WO2005042813A1

WO2005042813A1 - Electrostatic spinning equipment and method of preparing nano fiber using the same

Info

Publication number: WO2005042813A1
Application number: PCT/KR2004/002765
Authority: WO
Inventors: Sung-Chul Kim; Ki-Woo Park
Original assignee: Clean Air Technology Corp.
Priority date: 2003-10-30
Filing date: 2004-10-29
Publication date: 2005-05-12

Abstract

The present invention relates to an electrostatic spinning apparatus and a method for producing nanofibers using the same, and more particularly to an electrostatic spinning apparatus, which has the following advantages, as well as a method for producing nanofibers using the same: the generation of arc under high applied voltage between a nozzle and a collection electrode can minimized; mass production is possible; a film with a large width can be formed or a nonofiber surface with large width can be coated; a film with large width can be produced in one step; and discharge efficiency is increased so as to inlarge the spinning area of a polymer solution. In order to make the electrostatic spinning apparatus suitable for the mass production of nanofibers, the electrostatic spinning apparatus comprises an improved nozzle shape, a wire conductor, and a collection electrode coated with dielectric material.

Description

ELECTROSTATIC SPINNING EQUIPMENT AND METHOD OF PREPARING NANO FIBER USING THE SAME

Technical Field The present invention relates to an electrostatic spinning apparatus and a method for producing nanofibers using the same, and more particularly to an electrostatic spinning apparatus, which has the following advantages, as well as a method for producing nanofibers using the same: the generation of arc under a high voltage applied between a nozzle and a collection electrode can be minimized; a polymer solution is spun stably; sufficient electric force is applied to the polymer solution; the repulsive force between the polymer solution and the nozzle is maximized, thus making the mass production of nanofibers possible; the overall spinning area of fibers is increased such that a film with large width can be formed or a nanofiber film with large width can be coated; a film with large width can be produced in one step without repeated spinning operations, thus allowing the mass production of nanofibers with large width; discharge efficiency is increased so as to enlarge the spinning area of a polymer solution injected from an electrostatic spinning nozzle, so that a nanofiber film with large width can be formed while controlling the thickness of the film; and the electrostatic spinning apparatus is suitable for the mass production of nanofibers .

Background Art FIG. 1 shows a schematic diagram of an electrostatic spinning process. As shown in FIG. 1, electrostatic spinning is performed by applying strong electric field to a polymer solution or melt in a nozzle, bring the surface tension of the liquid and the electric stress into equilibrium with each other, and then deforming a liquid drop formed at the capillary end into a sharp conical shape while spinning the liquid. The fibers spun as described above are accelerated by electric field while becoming thin and unstable, so that they are collected in a discontinuous form onto the surface of an earthed metal, a collection electrode. Namely, if a polymer substance dissolved in a solution has low molecular weight, it will show a small particle form, and hence a process of producing fibers from such a substance is also called "electrostatic spraying"; however, if a polymer substance with high molecular weight is electrostatically spun, fibers with a very low diameter of about 100 nm will generally be obtained in the form of fibers having no orientation or regularity. Thus, such a process of obtaining fibers from the polymer substance with high molecular weight is called "electrostatic spinning" with distinction from the electrostatic spraying. In the case of the electrostatic spinning, however, high voltage is applied between a nozzle and a collection electrode, and thus, arc is frequently generated in which case there is a problem in that the discharge of high energy causes damages to nonofibers being produced by the prior process. Also, in a case where the nozzle undergoes a rotary or linear motion, it is necessary to maintain stability in the spinning of a polymer solution injected from the nozzle. Particularly, there is a need for studies on the cross-section shape of the nozzle tip, which, upon the rotary motion of the nozzle, can maintain stability in the spinning of the polymer solution while increasing the spinning area to the largest possible extent, but such studies are yet insufficient. Also, there is a problem in that the effect of electric force applied is reduced since the polymer solution is continuously fed into the nozzle applied with high voltage. Namely, the electric force becomes weak since the electric force applied to the nozzle is dispersed throughout the polymer solution, and a fresh polymer solution is continuously fed as electrostatic spraying progresses. This results in a reduction in the effect of electric force on fiber formation, thus making mass production difficult. In addition, there is a problem in that the effect of electric force applied is reduced since the polymer solution is continuously fed into the nozzle applied with high voltage. Namely, the electric force applied to the nozzle is dispersed throughout the polymer solution and a fresh polymer solution is continuously fed into the nozzle as electrostatic spraying progresses, and thus, the effect of the electric force on fiber formation is reduced to make mass production difficult, and the spinning area of the polymer solution becomes small. Accordingly, there is a further need for studies on an electrostatic spinning apparatus and method which can enlarge the spinning area of the polymer solution. Furthermore, the diameter of a spinning surface formed through one nozzle did not exceed a level of above 5-10 cm due to various problems, including limitations in allowable voltage, limitations in the interval between the nozzle and the collection electrode, and limitations in voltage which can be generated. Thus, by this small spinning area, a film with large width cannot be formed, making mass production difficult. Also in the case of coating a fiber layer with nanofibers, there is a problem in that the fiber layer should be coated in several steps, thus causing an increase in process time and a reduction in productivity. In order to solve such problems, a method for the production of nanofibers needs to be developed, by which the spinning of the polymer solution can be made uniformly on a fiber film with a large width of more than 1 m in one step, thus making the mass production of nanofiber films possible.

