are combined.

[0019] The type of resin forming the fibers constituting the electrospun nonwoven fabric can be appropriately adjusted depending on the application, required physical properties, etc. For example, polyolefin resins (e.g., polyethylene, polypropylene, polymethylpentene, polyolefin resins having a structure in which a part of the hydrocarbon is substituted with a nitrile group or a halogen such as fluorine or chlorine, etc.), styrene resins, polyvinyl alcohol resins, polyether resins (e.g., polyether ether ketone, polyacetal, modified polyphenylene ether, aromatic polyether ketone, etc.), polyester resins (e.g., polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polycarbonate, polyarylate, wholly aromatic polyester resins, etc.), polyimide resins, polyamides, etc. It can be constructed using known organic polymers such as imide resins, polyamide resins (e.g., aromatic polyamide resins, aromatic polyetheramide resins, nylon resins, etc.), resins having nitrile groups (e.g., polyacrylonitrile, etc.), urethane resins, epoxy resins, polysulfone resins (e.g., polysulfone, polyethersulfone, etc.), fluorine resins (e.g., polytetrafluoroethylene, polyvinylidene fluoride, etc.), cellulose fibers, polybenzimidazole resins, and acrylic resins (e.g., polyacrylonitrile resins copolymerized with acrylic acid esters or methacrylic acid esters, modacrylic resins copolymerized with acrylonitrile and vinyl chloride or vinylidene chloride, etc.).

[0020] The other resins may be of multiple types, and may be either linear or branched polymers, or may be block or random copolymers. The resins may have any three-dimensional structure or may have any crystallinity.

[0021] Alternatively, the fibers may be composite fibers made of multiple different resins, such as an island-in-the-sea type, a core-sheath type, an orange type, a side-by-side type, etc. However, in order to provide electrospun nonwoven fabrics that can be used for various industrial applications, it is preferable that the electrospun nonwoven fabric is made of fibers made of only one type of resin.

[0022] The electrospun nonwoven fabric of the present invention is characterized by its low content of iron, a type of heavy metal; specifically, the mass of iron contained per gram of resin constituting the constituent fibers is as low as less than 70.7 μg.

[0023] As used herein, heavy metals refer to a general term for metals with a specific gravity of 4 to 5 or more, as described in the Kojien dictionary (5th edition, editor: Shinmura Izuru, publisher: Iwanami Shoten, published on November 11, 1998), such as iron (specific gravity: 7.9), chromium (specific gravity: 7.2), nickel (specific gravity: 8.9), and zinc (specific gravity: 7.1).

[0024] The smaller the mass, the more versatile the electrospun nonwoven fabric that can be used for various industrial applications can be provided. Therefore, the mass of iron contained per gram of the resin constituting the fibers of the electrospun nonwoven fabric is preferably 70.0 μg or less, more preferably 65.0 μg or less, more preferably 60.0 μg or less, and more preferably 57.1 μg or less.

[0025] In addition, the lower the content of heavy metals other than iron contained in the electrospun nonwoven fabric, the more versatile the electrospun nonwoven fabric can be used for various industrial applications. Therefore, the content of heavy metals other than iron contained per gram of resin constituting the constituent fibers of the electrospun nonwoven fabric is preferably less than 70.7 μg. As a specific example, the mass of chromium is preferably 1.5 μg or less, preferably 1.3 μg or less, preferably 1.0 μg or less, and preferably 0.8 μg or less. And, the mass of nickel is preferably 2.0 μg or less, preferably 1.5 μg or less, preferably 1.0 μg or less, and preferably less than 0.5 μg. Furthermore, the mass of zinc is preferably 6.0 μg or less, preferably 5.5 μg or less, preferably 4.0 μg or less, and preferably 2.4 μg or less.

[0026] Ideally, the mass of heavy metals contained per gram of resin constituting the constituent fibers of the electrospun nonwoven fabric is preferably less than 60.8 μg, preferably 60.3 μg or less, preferably 50 μg or less, preferably 40 μg or less, preferably 30 μg or less, preferably 20 μg or less, preferably 10 μg or less, and most preferably 0 μg. The heavy metals such as iron defined in the present invention may be a concept including their salts. The mass of various heavy metals such as iron contained in the resin can be confirmed by the following method.

