JP2016183423A - Nonwoven fabric and carbon fiber nonwoven fabric - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nanofiber nonwoven fabric and a carbon fiber nonwoven fabric capable of exhibiting an effect of inorganic particles for a long term.SOLUTION: A nonwoven fabric contains a nanofiber containing polymer and inorganic particles and formed by an electrospinning method. The inorganic particles include first particles and second particles, a part of which is exposed on the surface of the polymer. In the first particles, volume Vof a part exposed on the surface of the polymer and volume Vof a part embedded into the polymer satisfy V<V. In the second particles, volume Vof a part exposed on the surface of the polymer and volume Vof a part embedded into the polymer satisfy V≥V. The average number Nof the first particles and the average number Nof the second particles per unit length of the nanofiber satisfy N>N.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a nonwoven fabric containing inorganic fibers and containing nanofibers formed by electrospinning, and a carbon fiber nonwoven fabric obtained by carbonizing the nonwoven fabric.

  A nanofiber nonwoven fabric having a fiber diameter of nanometer (nm) to sub-μm order can be manufactured by an electrospinning method using a polymer solution or the like. Nanofiber non-woven fabrics have a large surface area and are expected to be used for various purposes in addition to filter media. If the nanofiber nonwoven fabric can be given further functions, it can be used for various applications.

  Patent Document 1 proposes a method for producing a nanofiber nonwoven fabric by electrospinning from a spinning solution containing catalyst particles surface-coated with an inert substance and a polymer material.

  In Patent Document 2, it is proposed that ceramic ultrafine particles are supported on the surface of the fiber of the fiber filter member. In Patent Document 2, the fiber filter member is immersed in a solution containing the ceramic ultrafine particles, the excess solution is removed, and the ceramic ultrafine particles are supported by heat treatment.

JP 2014-145140 A JP-A-2005-040646

  When the particles are supported on the nonwoven fabric, it is considered that the action of the particles is more easily exhibited when the particles are present on the surface of the nanofiber. However, if the exposure of the particles increases, the particles easily fall off. Therefore, if a nonwoven fabric is used over a long period of time, the effect of particles cannot be obtained.

  The objective of this invention is providing the nonwoven fabric and carbon fiber nonwoven fabric which can exhibit the effect of an inorganic particle over a long period of time.

One aspect of the present invention includes nanofibers formed by an electrospinning method that includes a polymer and inorganic particles,
The inorganic particles include first particles and second particles partially exposed from the surface of the polymer,
In the first particle, the volume V _{1o of} the portion exposed from the surface of the polymer and the volume V _{1i of} the portion embedded in the polymer satisfy V _1o <V _1i ,
In the second particle, the volume V _{2o of} the portion exposed from the surface of the polymer and the volume V _{2i of} the portion embedded in the polymer satisfy V _2o ≧ V _2i ,
The average number N ₁ of the first particles and the average number N ₂ of the second particles per unit length of the nanofiber relate to a nonwoven fabric satisfying N ₁ > N ₂ .

  Another aspect of the present invention relates to a carbon fiber nonwoven fabric obtained by firing the nonwoven fabric described above.

  ADVANTAGE OF THE INVENTION According to this invention, even if the fiber which comprises a nonwoven fabric deteriorates, the nonwoven fabric and carbon fiber nonwoven fabric which can exhibit the effect of inorganic particles, such as a catalyst particle, can be provided over a long period of time.

It is a top view which shows typically the nanofiber contained in the nonwoven fabric which concerns on one Embodiment of this invention. It is a schematic sectional drawing which shows the structure of the nanofiber contained in the nonwoven fabric which concerns on one Embodiment of this invention. In the manufacturing method of the nonwoven fabric concerning one embodiment of the present invention, it is a figure showing roughly composition of a system for obtaining a nonwoven fabric. It is a front view which shows roughly the discharge | release part 42A of FIG. FIG. 4 is a side view schematically showing a discharge part 42A of FIG. 3. It is an expanded sectional view showing a discharge object roughly.

[Nonwoven fabric]
The nonwoven fabric which concerns on embodiment of this invention contains the nanofiber formed by the electrospinning method containing a polymer and an inorganic particle. The inorganic particles include first particles and second particles partially exposed from the surface of the polymer. Here, in the first particle, the volume V _{1o of} the portion exposed from the surface of the polymer and the volume V _{1i of} the portion embedded in the polymer satisfy V _1o <V _1i , and the second particle The volume V _{2o of} the portion exposed from the surface and the volume V _{2i of} the portion embedded in the polymer satisfy V _2o ≧ V _2i . The average number N ₁ of the first particles and the average number N ₂ of the second particles per unit length of the nanofiber satisfy N ₁ > N ₂ .

