US20160281284A1

US20160281284A1 - Non-woven fabric and carbon fiber non-woven fabric

Info

Publication number: US20160281284A1
Application number: US14/997,150
Authority: US
Inventors: Yuki Yoshioka; Takayoshi Yamaguchi
Original assignee: Panasonic Intellectual Property Management Co Ltd
Current assignee: Panasonic Intellectual Property Management Co Ltd
Priority date: 2015-03-25
Filing date: 2016-01-15
Publication date: 2016-09-29
Also published as: JP2016183423A; CN106012290A; JP6551776B2

Abstract

A non-woven fabric includes nanofibers which contain a polymer and inorganic particles, the nanofibers being formed by an electrospinning method. The inorganic particles contain first particles and second particles, some parts of which are exposed from a surface of the polymer. A volume V_1oof a portion of the first particles exposed from the surface of the polymer and a volume V_1iof a portion buried in the polymer satisfy a relationship of V_1o<V_1i, a volume V_2oof a portion of the second particles exposed from the surface of the polymer and a volume V_2iof a portion buried in the polymer satisfy a relationship of V_2o≧V_2iand an average number N₁of the first particles and an average number N₂of the second particles per unit length of the nanofibers satisfy a relationship of N₁>N₂.

Description

CROSS-REFERENCES TO RELATED APPLICATION(S)

This application is based on and claims priority from Japanese Patent Application No. 2015-62765 filed on Mar. 25, 2015, the entire contents of which are incorporated herein by reference.

BACKGROUND

1. Field of the Invention
The present invention relates to a non-woven fabric including inorganic particles and nanofibers formed by an electrospinning method, and a carbon fiber non-woven fabric obtained by carbonizing the non-woven fabric.
2. Description of Related Art
A nanofiber non-woven fabric having a fiber diameter of a nanometer (nm) to sub μm order can be manufactured by an electrospinning method using a solution of a polymer or the like. Since the nanofiber non-woven fabric has a large surface area, the nanofiber non-woven fabric is expected to be used for various purposes, in addition to a filter medium. The nanofiber non-woven fabric can be used for various purposes, when more functions can be applied to the nanofiber non-woven fabric.
JP-A-2014-145140 as Patent Document 1 discloses a method of manufacturing a nanofiber non-woven fabric from a spinning solution containing catalyst particles which are surface-coated with inert materials and a polymer material by the electrospinning method.
JP-A-2005-040646 as Patent Document 2 discloses a technology of supporting ultrafine ceramics particles on a surface of a fiber of a fiber filter member. In JP-A-2005-040646, the fiber filter member is immersed in a solution containing the ultrafine ceramics particles, the remaining solution is removed, thermal treatment is performed, and accordingly, the ultrafine ceramics particles is supported.
Patent Document 1: JP-A-2014-145140
Patent Document 2: JP-A-2005-040646

SUMMARY

When the particles are supported by the non-woven fabric, it is considered that the action of the particles is easily exhibited, when the particles exist on the surface of the nanofibers. However, when the particles are exposed for a long time, the particles are easily removed. Accordingly, when the non-woven fabric is used for a long time, the effect of the particles may be lost.
A non-limited object of the present invention is to provide a non-woven fabric and a carbon fiber non-woven fabric which can exhibit the effect of the inorganic particles for a long time.
According to an aspect of the present invention, there is provided a non-woven fabric includes nanofibers which contain a polymer and inorganic particles, the nanofibers being formed by an electrospinning method, wherein the inorganic particles contain first particles and second particles, some parts of which are exposed from a surface of the polymer, a volume V_1oof a portion of the first particles exposed from the surface of the polymer and a volume V_1iof a portion buried in the polymer satisfy a relationship of V_1o<V_1i, a volume V_2oof a portion of the second particles exposed from the surface of the polymer and a volume V_2iof a portion buried in the polymer satisfy a relationship of V_2o≧V_2i, and an average number N₁of the first particles and an average number N₂of the second particles per unit length of the nanofibers satisfy a relationship of N₁>N₂.
According to another aspect of the present invention, there is provided a carbon fiber non-woven fabric which can be obtained by firing the non-woven fabric.
According to some aspects of the present invention, it may be possible to provide a non-woven fabric and a carbon fiber non-woven fabric which can exhibit the effect of the inorganic particles such as catalyst particles for a long time, even when the fiber configuring the non-woven fabric is deteriorated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view schematically showing nanofibers contained in a non-woven fabric according to one embodiment of the present invention.

FIG. 2 is a sectional view schematically showing a structure of the nanofibers contained in the non-woven fabric according to one embodiment of the present invention.