[0027] (Method for checking the mass of various heavy metals such as iron contained in resin) 1. Prepare 100 mg of the resin to be measured and use this as a sample. As a specific example, take 100 mg of constituent fibers from an electrospun nonwoven fabric and use this as a sample. Alternatively, if the electrospun nonwoven fabric is composed only of fibers made of the resin, prepare 100 mg of the electrospun nonwoven fabric and use this as a sample. 2. Place the sample in a conical beaker containing 10 ml of 95 wt% sulfuric acid. 3. Heat the conical beaker until white sulfuric acid smoke is released and the sulfuric acid turns brown to black, then leave it to cool to room temperature. 4. Add 3 ml of 60 wt% nitric acid to the conical beaker, heat the conical beaker again until white sulfuric acid smoke appears, then allow the sulfuric acid to cool to room temperature. 5. Repeat steps 3 and 4 above until the sulfuric acid no longer turns brown or black, even if white sulfuric acid smoke is produced by heating. 6. After carrying out step 5 above, heat the conical beaker until the amount of sulfuric acid is reduced to 2 ml or less, then allow it to cool to room temperature. 7. After allowing to cool, add 1 ml of 60 wt% nitric acid to the sulfuric acid, then add ultrapure water up to 50 ml to prepare the test solution. 8. The test liquid is subjected to an atomic absorption spectrometer to measure the mass of various heavy metals, such as iron, contained in the test liquid. 9. The measured masses (unit: μg) of various heavy metals such as iron are multiplied by 10 to obtain the mass (unit: μg) of various heavy metals such as iron contained in 1 g of the resin that constitutes the constituent fibers of the electrospun nonwoven fabric. The type of metal contained in the resin can be confirmed by subjecting the test liquid to an atomic absorption spectrometer.

[0028] The electrospun nonwoven fabric according to the present invention may contain additives such as a binder that bonds the constituent fibers together, a flame retardant, a fragrance, a pigment, an antibacterial agent, an antifungal material, photocatalyst particles, an emulsifier, a dispersant, a surfactant, a thickener, etc. However, in order to provide an electrospun nonwoven fabric that can be used for various industrial applications, it is preferable that the electrospun nonwoven fabric is composed only of fibers.

[0029] An electrospun nonwoven fabric manufacturing apparatus capable of manufacturing the electrospun nonwoven fabric according to the present invention will be described with reference to Fig. 1. Note that a manufacturing method for electrospun nonwoven fabric capable of manufacturing the electrospun nonwoven fabric according to the present invention will be described together with the manufacturing apparatus.

[0030] The electrospun nonwoven fabric manufacturing apparatus (100) shown in Fig. 1 includes a liquid storage section (1) capable of storing a spinning solution containing a resin that forms the constituent fibers of the electrospun nonwoven fabric (11), a discharge member (2) capable of discharging the spinning solution, a liquid supply path (3) capable of supplying the spinning solution from the liquid storage section (1) to the discharge member (2), a voltage application member (4) constituting the liquid supply path capable of contacting the spinning solution passing through the liquid supply path (3) and applying a voltage to the spinning solution, and a collector (5) capable of collecting the spinning solution (10) discharged from the discharge member (2) and turned into fibers. The period from when the spinning solution comes into contact with the voltage application member (4) until it is discharged from the discharge member (2) is shown as (6).

[0031] 1 further includes a liquid delivery means (7) for delivering the spinning liquid from the liquid storage section (1) to the liquid supply path (3), a power supply (8) for supplying electricity to the voltage application member (4), and a ground (9) for the power supply (8) and the collector (5). Note that the wavy lines connecting the voltage application member (4) and the power supply (8), between the power supply (8) and the ground (9), and between the collector (5) and the ground (9) are illustrations of electric wires.

[0032] First, the spinning solution stored in the storage section (1) passes through a liquid supply path (3) such as a pipe by the action of the liquid delivery means (7) and is discharged from a discharge member (2) such as a nozzle. A voltage application member (4) constituting a part of the liquid supply path (3) is present in the middle of the liquid supply path (3), and the voltage application member (4) comes into contact with the spinning solution. The voltage application member (4) may have a shape protruding from the inner wall surface of the liquid supply path (3). A voltage is applied to the voltage application member (4) by the power supply (8), so that a voltage is applied to the spinning solution in contact with the voltage application member (4). The spinning solution discharged from the discharge member (2) such as a nozzle and to which a voltage has been applied is attracted toward the collector (5) earthed (9) and is thinned to be fiberized, while flying in the space between the discharge member (2) and the collector (5), and is collected on the collector (5) to produce an electrospinning nonwoven fabric (11).

