Manufacturing method of nanofiber and nanofiber

Abstract

To provide a manufacturing method of a nanofiber capable of manufacturing a nanofiber that has hydrophilicity and is capable of being used in water treatment, etc., at low cost.SOLUTION: A manufacturing method of a nanofiber relating to the present invention includes a thermofusion step for thermofusion of a thermoplastic resin and a functionality giving agent and a melt blow step for converting the resin thermofused in the thermofusion step to a fiber by a melt blow method. The functionality giving agent includes a composition comprising a surfactant as the main component.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to nanofibers that are hydrophilic and can be used for water treatment and the like, and to a method for producing nanofibers. [Background technology]

[0002] A method for producing nanofibers has been proposed using the melt-blowing method, in which a thermoplastic resin such as polyethylene resin or polypropylene resin is melted and extruded from an extruder, stretched by a high-speed airflow, and released into the air to obtain nanofibers (entangled long fibers) consisting of long fibers with nanometer diameters ranging from several tens of microns to submicrons.It has also been proposed to combine functional particles with nanofibers obtained by this melt-blowing method to give them predetermined functions.

[0003] For example, Patent Document 1 (JP 2023-44529 A) proposes a technology in which a thermoplastic resin is melted and continuously discharged from a resin nozzle of a nozzle head, and an airflow is formed by directing the melted thermoplastic resin horizontally from a gas nozzle provided on the nozzle head adjacent to the resin nozzle, stretching the thermoplastic resin with the airflow and releasing self-adhesive long fibers into the air to form an entangled long-fiber body, in which powder particles are supplied to a predetermined position along the airflow from the nozzle head while the thermoplastic resin is stretched and the powder particles come into contact with and adhere to the surface of the thermoplastic resin. [Patent Document 1] Japanese Patent Application Publication No. 2023-44529 Summary of the Invention [Problem to be solved by the invention]

[0004] By using inexpensive and versatile polyethylene resin or polypropylene resin as the raw thermoplastic resin, it is possible to obtain low-cost nanofibers (entangled long fibers). However, such nanofibers have the problem that they are not hydrophilic due to the characteristics of the raw materials, and therefore cannot be used for water treatment, etc.

[0005] In the conventional technology described in Patent Document 1, it is conceivable to impart hydrophilicity to nanofibers by using functional particles having hydrophilic groups as powder particles, but the nanofiber manufacturing method described in Patent Document 1 has the problem that the functional particles tend to fall off from the nanofibers, making them prone to losing their hydrophilicity. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the nanofiber manufacturing method of the present invention is a nanofiber manufacturing method comprising a heat-melting step of heat-melting a thermoplastic resin and a functionalizing agent, and a melt-blowing step of fiberizing the resin heat-melted in the heat-melting step by a melt-blowing method, wherein the functionalizing agent contains a composition whose main component is a surfactant.

[0007] Furthermore, the method for producing nanofibers according to the present invention is characterized in that the thermoplastic resin is a polyolefin resin.

[0008] The nanofiber production method according to the present invention is characterized in that the melt flow rate (MFR) of the thermoplastic resin is 100 [g / 10 min] or more.

[0009] The nanofiber production method according to the present invention is characterized in that the functionality-imparting agent is in the form of a masterbatch.

[0010] The method for producing nanofibers according to the present invention is characterized in that the functionality-imparting agent further contains a heavy metal adsorbent.

[0011] Furthermore, the method for producing nanofibers according to the present invention is characterized in that the functionality-imparting agent further contains a flocculating and precipitating agent.

[0012] The nanofiber production method according to the present invention is characterized in that the functionality-imparting agent further contains a neutralizing agent.

[0013] The nanofiber according to the present invention is characterized by being produced by the above-described method for producing a nanofiber. [Effects of the Invention]