FIG. 3 is a diagram schematically showing a configuration of a system for obtaining a non-woven fabric, in a manufacturing method of a non-woven fabric according to one embodiment of the present invention.

FIG. 4 is a top view schematically showing a release unit 42A of FIG. 3.

FIG. 5 is a side view schematically showing the release unit 42A of FIG. 3.

FIG. 6 is an enlarged sectional view schematically showing an emitter.

DETAILED DESCRIPTION

(Non-Woven Fabric)
A non-woven fabric according to an embodiment of the present invention contains nanofibers which contain a polymer and inorganic particles and are formed by an electrospinning method. The inorganic particles contain first particles and second particles, some parts of which are exposed from the surface of the polymer. Herein, regarding the first particles, a volume V_1oof a portion exposed from the surface of the polymer and a volume V_1iof a portion buried in the polymer satisfy a relationship of V_1o<V_1i, and regarding the second particles, a volume V_2oof a portion exposed from the surface of the polymer and a volume V_2iof a portion buried in the polymer satisfy a relationship of V_2o≧V_2i. An average number N₁of the first particles per unit length of the nanofibers and an average number N₂of the second particles thereof satisfy a relationship of N₁>N₂.
As described above, in the embodiment, the average number N₁of the first particles, less than 50% by volume of which is exposed from the surface of the polymer configuring the matrix of the nanofibers, is greater than the average number N₂of the second particles, equal to or greater than 50% by volume of which is exposed. Since a large number of the first particles which are hardly removed are contained, the effect of the inorganic particles can be exhibited for a long time, even when the nanofibers are deteriorated due to the use of the non-woven fabric. In addition, since the second particles having a high degree of exposure are contained and the first particles are exposed from the outer side of the nanofibers from an initial state, although the first particles have a low degree of exposure, the effect of the inorganic particles is sufficiently obtained, even in the initial period of the usage. Since such a non-woven fabric is easily formed by the electrospinning method, it is possible to obtain a non-woven fabric with high productivity.
FIG. 1 is a top view schematically showing the nanofibers contained in the non-woven fabric according to the embodiment and FIG. 2 is a sectional view (sectional view orthogonal to a length direction of the nanofibers) schematically showing the structure of the nanofibers contained in the non-woven fabric according to the embodiment. Nanofibers 5 contains a polymer (polymer matrix) 6 to be applied to a shape of the fiber and inorganic particles 4 which are dispersed in the polymer 6. In the example of the drawings, the inorganic particles 4 contain first particles 1, second particles 2, and third particles 3 which have different degrees of exposure from the polymer 6, but it is not necessary to compulsorily contain the third particles 3. The degree of exposure of the first particles 1 from the surface of the polymer 6 is smaller than 50% by volume, the degree of exposure of the second particles 2 from the surface of the polymer 6 is equal to or greater than 50% by volume, and the third particles 3 are completely buried in the polymer 6. When a region of the nanofibers 5 having a predetermined length is observed, the number of first particles 1 is greater than the number of second particles 2 and accordingly, the removal of the inorganic particles (particularly, second particles 2) is prevented.
The number of first particles 1 and the number of second particles 2 are compared using the average numbers N₁and N₂per unit length of the nanofibers. Specifically, first, in a scanning electron microscope (SEM) image of the non-woven fabric, the number of each of first particles 1 and the second particles 2 is counted, regarding each region having a predetermined length L (μm) of a plurality of (for example, five) nanofibers arbitrary selected. The length L may be, for example, from 3 μm to 5 μm. The number of each of two particles is doubled, converted into a value per unit length (1 μm), and averaged, and accordingly, it is possible to obtain the average numbers N₁and N₂. In addition, in the SEM image, a first linear line orthogonal to the length direction of the nanofibers and a second linear line having a distance from the first linear line as L (μm) (herein, the first linear line and the second linear line are parallel to each other) are drawn on one nanofiber, and the region having the predetermined length L (μm) means a region between the first linear line and the second linear line.
In addition, the first particles and the second particles may be visually distinguished in the SEM image. When it is difficult to visually distinguish the particles, a particle diameter (maximum particle diameter) of a portion exposed from the polymer in the SEM image of the nanofibers is measured, and when this particle diameter is equal to or greater than an average particle diameter of the inorganic particles used for the manufacturing of the non-woven fabric, the portion may be determined as the second particles, and when the particle diameter is smaller than the average particle diameter, the portion may be determined as the first particles.
As in the example of the drawings, the inorganic particles may further include the third particles which are completely buried in the polymer. Since the third particles are contained in the polymer, the third particles are hardly removed, even when the deterioration of the nanofibers proceeds. Accordingly, the effect of the inorganic particles can be exhibited for a longer time.