[0033] As a result of investigations, the applicant of the present application has found that in a method for producing an electrospun nonwoven fabric comprising a step of applying a voltage to the spinning liquid passing through a liquid supply path (3) by means of a voltage application member (4) constituting a liquid supply path that comes into contact with the spinning liquid supplied from a liquid storage section (1) to a discharge member (2) through the liquid supply path (3), the electrospun nonwoven fabric (11) according to the present invention can be produced by not bringing the spinning liquid into contact with a heavy metal-containing member during the period (6) from when the spinning liquid comes into contact with the voltage application member (4) until it is discharged from the discharge member (2).

[0034] Similarly, it has been found that in an electrospun nonwoven fabric manufacturing apparatus (100) including a liquid supply path (3) connecting a liquid storage section (1) and a discharge member (2), and a voltage application member (4) constituting the liquid supply path (3) that is capable of applying a voltage to the spinning liquid by coming into contact with the spinning liquid passing through the liquid supply path (3), the present inventors have found that the electrospun nonwoven fabric (11) according to the present invention can be manufactured by not having a heavy metal-containing member that comes into contact with the spinning liquid during the period (6) from when the spinning liquid comes into contact with the voltage application member (4) until it is discharged from the discharge member (2).

[0035] In other words, it has been found that an electrospun nonwoven fabric (11) having a low mass of heavy metals contained in the resin constituting the constituent fibers can be provided by a manufacturing method and manufacturing apparatus (100) for electrospun nonwoven fabric, in which a spinning solution to which a voltage is applied is discharged from a discharge member (2) and turned into fibers without contacting the spinning solution with a heavy metal-containing component.

[0036] The term "heavy metal-containing member" used herein refers to a member that contains heavy metals such as iron.

[0037] In particular, the manufacturing method and manufacturing apparatus (100) for electrospun nonwoven fabric (11) according to the prior art employs stainless steel pipe electrodes and stainless steel nozzles, which are alloys containing iron and chromium or alloys containing nickel in addition, as metal-containing members for applying voltage to the spinning solution. Therefore, as long as the manufacturing method and manufacturing apparatus (100) for electrospun nonwoven fabric (11) according to the prior art are employed, it is impossible to realize an electrospun nonwoven fabric (11) in which the mass of iron contained per gram of the resin constituting the fibers is less than 70.7 μg. Similarly, it is impossible to realize an electrospun nonwoven fabric (11) in which the chromium or nickel content of the resin constituting the fibers is low.

[0038] However, in the above-mentioned manufacturing method and manufacturing device (100) for electrospun nonwoven fabric, the spinning solution to which a voltage is applied is discharged from the discharge member (2) and fiberized without contacting the heavy metal-containing member. As a result, it is possible to provide an electrospun nonwoven fabric (11) in which the mass of iron contained per gram of resin constituting the constituent fibers is less than 70.7 μg.

[0039] Hereinafter, the manufacturing method and manufacturing apparatus (100) for the above-mentioned electrospun nonwoven fabric will be described in detail.

[0040] The method for producing an electrospun nonwoven fabric according to the present invention can have the following configuration.

[0041] A method for producing an electrospun nonwoven fabric, comprising: (1) preparing a spinning solution containing a resin that forms the constituent fibers of the electrospun nonwoven fabric; (2) preparing a liquid storage section for storing the spinning solution; (3) supplying the spinning solution from the storage section to a discharge member that discharges the spinning solution through a liquid supply path; (4) applying a voltage to the spinning liquid passing through the liquid supply path by a voltage application member constituting the liquid supply path, the voltage application member being in contact with the spinning liquid passing through the liquid supply path and capable of applying a voltage to the spinning liquid; (5) a step of collecting the spinning solution discharged from the discharge member and turned into fibers in a collector; The spinning solution does not come into contact with a heavy metal-containing member during the period from when the spinning solution comes into contact with the voltage application member until when the spinning solution is discharged from the discharge member. A method for producing electrospun nonwoven fabric.

[0042] Moreover, the electrospun nonwoven fabric manufacturing apparatus (100) according to the present invention may have the following configuration.

