Electrospinning Equipment

Abstract

To provide an electrospinning device enabling stable melt-electrospinning.SOLUTION: An electrospinning device 10 includes a nozzle 31, an electrode 32, and a gas ejection part 40a. The electrode 32 includes an electric insulating and heat resistant surface covering part 35a disposed on a surface facing the nozzle 31. The surface covering part 35a is made of a stacked structure consisting of plural covering materials 45. The covering materials 45 are layered in a direction crossing a normal line with respect to an extending direction X of the electrode 32. Seal materials 46 having insulation properties and heat resistance are further disposed respectively in a position outside of both end parts of the electrode 32 in the extending direction X, the position at least overlapping a projected image of the electrode 32 when viewed in the extending direction X.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electrospinning apparatus. [Background technology]

[0002] Electrospinning has attracted attention as a technique that can easily and highly productively produce fiber sheets having nano-sized fibers by discharging a solution or melt of a raw resin. Generally, in electrospinning, a high voltage is applied between a nozzle for discharging the raw resin liquid and a collection electrode installed facing the nozzle at a predetermined distance, and the raw resin liquid is discharged under this condition. The raw resin liquid discharged from the tip of the nozzle is stretched by Coulomb force and then cooled and solidified, thereby forming fibers with a smaller diameter. The applicant has proposed an apparatus for producing fibers using this technique and a method for producing the same (see Patent Document 1).

[0003] In electrospinning, an electrode for applying a high voltage is placed near the nozzle that ejects the resin in order to impart an electric charge to the resin that is the raw material for the fiber. Because a high voltage is applied between the nozzle and the electrode, it is effective to place an electrically insulating coating on the surface of the electrode to prevent discharge between them. For this purpose, in the electrospinning apparatus described in Patent Document 1, a resin material such as nylon or bakelite is placed on the surface of the electrode that faces the nozzle. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-11665 Summary of the Invention [Problem to be solved by the invention]

[0005] In electrospinning devices that use molten resin, the coating that covers the electrodes must have not only electrical insulation but also heat resistance, but when resin materials are used for the coating, the heat resistance is not sufficient. On the other hand, thermal insulation materials are known as materials with high heat resistance, but because thermal insulation materials generally have a laminated structure, they cannot ensure sufficient electrical insulation in the direction parallel to the laminated surface.

[0006] Therefore, an object of the present invention is to provide an electrospinning apparatus in which an electrode is provided with a covering portion that has both electrical insulation and heat resistance. [Means for solving the problem]

[0007] The present invention includes a nozzle for discharging molten resin; an electrode for generating an electric field between the electrode and the nozzle; an electrospinning apparatus including a gas injection unit that injects a gas flow between the nozzle and the electrode, the electrode has an electrically insulating and heat-resistant surface coating portion disposed on a surface facing the nozzle, the surface coating portion is a laminated structure formed by laminating a plurality of coating materials, The electrospinning device provides a coating material that forms a layer in a direction that intersects with a normal to the extension direction of the electrodes. [Effects of the Invention]

[0008] The electrospinning device of the present invention is equipped with a coating on the electrode that is both electrically insulating and heat-resistant, enabling stable melt electrospinning. Furthermore, because it has higher heat resistance than conventional resin materials (nylon), it can also be used as a channel wall for high-temperature gas flow. This allows the electrode to be positioned close to the nozzle, improving charging efficiency. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional schematic diagram showing one embodiment of the electrospinning apparatus of the present invention. [Figure 2]FIG. 2 is a schematic diagram showing an example of the covering state of the electrodes in the electrospinning apparatus of the present invention. [Figure 3] FIG. 3 is a schematic diagram showing another example of the covering state of the electrodes in the electrospinning apparatus of the present invention. [Figure 4] FIG. 4 is a schematic diagram showing yet another example of the covering state of the electrodes in the electrospinning apparatus of the present invention. [Figure 5] 5(a) to 5(c) are process diagrams sequentially showing an example of a state in which an electrode is covered with a covering material. [Figure 6] 6(a) to 6(c2) are process diagrams sequentially showing another example of the state in which the electrodes are covered with the covering material. [Figure 7] 7(a) to 7(c) are schematic diagrams showing other examples of electrode arrangements in the electrospinning apparatus of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described below based on preferred embodiments with reference to the drawings. Figure 1 shows the structure of one embodiment of an electrospinning apparatus of the present invention. As shown in the figure, the electrospinning apparatus 10 includes a kneading device 20 and a spinning unit 30.

[0011] The kneading device 20 melts the resin that is the raw material for the fibers and extrudes it into the spinning unit 30. The kneading device 20 has a cylinder and a screw (not shown) equipped with a heater inside, and is configured to melt and knead the raw material resin supplied into the kneading device 20 and extrude and supply it to the spinning unit 30.

