JP2016160568A - Nonwoven fabric and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nanofiber nonwoven fabric having a high tensile strength.SOLUTION: There is provided a nonwoven fabric that includes a nanofiber comprising a core portion 2 and a sheath portion 3 which covers at least a part of a surface of the core portion 2, where the core portion 2 comprises a first polymer and the sheath portion 3 comprises a second polymer, and where the second polymer is a polyurethane and the first polymer has a higher hydrolysis resistance than the second polymer. The nanofiber may be formed by using an electrospinning method. The amount of the second polymer is 10 to 1000 pts.mass based on 100 pts.mass of the first polymer. The average ratio of a fiber diameter Df of the nanofiber to a diameter Dc of the core portion (Df/Dc) is 1.4 to 5. The first polymer is one selected from among polyether sulfone, polyacrylonitrile, and polyimide.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a nonwoven fabric containing fibers (nanofibers) having a sheath core structure and a method for producing the same.

  Fiber nonwoven fabrics are used for various purposes in addition to filter media. In recent years, from the viewpoint of increasing the surface area, it has been studied to use a nonwoven fabric using nanofibers having a fiber diameter on the order of nm to sub-μm for applications such as filter media. For example, Patent Document 1 proposes a wet nonwoven fabric including short fibers A, which are nanofibers, and binder fibers B having a single fiber fineness of 0.1 dtex or more. Patent Document 1 teaches that such a nonwoven fabric can be used for a filter or the like.

International Publication No. 2008/130019 Pamphlet

  Polyurethane has high tensile strength and tensile elongation, and is considered suitable for nanofiber materials. However, since polyurethane has low hydrolysis resistance, it is difficult to suppress deterioration even when a nanofiber nonwoven fabric is formed from polyurethane.

  The objective of this invention is providing the nonwoven fabric formed with the nanofiber which is excellent in tensile strength, and its manufacturing method.

One aspect of the present invention includes a nanofiber including a core and a sheath covering at least a part of the surface of the core,
The core includes a first polymer;
The sheath includes a second polymer;
The second polymer is polyurethane;
The first polymer relates to a nonwoven fabric which is a polymer having higher hydrolysis resistance than the second polymer.

Another aspect of the present invention is a first step of preparing a solution containing a first polymer or a precursor thereof, a second polymer, and a solvent,
A second step of forming nanofibers from the solution by electrostatic force in the nanofiber formation space, and depositing the generated nanofibers to form a non-woven fabric,
The nanofiber includes a core including the first polymer, and a sheath covering at least a part of the surface of the core and including the second polymer,
The second polymer is polyurethane;
The first polymer relates to a method for producing a nonwoven fabric, which is a polymer having higher hydrolysis resistance and lower solubility in the solvent than the second polymer.

  ADVANTAGE OF THE INVENTION According to this invention, the nonwoven fabric formed with the nanofiber excellent in tensile strength can be provided.

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. It is a side view which shows roughly the discharge | release part 42A of FIG. It is an expanded sectional view showing a discharge object roughly. It is a schematic sectional drawing which shows the sheath core structure of the nanofiber contained in the nonwoven fabric which concerns on one Embodiment of this invention.

[Nonwoven fabric]
The nonwoven fabric which concerns on embodiment of this invention contains the nanofiber containing the core part and the sheath part which covers the surface of at least one part of a core part, a core part contains 1st polymer, and a sheath part is 2nd. Contains polymer. Here, the first polymer is a polymer having higher hydrolysis resistance than the second polymer.

  When the sheath part of the nanofiber having a sheath core structure contains polyurethane, high tensile strength can be secured in the nanofiber. On the other hand, since polyurethane has low hydrolysis resistance and is likely to deteriorate, it is difficult to obtain practical nanofibers even if used alone. In the present embodiment, a nanofiber having practical and high tensile strength can be obtained by forming the core of the nanofiber from a polymer having higher hydrolysis resistance than polyurethane as the second polymer. In addition, although the surface sheath part is formed of polyurethane, it is considered that a decrease in hydrolysis resistance is suppressed. Therefore, both high tensile strength and high hydrolysis resistance can be achieved. Thereby, deterioration of a nonwoven fabric can be suppressed and durability can also be improved.