[0043] An apparatus for producing an electrospun nonwoven fabric, comprising: (1) a liquid storage section capable of storing a spinning solution containing a resin that forms the constituent fibers of the electrospun nonwoven fabric; (2) a discharge member capable of discharging the spinning solution; (3) a liquid supply passage capable of supplying the spinning liquid from the liquid storage portion to the discharge member; (4) a voltage application member constituting the liquid supply path, which is in contact with the spinning liquid passing through the liquid supply path and can apply a voltage to the spinning liquid; (5) a collector capable of collecting the spinning solution discharged from the discharge member and turned into fibers; and wherein the spinning solution does not have a heavy metal-containing component that comes into contact with the spinning solution during the period from when the spinning solution comes into contact with the voltage application member until when the spinning solution is discharged from the discharge member. Electrospun nonwoven fabric manufacturing equipment.

[0044] The spinning solution may be, for example, a solution in which an organic polymer, an inorganic polymer, or a precursor of such a polymer is dissolved in a solvent.

[0045] The type of organic polymer or inorganic polymer constituting the spinning solution or the precursor of these polymers is not particularly limited as long as it can be spun in the present invention. For example, polyolefin resins (polyethylene, polypropylene, polymethylpentene, etc.), styrene resins, polyvinyl alcohol resins, polyether resins (polyether ether ketone, polyacetal, modified polyphenylene ether, aromatic polyether ketone, etc.), polyester resins (polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polycarbonate, etc.), , polyarylate, wholly aromatic polyester resin, etc.), polyimide resin, polyamideimide resin, polyamide resin (e.g., aromatic polyamide resin, aromatic polyetheramide resin, nylon resin, etc.), acrylic resin, resin having a nitrile group (e.g., polyacrylonitrile, etc.), urethane resin, epoxy resin, polysulfone resin (polysulfone, polyethersulfone, etc.), fluorine resin (polytetrafluoroethylene, polyvinylidene fluoride, etc.), cellulose resin, polybenzimidazole resin, and other known organic polymers, as well as polymers made of metal oxides such as silicon that are not conductive, can be used.

[0046] These polymers may be either linear or branched polymers, may be block or random copolymers, and may have any three-dimensional structure or crystallinity, without any particular limitations. Polymers other than those exemplified may also be used, and a spinning solution may be prepared that is composed of two or more polymers, including resins other than those exemplified.

[0047] In addition, when the components constituting the spinning solution are precursors capable of forming an inorganic polymer (monomer compounds or oligomer compounds), the type of the precursor is not particularly limited as long as it can be spun in the present invention. For example, the compound may be a metal organic compound of a non-conductive metal, such as an alkoxide, acetylacetonate, acetate, or oxalate of a non-conductive metal, either alone or in combination.

[0048] The solvent for dissolving the organic polymer or inorganic polymer or the precursor of these polymers varies depending on the spinning conditions and is not particularly limited, but examples thereof include water, acetone, methanol, ethanol, propanol, isopropanol, tetrahydrofuran, dimethyl sulfoxide, 1,4-dioxane, pyridine, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, acetonitrile, formic acid, toluene, benzene, cyclohexane, cyclohexanone, carbon tetrachloride, methylene chloride, chloroform, trichloroethane, ethylene carbonate, diethyl carbonate, propylene carbonate, etc. Solvents other than these examples can also be used, and a mixed solvent in which two or more solvents are mixed, including solvents other than the examples, can also be used.

[0049] The concentration of the organic polymer, inorganic polymer, or precursor of these polymers in the spinning solution is also appropriately adjusted depending on the spinning conditions. However, if the concentration (the percentage of the mass of the dissolved polymer or polymer precursor in the mass of the spinning solution) is too high or too low, spinning tends to become difficult, so the concentration is preferably 0.1% by mass to 90% by mass, more preferably 0.5% by mass to 50% by mass, and most preferably 1% by mass to 30% by mass.

[0050] In addition, the spinning solution may be mixed with functional components, such as antibacterial agent particles, antiviral agent particles, antifungal agent particles, photocatalyst particles, deodorizing particles, pigment particles, flame retardant particles, insect repellent particles, bactericide particles, fragrance particles, and conductive particles, as necessary.

