Fiber and its manufacturing method

Abstract

To enable electret effects given to a fiber to be maintained for an extended period.SOLUTION: A fiber includes a fine fiber including a first phase and a second phase. The first phase includes a first polymer which is a paraelectric material and the second phase includes a second polymer which is other than the paraelectric material, and at least a part of the second phase is included in the first phase.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fiber containing fine fibers and a method for producing the same. [Background technology]

[0002] Fibers are used in a variety of fields, including clothing, masks, filters, separation membranes, and piezoelectric elements. Research is being conducted into ways to give fibers desired functions. For example, polarizing the dielectric contained in fibers to create electret fibers is being considered. For example, nonwoven fabrics made of electret fibers are used in masks, filters, separation membranes, and other applications.

[0003] Patent Document 1 proposes "a nonwoven fabric comprising nanofibers including a core and a sheath covering at least a portion of the surface of the core, wherein the core comprises a first polymer and the sheath comprises a second polymer, the second polymer having a lower polarity than the first polymer."

[0004] Non-Patent Document 1 proposes an electret fiber made of an all-polymer hybrid of polystyrene and polyvinylidene fluoride (PS / PVDF). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-125182 [Non-patent literature]

[0006] [Non-Patent Document 1] Chemical Engineering Journal,398,2020,125626 Summary of the Invention [Problem to be solved by the invention]

[0007] However, it is difficult to maintain the functions imparted to the fibers for a long period of time. For example, when electret fibers become wet, the effect brought about by dielectric polarization (the electret effect) is easily lost. [Means for solving the problem]

[0008] One aspect of the present invention relates to a fiber comprising a fine fiber including a first phase and a second phase, wherein the first phase includes a paraelectric first polymer, the second phase includes a non-paraelectric second polymer, and at least a portion of the second phase is encapsulated in the first phase.

[0009] Another aspect of the present invention relates to a yarn, fabric, knit, woven fabric or nonwoven fabric comprising the above-mentioned fiber.

[0010] Yet another aspect of the present invention relates to a method for producing fibers, comprising: a first step of preparing an emulsion solution containing a first paraelectric polymer and a second non-paraelectric polymer; and a second step of generating fine fibers from the emulsion solution by electrostatic force in a fine fiber formation space, wherein the first polymer and the second polymer have the property of being phase-separated into a first phase containing the first polymer and a second phase containing the second polymer in the fine fibers, and at least a part of the second phase is encapsulated in the first phase. [Effects of the Invention]

[0011] According to the present disclosure, the electret effect imparted to the fibers can be maintained for a long period of time. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram schematically illustrating the internal structure of a fiber (fine fiber) according to an embodiment of the present disclosure. [Figure 2] FIG. 1 is a conceptual diagram showing the configuration of an example of an electrospinning apparatus. [Figure 3]1 shows the difference spectrum (1900 to 700 cm −1 ) between the spectrum of U70-F30-CNF and the spectrum of U100, which are FTIR spectra of fibers of Examples and Comparative Examples. [Figure 4] 1 is a differential spectrum between the spectrum of U70-F30-CNF and the spectrum of U100, which are WAXD spectra of fibers of the examples and comparative examples. [Figure 5] 1 is a table showing the amounts of electric charge of fibers of Examples and Comparative Examples before and after immersion in water. [Figure 6] 1 is a table comparing the tensile strength and toughness of fibers of Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present disclosure will be described using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values, materials, etc. may be exemplified, but other numerical values, materials, etc. may be applied as long as the effects of the present disclosure are obtained. Note that known components may be applied to components other than those characteristic of the present disclosure. In this specification, when a "range of numerical value A to numerical value B" is mentioned, the range includes numerical value A and numerical value B.

[0014] In the following description, when lower and upper limits of numerical values ​​relating to specific physical properties, conditions, etc. are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be combined as desired, as long as the lower limit is not equal to or greater than the upper limit. When multiple materials are exemplified, one of them may be selected and used alone, or two or more may be used in combination, unless otherwise specified.

[0015] In the following description, the terms "contain" or "comprise" encompass "contain (or include)," "consist essentially of," and "consist of."

[0016] The present disclosure also encompasses combinations of two or more features arbitrarily selected from the appended claims, i.e., two or more features arbitrarily selected from the appended claims can be combined unless a technical contradiction arises.