The average number N₁of the first particles and an average number N₃of the third particles per unit length of the nanofibers may satisfy a relationship of N₁≧N₃. However, when a relationship of N₁<N₃is satisfied, the effect of the inorganic particles of the non-woven fabric can be ensured for a longer time. The average number N₃of the third particles can be calculated based on a transmission electron microscope (TEM) image of the non-woven fabric and a case of N₁, for example.
An average fiber diameter D_fof the nanofibers is, for example, equal to or greater than 100 nm, preferably from 150 nm to 200 nm, and even more preferably equal to or greater than 300 nm. D_fis, for example, smaller than 1000 nm and preferably equal to or smaller than 800 nm or equal to or smaller than 600 nm. The lower limit value and the upper limit value of these can be arbitrarily combined. D_fmay be, for example, equal to or greater than 100 nm and smaller than 1000 nm, equal to or greater than 150 nm and smaller than 1000 nm, or equal to or greater than 200 nm and smaller than 1000 nm.
The average fiber diameter D_fof the nanofibers can be obtained by measuring and averaging each one portion of arbitrary plurality of (for example, 10) fibers in the SEM image of the non-woven fabric, for example. A diameter of the fabric is a diameter of a cross section orthogonal to the length direction of the nanofibers. When such a cross section is not circular, a maximum diameter may be assumed as the diameter.
An average particle diameter D_pof the inorganic particles is, for example, equal to or greater than 5 nm, preferably equal to or greater than 10 nm, and may be equal to or greater than 15 nm or equal to or greater than 20 nm. D_pmay be equal to or smaller than 200 nm, equal to or smaller than 150 nm, equal to or smaller than 100 nm, or equal to or smaller than 80 nm. The lower limit value and the upper limit value of these can be arbitrarily combined. D_pmay be from 5 nm to 200 nm or from 20 nm to 200 nm, for example.
The average particle diameter D_pof the inorganic particles is a median diameter (D₅₀) of particle size distribution by volume which is obtained regarding the inorganic particles used for the manufacturing of the non-woven fabric.
A ratio D_f/D_pof the average fiber diameter D_fto the average particle diameter D_pis, for example, equal to or greater than 0.5, preferably equal to or greater than 3, and may be equal to or greater than 5 or equal to or greater than 7. The ratio D_f/D_pmay be equal to or smaller than 30 or equal to or smaller than 25, and is preferably smaller than 10 or equal to or smaller than 9. The lower limit value and the upper limit value of these can be arbitrarily combined. The ratio D_f/D_pmay be, for example, from 0.5 to 30, from 0.5 to 25, equal to or greater than 0.5 and smaller than 10, or from 3 to 9. It is difficult to form the nanofibers having the inorganic particles in the exposed state, by the electrospinning method. However, when the ratio D_f/D_pis adjusted, the degree of exposure of each of the first particles and the second particles are easily adjusted. The D_f/D_pis preferably smaller than 10, from such a viewpoint.
An amount of the inorganic particles is, for example, from 5 parts by mass to 50 parts by mass, preferably from 5 parts by mass to 30 parts by mass (for example, 10 parts by mass to 30 parts by mass), and more preferably from 5 parts by mass to 20 parts by mass, with respect to 100 parts by mass of the polymer.
When D_fand D_p, the ratio D_f/D_pand/or the amount of the inorganic particles are in the ranges described above, it is easy to bury the inorganic particles in the nanofibers and to significantly adjust the number of first particles and the third particles.
Hereinafter, the configuration of the non-woven fabric will be described in more detail.
(Polymer)
The polymer configures the matrix of the nanofibers. That is, the nanofibers contain the matrix of the polymer and the inorganic particles (first to third particles) dispersed in the matrix.
The polymer is not particularly limited as long as it can be subjected to the electrospinning, and examples thereof include polyolefin, a vinyl resin (a vinyl acetate resin or a saponified material thereof, polystyrene, or polyacrylonitrile (PAN)), an acrylic resin, a fluorine resin, polyether sulfone (PES), polysulfone, polyester (aromatic polyester), polyamide, polyimide (PI), a cellulose derivative, and a biodegradable polymer. These polymers can be used alone or in combination of two or more kinds thereof. Among these, PES, polysulfone, aromatic polyester (polyalkylene terephthalate such as polyethylene terephthalate), polyamide, PI (thermosetting polyimide such as condensation type polyimide obtained from polyamide acid or bismaleimide resin; or thermoplastic polyimide), PAN, and the like are preferable. The polymer may be a homopolymer or a copolymer. PAN and/or PI are preferable, in order to easily prepare a polymer solution (or first dispersion will be described later) and easily perform the electrospinning (and to obtain excellent thread forming property).
A weight average molecular weight M_wof the polymer depends on the type of the polymer, and is, for example, from 30000 to 120000 and preferably from 50000 to 100000 or from 50000 to 80000. A ratio (=M_w/M_n) of the weight average molecular weight M_wof the polymer to a number average molecular weight M_nis, for example, from 1.1 to 3.0.
In addition, in this specification, the weight average molecular weight and the number average molecular weight of the polymer is values obtained from molecular weight distribution measured by gel permeation chromatograph.