Thus, in the present embodiment, the average number N ₁ of the first particles in which less than 50% by volume is exposed from the surface of the polymer constituting the nanofiber matrix is the average of the second particles in which 50% by volume or more is exposed. More than the target number N ₂ . Even if the nanofibers deteriorate due to the use of the nonwoven fabric, the first particles that are difficult to drop out are contained in a large amount, so that the effect of the inorganic particles can be exhibited over a long period of time. In addition, since the first particles are exposed to the outside of the nanofiber from the beginning while containing the second particles having a high degree of exposure, the action of the inorganic particles can be sufficiently obtained even at the initial stage of use. Since such a nonwoven fabric is easily formed by the electrospinning method, the nonwoven fabric can be obtained with high productivity.

  FIG. 1 is a top view schematically showing nanofibers in the nonwoven fabric according to the present embodiment, and FIG. 2 is a schematic sectional view showing the structure of the nanofibers included in the nonwoven fabric according to the present embodiment (length of the nanofibers). It is sectional drawing perpendicular | vertical to a vertical direction). The nanofiber 5 includes a polymer (polymer matrix) 6 that gives the shape of the fiber and inorganic particles 4 dispersed in the polymer 6. In the illustrated example, the inorganic particles 4 include the first particles 1, the second particles 2, and the third particles 3 having different degrees of exposure from the polymer 6, but do not necessarily include the third particles 3. The first particles 1 have an exposure from the surface of the polymer 6 of less than 50% by volume, the second particles 2 have an exposure from the surface of the polymer 6 of 50% by volume or more, and the third particles 3 Fully embedded. When the region having the predetermined length of the nanofiber 5 is observed, the number of the first particles 1 is larger than the number of the second particles 2, and thus, the inorganic particles (particularly the second particles) are obtained. The dropout of 2) is suppressed.

The numbers of the first particles and the second particles are compared with average numbers N ₁ and N ₂ per unit length of the nanofiber, respectively. Specifically, first, in each scanning electron microscope (SEM) photograph of a nonwoven fabric, for each of a plurality of (for example, five) nanofibers having a predetermined length L (μm) selected arbitrarily. Count the number of one and second particles. The length L may be, for example, 3 to 5 μm. The average number N ₁ and N ₂ can be obtained by doubling the number of each particle, converting per unit length (1 μm), and averaging. Note that the region having a predetermined length L (μm) is a second line whose distance between the first straight line perpendicular to the length direction of the nanofiber and the first straight line is L (μm) in the SEM image. A straight line (however, the first straight line and the second straight line are parallel) is drawn on one nanofiber, and it means a region between the first straight line and the second straight line.

  In addition, you may distinguish a 1st particle and a 2nd particle visually in a SEM photograph. When it is difficult to distinguish visually, in the SEM photograph of the nanofiber, the particle diameter (maximum particle diameter) of the portion exposed from the polymer surface is measured, and this particle diameter is the average of the inorganic particles used for the production of the nonwoven fabric. If it is larger than the particle size, it may be determined as the second particle, and if it is less than the average particle size, it may be determined as the first particle.

  As in the illustrated example, the inorganic particles may further include third particles that are completely embedded in the polymer. Since the third particles are encapsulated in the polymer, they are difficult to fall off even when the nanofibers deteriorate. Therefore, the effect of inorganic particles can be exhibited for a longer period.

The average number N ₃ of the third particles per unit length of the average number N ₁ and nanofibres of the first particles may be N ₁ ≧ N _3, but if that satisfies N ₁ <N ₃ In addition, the effect of inorganic particles in the nonwoven fabric can be ensured over a longer period. The average number N ₃ of the third particles can be calculated according to the case of N ₁ based on, for example, a transmission electron microscope (TEM) photograph of the nonwoven fabric.

The average fiber diameter D _f of the nanofiber is, for example, 100 nm or more, preferably 150 nm or more, or 200 nm or more, and more preferably 300 nm or more. D _f is, for example, less than 1000 nm, and preferably 800 nm or less or 600 nm or less. These lower limit values and upper limit values can be arbitrarily combined. D _f may be, for example, 100 nm or more and less than 1000 nm, 150 nm or more and less than 1000 nm, or 200 nm or more and less than 1000 nm.