  The nanofibers constituting the nonwoven fabric are preferably formed by electrospinning. The electrospinning method is an industrially superior technique that can relatively easily produce fibers such as nanofibers using a polymer solution or the like. By using the electrospinning method, as described later, the sheath core structure as described above is easily produced by utilizing the difference in solubility between the first polymer and the second polymer in the solvent contained in the solution. This can increase the productivity of the nonwoven fabric.

  The amount of the second polymer is, for example, 10 to 1000 parts by mass, preferably 20 to 500 parts by mass, and more preferably 50 to 200 parts by mass with respect to 100 parts by mass of the first polymer. When the amount of the second polymer is within such a range, the second polymer can be easily attached to the surface of the core (that is, the sheath core structure can be easily formed stably). Therefore, high tensile strength can be maintained. In addition to making it easier to suppress degradation due to hydrolysis, it becomes easier to produce nanofibers by electrospinning.

FIG. 5 is a schematic cross-sectional view (cross-sectional view perpendicular to the length direction of the nanofiber) showing the sheath core structure of the nanofiber in the nonwoven fabric according to one embodiment of the present invention. In the illustrated example, the nanofiber 1 includes a core portion 2 formed of a first polymer and a sheath portion 3 that covers the surface of the core portion 2 and is formed of a second polymer. The fiber diameter of the nanofiber 1 is represented by D _f , and the core diameter is represented by D _c .

The average of the ratio D _f / D _c between the fiber diameter (diameter) D _{f of the} nanofiber and the diameter (diameter) D _c of the core is preferably 1.4 to 5. In such a range, high tensile strength can be maintained. Moreover, it is easy to suppress degradation due to hydrolysis. From the viewpoint of improving the electrospinning property and facilitating the formation of the sheath portion, the average of the ratio D _f / D _c is more preferably 1.4 to 4 or 1.4 to 3.5. In addition, when the shape of the cross section of the fiber and the core is not circular, the diameter of an equivalent circle having the same area as the cross section may be D _f and D _c , respectively.

The fiber diameter D _f of the nanofiber and the core diameter D _c can be measured from the transmission electron microscope (TEM) image of the nanofiber. Specifically, first, an arbitrary plurality of locations (for example, 10 locations) where a cross section perpendicular to the length direction of the nanofiber can be observed is selected from the TEM image. At each location, the fiber diameter _Df and the core diameter _Dc are measured to calculate the ratio _Df / _Dc, and the average value can be calculated.

  The nonwoven fabric which concerns on this embodiment can be obtained by the electrospinning method using the solution containing both the 1st polymer (or its precursor) and a 2nd polymer, for example. Specifically, in the first step of preparing a solution (polymer solution) containing the first polymer or its precursor, the second polymer and a solvent, and in the fiber formation space, nanofibers are generated from the polymer solution 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 the nanofiber is generated, a sheath core structure is formed due to the difference in solubility between the first polymer and the second polymer in the solvent. More specifically, the second polymer having a high solubility in a solvent tends to be stably present in the polymer solution, and the first polymer having a low solubility is first spun to form a core. Since the second polymer is spun after the formation of the core, the sheath is formed around the core formed of the first polymer so as to cover at least part of the core.

  In the case where the first polymer is polyimide or the like, the polyimide polymer (such as polyamic acid) and the second polymer are used as the above polymer solution and heated appropriately in the process of manufacturing the nonwoven fabric. Polyimide (first polymer) may be generated from the precursor.

Below, the structure of a nonwoven fabric is demonstrated more concretely.
(First polymer)
The first polymer forming the core part has higher hydrolysis resistance than the second polymer (polyurethane). Due to the high hydrolysis resistance of the core part, it is possible to suppress deterioration due to hydrolysis of the polyurethane, although the sheath part is formed of polyurethane having low hydrolysis resistance. In order to form the core portion with the first polymer, it is desirable that the first polymer has a lower solubility in the solvent of the polymer solution when forming the nanofibers than the polyurethane.