[0017] The present disclosure relates to a fiber (hereinafter also referred to as "fiber F") containing fine fibers (hereinafter also referred to as "fine fibers f") containing a first phase and a second phase. The form of fiber F is not particularly limited. Fiber F may be contained in, for example, a yarn, a woven fabric, a knitted fabric, a woven cloth, a nonwoven fabric, etc. Fiber F containing fine fibers f and yarn, a woven fabric, a knitted fabric, a woven cloth, or a nonwoven cloth containing fiber F may contain other fine fibers or fibers. In fine fibers f, the first phase and the second phase are phase-separated from each other.

[0018] The fine fibers f include, for example, fibers having an average diameter (average fiber diameter) of 20 μm or less, microfibers having an average diameter of 5 μm or less, nanofibers having an average diameter of 1 μm or less, etc. The length of the fine fibers f is not particularly limited. The average diameter is obtained by measuring the diameter at one location on each of ten arbitrary fine fibers f, for example, and averaging these values. The diameter of the fine fibers f is the diameter of a cross section perpendicular to the longitudinal direction of the fine fibers f.

[0019] The first phase includes a paraelectric first polymer. The second phase includes a non-paraelectric second polymer. The paraelectric first polymer is a polymer in which dielectric properties predominate over electrical conductivity. The second polymer is a non-paraelectric dielectric and exhibits hysteresis in dielectric polarization. That is, the second phase may include a second polymer exhibiting hysteresis in dielectric polarization. As a result, polarization charges are formed. The second polymer may be any polymer capable of forming polarization charges, such as a piezoelectric or pyroelectric polymer. That is, the second phase may include at least one polymer selected from the group consisting of piezoelectric polymers and pyroelectric polymers. The "second phase" may also be referred to as a "piezoelectric phase" or a "pyroelectric phase." Among these, the second polymer is preferably at least one polymer selected from the group consisting of ferroelectric polymers, antiferroelectric polymers, and ferrielectric polymers. That is, the second phase may include at least one polymer selected from the group consisting of ferroelectric polymers, antiferroelectric polymers, and ferrielectric polymers. Dielectrics other than paraelectrics exhibit different magnitudes of polarization when the electric field strength is increased and then decreased. Ferroelectrics, among others, can retain a large polarization charge. On the other hand, paraelectrics do not have hysteresis in dielectric polarization.

[0020] The first phase may contain only one type of first polymer, or may contain two or more types of first polymers. When the first phase contains two or more types of first polymers, the first polymers may be phase-separated within the first phase, or may form a homogeneous first phase without phase separation. The first phase may be composed only of the first polymer, but may also contain components other than the first polymer (for example, the first polymer or additives used in producing the fine fiber f). The content of components other than the first polymer is desirably 50 mass % or less of the first phase.

[0021] The second phase may contain only one type of second polymer, or may contain two or more types of second polymers. When the second phase contains two or more types of second polymers, the second polymers may be phase-separated within the second phase, or may form a homogeneous second phase without phase separation. The second phase may be composed only of the second polymer, but may also contain components other than the second polymer (for example, the second polymer or additives used in producing fine fibers). The content of components other than the second polymer is preferably 50 mass% or less of the second phase.

[0022] Specific examples of the second polymer include halogen-based polymers. Halogen-based polymers are prone to dielectric polarization and can crystallize in a dielectrically polarized state. Halogen-based polymers have hysteresis in dielectric polarization. Therefore, halogen-based polymers can constitute either piezoelectric or pyroelectric materials. Furthermore, halogen-based polymers can constitute either ferroelectric materials, antiferroelectric materials, or ferroelectric materials. Halogen-based polymers are composed of monomer units containing halogen atoms. Halogen-based polymers are composed of, for example, monomer units containing hydrogen atoms and halogen atoms. Note that halogen-based polymers may contain monomer units that do not contain halogen atoms, for example, at a content of 50 mol% or less.