The average fiber diameter D _f of the nanofibers, for example, in nonwoven SEM image, any multiple (e.g., ten) to measure the diameter of each one place for fibers, can be obtained by averaging. The diameter of the fiber is a diameter of a cross section perpendicular to the length direction of the nanofiber. If such a cross section is not circular, the maximum diameter may be considered as the diameter.

The average particle diameter D _p of the inorganic particles is, for example, 5nm or more, preferably 10nm or more, may be 15nm or more, or 20nm or more. D _p may be 200 nm or less or 150 nm or less, or 100 nm or less or 80 nm or less. These lower limit values and upper limit values can be arbitrarily combined. D _p may be, for example, 5 to 200 nm, or 20 to 200 nm.

The average particle diameter D _p of the inorganic particles is the median diameter (D ₅₀ ) in the volume-based particle size distribution required for the inorganic particles used for producing the nonwoven fabric.

The ratio D _f / D _p of the average fiber diameter D _{f to} the average particle diameter D _p is, for example, 0.5 or more, preferably 3 or more, and may be 5 or 7 or more. The ratio D _f / D _p may be 30 or less or 25 or less, but is preferably less than 10 or 9 or less. These lower limit values and upper limit values can be arbitrarily combined. The ratio D _f / D _p is, for example, may be less than 10, or 3 to 9 or more 0.5～30,0.5～25,0.5. It is difficult to form nanofibers with inorganic particles exposed by electrospinning. However, adjusting the ratio D _f / D _p makes it easier to adjust the degree of exposure of the first particles and the second particles. From such a viewpoint, the ratio D _f / D _p is preferably less than 10.

  The amount of the inorganic particles is, for example, 5 to 50 parts by mass, preferably 5 to 30 parts by mass (for example, 10 to 30 parts by mass), and more preferably 5 to 20 parts by mass with respect to 100 parts by mass of the polymer. is there.

When D _f and D _p , the ratio D _f / D _p and / or the amount of inorganic particles are in the above ranges, the inorganic particles can be easily embedded in the nanofiber, and the number of the first particles and the third particles can be determined. Easy to adjust greatly.

  Below, the structure of a nonwoven fabric is demonstrated more concretely.

(polymer)
The polymer constitutes a matrix of nanofibers. That is, the nanofiber includes a polymer matrix and inorganic particles (first to third particles) dispersed in the matrix.

  The polymer is not particularly limited as long as it can be electrospun. For example, polyolefin, vinyl resin (vinyl acetate resin or a saponified product thereof, polystyrene, polyacrylonitrile (PAN), etc.), acrylic resin, fluororesin, polyethersulfone (PES) ), Polysulfone, polyester (such as aromatic polyester), polyamide, polyimide (PI), cellulose derivative, and biodegradable polymer. These polymers can be used individually by 1 type or in combination of 2 or more types. Among these, PES, polysulfone, aromatic polyester (polyalkylene terephthalate such as polyethylene terephthalate), polyamide, PI (condensation polyimide obtained from polyamic acid, thermosetting polyimide such as bismaleimide resin; thermoplastic polyimide, etc.) , PAN and the like are preferable. The polymer may be a homopolymer or a copolymer. From the viewpoint of easy preparation of a polymer solution (or first dispersion described later) and ease of electrospinning (and excellent spinnability), PAN and / or PI are preferred.

Although the weight average molecular weight _Mw of a polymer is based also on the kind of polymer, it is 30000-120,000, for example, and it is preferable that it is 50000-100000 or 50000-80000. The ratio to the number average molecular weight _{M n} of weight average molecular weight _{M w} of the polymer _{(= M} w / M _n) is, for example, 1.1 to 3.0.

  In addition, in this specification, the weight average molecular weight and number average molecular weight of a polymer are the values calculated | required from the molecular weight distribution measured by a gel permeation chromatograph.

  The nanofibers constituting the nonwoven fabric may contain a known additive in addition to the polymer and the inorganic particles, if necessary. The content of the additive may be 5% by mass or less of the entire nanofiber (or the entire nonwoven fabric) constituting the nonwoven fabric.

(Inorganic particles)
The inorganic particles can be appropriately selected according to the use, and those that do not dissolve or deteriorate in the polymer solution (specifically, the solvent of the solution) when the nanofiber is formed by electrospinning are preferable. Examples of the inorganic particles include metal particles and metal compound particles (oxide, hydroxide, nitride, carbide, halide, etc.). Of the inorganic particles, metal particles, metal oxide particles (including ceramics) and the like are preferable. Examples of the metal constituting the metal particles include transition metals such as titanium, manganese, cobalt, nickel, palladium, platinum, copper, silver, and gold. Examples of the metal oxide include oxides of the above metals (for example, titanium oxide, copper oxide, silver oxide, etc.). An inorganic particle can be used individually by 1 type or in combination of 2 or more types.