[0012] The spinning unit 30 discharges the molten resin supplied from the kneading device 20 to the outside to spin the resin. The spinning unit 30 is equipped with a hollow nozzle 31 that communicates with the kneading device 20. The nozzle 31 is composed of a tip region 31a and a cylindrical resin supply path 31b connected to the rear end of the tip region 31a. The nozzle 31 is configured so that the molten resin supplied from the kneading device 20 can be discharged from the tip region 31a via the resin supply path 31b. From the viewpoint of improving charging properties, it is preferable that the tip region 31a of the nozzle 31 is made of a conductor such as metal. Also, from the viewpoint of improving heat resistance, it is preferable that the resin supply path 31b of the nozzle 31 is made of metal. In the following description, unless otherwise specified, the direction in which the nozzle 31 extends (the left-right direction of the paper in Figure 1) toward the kneading device 20 (the left side of the paper in Figure 1) is also referred to as the "rear", and the direction opposite to that direction (the right side of the paper in Figure 1) is also referred to as the "front".

[0013] As shown in FIG. 1, the spinning unit 30 includes an electrode 32 for charging the tip region 31a of the nozzle 31 and generating an electric field between the tip region 31a and the electrode 32. The electrode 32 is made of a conductive material. The electrode 32 in FIG. 1 has a cylindrical shape and is arranged to surround the nozzle 31 in the circumferential direction. The surface of the electrode 32 facing the nozzle 31 is formed as a concave curved surface on the inner surface of the cylinder. For convenience of explanation, in the following explanation, the surface of the electrode 32 facing the nozzle 31 will also be referred to as the "concave curved surface 32a." The electrode 32 has an open end 32c on the tip side of the nozzle 31. The planar shape of the open end 32c is a circular shape, such as a perfect circle or an ellipse. The open end 32c is located forward of the tip of the tip region 31a of the nozzle 31. The electrode 32 is connected to a high-voltage power supply (not shown), and a positive or negative voltage is applied to the electrode 32 by the power supply.

[0014] 1 has a structure formed between the kneading device 20 and the tip region 31a of the nozzle 31, including a cylindrical resin supply path 31b that forms part of the nozzle 31, an inner cylinder 36 that is arranged to surround the resin supply path 31b, and an outer cylinder 37 that covers the inner cylinder 36. The rear end of the resin supply path 31b communicates with the kneading device 20, allowing the molten resin supplied from the kneading device 20 to flow toward the tip region 31a of the nozzle 31. The cylindrical space formed between the resin supply path 31b and the inner cylinder 36 serves as a first gas flow path 40 through which the heated first gas flow A can flow. In other words, the first gas flow path 40 is arranged to surround the nozzle 31 in the circumferential direction. As shown in FIG. 1, the first gas flow path 40 is configured so that the first gas flow A flows along the extension direction of the nozzle 31 from the rear end side of the nozzle 31 (i.e., the kneading device 20 side) toward the tip region 31a. A first gas injection unit 40a is connected to the rear end of the first gas flow path 40. The first gas injection unit 40a is connected to a first gas supply source (not shown), and supplies a heated first gas flow A supplied from the first gas supply source to the first gas flow path 40, so that the first gas flow A is injected between the nozzle 31 and the electrode 32. For convenience, the first gas flow A may be, for example, an air flow.

[0015] The first gas injection section 40a extends in a direction intersecting the extension direction of the first gas flow path 40. In the embodiment shown in Fig. 1, the extension direction of the first gas injection section 40a and the extension direction of the first gas flow path 40 are generally perpendicular to each other. Therefore, the first gas flow A supplied from a first gas supply source (not shown) flows through the first gas injection section 40a, and then its flow direction is changed by 90 degrees at the connection section between the first gas injection section 40a and the first gas flow path 40, and then the first gas flow A flows through the first gas flow path 40. In the device of the present invention, the angle of intersection between the first gas ejection part 40a and the first gas flow path 40 is not limited to 90 degrees, and they may intersect at another angle.