[0023] At least a portion of the second phase is encapsulated within the first phase. In other words, the paraelectric first phase surrounds the second phase, which has a polarized charge. The first phase is dielectrically polarized by the electric field formed by the polarization charge of the second phase, resulting in the fine fiber f having a surface charge. The surface charge improves the electret effect of yarns, textiles, woven fabrics, nonwoven fabrics, etc. that contain the fine fiber f. Specifically, it is used to improve the electrostatic adsorption function of masks, filters, separation membranes, etc. that use these. Furthermore, even if the surface charge of the fine fiber f is temporarily lost, for example, due to wetting the surface with water, the polarization charge of the second phase causes the first phase to become dielectrically polarized again, so the surface charge is easily restored. In other words, the electret effect is not easily lost and can be maintained for a long time.

[0024] If the second phase is not enclosed within the first phase and is exposed to the outside, the second phase will be more susceptible to the effects of external charges. If charges are injected into the second phase due to wetting or other reasons, and the polarization charge decreases or disappears, the first phase will no longer be dielectrically polarized, and the electret effect will also decrease or disappear.

[0025] The fine fibers (f) may contain one or more additional phases in addition to the first and second phases. For example, the fine fibers (f) may contain a phase (non-polymer phase) composed of a material other than a polymer. Examples of materials that can constitute the non-polymer phase include additives used in producing the fine fibers (f), inorganic fillers, pigments, water-repellent agents, hydrophilic agents, flame retardants, antibacterial agents, antiviral agents, cool-to-the-touch agents, moisture-absorbing heat-generating agents, and stain-resistant agents. When these materials are phase-separated from the first and second phases, they constitute the non-polymer phase.

[0026] Cellulose nanofibers (CNF) are desirable as additives used when producing the fine fibers (f). CNFs act as reinforcing materials that increase the mechanical strength of the fine fibers (f). When producing the fine fibers (f) by electrospinning (or electrostatic spinning), they also play a role in increasing the uniformity or stability of the emulsion solution, which is the raw material liquid. Note that, in addition to CNFs, amphiphilic surfactants may also be used to increase the uniformity or stability of the emulsion solution.

[0027] The content of CNF contained in the fine fibers f may be, for example, 0.01% to 10% by mass, 0.1% to 5% by mass, or 0.1% to 2% by mass. Within the above range, aggregation of CNF is unlikely to occur, and the effects of increasing the mechanical strength of the fine fibers f and improving the uniformity or stability of the emulsion solution when producing the fine fibers f by electrospinning are significantly exhibited.

[0028] The average diameter of the CNF is, for example, 3 nm to 50 nm, and the aspect ratio is, for example, 100 or more.

[0029] In the fine fiber f, the first phase and the second phase may form an island-in-a-sea structure. It is desirable that as much of the second phase as possible is encapsulated in the first phase. Therefore, a sea-in-a-sea structure in which the second phase is distributed in islands in the matrix of the first phase is desirable.

[0030] Figure 1 shows a schematic diagram of the internal structure of a fine fiber having an islands-in-a-sea structure. Figure 1(a) shows a portion of a fine fiber f (fine fiber 10) having a diameter D. Figure 1(b) shows a cross section of the fine fiber 10 taken along the diameter D. Figure 1(c) is an enlarged, more conceptualized view of a portion of the cross section of the fine fiber 10 taken along the diameter D.

[0031] As shown in FIG. 1(b), inside the fine fiber 10, the second phases 12, which have polarized charges, are surrounded by a matrix of the paraelectric first phases 11. The second phases 12 are separated and confined within the first phase. That is, a sea-island structure is formed in which the second phases are distributed in islands within the matrix of the first phase. As a result, as shown in FIG. 1(b), the first phases 11 are dielectrically polarized by the electric field formed by the polarized charges of the second phases 12. This state is maintained even when the surface of the fine fiber 10 is wetted with water, and the electret effect can be maintained for a long period of time.

[0032] The content of the second phase contained in the fine fibers f may be, for example, 5% by mass to 50% by mass, or 7% by mass to 50% by mass. The content of the second polymer contained in the fine fibers f may be considered as the content of the second phase contained in the fine fibers f. The content of the second phase contained in the fine fibers f may be 10% by mass to 49% by mass, 15% by mass to 45% by mass, or 15% by mass to 40% by mass. In this case, the fine fibers f having a large electret effect and excellent mechanical strength are likely to be formed. Furthermore, the fine fibers f are likely to form a sea-island structure in which the second phase is distributed in the form of islands in a matrix of the first phase.