  The thickness of the nonwoven fabric can be selected from a range of about 1 to 1000 μm per sheet, and is, for example, 10 to 700 μm, preferably 10 to 600 μm or 20 to 500 μm.

  In the nonwoven fabric according to the present embodiment, the number of the first particles with small exposure is larger than the number of the second particles with large exposure on the nanofiber surface. Therefore, even if the nanofiber is deteriorated, the effect of the inorganic particles can be exhibited for a long time.

(Nonwoven fabric manufacturing method)
The non-woven fabric can be obtained by, for example, an electrospinning method using a dispersion liquid in which inorganic particles are dispersed in a solution containing a polymer (or a precursor thereof). Specifically, in the first step of preparing a dispersion (first dispersion) containing a polymer or a precursor thereof and inorganic particles, and in the fiber forming space, nanofibers are generated from the first dispersion by electrostatic force. And the second step of forming the nonwoven fabric by depositing the generated nanofibers, the nonwoven fabric can be produced. In the second step, when nanofibers are generated, a part of each of the inorganic particles or a part of all the inorganic particles are exposed from the nanofibers to become first particles and second particles. In some cases, some inorganic particles become third particles embedded in the nanofiber.

  When the polymer is polyimide or the like, a polyimide precursor (polyamide acid or the like) and a dispersion containing inorganic particles are used as the first dispersion and heated appropriately in the process of manufacturing the nonwoven fabric. Polyimide (polymer) may be produced from

(First step)
In the first step, the method for preparing the first dispersion is not particularly limited. For example, the first dispersion may be prepared by dispersing inorganic particles in a polymer solution in which a polymer (or a precursor thereof) is dissolved in a solvent. The inorganic particles may be used in the form of a powder, but can also be used in the form of a dispersion (second dispersion). For example, the first dispersion liquid may be prepared by adding a polymer to a second dispersion liquid in which inorganic particles are dispersed in a solvent that dissolves the polymer (or a precursor thereof) and dissolving the polymer in the solvent. Moreover, when a polymer solution and the 2nd dispersion liquid containing an inorganic particle are mixed and the 1st dispersion liquid containing a polymer and an inorganic particle is prepared, it will be easy to improve the dispersibility of an inorganic particle.

  The solvent is not particularly limited as long as it dissolves the polymer (or its precursor) and can be removed by volatilization or the like. Examples of such a solvent include aprotic polar organic solvents. Although depending on the type of polymer or its precursor, it is preferable to use an aprotic polar organic solvent having a polarity parameter P ′ of Rohrschneider of 5 or more (for example, 5 to 7.5). Examples of such a solvent include amides such as N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), and N-methyl-2-pyrrolidone (NMP) (chain or cyclic amide). A sulfoxide such as dimethyl sulfoxide; These solvent may be used individually by 1 type, and may be used in combination of 2 or more type.

  It is also preferable to use a solvent containing an amide. For example, if the polymer contains PES and / or PAN, a solvent containing DMF and / or DMAc may be used. When the polymer contains PI or a precursor thereof, a solvent containing NMP may be used.

  From the viewpoint of suppressing the aggregation of the inorganic particles in the nanofiber, it is preferable to prepare the first dispersion by mixing the polymer solution and the second dispersion containing the inorganic particles. In this case, in particular, the solvent contained in the polymer solution is preferably used as a dispersion medium for dispersing inorganic particles in the second dispersion. For example, 50 mass% or more (preferably 70 mass% or more or 80 mass% or more) of the dispersion medium of the second dispersion liquid is used as the main solvent (50 mass of the solvent contained in the polymer solution) among the solvents contained in the polymer solution. % Of the solvent) is preferred.

  The polymer concentration in the first dispersion is, for example, 3 to 60% by mass, and preferably 5 to 50% by mass.

  The first dispersion may contain a known additive used in electrospinning, if necessary.

(Second step)
In the second step, the first dispersion obtained in the first step is fibrillated by electrospinning to form a nonwoven fabric.