[0016] 1, the spinning unit 30 further includes a second gas flow path 50 for spraying the heated second gas flow B. When the spinning unit 30 is viewed from the front, the second gas flow path 50 is disposed so as to surround the first gas flow path 40 at a position more outer than the first gas flow path 40 with respect to the position of the nozzle 31. When the spinning unit 30 is viewed from the front, the second gas flow path 50 is disposed more inner than the electrode 32 and more outer than the first gas flow path 40 with respect to the position of the nozzle 31. The second gas flow path 50 is a cylindrical space defined by the outer surface of the inner cylinder 36 and the inner surface of the outer cylinder 37. The second gas flow path 50 is configured so that the heated second gas flow B can be sprayed from the rear end side of the nozzle 31 toward the tip region 31a along the extension direction of the nozzle 31. A second gas injection unit 50a is connected to the rear end of the second gas flow path 50. The second gas injection unit 50a is connected to a second gas supply source (not shown), and supplies a heated second gas flow B supplied from the second gas supply source to the second gas flow path 50, so that the second gas flow B is injected between the nozzle 31 and the electrode 32. The second gas injection part 50a extends in a direction intersecting the extension direction of the second gas flow path 50. In the embodiment shown in Fig. 1, the extension direction of the second gas injection part 50a and the extension direction of the second gas flow path 50 are substantially perpendicular to each other. For convenience, the second gas flow B may be, for example, an air flow.

[0017] The term "heated" in the context of the first gas flow A and the second gas flow B refers to a gas flow whose temperature is higher than the standard temperature (20°C).

[0018] The electrospinning apparatus 10 may have a collecting section (not shown) opposite the nozzle 31 to collect the spun fibers. A collecting electrode made of a conductive material such as metal is disposed in the collecting section, and the spun fibers can be collected on the collecting section due to the potential difference between the nozzle 31 and the collecting electrode. The collecting electrode is preferably flat, and it is also preferable that the plate surface of the collecting electrode is approximately perpendicular to the direction in which the nozzle 31 extends. The collecting electrode is preferably grounded or has a voltage applied thereto by a high-voltage power supply. In this case, it is also preferable that a voltage different from that applied to the nozzle 31 is applied to the collecting section. The collecting section may also have a conveying means such as a belt conveyor disposed between the nozzle 31 and the collecting electrode. The fibers collected after spinning can be transported to a downstream process by the conveying means. When a collection section is provided, from the viewpoint of fiber collection efficiency, the distance between the tip of the nozzle 31 and the collection section is set to preferably 50 mm or more, more preferably 100 mm or more, preferably 2000 mm or less, and more preferably 1500 mm or less.

[0019] In the electrospinning apparatus having the above configuration, the heated first gas flow A is injected from the first gas flow path 40, which is relatively close to the tip region 31a of the nozzle 31. This allows the first gas flow A to easily come into contact with the molten resin discharged from the tip region 31a. As a result, the application of external force by the injection of the first gas flow, in addition to Coulomb force, can more effectively stretch the molten resin, resulting in efficient production of fibers with smaller diameters. Furthermore, the heated second gas flow B can be injected from a position closer to the outer periphery than the first gas flow path 40. This maintains a high temperature in the space around the nozzle 31 in the direction of the molten resin discharge, and this space can be formed over a wide area. This delays the cooling and solidification of the molten resin, maintaining the stretched state of the molten resin for a long period of time, resulting in efficient production of fibers with smaller diameters. Furthermore, the second gas flow B prevents the discharged molten resin or the fibers after cooling and solidification from unintentionally adhering to the electrode 32, allowing the fibers to be transported in the desired direction, thereby improving production efficiency.

[0020] From the viewpoint of making the above-mentioned effects more pronounced, the spinning unit 30 preferably includes an electrically insulating surface coating portion 35a disposed at least on the concave curved surface 32a of the electrode 32 facing the nozzle 31. This prevents discharge between the nozzle 31 and the electrode 32, enabling stable fiber spinning. The surface coating portion 35a shown in FIG. 1 is in direct contact with the electrode 32 and covers the entire surface of the electrode 32 facing the nozzle 31. The surface coating portion 35a is a concave curved surface on the inner surface of a cylinder. The surface coating portion 35a is disposed so as to surround the nozzle 31 in the circumferential direction.

[0021] The spinning unit 30 preferably also includes an electrically insulating back surface covering part 35b disposed on the convex curved surface 32b, which is the surface of the electrode 32 opposite to the concave curved surface 32a, which is the surface facing the nozzle 31. The back surface covering part 35b is a convex curved surface on the outer surface of a cylinder. Furthermore, as shown in Fig. 1, the spinning unit 30 preferably includes end covering portions 35c on the outer side of both ends in the extending direction of the electrode 32. In other words, as shown in Fig. 1, it is preferable that the entire area of ​​the electrode 32 is covered. With this configuration, the covering portions 35a, 35b, and 35c can also function as support members for supporting the electrode 32.

[0022] The front surface covering portion 35a, the back surface covering portion 35b, and the end covering portion 35c are preferably made of a material that electrically insulates the nozzle 31 from the electrode 32. In this specification, electrical insulation means a material having a volume resistivity of 10 or more at 25°C. 8 The volume resistivity is measured by cutting out a portion of each of the covering portions 35a, 35b, and 35c, processing it into a test piece, and measuring it according to the method specified in JIS K6911-1995.