In addition to the polymer and the inorganic particles, the nanofibers configuring the non-woven fabric may contain a well-known additive, if necessary. The content of the additive may be equal to or smaller than 5% by mass of the entire nanofibers configuring the non-woven fabric (or entire non-woven fabric).
(Inorganic Particles)
The inorganic particles can be suitably selected according to the purpose, and a material which is not dissolved in the polymer solution (specifically, solvent of the solution) or not deteriorated is preferable when forming the nanofibers by the electrospinning. Examples of the inorganic particles include metal particles and particles of a metal compound (oxide, hydride, nitride, carbide, or halide). Among the inorganic particles, metal particles and particles of metal oxide (also containing ceramics) are preferable. Examples of metal configuring the metal particles include transition metal such as titanium, manganese, cobalt, nickel, palladium, platinum, copper, silver, or gold. As the metal oxide, oxide of metal described above (for example, titanium oxide, copper oxide, or silver oxide) is used. The inorganic particles can be used alone or in combination of two or more kinds thereof.
A thickness of one sheet of the non-woven fabric can be selected from a range of approximately 1 μm to 1000 μm, and is, for example, from 10 μm to 700 μm, and preferably from 10 μm to 600 μm or 20 μm to 500 μm.
In the non-woven fabric according to the embodiment, the number of first particles having a small degree of exposure is greater than the number of second particles having a small degree of exposure on the surface of the nanofibers. Accordingly, the effect of the inorganic particles can be exhibited for a long time, even when the nanofibers are deteriorated.
(Manufacturing Method of Non-Woven Fabric)
The non-woven fabric can be obtained by the electrospinning method using a dispersion which is obtained by dispersing the inorganic particles in a solution containing the polymer (or a precursor thereof), for example. Specifically, the non-woven fabric can be manufactured by performing a first step of preparing a dispersion (first dispersion) containing the polymer or the precursor thereof and the inorganic particles, and a second step of generating the nanofibers from the first dispersion by an electrostatic force in a fiber formation space and laminating the generated nanofibers to form the non-woven fabric. In the second step, when generating the nanofibers, some of a part or the entire inorganic particles are exposed from the nanofibers to become the first particles and the second particles. In addition, some inorganic particles may become the third particles in a state of being buried in the nanofibers.
In addition, in a case where the polymer is polyimide, the heating is suitably performed in the manufacturing process of the non-woven fabric using a dispersion containing the polyimide precursor (polyamide acid) and the inorganic particles as the first dispersion, and accordingly, polyimide (polymer) may be generated from the polyimide precursor.
(First Step)
In the first step, the preparation method of the first dispersion is not particularly limited, and the first dispersion may be prepared by dispersing the inorganic particles in the polymer solution which is obtained by dissolving the polymer (or the precursor thereof) in the solvent, for example. The inorganic particles may be used in the state of powder, but can also be used in a state of a dispersion (second dispersion). For example, the first dispersion may be prepared by adding the polymer to a second dispersion which is obtained by dispersing the inorganic particles in a solvent for dissolving the polymer (or precursor thereof) and dissolving the polymer in the solvent. In addition, when the first dispersion containing the polymer and the inorganic particles is prepared by mixing the polymer solution and the second dispersion containing the inorganic particles, a dispersing property of the inorganic particles is easily increased.
The solvent is not particularly limited, as long as it can dissolve the polymer (or precursor thereof) and be removed by volatilization. As such a solvent, an aprotic polar organic solvent is used. The type of solvent also depends on the type of the polymer or the precursor thereof, but as the solvent, an aprotic polar organic solvent having a Rohrschneider polar parameter P′ equal to or greater than 5 (for example, from 5 to 7.5) is preferably used. Examples of the solvent include amide (chain or cyclic amide) such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), or N-methyl-2-pyrolidone (NMP); and sulfoxide such as dimethyl sulfoxide. These solvents may be used alone or in combination of two or more kinds thereof.
The solvent containing amide is preferably used. For example, when the polymer contains PES and/or PAN, the solvent containing DMF and/or DMAc may be used. When the polymer contains PI or the precursor thereof, the solvent containing NMP may be used.
In order to prevent aggregation of the inorganic particles in the nanofibers, it is preferable to prepare the first dispersion by mixing the polymer solution and the second dispersion containing the inorganic particles. In this case, it is particularly preferable to use the solvent contained in the polymer solution as a dispersion medium for dispersing the inorganic particles in the second dispersion. For example, equal to or greater than 50% by mass (preferably equal to or greater than 70% by mass or equal to or greater than 80% by mass) dispersion medium of the second dispersion is preferably set as the same solvent as a main solvent (solvent occupying equal to or greater than 50% by mass among the solvents contained in the polymer solution) among the solvents contained in the polymer solution.