Disclosure of Invention Technical Problem Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and it is an object of the present invention to provide an electrostatic spinning nozzle with a right angle cross-section, which can minimize the generation of arc even under a high voltage applied between the nozzle and the collection electrode, spin a polymer solution stably even upon the movement or rotation of the nozzle, and increase the spinning area of a polymer solution, thus allowing the production of a nanofiber film with large width, as well as a method for producing a nanofiber film using the same. Another object of the present invention is to provide an electrostatic spinning nozzle including a wire, which minimizes the distance between a polymer solution and a charged body without influencing a process, so that the spinning of the polymer solution is easily made without causing a reduction in electric force, as well as a method for producing nanofibers using the same. Still another object of the present invention is to provide an electrostatic spinning nozzle including a wire, which provides sufficient electric force to a polymer solution and maximizes a repulsive force between a polymer solution and the nozzle, thus making mass production possible, as well as a method for producing nanofibers using the same. Still another object of the present invention is to provide an electrostatic spinning nozzle including a wire, which spins nanofibers uniformly in a straight direction such that the nanofibers have uniform thickness and are easily produced, as well as a method for producing nanofibers using the same. Still another object of the present invention is to provide an electrostatic spinning nozzle including a wire, which can minimize the generation of arc even under a high voltage applied between the nozzle and the collection electrode, spin a polymer solution stably even upon the movement or rotation of the nozzle, and enlarge the spinning area of the polymer solution, thus allowing the production of a nanofiber film with large width, as well as a method for producing nanofibers using the same. Still another object of the present invention is to provide an electrostatic spinning apparatus comprising a dielectric film-coated collection electrode, which can increase discharge efficiency so as to enlarge the spinning area of a polymer solution injected from an electrostatic spinning nozzle, thus allowing nanofibers with large width to be formed, as well as a method for producing nanofibers using the same. Still another object of the present invention is to provide an electrostatic spinning apparatus comprising a dielectric film-coated collection electrode, which can minimize the generation of arc even under a high voltage applied between the nozzle and the collection electrode, and maximize a repulsive force between the polymer solution and the nozzle so as to make mass production possible, as well as a method for producing nanofibers using the same. Still another object of the present invention is to provide an electrostatic spinning apparatus comprising a dielectric film-coated collection electrode, which can form a nanofiber film with large width and uniform thickness, as well as a method for producing nanofibers using the same. Still another object of the present invention is to provide a method for producing nanofibers, which can increase the overall spinning area of a polymer solution so as to form a film with large width or to coat a fiber surface with large width . Still another object of the present invention is to provide a method for producing nanofibers, which can produce a film with large width in one step without repeated spinning operations. Still another object of the present invention is to provide a method for producing nanofibers, which can minimize the generation of arc even under a high voltage applied between a nozzle and a collection electrode, spin a polymer solution stably even upon the movement or rotation of a nozzle, and enlarge the spinning area of a polymer solution so as to produce a nanofiber film with large width. Yet another object of the present invention is to provide a method for producing nanofibers, by which the spinning of a polymer solution can be easily made without a reduction in electric force so as to make their mass production possible, and nanofibers can be spun uniformly in a straight direction such that the nanofibers have uniform thickness and can be easily produced. Another further object of the present invention is to provide a method for producing nanofibers, in which the electric field between a nozzle and a collection electrode is uniformly formed^' so that the spinning of nanofibers is uniformly performed so as to make mass production possible.