[0023] To ensure sufficiently high electrical insulation, the thickness of the front surface covering portion 35a and the back surface covering portion 35b is preferably 2 mm or more, and more preferably 4 mm or more. From the viewpoint of electrical insulation, there is no particular upper limit to the thickness, but from the viewpoint of preventing the device 10 from becoming large, the thickness is preferably 30 mm or less, and more preferably 15 mm or less.

[0024] As described above, the electrospinning apparatus 10 of this embodiment is used to extrude molten resin. In other words, it is a melt electrospinning apparatus, and therefore the entire apparatus 10 is exposed to high temperatures. As a result, if the heat resistance of the above-described coatings 35a, 35b, and 35c is low, the coatings 35a, 35b, and 35c may be softened or deteriorated by heat. The deterioration of the coatings 35a, 35b, and 35c can be a factor that interferes with stable electrospinning. Therefore, it is desirable that the coatings 35a, 35b, and 35c have high heat resistance in addition to high electrical insulation. Therefore, in this embodiment, the coatings 35a, 35b, and 35c have the following structure.

[0025] 2 shows the structure of each of the covering portions 35a, 35b, and 35c that cover the electrode 32. As shown in the figure, the front surface covering portion 35a is composed of a laminated structure in which multiple covering materials 45 are stacked. Similarly, the back surface covering portion 35b and the end covering portion 35c are also composed of a laminated structure in which multiple covering materials 45 are stacked. The covering materials 45 are layered in a direction Y that intersects with a normal to the extension direction X of the electrode 32. The layering direction of the covering material 45 can be determined by checking the end face or cut cross section of the covering material 45 . Each covering material 45 is composed of a sheet made of an electrically insulating and heat-resistant material. The sheet that constitutes each covering material 45 has two opposing, parallel main surfaces. Each covering material 45 is bonded together with a binder made of an electrically insulating and heat-resistant material. In this specification, heat resistance means that the appearance of the covering material does not change (it is not melted) when exposed to an environment of 200°C for 1 hour, and the dimensional change after cooling to room temperature is within ±5%.

[0026] By having each of the coating portions 35a, 35b, and 35c have such a structure, thermal denaturation of each of the coating portions 35a, 35b, and 35c is suppressed, and melt electrospinning can be stably performed while maintaining the electrical insulation of each of the coating portions 35a, 35b, and 35c. To further enhance this advantage, it is preferable that the stacking direction of the coating material 45 constituting the surface coating portion 35a coincides with the stacking direction of the coating material 45 constituting the back coating portion 35b. It is also preferable that the stacking direction of the coating material 45 constituting the end coating portion 35c coincides with the stacking direction of the coating materials 45 constituting the surface coating portion 35a and the back coating portion 35b.

[0027] The covering material 45 is preferably a sheet body with a fiber skeleton, i.e., a fiber sheet. The fiber preferably contains inorganic fiber, which is a material with high electrical insulation and heat resistance. In particular, the covering material 45 preferably contains glass fiber, glass wool, rock wool, or silica cloth. In particular, the covering material 45 preferably contains glass cloth made of glass fiber. Whether or not fibers are contained can be confirmed by examining a cross section of the coating material 45. Furthermore, it is possible to determine whether or not the fibers are inorganic fibers by elemental analysis means such as SEM-EDS.

[0028] The coating material 45 preferably includes other materials in addition to fibers. The other materials preferably include an inorganic material as a binder for fixing the inorganic fibers. Examples of inorganic materials include silicate-based binders, phosphate-based binders, and borate-based binders. Such inorganic materials are well known in the technical field of thermal insulation. Whether or not the coating material 45 is an inorganic material can be determined by examining a cross section of the coating material 45 and examining non-fiber portions using elemental analysis techniques such as SEM-EDS.

[0029] As described above, the coating material 45 forms a layer in the direction Y intersecting the normal to the extension direction X of the electrode 32. It is preferable that the extension direction X of the electrode 32 and the layer direction Y of the coating material 45 be orthogonal to each other, as this minimizes the likelihood of dielectric breakdown when a high voltage is applied between the nozzle 31 and the electrode 32. However, it is not essential in this embodiment that the extension direction X of the electrode 32 and the layer direction Y of the coating material 45 be orthogonal to each other. For example, as shown in Fig. 3 , the extension direction X of the electrode 32 and the layer direction Y of the coating material 45 may intersect at an angle other than 90 degrees.