[0033] The content PC2 of the second phase contained in the fine fibers f may be less than the content PC1 of the first phase contained in the fine fibers f. The content of the first polymer contained in the fine fibers f may be considered as the content of the first phase contained in the fine fibers f. PC2 / PC1 may be 0.95 or less, 0.8 or less, or 0.6 or less. PC2 / PC1 may be 0.1 or more, or 0.2 or more. When PC2 / PC1 is within such a range, a sea-island structure in which the second phase is distributed in islands in a matrix of the first phase is likely to be formed in the fine fibers f.

[0034] The first polymer may be any polymer capable of forming a paraelectric material. The dielectric constant of the first polymer is 6 In terms of Hz, it is, for example, 10 or less, and may be 5 or less.

[0035] The weight average molecular weight Mw of the first polymer varies depending on the type of polymer, but may be, for example, 30,000 to 800,000, or 50,000 to 500,000. In this specification, the weight average molecular weight of a polymer is a value determined from the molecular weight distribution measured by gel permeation chromatography.

[0036] The first polymer may be at least one selected from the group consisting of polyurethane, rubber, polyamide, polyolefin, polyester, acrylic polymer, polystyrene, polyvinyl chloride, polyvinyl fluoride, and copolymers of two or more monomer units constituting these polymers. Examples of rubber include natural rubber, polyisoprene, and polybutadiene. Examples of polyolefin include polypropylene and polyethylene. Examples of acrylic polymers include polyacrylic acid, polyacrylic acid ester, polymethacrylic acid, polymethacrylic acid ester, and copolymers of two or more monomer units constituting these polymers. Examples of polyesters include polyethylene terephthalate, polybutylene terephthalate, and polycarbonate.

[0037] The second polymer may be, for example, a halogen-based polymer that can form a dielectric material other than a paraelectric material.

[0038] The weight average molecular weight Mw of the second polymer may be, for example, 30,000 to 1,000,000, or 50,000 to 500,000, although it may vary depending on the type of polymer.

[0039] The second polymer may be, for example, at least one selected from the group consisting of polyvinylidene fluoride, polytrifluoroethylene, polyvinylidene chloride, and copolymers of two or more of the monomer units constituting these polymers, although the second polymers exemplified here may contain monomer units other than vinylidene fluoride, trifluoroethylene, and vinylidene chloride, for example, at a content of 50 mol% or less.

[0040] When as much of the second phase as possible is encapsulated in the first phase (for example, when forming a sea-island structure in which the second phase is distributed in islands in the matrix of the first phase), it is desirable for the first phase to have sufficient flexibility. That is, it is desirable for the elongation at break of the first polymer to be greater than the elongation at break of the second polymer. Examples of such combinations of the first polymer and the second polymer include a combination in which the first polymer is at least one selected from the group consisting of polyurethane, rubber, polyolefin, polyester, polyvinyl chloride, and polyvinyl fluoride, and the second polymer is the aforementioned halogen-based polymer.

[0041] The nonwoven fabric containing the fine fibers f or fibers F according to the present disclosure can be produced, for example, by electrospinning or electrostatic spinning as shown in the following examples. The electrospinning method as shown in the following examples has a first step and a second step.

[0042] In the first step, an emulsion solution containing a paraelectric first polymer and a non-paraelectric second polymer is prepared. Here, the term emulsion solution is used as a broad concept including dispersions, colloidal solutions, intermediate liquids between solutions and dispersions, and solutions in which the polymers are completely dissolved.

[0043] The emulsion solution may be prepared, for example, by mixing two or more precursor solutions. Specifically, a first emulsion solution (first solution) containing a first polymer but not a second polymer is prepared, and a second emulsion solution (second solution) containing a second polymer but not the first polymer is separately prepared. The first and second solutions may then be mixed to form the emulsion solution.

[0044] The proportion of the second polymer in the total of the first polymer and the second polymer contained in the emulsion solution may be, for example, 7% by mass to 50% by mass, 10% by mass to 49% by mass, 15% by mass to 45% by mass, or 15% by mass to 40% by mass.

[0045] If the first and second liquids are difficult to mix uniformly, a predetermined amount of CNF or surfactant may be added to the emulsion solution. The CNF or surfactant may be added in advance to at least one of the first and second liquids.