[0051] In order to improve the spinnability of the spinning solution, the conductivity of the spinning solution may be increased. For example, a spinning solution in which a salt is dissolved, or a spinning solution containing conductive particles such as carbon particles may be used. Examples of the salt that can be used to improve the conductivity of the spinning solution include organic salts such as ammonium acetate, ammonium formate, and ammonium oxalate. The percentage of the mass of the salt in the mass of the spinning solution is appropriately adjusted, but is preferably 0.001% by mass to 90% by mass.

[0052] The type of the liquid storage portion (1) can be appropriately selected, for example, a tank, a syringe, or a bag. The material selected is one that is not melted, dissolved, or denatured by the spinning solution. In addition, it is preferable that the material does not contain heavy metals such as iron so that the electrospun nonwoven fabric (11) according to the present invention can be easily provided.

[0053] The spinning solution may contain a resin that constitutes the fibers of the electrospun nonwoven fabric (11) and a solvent or dispersion medium for the resin. The type of solvent or dispersion medium may be appropriately selected, and examples of the solvent or dispersion medium include water, acetone, methanol, ethanol, propanol, isopropanol, tetrahydrofuran, dimethyl sulfoxide, 1,4-dioxane, pyridine, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, 2-butanone, 3-pentanone, acetonitrile, formic acid, toluene, benzene, cyclohexane, cyclohexanone, carbon tetrachloride, methylene chloride, chloroform, trichloroethane, ethylene carbonate, diethyl carbonate, and propylene carbonate. Solvents other than those exemplified may also be used, and a mixed solvent in which two or more solvents are mixed, including those other than those exemplified, may also be used.

[0054] As described above, the composition of the solvent or dispersion medium can be adjusted as appropriate. However, in order to easily provide the electrospun nonwoven fabric (11) according to the present invention, it is preferable to use a solvent or dispersion medium that does not contain heavy metals such as iron.

[0055] In order to improve the spinnability of the spinning solution, a salt of an organic acid and a nitrogen compound that volatilizes by heat treatment may be added to the spinning solution, with reference to the invention disclosed in JP 2012-046844 A. Also, a functional component may be added to the spinning solution.

[0056] The molten resin may be used as the spinning solution.

[0057] The type of the liquid delivery means (7) can be appropriately selected, and can be, for example, a pump or a pressurized tank. Note that the liquid storage section (1) and the liquid delivery means (7) may be a member combining the liquid storage section (1) and the liquid delivery means (7), such as a syringe. The material to be selected is one that is not melted, dissolved, or denatured by the spinning solution. In addition, it is preferable that the material does not contain heavy metals such as iron so that the electrospun nonwoven fabric (11) according to the present invention can be easily provided.

[0058] The amount of the spinning solution delivered by the liquid delivery means (7) can be appropriately adjusted depending on the application and required properties of the electrospun nonwoven fabric (11) to be produced, and can be 0.05 to 50 g / h, 0.1 to 20 g / h, or 0.5 to 10 g / h per outlet of the spinning solution in the discharge member (2) (e.g., per nozzle).

[0059] The type of discharge member (2) can be appropriately selected, and for example, a nozzle, a member equipped with a slit such as a melt blow die, etc. can be used. The material is preferably selected from materials that do not contain heavy metals such as iron, and is not dissolved or denatured by the spinning solution. As an example, a discharge member (2) made of organic resin or carbon can be used. In particular, a voltage can be applied to the discharge member (2) itself, and it is preferable that the discharge member (2) is made of carbon (for example, a nozzle made of carbon, a nozzle made of conductive organic resin containing a nonmetallic conductive material such as carbon), because this is likely to produce the effect of producing an electrospun nonwoven fabric with a finer average fiber diameter and a more uniform size.

[0060] In addition, the diameter of the openings in the discharge member (2) for discharging the spinning solution, the number and shape of the portions of the discharge member (2) for discharging the spinning solution, and the intervals between the portions can be appropriately adjusted.

[0061] The type of the liquid supply passage (3) can be appropriately selected, and a pipe is preferable from the viewpoint of ease of handling. The material is preferably selected from materials that do not contain heavy metals such as iron, and is not dissolved or degraded by the spinning liquid. As an example, a pipe made of polyethylene resin is preferable.