[0030] Fig. 4 shows a modified example of the electrospinning apparatus 10 of this embodiment. This figure shows another example of covering the electrode 32. In the embodiment shown in Fig. 4, a sealant 46 is disposed outside both ends of the electrode 32 in the extension direction X and at a position that overlaps at least with a projected image of the electrode 32 when viewed from a direction perpendicular to the direction Y. The sealant 46 is made of a material that is electrically insulating and heat resistant. In the embodiment shown in FIG. 4 and the previously described FIGS. 2 and 3 , multiple coating materials 45 form a laminated structure. While the electrical insulation of the coating materials 45 is sufficiently high in the direction Y in which the layers of the coating materials 45 are formed, the electrical insulation in a direction perpendicular to the direction Y tends to be lower than in the direction Y in which the layers of the coating materials 45 are formed. As a result, when a high voltage is applied between the nozzle 31 and the electrode 32, an unintended discharge may occur between the nozzle 31 and the electrode 32. Therefore, in order to further improve the electrical insulation in the direction perpendicular to the direction Y in which the layers of the coating materials 45 are formed, in the embodiment shown in FIG. 4 , an electrically insulating and heat-resistant sealing material 46 is disposed outside both ends of the electrode 32 in the extension direction X and at a position that at least overlaps with a projected image of the electrode 32 viewed from the direction perpendicular to the direction Y. Electrical insulation is defined as a material having a volume resistivity of 10 at 25°C. 8 This refers to a material with a dielectric constant of Ω·cm or more. Heat resistance means that there is no change in the appearance of the coating material (it is not melted) when it is left in an environment of 200°C for 1 hour, and the dimensional change after cooling to room temperature is within ±5%. Electrical insulation and heat resistance can be measured by peeling the sealing material from the coating material and processing it into a test piece.

[0031] A gasket or O-ring having electrical insulation and heat resistance can be used as the sealing material to further enhance the advantages of providing the sealing material 46. Alternatively, the sealing material 46 can be formed by using a liquid adhesive containing an inorganic material such as water glass, applying it to the desired location, and then solidifying it.

[0032] 5(a) to 5(c) show the order in which the covering portions 35a, 35b, and 35c are arranged around the electrode 32. FIG. 5(a), a first member 51 having a front surface covering portion 35a and an end covering portion 35c, and a second member 52 having a back surface covering portion 35b are prepared. A recess 51a is formed in the first member 51. The recess 51a has a shape that is approximately complementary to the electrode 32. Next, as shown in Figure 5(b), an electrode 32 is placed in the recess 51a of the first member 51, and then a second member 52 is placed on the electrode 32, and these are joined together, so that the periphery of the electrode 32 is covered with each of the covering portions 35a, 35b, and 35c. Finally, as shown in FIG. 5(c), a sealant 46 is disposed outside both ends of the electrode 32 in the extension direction X and at a position that overlaps at least with a projected image of the electrode 32 when viewed from the extension direction X. For simplicity, FIGS. 5(a) and 5(b) do not illustrate the space in which the sealant 46 is disposed. As shown in FIG. 5(a), the sealant 46 is disposed not only at the position that overlaps with the projected image of the electrode 32 when viewed from the extension direction X, but also on both sides in the Y direction beyond the overlapping position. This means that the interface between the first member 51 and the second member 52 is also covered with the sealant 46, thereby providing more effective insulation.

[0033] 6(a) to 6(c2) show another order in which the covering portions 35a, 35b, and 35c are arranged around the electrode 32. In FIG. First, as shown in FIG. 6(a), a first member 51' and a second member 52' ​​are prepared. The second member 52' ​​is made up of a part of the back surface covering portion 35b and has the same length as the length of the electrode 32 in the extension direction X. The first member 51' is made up of the front surface covering portion 35a, the end covering portion 35c, and the remaining part of the back surface covering portion 35b, and has a recess 51a'. The recess 51a' has a shape that is approximately complementary to the shape of the electrode 32 and the second member 52' ​​combined. 6(b), the electrode 32 is placed in the recess 51a' of the first member 51', and then the second member 52' ​​is placed on the electrode 32 and joined together, thereby covering the periphery of the electrode 32 with the covering portions 35a, 35b, and 35c. At this time, at both ends of the electrode 32 in the extension direction X, there are boundaries 53 between the recess 51a' of the first member 51' and the electrode 32 and the second member 52'. A space may be generated at the boundary portion 53. Therefore, in order to fill the space at the boundary portion 53 and improve electrical insulation, a sealant 46 is filled at the boundary portion 53 as shown in FIG. 6(c1). For simplicity, the space where the sealant 46 is disposed is not shown in FIGS. 6(a) and 6(b). Note that the sealant 46 filled at the boundary portion 53 may extend beyond the outermost layer of the back surface covering portion 35b, or may fill up to the gap between the outermost layer of the back surface covering portion 35b and the layer adjacent to that layer.