[0014] The nanofiber manufacturing method according to the present invention comprises a heat-melting step in which a thermoplastic resin and a functionalizing agent are heat-melted, and a melt-blowing step in which the resin heat-melted in the heat-melting step is converted into fibers by a melt-blowing method, wherein the functionalizing agent contains a composition whose main component is a surfactant. This nanofiber manufacturing method according to the present invention makes it possible to produce hydrophilic nanofibers that can be used for water treatment and the like at low cost. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view (partially a block diagram) of a main part of a resin fiber manufacturing apparatus in one embodiment according to the present invention. [Figure 2] 2A and 2B are a front view and a side cross-sectional view, respectively, of a nozzle head. [Figure 3] FIG. 2 is a cross-sectional view of a nozzle head. [Figure 4] 1 is a micrograph of hydrophilic resin nanofibers using a surfactant as a functionality-imparting agent. [Figure 5] FIG. 1 shows (A) the results of an adsorption test of hydrophilic resin nanofibers, and (B) the results of a desorption test from hydrophilic resin nanofibers. [Figure 6] 1 is a table showing the weight of hydrophilic resin nanofibers required for total adsorption. [Figure 7] FIG. 1 shows (A) the results of an adsorption test of a hydrophilic resin microfiber, and (B) the results of a release test from a hydrophilic resin microfiber. [Figure 8] FIG. 1 shows (A) the results of an adsorption test of resin-made hydrophilic heavy metal adsorbent-added nanofibers 1, and (B) the results of a desorption test from resin-made hydrophilic heavy metal adsorbent-added nanofibers 1. [Figure 9] 1 is a micrograph of resin-made hydrophilic heavy metal adsorbent-added nanofiber 2 (Denite manufactured by Taiheiyo Cement Corporation is added as a heavy metal adsorbent). [Figure 10] 1A and 1B show the results of an adsorption test of resin nanofibers 2 loaded with a hydrophilic heavy metal adsorbent, and (B) the results of a desorption test from resin nanofibers 2 loaded with a hydrophilic heavy metal adsorbent. [Figure 11] FIG. 1 shows the results of adsorption tests for (A) cadmium, (B) selenium, (C) lead, and (D) arsenic when the packing density of resin-made hydrophilic heavy metal adsorbent-added nanofiber 2 is changed. [Figure 12] (A) shows the results of an adsorption test of nanofibers with added flocculating and precipitating agents, and (C) shows the results of a desorption test from nanofibers with added flocculating and precipitating agents. (B) is a graph in which the results for F and B are plotted on a different vertical axis from (A). [Figure 13] 10 is a table showing the weight of nanofibers with added flocculating sedimentation material required for total adsorption. [Figure 14] FIG. 1 shows the results of neutralization tests for (A) hydrated lime nanofibers and (B) limestone residue nanofibers. [Figure 15] FIG. 1 shows the results of a neutralization test of sulfur nanofibers. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First, a nanofiber production apparatus 9 used in the nanofiber production method according to the present invention will be described.

[0017] As shown in Figure 1, the nanofiber production apparatus 9 is a production apparatus for nanofibers, which are ultrafine long fibers obtained by stretching a thermoplastic resin using a high-pressure gas flow, and includes an extruder 1 that extrudes molten resin from a nozzle 2a, and a nozzle head 10 attached to the tip of the nozzle 2a.

[0018] The extruder 1 includes a barrel 2 and a screw 3 that heat and melt raw materials such as pellets made of thermoplastic resin, knead them, and transport them toward a nozzle 2a, and is equipped with a hopper 4 for supplying the raw materials into the barrel 2. The screw 3 is connected at its base end to a screw drive motor 21, is supported by the barrel via a rotary bearing (not shown), and is driven to rotate around the axial direction of the barrel 2 by the screw drive motor 21.

[0019] The barrel 2 is also provided with a heater 5 on its outer periphery, allowing the interior to be heated. A nozzle head 10 for discharging resin is fixed to the tip of a nozzle 2a provided in the resin extrusion direction of the barrel 2. The nozzle head 10 is connected to a gas heating unit 7 by piping or the like, and is supplied with high-pressure gas supplied from a gas supply unit 6 such as a gas compressor connected to the nozzle head 10 after heating it. The gas heating unit 7 can be, for example, provided with a heating unit such as a heater around a gas pressure delivery pipe.

[0020] 2, the nozzle head 10 includes an outer peripheral mounting portion 19 for mounting the nozzle head 10 to the extruder 1, and a central face portion 11 whose main surface is arranged substantially vertically (the normal to the main surface is oriented horizontally) when mounted to the extruder 1. The mounting portion 19 is provided with bolt holes and the like (not shown) for fixing the nozzle head 10 to the extruder 1. The face portion 11 is also provided so as to protrude from the mounting portion 19 in the extrusion direction of the resin.

[0021] The face portion 11 is provided with a discharge port 12 for discharging resin and a gas outlet 13 for discharging high-pressure gas. The discharge port 12 and the gas outlet 13 are paired and arranged adjacent to each other. In this embodiment, a plurality of pairs of discharge port 12 and gas outlet 13 are provided, which is preferable because it can improve the production amount of nanofibers per unit time.

[0022] The discharge port 12 communicates with a resin inlet chamber 16. When the nozzle head 10 is attached to the extruder 1, the resin inlet chamber 16 is positioned in the resin extrusion direction relative to the nozzle 2a of the barrel 2, thereby serving as a flow path for the molten resin supplied from the nozzle 2a and directing the molten resin to the discharge port 12. The resin inlet chamber 16 is separated by a partition 15 from a gas inlet chamber 14, which serves as a gas flow path. The gas inlet chamber 14 is connected to a gas outlet 13 and to an inlet 14a for high-pressure gas introduced from outside the nozzle head 10. The inlet 14a is connected to the gas heating unit 7. This allows the gas inlet chamber 14 to direct the high-pressure gas that has flowed in to the gas outlet 13. The gas outlet 13 is also arranged with its axis oriented substantially horizontally so that the high-pressure gas ejected forms a gas flow in a substantially horizontal direction. The discharge port 12 is also preferably oriented substantially horizontally in accordance with the orientation of its paired gas outlet 13.