  Examples of the first polymer include polyethersulfone (PES), polysulfone, aromatic polyester (polyalkylene terephthalate such as polyethylene terephthalate), polyamide, polyimide (PI), polyacrylonitrile (PAN), and the like. . These polymers may be homopolymers or copolymers. The core part may contain one kind of these first polymers, or may contain two or more kinds. PES, PAN, and / or PI are preferred from the viewpoints of suppressing deterioration due to hydrolysis, facilitating preparation of a polymer solution and facilitating electrospinning (and excellent spinnability).

Although the weight average molecular weight _Mw of a 1st 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 of the weight average molecular weight _Mw of the first polymer to the number average molecular weight _Mn (= _Mw / _Mn ) 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.

(Second polymer)
The polyurethane as the second polymer is a polymer having a urethane bond (—O—C (═O) —NH—), and is obtained by a reaction between a polyisocyanate compound and a polyol compound. The polyurethane may be an aliphatic polyurethane, and may be a polyether polyurethane, a polyester polyurethane, a polycarbonate polyurethane, a polycaprolactone polyurethane, or the like depending on the type of the polyol compound. Polyurethanes may be used alone or in combination of two or more.

The weight average molecular weight _Mw of the polyurethane is, for example, 30000-200000, and preferably 40000-150,000. The ratio of the weight average molecular weight _Mw of the polyurethane to the number average molecular weight _Mn (= _Mw / _Mn ) is preferably 1.8 to 3.0 or 2.0 to 3.0. When the _Mw or ratio _Mw / _{Mn of the} polyurethane is within such a range, the sheath portion is more easily formed.

In the nanofiber, the sheath portion only needs to cover the surface of at least a part of the core portion, and may cover the entire surface of the core portion. From the viewpoint of balancing hydrolysis resistance and tensile strength, the entire surface of the core is preferably covered as much as possible, and the thickness of the sheath is preferably as uniform as possible. From such a viewpoint, in the cross section perpendicular to the axial direction of the nanofiber, the ratio T _min / T _max of the minimum value T _min of the sheath part to the maximum value T _max of the sheath part is, for example, 0.8 It is -1 and it is preferable that it is 0.9-1. The ratio T _min / T _max may be less than 1.

The minimum value T _min and the maximum value T _max of the sheath thickness can be measured from an image of a nanofiber transmission electron microscope (TEM). Specifically, first, an arbitrary plurality of locations (for example, 10 locations) where a cross section perpendicular to the length direction of the nanofiber can be observed is selected from the TEM image. And in each location, the minimum value _Tmin and the maximum value _Tmax of the thickness of a sheath part are measured, ratio _Tmin / _Tmax is calculated, and an average value can be calculated by averaging.

The average fiber diameter of the nanofiber is, for example, 5 nm or more and less than 1000 nm, preferably 10 to 900 nm or 20 to 800 nm, and more preferably 100 to 800 nm or 200 to 700 nm.
Here, the average fiber diameter may be obtained as an average value by measuring the diameter at one location for each of a plurality of (for example, 10) fibers. In this case, the diameter of the fiber can be a diameter of a cross section perpendicular to the length direction of the fiber. If this cross section is not circular, the maximum diameter may be regarded as the diameter.

  The nanofiber constituting the nonwoven fabric may contain a known additive in addition to the first polymer and the second polymer, 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.

  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 second polymer constituting the sheath portion of the nanofiber is polyurethane having high tensile strength, and the first polymer constituting the core portion has higher hydrolysis resistance than the second polymer. . Therefore, the nonwoven fabric has high tensile strength, suppresses deterioration, and provides high durability. Therefore, it is useful for various applications that require durability. Moreover, the deterioration by hydrolysis of a nonwoven fabric can also be suppressed. Since the nonwoven fabric is formed of nanofibers, the surface area is large even if the fiber structure is not dense. Therefore, the nonwoven fabric is also suitable for applications such as a filter, and can reduce pressure loss while being excellent in collection performance.