Technical Solution To achieve the above objects, the present invention provides an electrostatic spinning nozzle in which the shape of the nozzle end is at a right angle to the nozzle hole. Also, the present invention provides an electrostatic spinning nozzle comprising a wire charged by the application of voltage, as well as a method for producing nanofibers using the same . Also, the present invention provides an electrostatic spinning apparatus comprising an electrostatic spinning nozzle and a collection electrode, in which the surface of the collection electrode is coated with a dielectric material. Also, the present invention provides a method for producing nanofibers using the electrostatic spinning apparatus. Also, the present invention provides nanofibers produced by said production method. Also, the present invention provides a method for the mass production of nanofibers, which comprises the steps of:

(a) feeding a polymer solution into at least two regularly arranged rotary spinners which are rotationally driven by a rotating device 30 and its driving unit 25 and include a plurality of electrostatic spinning nozzle holes in the lower side of each thereof, the nozzle holes being offset from the center of the rotating axis of the spinner; b) spinning the polymer solution through the electrostatic spinning nozzle which eccentrically rotates by the rotating device 30 and is applied with high voltage; and c) collecting the spun fibers on an earthed collection electrode placed below the nozzle.

Advantageous Effects According to the present invention, by the nozzle with a right angle cross section, the generation of arc can be minimized even under a high voltage applied between the nozzle and the collection electrode, and also a polymer solution can be spun stably even upon the movement or rotation of the nozzle. Also, according to an increase in spinning area and a reduction in arc generation by the use of the right-angled nozzle, the application voltage between the nozzle and the collection electrode can be further increased such that the distance therebetween can be increased so as to enlarge the spinning area of the polymer solution, and thus, nanofibers with large width can be produced. Accordingly, the rate of inferior products in mass production can be reduced and production cost can be saved. Moreover, by the construction of the electrostatic spinning nozzle including the wire, the distance between the polymer solution and the nozzle can be minimized without influencing a process, so as to supply sufficient electric force to the polymer solution and to maximize a repulsive force between the polymer solution and the nozzle. Thus, the problems of a reduction in fiber formation and difficult mass production can be solved, and the application of nanofibers with uniform thickness is possible by linearly arranged fine holes so as to produce an excellent nanofiber film. Also, the generation of arc can be minimized even under a high voltage applied between the nozzle and the collection electrode, and the polymer solution can be spun stably even upon the movement or rotation of the nozzle. Moreover, according to an increase in spinning area and a reduction in arc generation by the use of the right-angled nozzle, the application voltage between the nozzle and the collection electrode can be increased such that the distance therebetween can be extended so as to enlarge the spinning area of the polymer solution, and thus, a nanofiber film with large width can be produced. Accordingly, the rate of inferior products in mass production can be reduced and production costs can be saved. In addition, by the collection electrode comprising the dielectric layer, discharge efficiency can be increased so as to maximize the spinning area of the polymer solution injected from the electrostatic spinning nozzle, thus forming a nanofiber film with large width. Also, the generation of arc can be minimized under a high voltage applied between the nozzle and the collection electrode, and a repulsive force between the polymer solution and the nozzle can be maximized so as to make mass production possible, and also a nanofiber film with large width can be formed. Furthermore, in the electrostatic spinning apparatus according to the present invention, the distance between the polymer solution and the nozzle can be minimized without influencing a process, so as to supply sufficient electric force to the polymer solution, and a