[0023] As described above, the gas outlet 13 is disposed near the discharge port 12. In particular, the gas outlet 13 is disposed close to the discharge port 12 so that the molten resin can be drawn from the inside of the discharge port 12 to the outside by the negative pressure generated by the formed gas flow and released into the air while being stretched. The inner diameter of the discharge port 12 is determined so that the flow resistance of the molten resin is reduced and the resin can be drawn from the inside by the negative pressure caused by the gas flow. The flow resistance of the molten resin decreases as the inner diameter increases. For example, the inner diameter of the outlet portion of the discharge port 12 (near the surface of the face portion 11) is preferably 0.5 mm or more. In this embodiment, the inner diameter of the discharge port 12 is 1.0 mm, the inner diameter of the gas outlet 13 is 1.5 mm, and the distance between their centers is 1.75 mm.

[0024] As long as the resin can be drawn out as described above, gas outlets 13 can be arranged in any direction, regardless of whether they are above, below, or to the side of discharge port 12. In this embodiment, in face portion 11, pairs of gas outlets 13 arranged below discharge port 12 are lined up in the upper row, and pairs of gas outlets 13 arranged above discharge port 12 are lined up in the lower row.

[0025] As shown in FIG. 3 , in the multiple pairs of outlets 12 and gas outlets 13 arranged in the lower row of the face portion 11, the axes of the gas outlets 13 are arranged so as to fan out from each other in the ejection direction (upward in the drawing) in a horizontal plane. For example, the axes of the gas outlets 13 at both ends overlap on both radii of a sector with a central angle α enclosed by two radii and an arc, and the axes of the other outlets 13 are also arranged so as to pass through the center point where the two radii of the same sector intersect. Similarly, the axes of the outlets 12 are arranged so as to fan out from each other in the ejection direction. This arrangement can be adjusted to suppress excessive entanglement between the nanofibers drawn from each pair and released into the air, thereby increasing the amount of resin discharged per unit time and thus increasing production volume per unit time, which is preferable. The same applies to the multiple pairs of outlets 12 and gas outlets 13 arranged in the upper row of the face portion 11.

[0026] Other details of the extruder 1 are publicly known and will not be described here. The production apparatus 9 also includes a collection section for collecting the released nanofibers.

[0027] Referring again to FIG. 1, when nanofibers are produced using production apparatus 9, molten resin is supplied to nozzle head 10 by extruder 1 and discharged from outlet 12, while high-pressure gas heated by gas supply unit 6 and gas heating unit 7 is supplied to nozzle head 10 and discharged from gas outlet 13 to form a gas flow. This gas flow from gas outlet 13 applies negative pressure to the front side of outlet 12, drawing the molten resin inside outlet 12 outward and stretching it into ultrafine long fibers, which are then released into the air. In other words, nanofibers can be produced using a type of melt-blowing method in which the molten resin is released into the air and stretched while being cooled. In this case, operation can be easily stabilized by maintaining a constant resin extrusion rate and adjusting the gas flow rate accordingly.

[0028] In particular, even if the supply of molten resin from extruder 1 is stopped during nanofiber production, nanofibers can be continuously produced for a while by supplying only high-pressure gas. In other words, it can be seen that the resin remaining inside discharge port 12 is reliably drawn to the outside and stretched by the negative pressure caused by the gas flow from gas outlet 13.

[0029] The nanofibers produced by the production apparatus 9 are ultrafine long fibers with diameters ranging from the order of microns to several hundred nanometers. Furthermore, the nanofibers are moderately entangled with each other, and there is almost no short, broken fibers or particulate resin.

[0030] According to the manufacturing apparatus 9, the molten resin in the discharge port 12 is drawn out by the negative pressure of the gas flow from the gas outlet 13 and released into the air, where it is cooled and stretched, thereby producing nanofibers, which are ultrafine long fibers. Because the resin is drawn out from the discharge port 12, operation can be stabilized and high operability can be achieved simply by adjusting the amount of gas flow according to the amount of resin extruded from the extruder 1. As described above, even when the amount of resin discharged is increased by arranging multiple pairs of discharge port 12 and gas outlet 13, the amount of gas flow can be adjusted accordingly, allowing for even greater increases in production volume with high productivity.

[0031] Furthermore, while the production apparatus 9 can produce ultrafine long fibers such as nanofibers, the inner diameter of the discharge port 12 is much larger than the fiber diameter, and as described above, it is set to 1 mm in this embodiment. In other words, the diameter of the nanofibers produced by the production apparatus 9 is considered to depend not on the diameter of the discharge port 12 but on the balance between the gas flow from the discharge port 13 and the amount of resin supplied. In other words, the flow rate and negative pressure from the discharge port 13 are adjusted by adjusting the amount of gas flow according to the amount of molten resin supplied. This adjusts the amount of resin extracted, and the diameter is considered to be adjusted in relation to the flow rate of the gas flow. By balancing the amount of gas flow according to the amount of molten resin supplied, ultrafine long fibers with the desired diameter can be produced. Therefore, it is preferable to make the diameter of the discharge port 12 relatively large to reduce the flow resistance of the molten resin and facilitate the extraction of the molten resin as described above. Furthermore, by making the diameter of the discharge port 12 relatively large, the amount of resin discharged can be increased, and by adjusting the amount of gas flow accordingly, it is easy to further increase the production volume per unit time.