  In the electrospinning method, nanofibers are generated by an electrostatic stretching phenomenon. More specifically, when the first dispersion liquid is used as the raw material liquid for electrospinning, the solvent gradually evaporates from the raw material liquid that has flowed into the charged space while flying through the space. As a result, the volume of the raw material liquid in flight gradually decreases, but the charge imparted to the raw material liquid remains in the raw material liquid. As a result, the charge density of the raw material liquid in flight through the space gradually increases. Then, when the charge density of the raw material liquid increases and the repulsive Coulomb force generated in the raw material liquid exceeds the surface tension of the raw material liquid, a phenomenon occurs in which the raw material liquid is explosively stretched linearly. . This phenomenon is an electrostatic stretching phenomenon. According to the electrostatic stretching phenomenon, nanofibers can be produced efficiently.

  By depositing nanofibers generated in the fiber formation space on the surface of the substrate, the nonwoven fabric according to this embodiment is obtained. You may peel the formed nonwoven fabric from the surface of a base material. In this case, the manufacturing method of a nonwoven fabric can further include the process of peeling a nonwoven fabric from the surface of a base material. Here, as the substrate, a peelable substrate sheet, a conveyor belt for conveying fibers, or the like can be used. In addition, by using a base material having a non-woven fiber structure (such as a commercially available non-woven fabric) as the base material and depositing nanofibers on this surface, a non-woven fabric in which the non-woven fabric and the base material having the non-woven fiber structure are integrated. It may be formed.

  In the step of forming the nonwoven fabric, if necessary, a plurality of electrospinning units may be used to generate and deposit different nanofibers in each unit. For example, in each unit, nanofibers having different fiber diameters and / or polymer compositions may be generated and deposited to form a nonwoven fabric. The nanofiber diameter can be adjusted by the state of the raw material liquid, the configuration of the emitter, the magnitude of the electric field formed by the charging means, and the like.

  FIG. 3 is a diagram schematically showing a configuration of a manufacturing system for carrying out the method for manufacturing a nonwoven fabric according to one embodiment of the present invention. FIG. 3 is an example in the case of using a base material E having a non-woven fiber structure.

  The manufacturing system of FIG. 3 constitutes a manufacturing line for manufacturing a nonwoven fabric. The manufacturing system includes a nonwoven fabric forming device 40 and a collection device 70 for collecting the formed nonwoven fabric. In the manufacturing system of FIG. 3, the base material E is conveyed from the upstream to the downstream of the manufacturing line. A nanofiber nonwoven fabric is formed on the substrate E in the middle of conveyance as needed.

  In the uppermost stream of the manufacturing system, a base material supply device 20 that houses therein the base material E wound in a roll shape is provided. The base material supply apparatus 20 rolls out the roll-shaped base material E, and supplies the base material E to another apparatus adjacent to its downstream side. Specifically, the substrate supply device 20 rotates the supply reel 22 by the motor 24 and supplies the substrate E wound around the supply reel 22 to the first transport roller 21.

  The unrolled base material E is transferred to the nonwoven fabric forming apparatus 40 by the first transport roller 21.

  The nonwoven fabric forming apparatus 40 includes an electrospinning mechanism. More specifically, the electrospinning mechanism includes a discharge unit 42A including a nozzle (discharger) for discharging the raw material liquid installed above the apparatus, and the discharged raw material liquid (first dispersion). A charging means for charging and a transport conveyor 41 for transporting the nonwoven fabric E from the upstream side to the downstream side so as to face the discharge portion 42A are provided. The conveyor 41 functions as a collector unit that collects fibers together with the base material E, and the nanofibers emitted from the emission unit 42A are deposited on the surface (main surface) of the base material E.

  The charging means includes a voltage applying device 43 that applies a voltage to the emitter, and a counter electrode 44 that is installed in parallel with the conveyor 41 and is electrically connected. The counter electrode 44 is grounded. Thereby, a potential difference (for example, 20 to 200 kV) corresponding to the voltage applied by the voltage application device 43 can be provided between the emitter and the counter electrode 44. The configuration of the charging unit is not particularly limited. For example, the counter electrode 44 may not necessarily be grounded, and a high voltage may be applied. Moreover, you may comprise the belt part of the conveyance conveyor 41 from a conductor instead of providing the counter electrode 44. FIG.

  4 is a front view schematically showing the discharge part 42A of FIG. 3, and FIG. 5 is a side view schematically showing the discharge part 42A of FIG. FIG. 6 is a schematic longitudinal sectional view in which the emitter 42 of FIGS. 4 and 5 is cut by a plane passing through the outlet 42a and a part thereof is enlarged.