[0046] The first liquid can be prepared by dispersing or dissolving the first polymer (or its precursor) in a first solvent. The first solvent is not particularly limited as long as it can produce a stable first liquid, and may be appropriately selected depending on the type, molecular weight, etc. of the first polymer.

[0047] The second liquid can be prepared by dispersing or dissolving the second polymer (or its precursor) in a second solvent. The second solvent is not particularly limited as long as it can produce a stable second liquid, and may be selected appropriately depending on the type, molecular weight, etc. of the second polymer.

[0048] When precursors of the first polymer and the second polymer are used, the precursors may be polymerized in a solvent. The precursors may contain monomers or oligomers corresponding to the monomer units constituting the first polymer or the second polymer.

[0049] Examples of possible first and second solvents include alcohols (e.g., C2-4 alcohols) such as methanol, ethanol, n-propanol, and isopropanol; ethylene glycol; ketones such as acetone and methyl ethyl ketone; nitriles such as acetonitrile; amides (e.g., linear or cyclic amides) such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methyl-2-pyrrolidone (NMP); sulfoxides such as dimethyl sulfoxide; halogenated alkanes such as dichloromethane, ethylene dichloride, and chloroform; cyclic ethers such as tetrahydrofuran and dioxane; esters such as ethyl acetate; cycloalkanes such as cyclohexane and methylcyclohexane; alkanes such as n-hexane; aromatic hydrocarbons such as toluene and xylene; symmetric ethers such as diisopropyl ether; and carbon tetrachloride. These solvents may be used alone or in combination.

[0050] In the second step, fine fibers are generated from the emulsion solution by electrostatic force in the fine fiber formation space, and the generated fine fibers may be deposited on a predetermined substrate to form a nonwoven fabric.

[0051] In the electrospinning method, fine fibers are produced by electrostatic stretching. For example, an emulsion solution is discharged from a nozzle with a minute inner diameter into a space to which an electric field is applied. The solvent gradually evaporates from the discharged emulsion solution as it flies through the electric field. As the volume of the emulsion solution gradually decreases due to the evaporation of the solvent, the charge density in the emulsion solution increases. When the Coulomb force caused by the repulsion of the charges exceeds the surface tension of the emulsion solution, the emulsion solution is explosively stretched into a linear shape, producing fine fibers (particularly nanofibers).

[0052] In the electrospinning method, when fine fibers (f) are produced in an electric field, the first polymer and the second polymer undergo phase separation, forming a first phase containing the first polymer and a second phase containing the second polymer in the fine fibers (f). This phase separation is thought to be promoted by the difference in polarity between the first polymer and the second polymer. After phase separation, the ferroelectric second polymer is dielectrically polarized by the electric field, forming a second phase in this state, at least a portion of which (e.g., 50% by volume or more) is thought to be encapsulated in the first phase. Furthermore, in the electrospinning method, the polymer is pulled by the electric field, promoting molecular orientation. At that time, many β-phase crystals are formed in the second phase. These results improve the electret effect.

[0053] 2 is a conceptual diagram showing the configuration of an example of an apparatus for producing fine fibers f by electrospinning. The electrospinning apparatus 20 includes a syringe (nozzle) 21 for discharging an emulsion solution, a syringe pump 22 for feeding the solution to the syringe 21, a voltage application device (charging means) 23 for charging the syringe 21, and a rotor 24 (collector unit) for depositing the fine fibers. The rotor 24 is grounded. An electric field is formed in the space between the syringe 21 to which a voltage is applied and the grounded rotor 24. The fine fibers f are generated in this space and are taken up around the rotating rotor 24 as a sheet-like nonwoven fabric.

[0054] The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0055] Example 1 (1) Preparation of Solution 1 As the first polymer, frequency 10 6 Polyurethane (PU) with a relative dielectric constant of 5.0 at Hz and a weight-average molecular weight of 161,000 was used. PU was dispersed in a solvent mixture of equal parts dimethylformamide (DMF) and tetrahydrofuran (THF) (DMF / THF = 1:1) to prepare a first liquid containing PU at a concentration of 16% by mass. PU is a paraelectric material.

[0056] (2) Preparation of second liquid The second polymer used was polyvinylidene fluoride (PVDF) with a weight-average molecular weight of 275,000. PVDF was dispersed in a solvent mixture of equal parts DMF and THF (DMF / THF = 1:1) to prepare a second liquid containing PVDF at a concentration of 4% by mass. PVDF is a ferroelectric substance.