[0034] Instead of the operation shown in FIG. 6(c1), the operation shown in FIG. 6(c2) may be performed. In FIG. 6(c2), instead of filling the entire space of the boundary portion 53 shown in FIG. 6(b), the sealant 46a is filled in the portion of the boundary portion 53 that is exposed to the outside. Furthermore, the sealant 46b is disposed outside both ends of the electrode 32 in the extension direction X and at a position that overlaps at least a projected image of the electrode 32 when viewed from the extension direction X, and the sealant 46b is disposed at a position that overlaps at least a projected image of the boundary portion 53 that is not filled with the sealant when viewed from the extension direction X. This embodiment also improves the electrical insulation at the boundary portion 53.

[0035] Next, matters that are commonly applicable to the above-described embodiments will be described. The inner diameter of the tip region 31a of the nozzle 31 is preferably 50 μm or more, more preferably 100 μm or more, and preferably 3000 μm or less, more preferably 2000 μm or less. By setting the inner diameter of the tip region 31a within this range, molten resin can be easily and quantitatively discharged. The inner diameter of the resin supply path 31b in the nozzle 31 can be the same as or larger than the inner diameter of the tip region 31a.

[0036] The gap D1 (see FIG. 1) of the first gas flow path 40 is preferably 1 mm or more, more preferably 2 mm or more, and preferably 10 mm or less, and more preferably 7 mm or less. The gap D2 (see FIG. 1) of the second gas flow path 50 is preferably 1 mm or more, more preferably 5 mm or more, and preferably 100 mm or less, and more preferably 70 mm or less. By setting each gap in such a range, the first gas flow A and the second gas flow B can be adjusted to the desired air velocity and air volume, thereby further improving the efficiency of stretching the molten resin.

[0037] From the viewpoint of successfully supplying the molten resin from the kneading device 20, it is preferable that a heating means (not shown) for heating or keeping the molten resin warm is provided between the kneading device 20 and the spinning unit 30. As the heating means, a known means such as a heater can be used. The temperature for heating or keeping the temperature is preferably equal to or higher than the melting point of the raw resin used in fiber production. Furthermore, from the viewpoints of thermal conductivity and mechanical strength, the resin supply path 31b is preferably made of, for example, metal, and is preferably grounded from the viewpoint of preventing voltage load on the kneading device 20 in the melt electrospinning method.

[0038] The terminal positions of the first gas flow path 40 and the second gas flow path 50 in the front-rear direction in the spinning unit 30 are not particularly limited as long as the effects of the present invention are achieved. However, when the position of the tip of the nozzle 31 in the tip region 31a is taken as the reference (zero), the position in front of the nozzle 31 is expressed as a positive value, and the position behind the nozzle 31 is expressed as a negative value, the terminal positions of each gas flow path are each independently preferably in the range of −50 mm to +50 mm. The terminal position of each gas flow path is defined as the position of the front end of an outer member constituting each gas flow path, with the position of the nozzle 31 taken as the reference, when the spinning unit 30 is viewed from the front. Furthermore, the terminal position of the first gas flow path 40 is preferably located at the same position as the tip of the nozzle 31 in the tip region 31a or rearward of the tip, and the terminal position of the second gas flow path 50 is preferably located at the same position as the tip of the nozzle 31 in the tip region 31a or forward of the tip.

[0039] The above has been a description of the electrospinning apparatus 10. The following describes a method for producing fibers using the apparatus 10, namely, electrospinning. In the fiber manufacturing method using the electrospinning apparatus 10, an electric field is generated between the nozzle 31 and the electrode 32, and a molten resin is discharged from the tip region 31a of the nozzle 31 while a first gas flow A and a second gas flow B are being jetted. The discharged molten resin is three-dimensionally stretched and refined by the Coulomb force generated inside the nozzle 31 and the jetting of the first gas flow A and the second gas flow B, and at the same time, the resin is cooled and solidified, forming fine fibers.

[0040] The fibers produced by the method of the present invention are thin fibers called nanofibers, with a fiber diameter of 30 μm or less when expressed as an equivalent circle diameter. The nanofibers preferably have a fiber diameter of 0.1 μm or more, preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less.

[0041] The fiber diameter of a fiber can be measured by, for example, randomly selecting 500 fibers from a two-dimensional image obtained by observation under a scanning electron microscope, excluding defects such as clumps of spun fibers, intersections between fibers, and polymer droplets, and directly reading the length of a line drawn perpendicular to the longitudinal direction of the fiber as the fiber diameter. The median diameter is determined from the distribution of the measured fiber diameters, and this is defined as the fiber diameter in this specification.

[0042] In fiber production, when the first gas flow A and the second gas flow B are sprayed, it is preferable to spray them so that the wind speed of the first gas flow A is equal to or greater than the wind speed of the second gas flow B. By adjusting the wind speed of each gas flow, the discharged molten resin can be stretched more strongly by the external force generated by the spraying of the first gas flow, and as a result, fibers with an even smaller diameter can be obtained efficiently.