  As shown in FIGS. 4 and 5, the discharge section 42 </ b> A has a discharge body 42 for discharging the raw material liquid, and supplies the raw material liquid 45 to the discharge body 42 above the discharge body 42. A conduit 50 is connected. A blower mechanism (not shown) is provided above the emitter 42. By blowing air from above the emitter 42 by the blower mechanism, it is possible to efficiently ventilate the solvent vapor or ion wind that inhibits nanofiber production.

  The emitter 42 has a long shape, and a hollow cylindrical housing 52 having a diameter D1 is formed inside the emitter 42. On the side of the discharge body 42 facing the belt (base material) of the conveyor 41, a plurality of discharge ports 42a are provided in a regular array at regular intervals.

  The upper part of the emitter 42 has a square cross section, and a tapered portion 42b is formed with the width of the cross section gradually decreasing toward the discharge port 42a. In this manner, by forming the tapered portion 42b around the discharge port 42a of the emitter 42, it is possible to suppress the generation of ion wind due to the concentration of charges on the corners and the like.

  Further, by gradually reducing the width of the cross-sectional shape of the emitter 42 toward the discharge port 42a, the charge can be concentrated appropriately, and the charge is efficiently supplied to the raw material liquid discharged from the discharge port 42a. can do. The diameter of the through-hole which connects the accommodating part 52 and the discharge port 42a is 0.25-0.4 mm, for example, and the length of a through-hole is 0.1-5 mm, for example. As the cross-sectional shape of the through hole, any shape such as a circle, a polygon such as a triangle or a quadrangle, or a shape having a protruding portion inside such as a star can be selected.

  The raw material liquid 45 is supplied from the raw material liquid tank 45 a through the conduit 50 to the accommodating portion 52 of the emitter 42 by the pressure of the pump 46 communicating with the hollow portion of the emitter 42. And the raw material liquid 45 is discharge | released toward the main surface of the nonwoven fabric E from the some discharge port 42a by the pressure of the pump 46. FIG. The discharged raw material liquid undergoes electrostatic explosion while moving in the space between the emitter 42 and the transport conveyor 41 (or the nonwoven fabric E) in a charged state, and generates nanofibers having a sheath core structure. The produced nanofibers are attracted to the main surface of the substrate by electrostatic attraction and are deposited there. Thereby, the nonwoven fabric F is formed.

  The belt portion of the conveyor 41 may be a dielectric. In the case where the belt portion is made of a conductor, the nanofibers tend to be concentrated and deposited on the collector portion near the discharge port of the emitter 42. From the viewpoint of more uniformly dispersing the nanofibers in the collector portion, it is more desirable to form the belt portion of the transport conveyor 41 with a dielectric.

  When the belt portion is formed of a dielectric, the counter electrode 44 may be brought into contact with the inner peripheral surface of the belt portion (the surface opposite to the surface that contacts the nonwoven fabric E). Due to such contact, dielectric polarization occurs inside the belt portion, and a uniform charge is generated on the contact surface with the substrate E. Thereby, the possibility that the nanofibers concentrate and deposit on a part of the surface Ea of the substrate E is further reduced.

  In FIG. 3, a static eliminator that neutralizes the nonwoven fabric F is provided at a location where the nonwoven fabric F and the belt of the conveyor 41 are separated (peeled) in order to suppress the occurrence of sparks that may occur when the nonwoven fabric F peels. Also good. In addition, in the vicinity of the window between the nonwoven fabric forming device 40 and each adjacent device, there is a suction duct that ventilates the charged solvent vapor and charged air generated in the spinning space to improve the spinning performance. It may be provided.

  The completed non-woven fabric F unloaded from the non-woven fabric forming device 40 is collected by the collecting device 70 via the transport roller 71. The collection device 70 has a built-in collection reel 72 that scrapes the conveyed nonwoven fabric F. The collection reel 72 is rotationally driven by a motor 74.

  In the manufacturing system as shown in FIG. 3, the motor 74 that rotates the collection device 70 that collects the nonwoven fabric is controlled to a rotational speed at which the conveyance speed of the nonwoven fabric F (the speed of the conveyance conveyor 41) is constant. Thereby, the nonwoven fabric F is conveyed, maintaining a predetermined tension. Such control is performed by a control device (not shown) provided in the manufacturing system. The control device is configured to control and manage each device constituting the manufacturing system in an integrated manner.