[0062] The type of the voltage application member (4) can be appropriately selected, and can be a pipe that can form the liquid supply path (3) and can apply a voltage by contacting the spinning liquid. The material is preferably selected from materials that do not contain heavy metals such as iron, and is not dissolved or denatured by the spinning liquid. As an example, a pipe containing an organic resin or carbon having conductivity can be used. In particular, it is preferable that the material contains carbon, since it can efficiently apply a voltage to the spinning liquid. In addition, the voltage application member (4) may play a role as the liquid supply path (3), and from the viewpoint of easy handling, it is preferable that the voltage application member (4) is a pipe made of an organic resin and has carbon exposed on the inner surface of the pipe that comes into contact with the spinning liquid. An example of such a pipe is a PFA tube with antistatic functions on the inside and outside made by Nichias Corporation.

[0063] The type of power supply (8) can be appropriately selected, and for example, a high-voltage DC generator or a Van de Graaff generator can be used. The value of the voltage applied to the voltage application member (4) by the power supply (8) can be appropriately adjusted depending on the application and required properties of the electrospinning nonwoven fabric (11) to be produced, and can be 0.1 to 50 kV, or 1 to 30 kV. The power supply may apply a positive voltage or a negative voltage to the voltage application member (4). It can be appropriately selected whether the electricity passed through the voltage application member (4) to apply the voltage is a direct current, an alternating current, or a pulsating current.

[0064] The type of collector (5) can be appropriately selected, and may be a mesh, flat plate, or rod-shaped member made of carbon, conductive organic resin, or metal.

[0065] When it is not desired to bring the electospinning nonwoven fabric (11) into contact with the collector (5), a fabric such as a nonwoven fabric, a film, or a foam may be laminated on the portion of the collector (5) that collects the electospinning nonwoven fabric (11), and the electospinning nonwoven fabric (11) may be collected on the fabric, film, or foam. Also, a laminate of the fabric, film, or foam and the electospinning nonwoven fabric (11) may be produced.

[0066] The distance between the part of the discharge member (2) from which the spinning solution is discharged and the collector (5) can be appropriately adjusted depending on the application and required properties of the electrospinning nonwoven fabric (11) to be produced, and can be 1 to 100 cm, 2 to 50 cm, or 3 to 20 cm.

[0067] The spinning atmosphere can also be appropriately adjusted, and the temperature of the spinning atmosphere can be 0 to 100° C., 5 to 80° C., or 10 to 50° C. The humidity of the spinning atmosphere can be 0 to 100%, 5 to 80%, or 10 to 50%. EXAMPLES

[0068] The present invention will be specifically described below with reference to examples, but the scope of the present invention is not limited thereto.

[0069] (Preparation of spinning solution) Polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), and polyethersulfone (PESU) were dissolved in dimethylformamide (boiling point: 153°C) to prepare PVDF spinning solution, PAN spinning solution, and PESU spinning solution. Note that dimethylformamide did not contain heavy metals such as iron. In addition, the mass of iron contained per 1 g of PVDF in the PVDF spinning dope was 57.1 μg or less, the mass of chromium was 0.8 μg or less, the mass of nickel was less than 0.5 μg, and the mass of zinc was 2.4 g or less. The mass of iron contained per 1 g of PAN in the PAN spinning dope was 4.5 μg or less, and the mass of iron contained per 1 g of PESU in the PESU spinning dope was 2.2 μg or less.

[0070] Comparative Example 1 An electrospun nonwoven fabric manufacturing device was prepared as shown in Figure 1. A stainless steel pipe, an alloy containing iron, chromium, and nickel, was used as the voltage application member. A carbon-mixed polyether ether ketone nozzle (inner diameter: 0.33 mm), which does not contain heavy metals, was used as the discharge member. Furthermore, a polyethylene resin pipe, which does not contain heavy metals, was used as the liquid supply path. The speed of the spinning solution sent by the pump used as the solution sending means was adjusted so that the amount of the spinning solution discharged from the nozzle was 3 g / h. The voltage applied by the power supply was adjusted so that the voltage applied to the spinning solution by contact with the voltage application member was 21 kV. The distance between the nozzle part that discharges the spinning solution and the collector was set to 9 cm. In the electrospun nonwoven fabric manufacturing apparatus prepared in this manner, the spinning solution came into contact with a heavy metal-containing member (a stainless steel pipe which is a voltage application member) from the time when the spinning solution came into contact with the voltage application member until it was discharged from the discharge member. Using the electrospun nonwoven fabric manufacturing device having the above configuration, the PVDF spinning solution was converted into fibers to produce an electrospun nonwoven fabric.