[0032] In addition, since the diameter of the discharge port 12 of the manufacturing device 9 is large, clogging is less likely to occur and maintenance is very easy.

[0033] Furthermore, in the manufacturing apparatus 9, the number of pairs of outlets 12 and gas outlets 13 of the nozzle head 10 can be further increased, for example, by providing three or more rows of pairs on the face portion 11, thereby further increasing the production volume per unit time.

[0034] Next, a method for producing hydrophilic nanofibers using the nanofiber production apparatus 9 configured as above will be described.

[0035] The base thermoplastic resin to be fed into the hopper 4 is pellets of a polyolefin resin such as polyethylene resin, polypropylene resin, or olefin copolymer. The melt flow rate (MFR) of the thermoplastic resin used in the nanofiber production method according to the present invention is preferably 100 [g / 10 min] or more, more preferably 1000 [g / 10 min] or more, and even more preferably 1800 [g / 10 min] or more.

[0036] While polyolefin resins are inexpensive and readily available, nanofibers based on polyolefin resins lack hydrophilicity and cannot be used for applications such as water treatment. Therefore, in the nanofiber manufacturing method of the present invention, a functionalizing agent is added to a hopper 4 along with a thermoplastic resin, and both are thermally melted inside a barrel 2. This functionalizing agent contains a composition primarily composed of a surfactant, which is a compound having both hydrophobic and hydrophilic groups, thereby imparting hydrophilicity to the nanofibers produced. Here, the "main component" refers to the component that occupies the largest amount in the composition. The surfactant may be added to the nanofiber manufacturing apparatus 9 in the form of a masterbatch.

[0037] Suitable examples of surfactants that can be used in the nanofiber production method of the present invention include various surfactants such as anionic surfactants and nonionic surfactants. Examples of anionic surfactants include carboxylates, sulfonates, sulfates, and phosphates. Examples of nonionic surfactants include esters, ethers, ester-ethers, and fatty acid alkanolamides in which the hydrophobic group and the hydrophilic group are bonded via an amide bond. Examples of cationic surfactants include amine salts and quaternary ammonium salts. Fatty acid amides may also be used as adhesion improvers. These adhesion improvers can be used alone or in combination.

[0038] In a preferred embodiment, a phosphate ester is used as the surfactant. Examples of the phosphate ester include alkyl phosphate esters such as lauryl phosphate and lauryl phosphate salts, phosphate esters having an oxyethylene chain, and salts thereof. The salts may be, for example, sodium salts, potassium salts, barium salts, triethanolamine salts, etc. of the phosphate esters. The term "phosphate ester" is used to include salts. (Example 1: Resin Hydrophilic Nanofibers Using Surfactants as Functionality-Providing Agents) Polypropylene resin pellets (SunAllomer PP PWH00N manufactured by SunAllomer Co., Ltd.) were used as the thermoplastic resin, and a surfactant (Delion: NW-4031-K from the Delion series manufactured by Takemoto Oil & Fat Co., Ltd.) was used as the functionality imparting agent, and nanofibers were produced using production apparatus 9. The surfactant was in the form of a masterbatch and was charged into hopper 4 together with the polypropylene resin pellets, yielding the hydrophilic resin nanofibers shown in Figure 4.

[0039] Here, by adjusting the surfactant content to 5% by mass or more and 20% by mass or less, more preferably 8% by mass or more and 10% by mass or less, nanofibers that retain appropriate hydrophilicity could be produced.