Polymer concentration in the first dispersion is, for example from 3% by mass to 60% by mass and preferably from 5% by mass to 50% by mass.
The first dispersion may contain a well-known additive used by the electrospinning, if necessary.
(Second Step)
In the second step, the first dispersion obtained in the first step is formed as the fiber by the electrospinning and the non-woven fabric is formed.
In the electrospinning, the nanofibers are generated by an electrostatic drawing phenomenon. More specifically, when the first dispersion is used as a raw material of the electrospinning, the solvent is slowly evaporated while flying the space, from the raw material solution flowing to the charged space. Accordingly, the volume of the flying raw material solution is slowly decreased, but the charges applied to the raw material solution are maintained in the raw material solution. As a result, the charge density of the raw material solution flying the space is slowly increased. When the charge density of the raw material solution is increased and a Coulomb force generated in the raw material solution in a repulsion direction is greater than surface tension, a phenomenon in which the raw material solution is explosively linearly drawn occurs. This phenomenon is the electrostatic drawing phenomenon. According to the electrostatic drawing phenomenon, it is possible to effectively manufacture the nanofibers.
The non-woven fabric according to the embodiment is obtained by laminating the nanofibers generated in the fiber formation space on the surface of a base material. The formed non-woven fabric may be peeled off from the surface of the base material. In this case, the manufacturing method of the non-woven fabric can further include a step of peeling off the non-woven fabric from the surface of the base material. Herein, as the base material, a base material sheet having a peeling property or a belt of a transportation conveyer for transporting the fiber can be used. In addition, by laminating the nanofibers on the surface by using the base material (commercially available non-woven fabric) having a non-woven fiber structure as the base material, the non-woven fabric obtained by integrating the non-woven fabric and the base material having the non-woven fiber structure may be formed.
In the step of forming the non-woven fabric, a plurality of electrospinning units are used, if necessary, and the nanofibers different from each other may be generated by each unit and laminated. For example, the nanofibers having different fiber diameters and/or polymer compositions may be generated by each unit and laminated to form the non-woven fabric. In addition, the nanofiber diameter can be adjusted according to the state of the raw material solution, the configuration of the emitter, or the magnitude of the electric field formed by the charging means.
FIG. 3 is a diagram schematically showing a configuration of a manufacturing system for executing the manufacturing method of the non-woven fabric according to one embodiment of the present invention. FIG. 3 is an example when using a base material E having the non-woven fiber structure.
The manufacturing system of FIG. 3 configures a manufacturing line for manufacturing the non-woven fabric. The manufacturing system includes a non-woven fabric forming device 40 and a collection device 70 for collecting the formed non-woven fabric. In the manufacturing system of FIG. 3, the base material E is transported from the upstream side to the downstream side of the manufacturing line. The formation of the non-woven fabric of the nanofibers is performed with the base material E being transported, as required.
A base material supply device 20 which accommodates the base material E wound in a roll shape therein is provided on the uppermost stream of the manufacturing system. The base material supply device 20 winds the unwinds the roll-shaped base material E and supplies the base material E to another device adjacent to the base material supply device 20 on the lower stream side. Specifically, the base material supply device 20 rotates a supply reel 22 by a motor 24 and supplies the base material E wound by the supply reel 22 to a first transportation roller 21.
The unwound base material E is transported to the non-woven fabric forming device 40 by the first transportation roller 21.
The non-woven fabric forming device 40 has an electrospinning mechanism. More specifically, the electrospinning mechanism includes a release unit 42A which includes nozzles (emitters) for releasing the raw material solution installed on the upper portion of the device, charging means for charging the released raw material solution (first dispersion), and a transportation conveyer 41 which transports the non-woven fabric E from the upstream side to the downstream side so as to oppose the release unit 42A. The transportation conveyer 41 functions as a collector unit which collects the fibers with the base material E and the nanofibers released from the released from the release unit 42A are laminated on the surface (main surface) of the base material E.
