JP7660366B2 - Electrospun nonwoven fabric - Google Patents

Description

The present invention relates to electrospun nonwoven fabrics.

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

In particular, it is expected that by narrowing the fiber diameter of the fibers that make up the nonwoven fabric, the fiber surface area of the nonwoven fabric can be increased, and the functionality in the above-mentioned applications can be improved. In recent years, the use of electrospun nonwoven fabrics has attracted attention as a nonwoven fabric made of such fibers with a narrow fiber diameter. As is well known from its description in "Electrospinning Frontier (Non-Patent Document 1)," electrospun nonwoven fabrics are formed by applying a voltage to a voltage application member that contacts the spinning solution that passes through a liquid supply path and is supplied to a discharge member such as a nozzle, and then discharging the spinning solution to which the voltage has been applied from the discharge member to turn the spinning solution into fibers, which are then collected in a collector that is earthed or the like, to form a nonwoven fabric.

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 of installing electrodes as voltage application members in a liquid delivery pipe that is a liquid supply path can be adopted.
- 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.

The Frontline of Electrospinning (Author: Yoshihiro Yamashita, Publisher: Sen-i-sha Co., Ltd., Publication Year: 1st Edition, January 20, 2007) JP 2011-102455 A (claims, 0023, 0088, table 12, etc.)

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 for various industrial applications. For example, when the electrospun nonwoven fabric according to the prior art is used in industrial applications in which it comes into contact with liquid, the concentration of iron, a type of heavy metal, in the liquid may increase. Furthermore, 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.

The applicant of the present application has investigated the cause of this and found that in electrospun nonwoven fabrics according to conventional technology, the mass of iron contained in the resin that constitutes the constituent fibers is greater than the mass of iron contained in the resin that constitutes the spinning solution used to manufacture the electrospun nonwoven fabric. In other words, as long as the electrospun nonwoven fabrics are based on conventional technology, it has not been possible to provide an electrospun nonwoven fabric with a small mass of iron contained in the resin that constitutes the constituent fibers.

Based on these new findings, it was thought 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 variety of industrial applications.

In addition, in order to investigate the cause of the above-mentioned problems, the applicant of the present application conducted detailed observations using a microscope and disassembling each component of the electrospun nonwoven fabric manufacturing device according to the conventional technology after the electrospun nonwoven fabric had been manufactured. As a result, traces of melting and precipitation of scale-like substances thought to be metal salts were found on heavy metal-containing members (e.g., stainless steel pipe electrodes and stainless steel nozzles, which are alloys containing at least iron and chromium) that come into contact with the spinning solution to which a voltage has been applied and contain heavy metals such as iron.

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 that 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.

The present invention relates to
" (Claim 1) An electrospun nonwoven fabric, in which the mass of iron contained per gram of polyethersulfone constituting the constituent fibers is 10 μg or less .
(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) 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.
Manufacturing method for electrospun nonwoven fabrics.
It is.

As a result of the applicant's investigations, the applicant has been able to provide an electrospun nonwoven fabric that contains less than 70.7 μg of iron per gram of resin constituting the constituent fibers, a lower iron content than electrospun nonwoven fabrics made using conventional technology, and that can be used for a variety of industrial applications.

FIG. 2 is a schematic side view showing a manufacturing apparatus for electrospun nonwoven fabric.

In the present invention, various configurations can be appropriately selected, such as the following configurations. Note that, unless otherwise specified, the various measurements described in the present invention were performed under normal pressure and at 25°C (room temperature). Furthermore, unless otherwise specified, the results of the various measurements described in the present invention were obtained by measurement 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 one decimal place, the value was obtained to one decimal place by measurement, and the obtained value to one decimal place was rounded off to the one decimal place, and this value was used as the desired value. Furthermore, the upper limit values and lower limit values exemplified in the present invention can be combined in any combination.

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 physical properties. The basis weight can be 0.01 to 100 g/ ^m2 , 0.05 to 50 g/ ^m2 , or 0.1 to 25 g/ ^m2 . The term "basis weight" refers to the mass converted to 1 m2 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 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.

The porosity can be 70-99%, 80-95%, or 85-90%. Note that "porosity" refers to the percentage of the volume of the components that make up the object relative to the apparent volume of the object.