(Nonwoven fabric manufacturing method)
A nonwoven fabric can be manufactured through the 1st process which prepares a polymer solution as mentioned above, and the 2nd process which produces | generates and deposits a nanofiber using a polymer solution. Below, it demonstrates in detail about a 1st process and a 2nd process.

(First step)
In the first step, the polymer solution can be prepared by dissolving the first polymer (or its precursor) and the second polymer in a solvent. The first polymer has a lower solubility in a solvent than the second polymer, but it is preferable that the first polymer (or its precursor) is uniformly dissolved in the polymer solution obtained in the first step.

  The solvent is not particularly limited as long as it dissolves the first polymer (or its precursor) and the second polymer 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 the first polymer or a precursor thereof, 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, when the first polymer includes PES and / or PAN, a solvent including DMF and / or DMAc may be used. When the first polymer contains PI or a precursor thereof, a solvent containing NMP may be used.

The total concentration of the first polymer and the second polymer in the polymer solution is, for example, 10 to 60% by mass, and preferably 15 to 50% by mass.
The polymer solution may contain a known additive used in electrospinning, if necessary.

(Second step)
In the second step, the polymer solution obtained in the first step is fiberized by electrospinning to form a nonwoven fabric.
In the electrospinning method, nanofibers are generated by an electrostatic stretching phenomenon. More specifically, when a polymer solution 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.

  The polymer solution that is a raw material liquid includes a first polymer (or a precursor thereof) and a second polymer that have different solubility in a solvent. Since the first polymer has lower solubility in the solvent than the second polymer, it is first fiberized by electrospinning to form a fibrous core. Since the second polymer is more stable in the solution than the first polymer, the fiberization is delayed as compared with the first polymer, and the sheath part is formed so as to cover at least a part of the surface of the core part. In this way, nanofibers having a sheath core structure are formed from the polymer solution.

  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.

  Drawing 1 is a figure showing roughly composition of a manufacturing system for carrying out a manufacturing method of a nonwoven fabric concerning one embodiment of the present invention. FIG. 1 is an example in the case of using a base material E having a non-woven fiber structure.

  The manufacturing system of FIG. 1 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. 1, 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 charges the discharge portion 42A including a nozzle (discharger) for discharging the raw material liquid installed above the apparatus, and the discharged raw material liquid (polymer solution). A charging means 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.

2 is a front view schematically showing the discharge part 42A of FIG. 1, and FIG. 3 is a side view schematically showing the discharge part 42A of FIG. FIG. 4 is a schematic longitudinal sectional view in which the emitter 42 of FIGS. 2 and 3 is cut by a plane passing through the outlet 42a and a part thereof is enlarged.
As shown in FIGS. 2 and 3, the discharge unit 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. 1, a place where the nonwoven fabric F and the belt of the conveyor 41 are separated (peeled) is provided with a static eliminator that neutralizes the nonwoven fabric F in order to suppress the occurrence of sparks that may occur when they peel. 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. 1, the motor 74 that rotates the collection device 70 that collects the nonwoven fabric is controlled to a rotation 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 implement the manufacturing method of the nonwoven fabric which concerns on embodiment of this invention. The manufacturing method of a nonwoven fabric is not specifically limited as long as it has the 1st process of preparing a polymer solution, and the 2nd process of producing | generating and depositing a nanofiber from a polymer solution in a nanofiber formation space, and forming a nonwoven fabric.

  As for the second step, any electrospinning mechanism may be used as long as the nanofiber is generated from the polymer solution by electrostatic force in the predetermined nanofiber formation space and the generated nanofiber is deposited. Good. For example, the shape of the emitter is not particularly limited. As shown in FIG. 3, 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. 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.

  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 polymer solution PES (M _w = 75000, M _w / M _n = 2.4) as the first polymer and polyurethane (PU, polyester polyurethane, M _w = 120,000, M _w / M) as the second polymer _n = 2.3) was dissolved in DMAc to prepare a polymer solution. The concentrations of PES and polyurethane in the polymer solution were 9% by mass and 12% by mass, respectively.