repulsive force between the polymer solution and the nozzle can be maximized. Also, the problems of a reduction in fiber formation and difficult mass production caused by a reduction in electric force can be solved to facilitate mass production, and the application of nanofibers with uniform thickness is possible by linearly arranged fine holes, thus producing an excellent nanofiber film. Moreover, the generation of arc can be minimized even under a high voltage applied between the nozzle and the collection electrode, and the polymer solution can be spun stably even upon the movement or rotation of the nozzle, and according to an increase in spinning area and a reduction in arc generation by the use of the right-angled nozzle, the application voltage between the nozzle and the collection electrode can be increased such that the distance therebetween can be increased so as to enlarge the spinning area of the polymer solution, thus producing a nanofiber film with large width. Accordingly, the rate of inferior products in mass production can be reduced and production cost can be saved. Also, while a prior nozzle shape is used without an increase in the spinning area of each of the nozzles, the spinning area of the polymer solution can be increased by the combination of the centrifugal force according to rotation and a plurality of dischargers, so that a film with large width can be formed or a fiber layer with large width can be coated. Also, if the inventive method is used for the production of large-width fiber films, the problem of the prior method in that spinning operation must be performed in several steps while moving a spinner in a little each step will be eliminated and a large-width film can be produced in one step. Thus, in the inventive method, since the film is produced in one-step operation, no overlapped portions exist in the film so as to make the film thickness uniform and to make the control of the film thickness easy, and production cost and fixed expenditure are very low. This makes the inventive method suitable for mass production. Also, by the right-angled nozzle, the generation of arc can be minimized even under a high voltage applied between the nozzle and the collection electrode, and the polymer solution can be spun stably even upon the movement or rotation of the nozzle. In addition, according to an increase in spinning area and a reduction in arc generation by the use of the right-angled nozzle, the application voltage between the nozzle and the collection electrode can be increased such that the distance therebetween can be increased so as to enlarge the spinning area of the polymer solution, and thus, a nanofiber film with large width can be produced. Accordingly, the rate of inferior products in mass production can be reduced and production cost can be saved.

Brief Description of Drawings FIG. 1 is a schematic system view of an electrostatic spinning process. FIG. 2 is a cross-sectional view of a general needle-type nozzle . FIG. 3 is a cross-sectional view of a right-angled, needle-type nozzle according to one embodiment of the present invention . FIG. 4 shows a rear view and cross-sectional view of a needle-type nozzle according to one embodiment of the present invention. FIG. 5 shows a rear view and cross-sectional view of a fine hole-type nozzle according to one embodiment of the present invention. FIG. 6 shows a rear view and cross-sectional view of a wire-type electrostatic spinning nozzle according to one embodiment of the present invention. FIG. 7 shows a rear view and cross-sectional view of a wire-type electrostatic spinning nozzle according to another embodiment of the present invention. FIG. 8 is a schematic diagram of an electrostatic spinning system according to one embodiment of the present invention . FIG. 9 shows an electrostatic spinning apparatus comprising a collection electrode having a dielectric layer, according to one embodiment of the present invention. FIG. 10 is a perspective view showing an electrostatic spinning nozzle module according to one embodiment of the present invention, in which the nozzles are arranged in a plurality of rows. FIG. 11 is a perspective view showing an electrostatic spinning module comprising a left and light movement device, according to one embodiment of the present invention. FIG. 12 is a schematic diagram of an electrostatic spinning system using a barrier discharge system, according to one embodiment of the present invention.