The charging means is configured with a voltage application device 43 which applies a voltage to the emitter and a counter electrode 44 which is installed to be parallel to and electrically connected to the transportation conveyer 41. The counter electrode 44 is grounded. Accordingly, a potential difference (for example, from 20 kV to 200 kV) according to the voltage applied by the voltage application device 43 can be provided between the emitter and the counter electrode 44. In addition, the configuration of the charging means is not particularly limited, and for example, the counter electrode 44 may not be grounded and the high voltage may be applied thereto. In addition, instead of providing the counter electrode 44, the belt portion of the transportation conveyer 41 may be configured from a conductor.
FIG. 4 is a front view schematically showing the release unit 42A of FIG. 3 and FIG. 5 is a side view schematically showing the release unit 42A of FIG. 3. FIG. 6 is a schematic longitudinal sectional view which is obtained by cutting the emitter 42 of FIG. 4 and FIG. 5 along a plane passing through a release port 42 a and enlarging a part thereof.
As shown in FIG. 4 and FIG. 5, the release unit 42A includes the emitter 42 for releasing the raw material solution and a duct 50 for supplying the raw material solution 45 to the emitter 42 is connected to the upper portion of the emitter 42. In addition, a air blowing mechanism (not shown) is provided on the upper portion of the emitter 42. By performing air blowing from the upper portion of the emitter 42, ventilation of solvent stream or ion wind disturbing the generation of nanofibers can be effectively performed.
The emitter 42 has a elongated shape and a hollow cylindrical accommodation unit 52 having a diameter D1 is formed in the emitter 42. A plurality of release ports 42 a are provided at regular intervals with regular arrangement, on the side opposing the belt (base material) of the transportation conveyer 41 of the emitter 42.
The cross section of the upper portion of the emitter 42 is formed in a square shape, and a tapered portion 42 b having a width of the sectional shape which gradually decreases towards the release port 42 a is formed. As described above, by forming the tapered portion 42 b around the release portion 42 a of the emitter 42, it is possible to prevent generation of ion wind due to the concentration of charges on the corners.
In addition, by gradually decreasing the width of the sectional shape of the emitter 42 towards the release port 42 a, it is possible to suitably concentrate the charges and to effectively supply the charges to the raw material solution released from the release port 42 a. a diameter of a penetration hole connecting the accommodation unit 52 and the release port 42 a is, for example, from 0.25 mm to 0.4 mm and a length of the penetration hole is, for example, from 0.1 mm to 5 mm. As the sectional shape of the penetration hole, arbitrary shape such as a circle, a polygon such as a triangle or a square, or a shape having a portion protruded to the inner side such as a pentagram can be selected.
The raw material solution 45 is supplied from a raw material solution tank 45 a to the accommodation unit 52 of the emitter 42 through the duct 50 by pressure of a pump 46 connected to a hollow portion of the emitter 42. The raw material solution 45 is released towards the main surface of the non-woven fabric E from the plurality of release ports 42 a by the pressure of the pump 46. The electrostatic explosion occurs while the released raw material solution is moving through the space between the emitter 42 in the charged state and the transportation conveyer 41 (or non-woven fabric E), and the nanofibers having a sheath-core structure are generated. The generated nanofibers are attracted to the main surface of the base material by an electrostatic attraction force and are laminated thereon. Accordingly, a non-woven fabric F is formed.
The belt portion of the transportation conveyer 41 may be a derivative. When the belt portion is configured with a conductor, the nanofibers slightly tend to be concentrated and laminated on the collector unit close to the release port of the emitter 42. In order to more evenly disperse the nanofibers in the collector unit, the belt portion of the transportation conveyer 41 is desirably formed by the derivative.
When the belt portion is formed by the derivative, the counter electrode 44 may come into contact with the inner periphery surface (surface on the side opposite to the surface coming into contact with the non-woven fabric E) of the belt portion. With such contact, inducement polarization occurs in the belt portion and the even charges are generated on the contact surface with the base material E. Accordingly, a possibility of the concentration and lamination of the nanofibers are concentrated on a part of a surface Ea of the base material E is further reduced.
In FIG. 3, a charge removing device which removes the charge of the non-woven fabric F may be provided on a portion where the non-woven fabric F and the belt of the transportation conveyer 41 are separated or peeled from each other, in order to prevent generation of sparks which may occur when peeling these. In addition, an absorption duct which performs the ventilation of the charged solvent stream or charged air generated in the spinning space and improving spinning performance may be provided in the vicinity of a window portion between the non-woven fabric forming device 40 and each device adjacent thereto.
The completed non-woven fabric F which is transported from the non-woven fabric forming device 40 is collected in the collection device 70 through a transportation roller 71. A collection reel 72 which winds the transported non-woven fabric F is embedded in the collection device 70. The collection reel 72 is rotatably driven by a motor 74.