(2) Electrospinning Nanofibers on the main surface of the substrate by electrospinning the polymer solution obtained in (1) above as a raw material liquid under the following conditions using a production system as shown in FIG. Was deposited to prepare 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 length of the nanofiber was 490 nm. The nonwoven fabric had a thickness of 24 μm and a mass per unit area of 5.36 g / m ² .
The obtained nonwoven fabric was put into a thermostat and heated to near the melting point of PU. Thereafter, when observed with an electron microscope, the fiber shape was maintained although the fiber surface was melted. From this, it was confirmed that the sheath part was PU and the core part was PES.

(3) Evaluation The nonwoven fabric was subjected to a tensile test by the following procedure, and the maximum stress and elongation were measured.
The nonwoven fabric was cut into a size having a width of 10 mm and a length of 20 mm to prepare a test piece. One end of the test piece in the length direction was fixed, and the other end was sandwiched between chucks attached to a load measuring device (load cell), and pulled at a speed of 6 mm / s to break. And the maximum stress and elongation just before a test piece fracture | rupture was calculated | required. The elongation is expressed as a percentage (%) of elongation when the initial length is 100%.

Comparative Example 1
PES ( _Mw = 75000, _Mw / _Mn = 2.4) was dissolved in DMAc to prepare a polymer solution containing PES at a concentration of 22.5% by mass. A nonwoven fabric was produced and evaluated in the same manner as in Example 1 except that electrospinning was performed using the obtained polymer solution as a raw material liquid. The thickness of the obtained nonwoven fabric was 82 μm, the mass per unit area was 12.7 g / m ² , and the average fiber diameter of the fibers was 519 nm.

  As shown in Table 1, the maximum stress in the tensile test was larger and the elongation was larger in Example 1 than in Comparative Example 1, which is a nonwoven fabric formed of PES nanofibers. Moreover, when the nanofiber in the nonwoven fabric of Example 1 was observed with the electron microscope, although the sheath of the surface was PU, a crack was not seen but the hydrolysis-resistant fall was suppressed.

  Since the nonwoven fabric which concerns on embodiment of this invention has high tensile strength, it can suppress degradation by use. Therefore, it can be applied to various uses such as filters, battery separation sheets (separators), in vitro inspection sheets such as pregnancy test sheets, wiping sheets for wiping off dust and dirt, and substrates.

20: base material supply device, 21: first transport roll, 22: supply reel, 24: motor 40: nonwoven fabric forming device, 41: transport conveyor, 42A: discharge section, 42: discharge body, 42a: discharge port, 42b: Tapered portion, 43: voltage application device, 44: counter electrode, 45: raw material liquid (polymer solution), 45a: raw material liquid tank, 46: pump, 48: first support, 49: second support, 50: conduit 52: container 70: collection device, 71: transport 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 (6)

A nanofiber comprising a core and a sheath covering at least a part of the surface of the core;
The core includes a first polymer;
The sheath includes a second polymer;
The second polymer is polyurethane;
The first polymer is a non-woven fabric that is a polymer having higher hydrolysis resistance than the second polymer.   The nonwoven fabric according to claim 1, wherein the nanofiber is formed by an electrospinning method.   The nonwoven fabric according to claim 1 or 2, wherein the amount of the second polymer is 10 to 1000 parts by mass with respect to 100 parts by mass of the first polymer. The average of the ratio D _f / D _c of the fiber diameter D _f and diameter D _c of the core portion of the nano fiber is from 1.4 to 5, the nonwoven fabric according to any one of claims 1 to 3 .   The non-woven fabric according to any one of claims 1 to 4, wherein the first polymer is at least one selected from the group consisting of polyethersulfone, polyacrylonitrile, and polyimide. A first step of preparing a solution comprising a first polymer or a precursor thereof, a second polymer, and a solvent;
A second step of forming nanofibers from the solution by electrostatic force in the nanofiber formation space, and depositing the generated nanofibers to form a non-woven fabric,
The nanofiber includes a core including the first polymer, and a sheath covering at least a part of the surface of the core and including the second polymer,
The second polymer is polyurethane;
The method for producing a nonwoven fabric, wherein the first polymer is a polymer having higher hydrolysis resistance and lower solubility in the solvent than the second polymer.

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