[0043] The molten resin used in the present invention is a fluid resin composition containing a thermoplastic resin having a melting point. The term "having a melting point" means that when the resin is heated in differential scanning calorimetry, it exhibits an endothermic peak resulting from a phase change from solid to liquid before thermal decomposition. The melting point of the thermoplastic resin can be measured, for example, using a melting point / dropping point measuring device (manufactured by Mettler-Toledo, Model No. DP90 Automatic Dropping Point / Softening Point Measuring System) in accordance with JIS K 0064 or JIS K 2220.

[0044] Examples of thermoplastic resins include polyolefin resins such as polyethylene, polypropylene, and ethylene-α-olefin copolymers; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polylactic acid, and liquid crystal polymers; polyamide resins such as nylon 6 and nylon 66; vinyl polymers such as polyvinyl chloride, polyvinylidene chloride, and polystyrene; acrylic polymers such as polyacrylic acid, polyacrylic acid esters, polymethacrylic acid, and polymethacrylic acid esters; polyvinyl acetate and polyvinyl acetate-ethylene copolymers. These resins can be used alone or in combination. Among these thermoplastic resins, polyolefin resins such as polyethylene, polypropylene, and ethylene-α-olefin copolymers are preferred because of their ease of spinning due to their properties such as low melting point, high fluidity, and high ductility.

[0045] The molten resin may be a resin composition containing additives in addition to the thermoplastic resin, as long as the effects of the present invention are not impaired. Examples of additives include electrostatic agents, antioxidants, neutralizing agents, light stabilizers, UV absorbers, lubricants, antistatic agents, metal deactivators, and hydrophilizing agents. Examples of electrostatic agents include metal soaps in which organic acids such as stearic acid, lauric acid, and ricinoleic acid form metal salts with metals such as Ca, Li, Zn, and Ba, as well as ionic surfactants such as acyl alkyl taurine salts, alkyl sulfonates, and quaternary ammonium salts. Examples of antioxidants include phenolic antioxidants, phosphite antioxidants, and thio antioxidants. Examples of neutralizing agents include higher fatty acid salts such as calcium stearate and zinc stearate. Examples of light stabilizers and UV absorbers include hindered amines, nickel complex compounds, benzotriazoles, and benzophenones. Examples of lubricants include higher fatty acid amides such as stearic acid amide. Examples of antistatic agents include fatty acid partial esters such as glycerin fatty acid monoesters. Examples of metal deactivators include phosphones, epoxies, triazoles, hydrazides, and oxamides. Examples of hydrophilizing agents include polyhydric alcohol fatty acid esters, ethylene oxide adducts, and nonionic surfactants such as amine anamides.

[0046] When the molten resin contains an additive, the content of the additive is preferably 0.5% by mass to 50% by mass, more preferably 1% by mass to 40% by mass, and even more preferably 3% by mass to 30% by mass, from the viewpoint of successful electrospinning. In other words, the molten resin used in the production of the nanofiber of the present invention is mainly composed of a thermoplastic resin.

[0047] The method for producing the molten resin is not particularly limited, and it can be produced, for example, by adding additives as necessary to a thermoplastic resin that has been heated and melted, and then heating and kneading them. Such a molten resin may be produced by melting and kneading the thermoplastic resin in advance as a master batch, or by supplying the thermoplastic resin and additives as necessary to a kneading device 20 during production, and then heating, melting, and kneading them in the kneading device 20.

[0048] In the above-described fiber manufacturing method, for convenience of explanation, a configuration using a single electrospinning apparatus 10 equipped with one spinning unit 30 has been described. However, the present invention is not limited to this configuration. Specifically, electrospinning may be performed using multiple electrospinning apparatuses 10 equipped with one spinning unit 30, or electrospinning may be performed using a single or multiple electrospinning apparatuses 10 equipped with multiple spinning units 30 (hereinafter, these configurations are collectively referred to as "multiple-arrangement configurations"). In particular, by arranging electrospinning apparatuses 10 or spinning units 30 in close proximity to each other and performing electrospinning in this state, even when the air volume B2 of the second gas flow is reduced, the temperature of the space around and in front of the nozzle 31 can be maintained high and the space can be expanded to a wider area. As a result, the cooling and solidification of the molten resin can be delayed, allowing for more effective production of small-diameter fibers. In addition, since fibers can be produced simultaneously using multiple spinning units 30, there is the advantage that the cost of supplying heated gas flows can be reduced while further improving fiber production efficiency.