In the manufacturing system shown in FIG. 3, the motor 74 for rotating the collection reel 72 of the collection device 70 which collects the non-woven fabric is controlled to be a rotation speed so that a transportation speed (speed of the transportation conveyer 41) of the non-woven fabric F is constant. Accordingly, the non-woven fabric F is transported while maintaining a predetermined tension. Such controlling is performed by a control device (not shown) included in the manufacturing system. The control device is configured to generally control and manage each device configuring the manufacturing system.
A spare collection unit may be disposed between the non-woven fabric forming device 40 and the non-woven fabric collection device 70. The spare collection unit is provided so as to easily perform the collection of the completed non-woven fabric F by the collection device 70. Specifically, in the spare collection unit, the completed non-woven fabric F transported from the non-woven fabric forming device 40 is collected in a state of being loosened without being wound, when the non-woven fabric F has a certain length. Meantime, the collection reel 72 of the collection device 70 is not rotated and stopped. Each time the length of the loosened non-woven fabric F collected by the spare collection unit becomes a certain length, the collection reel 72 of the collection device 70 is rotated for predetermined time and the non-woven fabric F is wound by the collection reel 72.
By providing such a spare collection unit, it is not necessary to control the transportation speed of the transportation conveyer 41 and the rotation speed of the motor 74 included by the non-woven fabric collection device 70 to be strictly operate together, and it is possible to simplify the control device of the manufacturing system.
In addition, the manufacturing system of the non-woven fabric is merely an example of the manufacturing system which can be used for manufacturing the non-woven fabric according to the embodiment of the present invention. The manufacturing method of the non-woven fabric is not particularly limited, as long as it includes the first step of preparing the first dispersion, and the second step of generating the nanofibers from the first dispersion in the fiber formation space and laminating to form the non-woven fabric.
In addition, any electrospinning mechanism may be used, as long as the second step includes a step of generating the nanofibers from the first dispersion by an electrostatic force in the fiber formation space and laminating the generated nanofibers. For example, the shape of the emitter is not particularly limited, the shape of the cross section orthogonal to the longitudinal direction of the emitter is not limited to the shape (V-shaped nozzle), the size of which is gradually decreased from the upper portion towards the lower portion, as shown in FIG. 5, and the emitter may be configured with a rotator.
In the nanofibers forming device, it is possible to form the elongated non-woven fabric by continuously laminating the fibers on the main surface of the belt of the transportation conveyer. In addition, it is also possible to form the rectangular non-woven fabric by intermittently laminating the nanofibers.
(Carbon Fiber Non-Woven Fabric)
The embodiment of the present invention also includes a carbon fiber non-woven fabric which is obtained by firing the non-woven fabric. By firing the non-woven fabric, the polymer configuring the matrix of the nanofibers is carbonized, and the nanofibers of the polymer are converted into carbon fibers. In the carbon fiber non-woven fabric, since the inorganic particles are more easily fixed to the nanofibers, it is possible to further prevent the removal of the inorganic particles. Accordingly, the effect of the inorganic particles can be exhibited for a long time.
When forming the carbon fiber non-woven fabric, among the polymers described above, a material with which the carbonization easily proceeds, for example, PAN and/or PI are preferably used.
A firing temperature may be, for example, from 300° C. to 1300° C. or from 500° C. to 1000° C. The firing may be performed under the atmosphere of inert gas (nitrogen gas or argon gas) or may be performed under the reducing atmosphere (for example, under the existence of hydrogen gas). The firing time may be, for example, from 0.5 hours to 5 hours.
In addition, as the carbon fiber non-woven fabric, a material which is subjected to a well-known activation process may be used, if necessary.
An average fiber diameter of the carbon fibers of the carbon fiber non-woven fabric is, for example, from 50 nm to 500 nm and preferably from 80 nm to 400 nm. The average fiber diameter of the carbon fibers can be acquired as in the case of the average fiber diameter D_fof the nanofibers described above.
The inorganic particles contained in the non-woven fabric may be restored by the firing. For example, the metal oxide particles may be restored to the metal particles of copper or silver by firing the non-woven fabric containing the particles of metal oxide such as copper oxide or silver oxide under the reducing atmosphere. The carbon fiber non-woven fabric containing the inorganic particles restored by the firing is also included in the present invention.
In the carbon fiber non-woven fabric, an average particle diameter of the inorganic particles is, for example, from 5 nm to 80 nm and may be from 8 nm to 50 nm. the average particle diameter of the inorganic particles of the carbon fiber non-woven fabric can be calculated based on the TEM image of the carbon fiber non-woven fabric, for example. Specifically, regarding a plurality of (for example, 10) portions of the carbon fiber of the TEM image, it is possible to acquire an average particle diameter by acquiring and averaging a maximum diameter of the inorganic particle.