[0057] (3) Preparation of emulsion solution The first liquid and the second liquid are mixed with the first polymer (PU) and the second polymer ( PVDF The emulsion solution was mixed with the above in a volume ratio of 1:1 and stirred with a mixer to prepare an emulsion solution. The emulsion solution contained CNF (average diameter 27 nm) at a ratio of 0.1 mass%.

[0058] (4) Electrospinning Using the resulting emulsion solution and a manufacturing apparatus such as that shown in Figure 2, fine fibers f were deposited on the surface of an aluminum foil by electrospinning under the following conditions to produce a nonwoven fabric (U80-F20-CNF) of Example 1. In the resulting nonwoven fabric (U80-F20-CNF), the average diameter of the fine fibers was 697 nm, and the mass per unit area of ​​the nonwoven fabric was 4.64 g / m 2 The content of CNF in the fine fibers (nonwoven fabric) was 1% by mass.

[0059] <Electrospinning conditions> Applied voltage: 25 kV Emulsion solution discharge rate: 0.7mL / h Temperature: 25±3℃ Humidity: 40±9%RH Distance between nozzle and rotor: 12cm

[0060] Example 2 In preparing the emulsion solution, the first and second liquids were mixed with the first polymer (PU) and the second polymer ( PVDFA nonwoven fabric (U70-F30-CNF) of Example 2 was produced in the same manner as in Example 1, except that the concentrations of 14% and 6%, respectively, were used. In the obtained nonwoven fabric (U70-F30-CNF), the average diameter of the fine fibers was 490 nm, and the mass per unit area of ​​the nonwoven fabric was 6.60 g / m 2 The content of CNF in the fine fibers (nonwoven fabric) was 1% by mass.

[0061] Example 3 In preparing the emulsion solution, the first and second liquids were mixed with the first polymer (PU) and the second polymer ( PVDF A nonwoven fabric (U60-F40-CNF) of Example 3 was produced in the same manner as in Example 1, except that the concentrations of 12% and 8%, respectively, were used. The average diameter of the fine fibers in the obtained nonwoven fabric (U60-F40-CNF) was 448 nm, and the mass per unit area of ​​the nonwoven fabric was 5.33 g / m 2 The content of CNF in the fine fibers (nonwoven fabric) was 1% by mass.

[0062] Comparative Example 1 Only the first liquid was electrospun under the same conditions as in Example 1. The mass per unit area of ​​the obtained nonwoven fabric (U100) was 3.83 g / m 2 It was.

[0063] Comparative Example 2 Only the second liquid was electrospun under the same conditions as in Example 1. The mass per unit area of ​​the obtained nonwoven fabric (F100) was 9.64 g / m 2 It was.

[0064] (5) Evaluation (5-1)ATR-FTIR Spectrum The ATR-FTIR spectra of the nonwoven fabric of Example 2 (U70-F30-CNF), the nonwoven fabric of Comparative Example 1 (U100), and the nonwoven fabric of Comparative Example 2 (F100) were measured. The difference spectrum between the spectrum of U70-F30-CNF and the spectrum of U100 is shown in Figure 3. The resolution was 4 cm -1 , the number of accumulations is 64.

[0065] Figure 3 suggests that U70-F30-CNF has the same phase as U100 and F100, i.e., a phase separation between the first phase of PU and the second phase of PVDF. Figure 3 also reveals that U70-F30-CNF has β-phase crystals of PVDF. The β-phase is a ferroelectric with a high dielectric constant among PVDFs. In the electrospinning method, the electric field pulls the polymer, promoting molecular orientation, which is thought to have led to the formation of many β-phase crystals within the second phase of the fibers contained in the nonwoven fabric.

[0066] (5-2) WAXD Spectrum The WAXD spectra of the nonwoven fabric of Example 2 (U70-F30-CNF), the nonwoven fabric of Comparative Example 1 (U100), and the nonwoven fabric of Comparative Example 2 (F100) were measured. Figure 4 shows the difference spectrum between the spectrum of U70-F30-CNF and the spectrum of U100 at diffraction angles 2θ = 5° to 55°. The scan rate was 0.5° / min. Figure 4 also shows that U70-F30-CNF has β-phase PVDF crystals.