  A preliminary collection unit may be arranged between the nonwoven fabric forming apparatus 40 and the nonwoven fabric collection apparatus 70. The preliminary recovery unit is provided so that the completed nonwoven fabric F can be easily recovered by the recovery device 70. Specifically, in the preliminary collection unit, the completed nonwoven fabric F transferred from the nonwoven fabric forming apparatus 40 is collected in a slack state without being scraped off by a certain length. Meanwhile, the recovery reel 72 of the recovery device 70 is stopped without rotating. Then, each time the length of the loose nonwoven fabric F collected by the preliminary collection unit becomes a certain length, the collection reel 72 of the collection device 70 is rotated for a predetermined time, and the nonwoven fabric F is removed by the collection reel 72. Scatter it.

  By providing such a preliminary collection unit, it is not necessary to control the conveyance speed of the conveyance conveyor 41 and the rotation speed of the motor 74 included in the nonwoven fabric collection apparatus 70 in strict association with each other, and the manufacturing system control apparatus is simplified. Can be

  In addition, said nonwoven fabric manufacturing system is only an example of the manufacturing system which can be used in order to manufacture the nonwoven fabric which concerns on embodiment of this invention. As long as the manufacturing method of a nonwoven fabric has the 1st process of preparing the 1st dispersion, and the 2nd process of generating and depositing nanofibers from the 1st dispersion and forming the nonwoven fabric in the nanofiber formation space, There is no particular limitation.

  As for the second step, any electrospinning mechanism may be used as long as the nanofibers are generated from the first dispersion by electrostatic force in a predetermined nanofiber formation space and the generated nanofibers are deposited. May be. For example, the shape of the emitter is not particularly limited. As shown in FIG. 5, the shape of the cross section perpendicular to the longitudinal direction of the emitter is not limited to a shape (V-shaped nozzle) that gradually decreases from the top to the bottom, and the emitter may be constituted by a rotating body. Good.

In the nanofiber forming apparatus, a long nonwoven fabric can be formed by continuously depositing fibers on the main surface of the belt of the conveyor. Moreover, a rectangular nonwoven fabric can also be formed by intermittently depositing nanofibers.
[Carbon fiber nonwoven fabric]
The embodiment of the present invention includes a carbon fiber nonwoven fabric obtained by firing the above-described nonwoven fabric. By baking the nonwoven fabric, the polymer constituting the nanofiber matrix is carbonized, and the polymer nanofibers are converted into carbon fibers. In such a carbon fiber non-woven fabric, the inorganic particles are more easily fixed to the nanofibers, so that the falling off of the inorganic particles can be further suppressed. Therefore, the effect of inorganic particles can be exhibited over a long period of time.

  In the case of forming a carbon fiber nonwoven fabric, it is preferable to use a polymer that easily undergoes carbonization, such as PAN and / or PI, among the above-mentioned polymers.

  The firing temperature may be, for example, 300 to 1300 ° C or 500 to 1000 ° C. Firing may be performed in an atmosphere of an inert gas (nitrogen gas, argon gas, or the like), or may be performed in a reducing atmosphere (for example, in the presence of hydrogen gas or the like). The firing time may be, for example, 0.5 to 5 hours.

  Moreover, the carbon fiber nonwoven fabric may be subjected to a known activation treatment as necessary.

The average fiber diameter of the carbon fibers in the carbon fiber nonwoven fabric is, for example, 50 to 500 nm, and preferably 80 to 400 nm. The average fiber diameter of the carbon fiber can be determined according to the case of the average fiber diameter D _f of the nanofiber described above.

  The inorganic particles contained in the nonwoven fabric may be reduced by firing. For example, the metal oxide particles may be reduced to metal particles such as copper and silver by firing a non-woven fabric containing metal oxide particles such as copper oxide and silver oxide in a reducing atmosphere. A carbon fiber nonwoven fabric containing inorganic particles reduced by such firing is also included in the present invention.

  In the carbon fiber nonwoven fabric, the average particle diameter of the inorganic particles is, for example, 5 to 80 nm, and may be 8 to 50 nm. The average particle diameter of the inorganic particles in the carbon fiber nonwoven fabric can be calculated based on, for example, a TEM image of the carbon fiber nonwoven fabric. Specifically, the average particle diameter can be obtained by obtaining and averaging the maximum diameter of the inorganic particles at a plurality of places (for example, 10 places) of the carbon fibers in the TEM image.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
(1) Preparation of first dispersion PAN was dissolved in DMAc to prepare a polymer solution (concentration 5 to 10% by mass).