Best Mode for Invention Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. The present invention provides an electrostatic spinning nozzle for use in an electrostatic spinning apparatus, which characterized in that the shape of a nozzle end is at a right angle to a nozzle hole. As shown in FIG. 2, the cross-sectional shape of a general needle-type nozzle 10 is generally rounded at the end, in which case the above-mentioned problems occurred. The electrostatic spinning nozzle according to the present invention is characterized in that the nozzle end is at a right angle to the nozzle hole. In the inventive electrostatic spinning nozzle, the nozzle end is perpendicular to the nozzle hole, and the nozzle end is in parallel with a collection electrode. By the inventive electrostatic spinning nozzle, the electric field between the nozzle and the collection electrode can be uniformly developed, and the case where the distance between the two parts is shortened at local regions will not occur. An arcing phenomenon that can occur in the production of a nanofiber 45 can be minimized. Also, if the right-angled nozzles of FIG. 3 to 5 according to embodiments of the present invention are used, nozzles with the same shape can always be used in view of the shape control and standardization of the nozzles, so that variables can be reduced as compared to the general round-type nozzle. Thus, a polymer solution can be spun in a more stable manner. In the shape of the inventive electrostatic spinning nozzle, the end of the nozzle end is right-angled, and parts other than the nozzle end may have various shapes. As an example, as shown in FIG. 3, a needle-type nozzle 10 may be used. Moreover, as shown in FIG. 5, a fine hole-type nozzle may also be used which comprises a given volume of a body connected to the lower side of an electrostatic spinner 15 and blocked at the lower end, and fine holes 70 which are placed in the lower side of the body 65 and communicate the inside and outside of the body 65 with each other. Particularly, the body 65 and the electrostatic spinner 15 may be manufactured separately and then assembled with each other, or as shown in FIG. 8, may also be constructed an integral form where the electrostatic spinner 15 has nozzle holes at the lower side. In this case, some of the holes 70, which are close to the inner wall edge of the body 65, are preferably spaced apart from by a given distance from the inner wall of the body 65. Namely, if the fine holes 70 are too close to the edge of inner wall of the body 65, non-uniform spinning can occur due to the effect of interfacial energy between the inner wall of the body 65 and the polymer solution, and if they are too far away from the inner wall of the body 65, the spinning width of the polymer solution will be shortened to reduce productivity. For this reason, the holes 70 are preferably spaced apart by a given distance from the inner wall edge of the body 65. Furthermore, the fine hole-type nozzle may be constructed in a form where the fine holes 70 are 0.7-1.0 mm in diameter, and 4-6 mm spaced apart from the edge of the inner wall of the body 65, and the thickness of the lower side of the body is 4-6 mm. Preferably, the fine hole-type nozzle may be constructed in a form where they are 0.8 mm in diameter, and 3 mm spaced apart from the inner wall edge of the body 65, and the thickness of the lower side of the body is 3 mm. In such ranges, nanofibers with a diameter of 100-1000 nm can be spun stably. Also, the present invention provides an electrostatic spinning nozzle for use in the electrostatic spinning apparatus, which is characterized by including a wire 60 charged by the application of voltage. In this case, since voltage on the wire 60 and voltage on the nozzle or the body 65 are on an equipotential surface, the polymer solution spaced apart from the nozzle or the lower side of the body 65 can be strongly charged if it is close to the wires, thus preventing a reduction in the electric force of the polymer solution. Also, the number of the wires 60 included in the electrostatic nozzle may be one or two more. Specifically, as shown in FIGS. 6 and 7, the inventive nozzle including the wire may be constructed in a form where it comprises a given volume of a body 65 whose upper side is connected to the lower side of the electrostatic spinner 15 and whose lower side is blocked, and which includes linearly arranged holes 70 passed through the lower end, and a wire 60 which is in parallel with the row of the fine holes 70, and spaced apart upwards from the fine holes by a given distance, both ends of the wires being fixed to the inner wall surface of the body 65. Alternatively, the electrostatic spinning nozzle comprising the wire may be constructed in a form where it comprises: a given volume of the body 65 whose upper side is connected to the lower side of the electrostatic spinner 15 and whose lower side includes the linearly arranged fine holes 70 passed through the lower end; and the wire 60 which is in parallel with the arrangement of the fine holes 70 and spaced apart downwards from the fine holes 70, both ends of the wire being fixed to a protrusion extended downward from the edge of the lower end of the body. The nozzle and the electrostatic spinner 15 are either manufactured and assembled with each other, or manufactured in an integral form. The wire 60 should be placed above or below each of the linear arrangement of the fine holes 70 in such a manner that they correspond to the linear arrangement of the fine holes 70.