[0049] The positions of the multiple electrospinning devices 10 or spinning units 30 can be selected appropriately depending on the production environment and the use of the fiber to be produced. For example, when the spinning unit 30 is viewed from the front, multiple spinning units 30 may be arranged in one row or multiple rows in one direction, or adjacent spinning units 30 may be arranged so that they are alternately positioned in front of and behind the conveying direction in the collection section.

[0050] Nanofibers or their deposits produced by electrospinning using the electrospinning apparatus 10 described above can be used for various purposes as fiber molded articles. Examples of the molded articles include sheets, cotton-like bodies, and filaments. The fiber molded articles may be laminated with other sheets or may contain various liquids, fine particles, fibers, and the like. Fiber sheets are suitable for medical purposes and non-medical purposes, such as cosmetic and decorative purposes, as sheets attached to human skin, teeth, gums, and hair, as well as to the skin, teeth, gums, and plant surfaces such as branches and leaves of non-human mammals. They are also suitable for use as high-performance filters with high dust collection and low pressure loss, battery separators capable of use at high current densities, and cell culture substrates with highly porous structures. Fiber cotton-like bodies are suitable for use as soundproofing materials, heat insulating materials, and the like.

[0051] Although the present invention has been described above based on its preferred embodiments, the present invention is not limited to these embodiments. For example, the electrode 32 in the device 10 of the above embodiment is cylindrical, but instead, as shown in Figure 7(a), it may be a rectangular tube that is arranged to surround the nozzle 31 along its circumferential direction. Alternatively, as shown in Fig. 7(b), a pair of semi-cylindrical electrodes 32', 32' may be combined to form a substantially cylindrical electrode, which may be used as an electrode. In this case, the pair of semi-cylindrical electrodes 32', 32' may be spaced apart as shown in the figure. Furthermore, when a pair of electrodes is used, each electrode does not need to be semi-cylindrical, and for example, as shown in FIG. 7(c), a pair of flat electrodes 32'', 32'' may be used. However, it is preferable to make the electrode 32 cylindrical, since this makes the distance between the electrode and the nozzle equal at any position when the nozzle is taken as the central axis, thereby increasing the charging efficiency.

[0052] Furthermore, the device 10 of the above embodiment has gas flow paths 40, 50 through which two types of gas flows, the first gas flow A and the second gas flow B, flow, but instead, the device 10 may have only a single gas flow path through which only the first gas flow A flows. Alternatively, in some cases, the device 10 may have a gas flow path through which another gas flow flows in addition to the gas flow paths 40, 50 through which the two types of gas flows, the first gas flow A and the second gas flow B, flow. [Explanation of symbols]

[0053] 10. Electrospinning device 31 nozzles 32 electrodes 35a Surface coating part 40 first gas flow path 40a First gas injection section 45 Covering material

Claims

1. a nozzle for discharging molten resin; an electrode for generating an electric field between the electrode and the nozzle; an electrospinning apparatus including a gas injection unit that injects a gas flow between the nozzle and the electrode, the electrode has an electrically insulating and heat-resistant surface coating portion disposed on a surface facing the nozzle, the surface coating portion is a laminated structure formed by laminating a plurality of coating materials, the coating material includes inorganic fibers, An electrospinning apparatus, wherein the coating material forms a layer in a direction intersecting a normal to the extension direction of the electrode.

2. The electrospinning apparatus according to claim 1 , wherein the electrodes are arranged to surround the nozzle in a circumferential direction thereof.

3. 3. The electrospinning apparatus of claim 1, wherein the electrode is cylindrical.

4. The electrospinning apparatus according to claim 1 , wherein the surface covering portion is disposed so as to surround the nozzle in a circumferential direction thereof.

5. 5. The electrospinning apparatus according to claim 1, wherein the electrode has an electrically insulating back surface coating on a surface opposite to the surface facing the nozzle.

6. the back surface covering portion is made of a laminated structure in which a plurality of covering materials are laminated, The electrospinning apparatus according to claim 5 , wherein a lamination direction of the coating material constituting the back surface coating portion and a lamination direction of the coating material constituting the front surface coating portion are the same.

7. 7. The electrospinning apparatus according to claim 1, further comprising an electrically insulating and heat-resistant sealing material disposed outside both ends of the electrode in the extending direction and at a position overlapping at least a projected image of the electrode when viewed from the extending direction.

8. The coating material is composed of a sheet body made of a material having electrical insulation properties and heat resistance, 8. The electrospinning apparatus according to claim 1, wherein the heat resistance means that the appearance of the coating material remains unchanged after being exposed to an environment of 200°C for 1 hour, and the dimensional change after being cooled to room temperature is within ±5%.

9. The electrospinning apparatus according to claim 1 , wherein the material other than the fibers that constitutes the coating material is an inorganic material.

10. A method for producing fibers by electrospinning using the electrospinning apparatus according to any one of claims 1 to 9.

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