The average fiber diameter of the fibers constituting the electrospun nonwoven fabric can be adjusted as appropriate 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 fibers measured based on an electron microscope photograph taken at 5,000 times magnification of the measurement target portion containing the fibers. In addition, when the cross-sectional shape of the fiber is non-circular, the diameter of a circle having the same area as the cross-sectional area is regarded as the fiber diameter.

The cross-sectional shape of the fibers constituting the electrospun nonwoven fabric can be adjusted as appropriate depending on the application and required physical properties. In addition to circular, nearly circular, or elliptical fibers, irregular cross-section fibers may also be used. In addition, irregular cross-section fibers may have a fiber cross-section that is hollow, polygonal such as a triangular shape, alphabetic such as a Y-shape, irregular, multi-lobed, symbolic such as an asterisk shape, or a shape that combines multiple of these shapes.

The type of resin forming the fibers that make up the electrospun nonwoven fabric can be adjusted as appropriate depending on the application and required physical properties. For example, polyolefin resins (e.g., polyethylene, polypropylene, polymethylpentene, polyolefin resins in which part of the hydrocarbon is replaced with a nitrile group or a halogen such as fluorine or chlorine), styrene resins, polyvinyl alcohol resins, polyether resins (e.g., polyether ether ketone, polyacetal, modified polyphenylene ether, aromatic polyether ketone), polyester resins (e.g., polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polycarbonate, polyarylate, wholly aromatic polyester resins), polyimide resins, polyamides, etc. It can be made of 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.).

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

It may also be a composite fiber made of multiple different resins, such as an island-in-the-sea type, a core-sheath type, an orange type, or a side-by-side type. However, in order to provide an electrospun nonwoven fabric that can be used for a variety of industrial applications, it is preferable that the electrospun nonwoven fabric is made of fibers made of only one type of resin.

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.

Heavy metals here refer to metals with a specific gravity of 4 to 5 or more, as described in the Kojien dictionary (5th edition, edited by Shinmura Izuru, published by Iwanami Shoten, published on November 11, 1998), and include, for example, metals such as iron (specific gravity: 7.9), chromium (specific gravity: 7.2), nickel (specific gravity: 8.9), and zinc (specific gravity: 7.1).

The smaller the mass, the more usable the electrospun nonwoven fabric can be for various industrial applications. Therefore, the mass of iron contained per gram of resin constituting the constituent 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.

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 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. 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.

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, more preferably 60.3 μg or less, more preferably 50 μg or less, more preferably 40 μg or less, more preferably 30 μg or less, more preferably 20 μg or less, more preferably 10 μg or less, and most preferably 0 μg. The heavy metals such as iron defined in the present invention may be understood to include their salts. The mass of various heavy metals such as iron contained in the resin can be confirmed by the following method.

(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 fumes are released and the sulfuric acid turns brown to black, then allow 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, and 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 smoke is generated by heating.
6. After carrying out the above-mentioned operation 5, heat the conical beaker until the amount of sulfuric acid is 2 ml or less, and then leave it to cool to room temperature.
7. After cooling, add 1 ml of 60 wt % nitric acid to the sulfuric acid, and then add ultrapure water up to 50 ml to prepare a test solution.
8. The test liquid is subjected to an atomic absorption spectrometer to measure the masses 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 masses (unit: μg) of various heavy metals such as iron contained in 1 g of the resin constituting 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.

The electrospun nonwoven fabric of the present invention may contain additives such as a binder that bonds the constituent fibers together, and additives such as flame retardants, fragrances, pigments, antibacterial agents, antifungal materials, photocatalyst particles, emulsifiers, dispersants, surfactants, and thickeners. However, it is preferable that the electrospun nonwoven fabric is composed only of fibers so that an electrospun nonwoven fabric that can be used for various industrial applications can be provided.

The manufacturing apparatus for electrospun nonwoven fabric capable of producing the electrospun nonwoven fabric of the present invention will be described with reference to FIG. 1. The manufacturing method for electrospun nonwoven fabric capable of producing the electrospun nonwoven fabric of the present invention will be described together with the manufacturing apparatus.

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 that contacts the spinning solution passing through the liquid supply path (3) and can apply 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).