A polymer solution and a slurry (second dispersion, concentration of copper oxide particles of 15% by mass) containing copper oxide particles (average particle diameter D _p : 20 nm) are set to a mass ratio of PAN to copper oxide particles of 1.3. : The 1st dispersion liquid containing PAN and a copper oxide particle was prepared by mixing so that it might be set to 0.15.
(2) Electrospinning Using the production system as shown in FIG. 3, the main dispersion of the substrate is obtained by electrospinning the first dispersion obtained in (1) above as a raw material liquid under the following conditions. Nanofibers were deposited to produce a nonwoven fabric.

Electrospinning conditions:
Applied voltage: 60 kV
Solution discharge pressure: 25 kPa
Temperature: 26 ° C
Humidity: 37% RH
In the obtained nonwoven fabric, the average fiber through D _f nanofiber is 320 nm, the ratio D _f / D _p was 16. Moreover, the thickness of the nonwoven fabric was 100 micrometers, and the mass per unit area was 13 g / m < ² >.

Based on the SEM photograph of the nonwoven fabric, the average numbers N ₁ and N ₂ of the first particles and the second particles were determined by the method described above, and N ₁ > N ₂ was obtained.

Example 2
A nanofiber nonwoven fabric was prepared and evaluated in the same manner as in Example 1 except that PI was used instead of PAN, and the mass ratio of PI and copper oxide particles was changed to 2: 0.15. It was.

The thickness of the obtained nonwoven fabric is 20 μm, the mass per unit area is 5 g / m ² , the average fiber diameter D _f of the nanofiber is 440 nm, the ratio D _f / D _p is 22, and N ₁ > N ₂ .

Example 3
The nonwoven fabric obtained in Example 1 was baked at 800 ° C. for 0.5 hours in an argon atmosphere to produce a carbon fiber nonwoven fabric.

  When the state of the particles was confirmed by energy dispersive X-ray analysis, the copper oxide particles were converted to copper particles.

  The nonwoven fabric and the carbon fiber nonwoven fabric according to the embodiment of the present invention can be used for various uses such as a medical use, a hygiene use, an electricity storage device, and a catalyst sheet, in addition to a filter medium, depending on the type of inorganic particles.

  1: 1st particle, 2: 2nd particle, 3: 3rd particle, 4: Inorganic particle, 5: Nanofiber, 6: Polymer (polymer matrix), 20: Substrate supply device, 21: First transport roll, 22: Supply reel, 24: Motor, 40: Non-woven fabric forming device, 41: Conveyor, 42A: Ejector, 42: Ejector, 42a: Ejector, 42b: Taper, 43: Voltage application device, 44: Counter electrode 45: raw material liquid (first dispersion), 45a: raw material liquid tank, 46: pump, 48: first support, 49: second support, 50: conduit, 52: container, 70: recovery device, 71: Conveying roller, 72: Collection reel, 74: Motor, E: Base material having non-woven fiber structure, Ea: Main surface of base material, F: Non-woven fabric

Claims (7)

Comprising nanofibers formed by electrospinning comprising a polymer and inorganic particles;
The inorganic particles include first particles and second particles partially exposed from the surface of the polymer,
In the first particle, the volume V _{1o of} the portion exposed from the surface of the polymer and the volume V _{1i of} the portion embedded in the polymer satisfy V _1o <V _1i ,
In the second particle, the volume V _{2o of} the portion exposed from the surface of the polymer and the volume V _{2i of} the portion embedded in the polymer satisfy V _2o ≧ V _2i ,
The average number N ₁ of the first particles and the average number N ₂ of the second particles per unit length of the nanofiber satisfy N ₁ > N ₂ . The nonwoven fabric according to claim 1, wherein a ratio D _f / D _p of the average fiber diameter D _f of the nanofibers to the average particle diameter D _p of the inorganic particles is 0.5 or more and 30 or less. The average fiber diameter D _f is 150 nm or more and less than 1000 nm,
The average particle diameter D _p is 20 to 200 nm, nonwoven fabric according to claim 1 or 2. The inorganic particles further include third particles completely embedded in the polymer;
The average number N ₃ of the third particles per unit length of the average number N ₁ and the nano fibers of the first particle, satisfies N ₁ <N _3, one of the claims 1 to 3 1 The nonwoven fabric according to item.   The quantity of the said inorganic particle is a nonwoven fabric of any one of Claims 1-4 which is 5-50 mass parts with respect to 100 mass parts of said polymers.   The carbon fiber nonwoven fabric obtained by baking the nonwoven fabric of any one of Claims 1-5. The polymer is at least one selected from the group consisting of polyacrylonitrile and polyimide,
The carbon fiber nonwoven fabric according to claim 6, which is formed by carbonizing the polymer.

Images