[0040] It was assumed that the resin hydrophilic nanofibers produced as described above would adsorb Volatile Organic Compounds (VOCs), which are designated as Class 2 specified hazardous substances. Therefore, an adsorption / desorption test was conducted on the resin hydrophilic nanofibers, and the method for this adsorption / desorption test will be explained below. 1. VOCs adsorption / desorption test method 1.1 Test equipment Glass syringes were filled with hydrophilic resin nanofibers, and contaminated water and distilled water of a certain concentration were gradually injected into the three syringes and allowed to flow down by gravity, and the concentration of the wastewater was measured by official analysis.In addition, for performance comparison, a VOCs-contaminated water adsorption test was conducted using hydrophilic resin microfibers for ornamental fish. 1.2 Test conditions 1) Test Case Case 1: Injection of contaminated water (adsorption test) Case 2: Injection of distilled water (desorption test) 2) Preparation of target substances and contaminated water Contaminated water samples for carbon tetrachloride, 1,2-dichloroethane, 1,1-dichloroethylene, 1,2-dichloroethylene, 1,3-dichloropropene, dichloromethane, tetrachloroethylene, 1,1,1-trichloroethane, 1,1,2-trichloroethane, trichloroethylene, benzene, chloroethylene, and 1,4-dioxane were prepared by filling a gallon bottle with distilled water and mixing approximately two ampoules of the standard mixture with several mL of 1,4-dioxane. 3) Test Procedure Case 1: Inject contaminated water into a syringe and measure the water content of nanofibers, etc. → Inject 200 mL of contaminated water for the first time → Analyze the quality of the wastewater → Repeat this process three times Case 2 (performed after Case 1): Inject 200 mL of distilled water → Analyze the quality of the wastewater → Repeat this three times 3) The resin hydrophilic nanofiber filled in the syringe had a volume of approximately 75 cm 3 , weight approximately 6.8g, packing density approximately 0.091g / cm 3 In addition, 240 mL of contaminated water was allowed to flow by gravity at a rate of approximately 5 mL / min. 1.3 Test Results The results of the adsorption / desorption test, as shown in Figure 5, confirmed that a certain amount of all VOCs was adsorbed onto the resin hydrophilic nanofiber. The weight of resin nanofiber required to adsorb the entire amount would be approximately 14 to 30 g for 1 L of contaminated water at the concentration tested in this study, as shown in Figure 6. The contaminated water also contained 1,4-dioxane, but it was confirmed that it was not adsorbed. Furthermore, in the desorption test, although the contaminated water held by the nanofiber was diluted by the injection of distilled water and tended to temporarily reach a high concentration, there was almost no desorption of VOCs under the test conditions used in this study.

[0041] Although the above description has been given of an example in which the hydrophilic resin nanofiber according to the present invention is used as an adsorbent for VOCs, the hydrophilic resin nanofiber according to the present invention can also be used for other purposes, such as absorbent materials for sweat absorbents, diapers, sanitary products, etc. (Comparative example: Resin hydrophilic microfiber) VOCs are adsorbed by resin, so to compare the adsorption and desorption performance of resin nanofibers, we conducted an adsorption and desorption test of VOCs on a resin hydrophilic microfiber (Kotobuki Kogei Base Mat [HLS_DU] manufactured by Kotobuki Kogei Co., Ltd.) used to filter water for ornamental fish. The results are shown in Figure 7. The sample filled into the syringe had a volume of approximately 75 cm. 3 , weight approximately 6.8g, packing density approximately 0.091g / cm 3 120 mL of contaminated water was allowed to flow down the tube at a rate of approximately 31 mL / min. As a result of the adsorption / desorption test, no significant adsorption of VOCs was observed on the hydrophilic resin microfiber. (Example 2: Heavy metal adsorbent-added nanofiber using surfactant and heavy metal adsorbent as functional agents) Polypropylene resin pellets (SunAllomer PP PWH00N manufactured by SunAllomer Co., Ltd.) were used as the thermoplastic resin, and a surfactant (Delion Series Delion: NW-4031-K manufactured by Takemoto Oil & Fat Co., Ltd.) and a heavy metal adsorbent were used as the functionality imparting agent, and nanofibers were produced using production equipment 9. The surfactant was in the form of a masterbatch and was charged into hopper 4 together with the polypropylene resin pellets, yielding nanofibers with a hydrophilic heavy metal adsorbent added made of resin.

[0042] In this specification, the term "heavy metal adsorbent" is used, but this heavy metal adsorbent may contain metal elements that are not classified as "heavy metals," and the heavy metal adsorbent-added nanofiber described in this specification is expected to adsorb harmful metal elements as defined in the Soil Contamination Countermeasures Act.

[0043] Polypropylene resin pellets (SunAllomer PP PWH00N manufactured by SunAllomer Co., Ltd.) were used as the thermoplastic resin, a surfactant (Delion Series Delion: NW-4031-K manufactured by Takemoto Oil & Fat Co., Ltd.) was used as the functionality imparting agent, and either zeolite or Denite manufactured by Taiheiyo Cement Corporation was used as the heavy metal adsorbent, and nanofibers were produced using production equipment 9. The surfactant was in the form of a masterbatch and was charged into hopper 4 together with the polypropylene resin pellets and heavy metal adsorbent, yielding nanofibers with a resin-made hydrophilic heavy metal adsorbent added.

[0044] Here, by adjusting the surfactant content to 5% by mass or more and 20% by mass or less, more preferably 8% by mass or more and 10% by mass or less, nanofibers that retain appropriate hydrophilicity could be produced.

[0045] Furthermore, nanofibers with appropriate heavy metal adsorption function could be produced by using a heavy metal adsorbent in an amount of 1% by mass to 15% by mass, and more preferably 3% by mass to 10% by mass. If the amount of heavy metal adsorbent is too small, the heavy metal adsorption effect cannot be obtained, and if the amount of heavy metal adsorbent is too large, the nanofibers do not easily become long-chain fibers.