[0067] (5-3) Charge quantity (electret effect) Using a commercially available coulomb meter, the amount of charge on each nonwoven fabric was measured in an atmosphere of 21°C and 31% humidity. Next, the nonwoven fabric was immersed in pure water for 1 hour, dried, and then left to stand for 12 hours. The amount of charge on each nonwoven fabric (after immersion) was then measured again. The results are shown in a table in Figure 5. Figure 5 also shows the results of a similar measurement on a commercially available electret mask made of polypropylene (PP).

[0068] From FIG. 5, it can be seen that the nonwoven fabrics of Examples 1 to 3 (U80-F20-CNF, U70-F30-CNF, U60-F40-CNF) show little difference in charge amount before and after immersion in water, and the electret effect is sustained. Furthermore, it is believed that the high presence of β phases contributes to the high electret properties. On the other hand, the nonwoven fabric of Comparative Example 2 (F100) initially has a large charge, but after immersion in water, it loses most of the charge. Furthermore, a commercially available electret mask made of polypropylene (PP) initially has a charge similar to that of Examples 1 to 3, but after immersion in water, it loses most of the charge.

[0069] (5-4) Tensile strength and toughness Using a commercially available measuring device, the tensile strength (breaking strength) of each nonwoven fabric was measured and the toughness of the nonwoven fabric was also determined under the conditions of a pulling speed of 0.05 mm / sec and the number of tests being 3. The table of tensile strength and toughness results is shown in Figure 6.

[0070] 5 and 6 show that phase separation of PU and PVDF can increase the mechanical strength compared to PU or PVDF alone (especially PU60-F40-CNF). Because PU has a high elongation at break, it is thought that dispersing PVDF, which has a high elastic modulus, in a phase-separated state in the PU matrix resulted in a strong, highly stretchable fiber. [Industrial Applicability]

[0071] The present disclosure can be applied, for example, to imparting an electret effect to fibers, and the fibers according to the present disclosure can be used as piezoelectric fiber materials or pyroelectric fiber materials. [Explanation of symbols]

[0072] 10 Fine Fiber 11 Phase 1 12 Phase 2 20 Electrospinning device 21 Syringe (nozzle) 22 Syringe Pump 23 Voltage application device (charging means) 24 Rotating body (collector part)

Claims

1. The fiber includes fine fibers having a first phase and a second phase, the first phase comprises a paraelectric first polymer; the second phase comprises a second polymer other than a paraelectric material; At least a portion of the second phase is encapsulated in the first phase, In the fine fibers, the first phase and the second phase form a sea-island structure, A fiber in which the second phase is distributed in the form of islands in a matrix of the first phase.

2. The fiber according to claim 1, wherein the content of the second phase contained in the fine fibers is 5% by mass to 50% by mass.

3. The fiber of claim 1 , wherein the first polymer has a greater elongation to break than the second polymer.

4. the second polymer is a halogen-based polymer, 2. The fiber according to claim 1, wherein the halogen-based polymer is at least one selected from the group consisting of polyvinylidene fluoride, polytrifluoroethylene, polyvinylidene chloride, and copolymers of two or more types of monomer units constituting these polymers.

5. 2. The fiber according to claim 1, wherein the first polymer is at least one selected from the group consisting of polyurethane, rubber, polyamide, polyolefin, polyester, acrylic polymer, polystyrene, polyvinyl chloride, polyvinyl fluoride, and copolymers of two or more types of monomer units constituting these polymers.

6. A yarn, woven fabric, knitted fabric, woven cloth or nonwoven fabric comprising the fiber according to any one of claims 1 to 5.

7. A first step of preparing an emulsion solution containing a paraelectric first polymer and a non-paraelectric second polymer; a second step of generating fine fibers from the emulsion solution by electrostatic force in a fine fiber formation space, the first polymer and the second polymer have a property of being phase-separated into a first phase containing the first polymer and a second phase containing the second polymer in the fine fibers, The method for producing a fiber, wherein at least a portion of the second phase is encapsulated in the first phase.

8. The method for producing a fiber according to claim 7, wherein a proportion of the second polymer in the total of the first polymer and the second polymer contained in the emulsion solution is 5% by mass to 50% by mass.

Images