Namely, if the wire 60 is placed above the nozzle holes as shown in FIG. 6, both ends of the wire 60 may be fixed to the inner wall surface of the body 65 without a need for the formation of separate protrusions. If the wire 60 is placed below the nozzle holes as shown in FIG. 7, the circumferential edge of the body 65 may be extended to form a circumferential protrusion to which both ends of the wire 60 may be fixed.

Alternately, only at portions to which both ends of the wire are connected, fixing protrusions may be formed. The diameter of the wire 60 used in the electrostatic spinning nozzle may be selected in a range suitable for the purpose of a process, and it may be preferably 0.05-2 mm, and more preferably 0.1 mm. The wires with such a diameter range can hardly interfere with the spinning of the polymer solution, and can inhibit the arcing between the nozzle and the wire 60 and minimize a reduction in electric force. The wire 60 may be made of any conductive material, and preferably the same material as that of the nozzle, or copper with excellent conductivity, stainless steel with excellent corrosive resistance, etc. The nozzle form where the fine holes are formed through the lower side of the body 65 has many advantages over the needle-type nozzle 10. Namely, the needle-type nozzle 10 has problems in that its construction and assembling are difficult, and close attention to the protection of the needle in view of equipment management is required, and if the electrostatic spinner 15 moves in the left and right directions, the needle- type nozzle 10 will shake. In an attempt to solve such problems, the fine holes 70 are formed through the lower side of the spinner 15, or the nozzle with the fine holes 70 is coupled to the lower surface of the spinner 15, so that the nozzle which has the same construction as the needle-type nozzle 10 and at the same time, is solid, can be constructed. Also, this nozzle has a simple structure as compared to the nozzle-type needle and can be constructed in increased number. As shown in FIGS. 6 and 7 showing embodiments of the present invention, the end of the electrostatic spinning nozzle can be at a right angle to the nozzle hole. Namely, the nozzle end is perpendicular to the nozzle hole, and in parallel with a collection electrode. In this case, the electric field between the nozzle and the collection electrode 20 can be uniformly developed, and a case where the distance between the two parts is shortened at local regions will not occur. Thus, an arcing phenomenon that can occur in the production of the nanofibers 45 can be minimized. In addition, the right-angled nozzle is advantages in terms of the shape control and standardization of the nozzle, and FIG. 8 shows a perspective view of the rotary spinner 15. In this case, the electrostatic spinner 15 rotates while spinning the polymer solution, and upon the rotational spinning, the right-angled nozzle has the effect of increasing the spinning area of the polymer solution as compared to the general needle-type nozzle. This is because the polymer solution is directed outward by the centrifugal force according to the rotation of the nozzle, and at the same time, the corners of the nozzle and the polymer solution act with each other so that the polymer solution is directed outward as compared to the case of the general round-type nozzle. Moreover, the fine holes 70 formed through the lower side can be arranged in one row as shown in FIGS. 6 and 7. Alternatively, the fine holes may be arranged in the form of a plurality of linear rows which cross each other. Thus, the arrangement of the fine holes 70 may be in various configurations, such as a radial configuration and a network configuration, and thus, the wires 60 may be constructed in a form corresponding to the arrangement of the fine holes 70. Also, the number of the fine holes arranged in one row may vary depending on the cross-sectional area and shape of the spinner, uniform spinning and productivity, and the fine holes 70 may be arranged at a constant interval or so arranged that the interval between the holes becomes gradually narrower or wider toward the center