[0046] Here, we will explain the effects of using the heavy metal adsorbent-added nanofibers produced as described above in water treatment. Conventional water treatment has had the following problems. Specifically, because the heavy metal adsorbent itself is in granular or powder form, when it is filled into a water treatment tank for use, the filling density is fixed, making it difficult to adjust the water permeability. When contaminated water is flowed from top to bottom, the treatment volume is limited and it is prone to clogging. When contaminated water is flowed from bottom to top, the heavy metal adsorbent is disturbed during use, so it is necessary to drain the water through a filter to prevent it from being discharged outside the tank, or to settle the heavy metal adsorbent in a grit basin or the like before draining it.

[0047] On the other hand, the water permeability of nanofibers loaded with heavy metal adsorbents can be adjusted by changing the packing density in tanks, etc. Furthermore, since the heavy metal adsorbents are added to the nanofibers themselves, there is no risk of them leaking out of the tank, eliminating the hassle of handling the heavy metal adsorbents alone.

[0048] Next, an adsorption / desorption test was conducted on nanofibers containing a hydrophilic resinous heavy metal adsorbent, and the method for this test will be described. Note that this adsorption / desorption test method was also used to test nanofibers containing a hydrophilic resinous flocculating / sedimenting material, which will be described later. 2. Heavy metal adsorption / desorption test method 2.1 Test equipment A plastic syringe was filled with nanofibers containing a hydrophilic resin heavy metal adsorbent, and contaminated water and distilled water of a certain concentration were injected into the same syringe and allowed to flow naturally. The concentration of the wastewater was measured using official analysis. 2.2 Test conditions 1) Test Case Case 1: Injection of contaminated water (adsorption test) Case 2: Injection of distilled water (desorption test) 2) Preparation of target substances and contaminated water Reagents for cadmium, hexavalent chromium, selenium, lead, arsenic, fluorine, and boron were diluted with distilled water to create contaminated mixed water samples with concentrations approximately 10 times the environmental standard. 3) Test Procedure Case 1: Inject contaminated water into a syringe and measure the water content of the nanofibers → Inject 200 mL of contaminated water for the first time → Analyze the quality of the wastewater → Repeat this process three times Case 2 (performed after Case 1): Inject 200 mL of distilled water → Analyze the quality of the wastewater → Repeat this three times 2.3 Test Results Resin-made hydrophilic heavy metal adsorbent-added nanofiber 1 (zeolite added as a heavy metal adsorbent) The zeolite-loaded nanofibers packed in the syringe had a volume of approximately 100 cm 3The nanofiber weighed approximately 11.0 g and 200 mL of contaminated water was gravity-fed at a flow rate of approximately 67 mL / min. As shown in Figure 8, the adsorption test showed significant adsorption of lead (41%), from 0.13 mg / L to 0.051 mg / L, and cadmium (88%), from 0.033 mg / L to 0.0039 mg / L. Adsorption of selenium and arsenic was also observed. On the other hand, there was almost no adsorption of hexavalent chromium, fluorine, or boron. In the desorption test, the concentration values ​​were high when 200 mL of distilled water was passed through, but this is thought to be due to a temporary increase caused by dilution of the contaminated water retained in the nanofibers by the injection of distilled water. It was found that the adsorbed lead, cadmium, selenium, and arsenic were only slightly desorbed by distilled water. Resin-made hydrophilic heavy metal adsorbent-added nanofiber 2 (Denite manufactured by Taiheiyo Cement Corporation, which contains Fe, Al, and Mg, is added as a heavy metal adsorbent) As shown in Figure 9, the denite-added nanofibers were observed to have a morphology in which the additive dissolved in the nanofibers and solidified into spherical particles attached to the nanofibers. The resin-made hydrophilic heavy metal adsorbent-added nanofiber 2 filled in the syringe had a volume of approximately 100 cm. 3 The weight of the nanofiber was approximately 16.1 g, and 200 mL of contaminated water was gravity-fed at a flow rate of approximately 14 mL / min. As shown in Figure 10, the adsorption test results showed a significant adsorption of approximately 43% for cadmium, dropping from 0.053 mg / L to 0.030 mg / L. Adsorption of lead, selenium, and arsenic was also observed. On the other hand, there was almost no adsorption of hexavalent chromium, fluorine, or boron. In the desorption test, the concentration values ​​were high when 200 mL of distilled water was passed through, but this is thought to be due to a temporary increase caused by the dilution of the contaminated water held by the resin-made hydrophilic heavy metal adsorbent-added nanofiber 2 with the injection of distilled water. It was found that the adsorbed cadmium, lead, selenium, and arsenic were only slightly desorbed by distilled water. In the adsorption test of heavy metals, etc., with varying packing densities of resin-made hydrophilic heavy metal adsorbent-added nanofiber 2, as shown in Figure 11, the adsorption amount of cadmium differed depending on the packing density, but selenium, lead, and arsenic were significantly higher at a packing density of 0.098 g / cm. 3 and 0.161 g / cm 3 There was no significant difference in the amount of adsorption. (Example 3: Nanofibers with flocculating and precipitating agents added, using surfactant and flocculating and precipitating agent as functionality-imparting agents) The nanofibers according to Example 3 are nanofibers with a flocculating sedimentation material added, which were manufactured using a flocculating sedimentation material instead of the heavy metal adsorbent used in Example 2. The flocculating sedimentation material used was Kiyomaru-kun for muddy water, manufactured by HALVO Holdings Co., Ltd., which contains shirasu (volcanic ash) as its main component.