EXAMPLES

Hereinafter, the present invention will be described in detail based on Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Example 1

(1) Preparation of First Dispersion
PAN was dissolved in DMAc to prepare a polymer solution (concentration of 5% by mass to 10% by mass).
The polymer solution and slurry (second dispersion, concentration of copper oxide particles of 15% by mass) containing the copper oxide particles (average particle diameter D_p:20 nm) were mixed with each other so that a mass ratio between PAN and the copper oxide particles is 1.3:0.15, and accordingly, a first dispersion containing PAN and the copper oxide particles was prepared.
(2) Electrospinning
By the manufacturing system shown in FIG. 3, the nanofibers were laminated on the main surface by the electrospinning using the first dispersion obtained in (1) as the raw material solution under the following conditions, and a non-woven fabric was manufactured.
Electrospinning conditions:
Application voltage: 60 kV
Solution discharging pressure: 25 kPa
Temperature: 26° C.
Humidity: 37% RH
In the obtained non-woven fabric, the average fiber diameter D_fof the nanofibers was 320 nm and the ratio D_f/D_pwas 16. In addition, the thickness of the non-woven fabric was 100 μm and the mass per unit area was 13 g/m².
When the average numbers N₁and N₂of the first particles 1 and the second particles 2 are acquired based on the SEM image of the non-woven fabric by the method described above, a relationship of N₁>N₂was satisfied.

Example 2

The non-woven fabric of nanofibers was manufactured in the same manner as in Example 1, except for using PI instead of PAN and changing the mass ratio between PI and the copper oxide particles to 2:0.15, and the evaluation was performed.
The thickness of the obtained non-woven fabric was 20 μm, the mass per unit area was 5 g/m², the average fiber diameter D_fof the nanofibers was 440 nm, the ratio D_f/D_pwas 22, and a relationship of N₁>N₂was satisfied.

Example 3

The non-woven fabric obtained in Example 1 was fired under the argon atmosphere at 800° C. for 0.5 hours, and accordingly, a carbon fiber non-woven fabric was manufactured.
When the state of particles is observed by energy dispersion type X-ray analysis, the copper oxide particles were converted into copper particles.
The non-woven fabric and the carbon fiber non-woven fabric according to the embodiments of the present invention can be used for various purposes such as medical purpose, sanitary purpose, a storage device, a catalyst sheet, according to the type of the inorganic particles, in addition to a filtering material.

Claims

What is claimed is:

1. A non-woven fabric comprising:

nanofibers which contain a polymer and inorganic particles, the nanofibers being formed by an electrospinning method,

wherein the inorganic particles contain first particles and second particles, some parts of which are exposed from a surface of the polymer,

a volume V_1oof a portion of the first particles exposed from the surface of the polymer and a volume V_1iof a portion buried in the polymer satisfy a relationship of V_1o<V_1i,

a volume V_2oof a portion of the second particles exposed from the surface of the polymer and a volume V_2iof a portion buried in the polymer satisfy a relationship of V_2o≧V_2i, and

an average number N₁of the first particles and an average number N₂of the second particles per unit length of the nanofibers satisfy a relationship of N₁>N₂.

2. The non-woven fabric according to claim 1, wherein ratio D_f/D_pof an average fiber diameter D_fof the nanofibers to an average particle diameter D_pof the inorganic particles is from 0.5 to 30.

3. The non-woven fabric according to claim 1, wherein an average fiber diameter D_fof the nanofibers is equal to or greater than 150 nm and smaller than 1000 nm, and an average particle diameter D_pof the inorganic particles is from 20 nm to 200 nm.

4. The non-woven fabric according to claim 1, wherein the inorganic particles further contain third particles which are completely buried in the polymer, and

the average number N₁of the first particles and an average number N₃of the third particles per unit length of the nanofibers satisfy a relationship of N₁<N₃.

5. The non-woven fabric according to claim 1, wherein an amount of the inorganic particles is from 5 parts by mass to 50 parts by mass with respect to 100 parts by mass of the polymer.

6. A carbon fiber non-woven fabric which is obtained by firing the non-woven fabric according to claim 1.

7. The carbon fiber non-woven fabric according to claim 6, wherein the polymer is at least one kind selected from a group consisting of polyacrylonitrile and polyimide, and

the polymer is formed by carbonizing.