The electrospun nonwoven fabric manufacturing apparatus (100) shown in FIG. 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 an earth (9) for the power supply (8) and the collector (5). The wavy lines connecting the voltage application member (4) and the power supply (8), the power supply (8) and the earth (9), and the collector (5) and the earth (9) are illustrations of electric wires.

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 that protrudes from the inner wall surface of the liquid supply path (3). Then, 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 is applied is attracted toward the collector (5) that is earthed (9) and is thinned to form fibers, while flying through 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).

As a result of investigations, the applicant of the present application has found that in a method for producing an electrospun nonwoven fabric, which includes a step of applying a voltage to the spinning liquid passing through the liquid supply path (3) by using a voltage application member (4) constituting a liquid supply path that comes into contact with the spinning liquid supplied from the liquid storage section (1) to the 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).

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 can apply a voltage to the spinning liquid by contacting the spinning liquid passing through the liquid supply path (3), 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).

In other words, it has been discovered that an electrospun nonwoven fabric (11) with a low mass of heavy metals contained in the resin that constitutes the constituent fibers can be provided by a manufacturing method and manufacturing device (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 member.

Note that "heavy metal-containing materials" here refers to materials that contain heavy metals such as iron.

In particular, the manufacturing method and manufacturing apparatus (100) for electrospun nonwoven fabric (11) according to the prior art used stainless steel pipe electrodes and stainless steel nozzles that are alloys containing iron and chromium or alloys that also contain nickel as metal-containing members that apply 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 used, it was 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 was impossible to realize an electrospun nonwoven fabric (11) in which the resin constituting the fibers contains a small amount of chromium or nickel.

However, in the above-mentioned manufacturing method and manufacturing apparatus (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 material. 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.

The following describes in detail the manufacturing method and manufacturing apparatus (100) for the electrospun nonwoven fabric described above.

The method for producing electrospun nonwoven fabric according to the present invention can have the following configuration:

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) 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.

The electrospun nonwoven fabric manufacturing apparatus (100) according to the present invention can have the following configuration:

An apparatus for producing an electrospun nonwoven fabric, comprising:
(1) a liquid storage section capable of storing a spinning solution containing a resin that constitutes 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.

The spinning solution can be, for example, a solution of an organic polymer, an inorganic polymer, or a precursor of these polymers dissolved in a solvent.

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, , 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 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.

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 listed as examples may also be used, and a spinning solution may be made of two or more polymers, including resins other than those listed as examples.

When the components constituting the spinning solution are precursors capable of forming inorganic polymers (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 single or a mixture of multiple organic metal compounds of non-conductive metals, such as alkoxides, acetylacetonates, acetates, and oxalates of non-conductive metals.

The solvent for dissolving the organic polymers or inorganic polymers or precursors of these polymers described above varies depending on the spinning conditions and is not particularly limited. Examples of the solvent 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, and propylene carbonate. Solvents other than these examples can also be used, and mixed solvents in which two or more solvents are mixed, including solvents other than those listed above, can also be used.

The concentration of the organic polymer, inorganic polymer, or precursor of these polymers in the spinning solution is also adjusted appropriately 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 low, spinning tends to become difficult, so the concentration is preferably 0.1% to 90% by mass, more preferably 0.5% to 50% by mass, and most preferably 1% to 30% by mass.

The spinning solution may also be mixed with functional components such as antibacterial particles, antiviral particles, antifungal particles, photocatalyst particles, deodorizing particles, pigment particles, flame retardant particles, insect repellent particles, bactericide particles, fragrance particles, and conductive particles, as necessary.

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 has been dissolved, or a spinning solution containing conductive particles such as carbon particles, may be used. Examples of salts 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 can be adjusted as appropriate, but is preferably 0.001% to 90% by mass.

The type of the liquid storage section (1) can be appropriately selected, and can be, 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) of the present invention can be easily provided.

The spinning solution may contain a resin that constitutes the fibers of the electrospun nonwoven fabric (11) and its solvent or dispersion medium. The type of solvent or dispersion medium may be selected as appropriate, 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 these examples may also be used, and a mixed solvent in which two or more solvents are mixed, including solvents other than those listed above, may also be used.

As mentioned above, the composition of the solvent or dispersion medium can be adjusted as appropriate, but it is preferable to use a solvent or dispersion medium that does not contain heavy metals such as iron so that the electrospun nonwoven fabric (11) according to the present invention can be easily provided.