[0049] As in the previous examples, the surfactant was in the form of a masterbatch and was charged into hopper 4 together with polypropylene resin pellets and a flocculating and sedimenting agent to obtain nanofibers with added flocculating and sedimenting agent. The polypropylene resin pellets used were SunAllomer PP PWH00N manufactured by SunAllomer Co., Ltd.

[0050] In Example 3, nanofibers that retained appropriate hydrophilicity could be produced by adjusting the surfactant content to 5% by mass or more and 20% by mass or less, more preferably 8% by mass or more and 10% by mass or less.

[0051] Furthermore, nanofibers with appropriate coagulation and precipitation properties were produced by using a coagulation and precipitation material in an amount of 1% by mass to 15% by mass, and more preferably 3% by mass to 10% by mass. If the coagulation and precipitation properties are too low, the coagulation and precipitation effect cannot be obtained, and if the coagulation and precipitation properties are too high, the nanofibers do not easily become long-chain fibers.

[0052] The syringe was filled with nanofibers containing coagulation and sedimentation agents, and the volume was approximately 100 cm 3 The tube weighed approximately 17.4 g, and 200 mL of contaminated water was gravity-fed at a rate of approximately 1.8 mL / min. The results of the adsorption test, as shown in Figure 12, confirmed the adsorption of all target substances. The weight of the nanofiber coagulation and sedimentation material required to adsorb the entire amount would be approximately 17 to 37 g for 1 L of contaminated water with a concentration approximately 10 times the environmental standard, as shown in the table in Figure 13. In the desorption test, the contaminated water held by the nanofibers was diluted by the injection of distilled water, which tended to temporarily increase the concentration, but under the test conditions used, there was almost no desorption of the target substances. (Example 4: Neutralizer-added nanofibers using surfactant and neutralizer as functionality-imparting agents) There are two types of neutralizer-added nanofibers: alkaline neutralizer-added nanofibers, which are used when the water to be treated is acidic water, and acidic neutralizer-added nanofibers, which are used when the water to be treated is alkaline water. ●Nanofiber with alkaline neutralizer Hydrated lime or limestone residue was used as the alkaline neutralizer in the alkaline neutralizer-added nanofibers.

[0053] As in the previous examples, the surfactant was in the form of a masterbatch and was charged into hopper 4 together with polypropylene resin pellets and an alkaline neutralizer to obtain nanofibers with added alkaline neutralizer. The polypropylene resin pellets used were SunAllomer PP PWH00N manufactured by SunAllomer Co., Ltd.

[0054] In the production of nanofibers with added alkaline neutralizer, the surfactant content was set to 5% by mass or more and 20% by mass or less, more preferably 8% by mass or more and 10% by mass or less, thereby enabling the production of nanofibers that retain appropriate hydrophilicity.

[0055] Furthermore, when slaked lime is used as the alkaline neutralizing agent, nanofibers with appropriate acid neutralizing function can be produced by using a concentration of 1% by mass or more and 15% by mass or less, more preferably 3% by mass or more and 10% by mass or less.

[0056] Furthermore, when limestone residue is used as an alkaline neutralizing agent, nanofibers with appropriate acid neutralizing function can be produced by setting the amount to 1% by mass or more and 15% by mass or less, more preferably 3% by mass or more and 10% by mass or less. Nanofiber with acid neutralizer The acidic neutralizer used in the nanofibers with added acidic neutralizer was a white neutralizer containing sulfur as its main component, manufactured by UI Chemical Co., Ltd. Nanofibers with this acidic neutralizer are referred to as sulfur nanofibers.

[0057] As in the previous examples, the surfactant was in the form of a masterbatch and was charged into hopper 4 together with polypropylene resin pellets and an acidic neutralizer to obtain nanofibers with added acidic neutralizer. The polypropylene resin pellets used were SunAllomer PP PWH00N manufactured by SunAllomer Co., Ltd.

[0058] In the production of nanofibers with added acidic neutralizer, the surfactant content was set to 5% by mass or more and 20% by mass or less, more preferably 8% by mass or more and 10% by mass or less, thereby enabling the production of nanofibers with appropriate hydrophilicity.

[0059] Furthermore, by adjusting the amount of the acidic neutralizer to between 10% by mass and 15% by mass, and more preferably between 3% by mass and 10% by mass, nanofibers with an appropriate alkaline neutralizing function could be produced.