[0071] Example 1 An electrospun nonwoven fabric was produced in the same manner as in Comparative Example 1, except that a pipe made of heavy metal-free PFA resin (a copolymer of tetrafluoroethylene and perfluoroalkoxyethylene) with heavy metal-free carbon exposed on the inner surface that comes into contact with the spinning solution was used as the voltage application member. In the electrospun nonwoven fabric manufacturing apparatus thus prepared, the spinning solution did not come into contact with the heavy metal-containing member from the time when it came into contact with the voltage application member until it was discharged from the discharge member.

[0072] (Examples 2 to 3) An electrospun nonwoven fabric was produced in the same manner as in Example 1, except that a PAN spinning solution or a PESU spinning solution was used as the spinning solution instead of the PVDF spinning solution.

[0073] In the comparative examples and examples, the types of spinning solutions and voltage application members used to produce electrospun nonwoven fabrics, as well as various physical properties of the produced electrospun nonwoven fabrics, are summarized and described in Table 1. Items that were not measured are marked with "-" in the table.

[0074] [Table 1]

[0075] Comparing Comparative Example 1 with Example 1, an electrospun nonwoven fabric was realized in which the mass of iron contained per gram of the resin constituting the fibers was less than 70.7 μg (57.1 μg, 13.6 μg less than Comparative Example 1), the mass of chromium contained per gram of the resin constituting the fibers was less than 1.6 μg (0.8 μg, 0.8 μg less than Comparative Example 1), the mass of nickel contained per gram of the resin constituting the fibers was less than 2.3 μg (less than 0.5 μg, 1.8 μg less than Comparative Example 1), and the mass of zinc contained per gram of the resin constituting the fibers was less than 6.2 μg (2.4 μg, 3.8 μg less than Comparative Example 1).

[0076] Similarly, from the results of Examples 2 and 3, it was possible to realize an electrospun nonwoven fabric in which the mass of iron contained per gram of resin constituting the constituent fibers was less than 70.7 μg. As described above, the present invention makes it possible to provide an electrospun nonwoven fabric having a low mass of heavy metals such as iron contained in the resin that constitutes the constituent fibers. [Industrial Applicability]

[0077] The electrospun nonwoven fabric according to the present invention can be used for various industrial applications, for example, as supports for composite membranes such as liquid separation membranes and gas separation membranes, such as water treatment membranes, medical materials, ion exchange membranes, dialysis membranes, water electrolysis membranes, and polymer electrolyte membranes for fuel cells; or as separators for electrochemical elements such as capacitors and primary / secondary batteries, or separator support members, particle support materials forming sheets carrying particles, prepregs, gas filters, liquid filters, medicinal patch substrates, masks, and other medical applications; cushioning materials, sealing materials, liquid absorbent materials, interior skin materials, cell culture substrates, cell separation materials, conductive materials, insulating materials, heat dissipation materials, heat retaining materials, interlinings, and padding. [Explanation of symbols]

[0078] 100: Electrospun nonwoven fabric manufacturing equipment 1...Liquid storage part 2. Discharge member 3...Liquid supply path 4. Voltage application member 5...Collection body 6. The period from when the spinning solution comes into contact with the voltage application member until it is discharged from the discharge member 7. Liquid delivery means 8. Power supply 9. Earth 10 .... The spinning solution discharged from the discharge member and turned into fibers 11. Electrospun nonwoven fabric

Claims

1. An electrospun nonwoven fabric, comprising a constituent fiber of which the mass of iron contained per gram of polyethersulfone is 10 μg or less.

2. A method for producing an electrospun nonwoven fabric, comprising the steps of: (1) preparing a spinning solution containing a resin that forms the constituent fibers of the electrospun nonwoven fabric; (2) preparing a liquid storage section for storing the spinning solution; (3) a step of supplying the spinning solution from the storage portion to a discharge member that discharges the spinning solution through a liquid supply path; (4) applying a voltage to the spinning liquid passing through the liquid supply path by a voltage application member constituting the liquid supply path, the voltage application member being in contact with the spinning liquid passing through the liquid supply path and capable of applying a voltage to the spinning liquid; (5) A step of collecting the fiberized spinning solution discharged from the discharge member in a collector; The spinning solution does not come into contact with a heavy metal-containing member during the period from when the spinning solution comes into contact with the voltage application member until when the spinning solution is discharged from the discharge member. A method for producing electrospun nonwoven fabric.

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