In order to improve the spinnability of the spinning solution, a salt consisting of an organic acid and a nitrogen compound that volatilizes upon 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.

In addition, molten resin may be used as the spinning solution.

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 that combines the liquid storage section (1) and the liquid delivery means (7), such as a syringe. The material selected is one that does not melt, dissolve, or denature with 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.

The amount of spinning solution delivered by the liquid delivery means (7) can be adjusted as appropriate 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).

The type of discharge member (2) can be selected appropriately, and for example, a nozzle, a member with a slit such as a melt blow die, etc. can be used. It is preferable to select the material appropriately from materials that do not contain heavy metals such as iron, and select one that does not dissolve or denature in the spinning solution. As an example, a discharge member (2) made of organic resin or carbon can be used. In particular, it is preferable that the discharge member (2) itself is made of carbon (for example, a nozzle made of carbon, a nozzle made of conductive organic resin containing a non-metallic conductive material such as carbon), because a voltage can be applied to the discharge member (2) itself, and the effect of being able to produce an electrospun nonwoven fabric with a finer average fiber diameter and a more uniformity can be easily achieved.

In addition, the diameter of the openings in the discharge member (2) for discharging the spinning solution, the number and shape of the parts in the discharge member (2) for discharging the spinning solution, and the spacing between the parts can be adjusted as appropriate.

The type of the liquid supply path (3) can be selected as appropriate, 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 denatured by the spinning liquid. As an example, a pipe made of polyethylene resin is preferable.

The type of voltage application member (4) can be appropriately selected, and can be a pipe so that it can form the liquid supply path (3) and can apply a voltage by contacting the spinning liquid. It is preferable to select a material that does not contain heavy metals such as iron, and one that does not dissolve or denature in the spinning liquid is selected. 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, from the viewpoint of easy handling, since the voltage application member (4) may play a role as the liquid supply path (3), it is preferable that the voltage application member (4) is a pipe made of 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 function on the inside and outside made by Nichias Corporation.

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 physical 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 can apply a positive voltage or a negative voltage to the voltage application member (4). It can also be appropriately selected whether the electricity passed through the voltage application member (4) to apply the voltage is DC, AC, or pulsating.

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

If 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. A laminate of the fabric, film, or foam and the electospinning nonwoven fabric (11) may also be produced.

The distance between the part of the discharge member (2) where the spinning solution is discharged and the collector (5) can be adjusted as appropriate 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.

The spinning atmosphere can also be adjusted as appropriate, 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%.

The present invention will be described in detail below with reference to examples, but these are not intended to limit the scope of the present invention.

(Preparation of spinning solution)
Polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), and polyethersulfone (PESU) were each dissolved in dimethylformamide (boiling point: 153° C.) to prepare a PVDF spinning solution, a PAN spinning solution, and a PESU spinning solution. Note that the dimethylformamide did not contain heavy metals such as iron.
The mass of iron contained per gram 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.

(Comparative Example 1)
An electrospun nonwoven fabric manufacturing apparatus as shown in FIG. 1 was prepared. A stainless steel pipe, which is 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) that does not contain heavy metals was used as the discharge member. Furthermore, a polyethylene resin pipe that 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 for discharging 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 (the stainless steel pipe which is the 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.

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.

(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.

In the comparative examples and examples, the types of spinning solutions and voltage application members used to produce the electrospun nonwoven fabrics, as well as the 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.

Comparing Comparative Example 1 and 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).

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.
From the 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.

The electrospun nonwoven fabric according to the present invention can be used in various industrial applications, for example, as a support 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 and separator support members for electrochemical elements such as capacitors and primary/secondary batteries, particle support materials forming particle-supported sheets, 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.

100... Manufacturing apparatus for electrospun nonwoven fabric 1... Liquid storage section 2... Discharge member 3... Liquid supply path 4... Voltage application member 5... Collector 6... Between the time when the spinning solution comes into contact with the voltage application member and the time when it is discharged from the discharge member 7... Liquid delivery means 8... Power supply 9... Earth 10... Spinning solution discharged from the discharge member and turned into fibers 11... Electrospun nonwoven fabric

Claims (2)

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