[0060] The pH neutralization test was carried out on the nanofibers to which an alkaline neutralizer had been added and the nanofibers to which an acidic neutralizer had been added as described above. Next, the pH neutralization test method will be explained. 3 pH Neutralization Test Method 3.1 Test equipment Plastic syringes were filled with either nanofibers containing an alkaline neutralizer or nanofibers containing an acidic neutralizer, and neutralization tests were conducted by injecting acidic water or alkaline water into the syringes in multiple stages. 3.2 Test conditions 1) Test Case Case 1: Acidic water is injected into two types of nanofibers using hydrated lime and limestone residue as neutralizers (referred to as hydrated lime nanofibers and limestone residue nanofibers, respectively). Case 2: Injection of alkaline water into sulfur nanofibers 2) pH of the sample water 3) Test Procedure Case 1: 300-500mL of acidic water → Inject into the first stage → Measure the pH of the wastewater → Inject the remaining liquid into the second stage → Repeat this process for stages 4-6 Case 2: 300 mL of alkaline water → Inject into the first stage → Measure the pH of the wastewater → Inject the remaining liquid into the second stage → Repeat this process up to the fourth stage The results are explained below. Neutralization of acidic water using nanofibers containing alkaline neutralizers Acidic water neutralization tests were conducted using two types of nanofibers: slaked lime nanofibers and limestone residue nanofibers, which are made from the residue left over after lime refining in limestone mines. The slaked lime nanofibers were filled into syringes with a volume of approximately 100 cm3 and a weight of approximately 10 g, and 370 mL of acidic water was allowed to flow gradually through the syringes at a rate of approximately 23 mL / min. The limestone residue nanofibers were filled into syringes with a volume of approximately 100 cm3 and a weight of approximately 10 g, and 500 mL of acidic water was allowed to flow gradually through the syringes at a rate of approximately 10-20 mL / min. As shown in Figure 14, both nanofibers were able to neutralize the acidic water, but after neutralization, the slaked lime nanofibers produced a strongly alkaline solution with a pH of over 12, while the limestone residue nanofibers produced a pH of around 10. Since the discharge standards for public waters other than the sea are pH 5.8 or higher and pH 8.6 or lower, it is necessary to consider methods of use that control the rise in pH. Neutralization of alkaline water using nanofibers containing acidic neutralizers A neutralization test for alkaline water was conducted using sulfur nanofibers. The filled sample had a volume of approximately 100 cm3 and a weight of approximately 10.1 g. 375 mL of acidic water was allowed to flow down the stage liquid at a rate of approximately 20-24 mL / min. The results of the neutralization test, as shown in Figure 15, showed that although alkaline water could be neutralized, it became a strongly acidic water with a pH of about 1 after neutralization. Therefore, it is necessary to consider a method of use that controls the drop in pH.

[0061] As described above, the nanofiber manufacturing method according to the present invention comprises a heat-melting step in which a thermoplastic resin and a functionalizing agent are thermally melted together, and a melt-blowing step in which the resin thermally melted in the heat-melting step is converted into fibers by a melt-blowing method, and the functionalizing agent contains a composition whose main component is a surfactant. According to this nanofiber manufacturing method according to the present invention, it is possible to produce hydrophilic nanofibers that can be used for water treatment and the like at low cost.

[0062] Although the present invention has been described above based on the embodiments, the present invention is not limited to the above embodiments. Various modifications can be made to the above embodiments within the scope of the same or equivalent to the present invention.

[0063] The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit and scope of the present invention, all of which are included in the technical concept of the present invention. [Explanation of symbols]

[0064] 1. Extruder 1 2 barrels 2a Nozzle 3. Screw 4 Hopper 5. Heater 6. Gas supply section 7. Gas heating section 9...Manufacturing equipment 10 Nozzle head 11. Face part 12...Discharge port 13 Gas outlet 14 Gas inlet chamber 14a...Inlet 15...Divider 16...Resin inflow chamber 19 Mounting part 21 Screw drive motor

Claims

1. a thermal melting step of thermally melting a thermoplastic resin and a functionality imparting agent; A melt-blowing process in which the resin heat-melted in the heat-melting process is converted into fibers by a melt-blowing method, The nanofiber manufacturing method is characterized in that the functionality imparting agent contains a composition containing a surfactant as a main component.

2. The method for producing nanofibers according to claim 1, wherein the thermoplastic resin is a polyolefin resin.

3. 2. The method for producing nanofibers according to claim 1, wherein the thermoplastic resin has a melt flow rate (MFR) of 100 g / 10 min or more.

4. The method for producing nanofibers according to claim 1, wherein the functionality-imparting agent is in the form of a masterbatch.

5. The method for producing nanofibers according to claim 1, wherein the functionality-imparting agent further contains a heavy metal adsorbent.

6. The method for producing nanofibers according to claim 1, wherein the functionality-imparting agent further contains a flocculating and precipitating agent.

7. The method for producing nanofibers according to claim 1, wherein the functionality-imparting agent further contains a neutralizing agent.

8. A nanofiber produced by the method for producing a nanofiber according to claim 1.

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