of the lower side of the nozzle. The position of the fine holes 70 and their distance from the inner wall of the body 65, and their size, are the same as described for the angle-sided nozzle shown in FIG. 5. If the nozzle further includes the wire, the interval between the fine holes 70 may be selected from a wide range, and preferably 4-7 mm, and the distance between the wire 60 and the fine holes 70 may be 4-7 mm. More preferably, the interval between the fine holes may be 5 mm, and the distance between the wire 60 and the fine holes may be 5 mm. In such ranges, a more uniform spinning of the nanofibers 45 can be induced, the arcing between the nozzle and the wires 60 can be inhibited, and a reduction in electric force can be minimized. Furthermore, the present invention relates to an electrostatic spinning apparatus characterized by a collection electrode. During studies on a method capable of maximizing the repulsive force between the polymer solution and the nozzle so as to enlarge the spinning area of the polymer solution, the present inventors have found that, when a dielectric material is coated on the surface of a collection electrode, the spinning area of the polymer solution injected from the electrostatic spinning nozzle can be maximized such that a nanofiber film with large width can be formed. On the basis of this finding, the present invention has been perfected. The present invention provides an electrostatic spinning apparatus comprising an electrostatic spinning nozzle and a collection nozzle, which is characterized in that the surface of the collection electrode is coated with a dielectric material. As shown in FIG. 9, the electrostatic spinning apparatus comprises: a capillary-shaped electrostatic spinning nozzle 10 which is connected to a high-voltage feeder such that it is charged with high voltage; and a collection electrode 20 having a dielectric material 75 coated on a surface on which nanofibers 45 spun from the electrostatic spinning nozzle are collected. The dielectric material 75 used in the present invention may consist of a conventional dielectric material, and preferably urethane resin, heat-resistant synthetic resin, ceramic, silicone, polyimide resin or glass fiber. More preferred is urethane resin. The dielectric material 75 is coated on the surface of the collection electrode to a thickness of 0.1-5 mm, and preferably 1-3 mm. If the dielectric material is coated in this thickness range, the spinning area of the electrostatic spinning nozzle injected from the electrostatic spinning nozzle can be enlarged to increase discharge efficiency and to form the nanofiber film 45 with large width. The inventive electrostatic spinning apparatus comprising the collection electrode coated with the dielectric material 75 is 1.5-2 times larger in the width of spun nanofibers than that of the case of using a collection electrode uncoated with the dielectric material. Thus, the inventive apparatus is particularly suitable for the mass production of nanofibers. Also, the electrostatic spinning apparatus of the present invention comprises the electrostatic spinning nozzle 10 and the collection electrode 20 coated with the dielectric material 75. It is to be understood that the electrostatic spinning nozzle 10 may consist of a nozzle conventionally used in electrostatic spinning, and preferably consist of either the nozzle where the nozzle end is at a right angle to the nozzle hole, or the nozzle including a wire charged by the application of voltage. The specific practice and construction of the electrostatic spinning nozzle 10 are the same as described above. One embodiment thereof is as shown in FIG. 12. The present invention provides a method for producing nanofibers using the inventive electrostatic nozzle or apparatus. The nanofibers of the present invention include nanofibers in all media which can be molten or dissolved and electrostatically spun, and the present invention provides a method for producing nanofibers 45, which comprises electrostatically spinning a polymer solution by the above- described electrostatic nozzle or apparatus. Particularly if the electrostatic spinning apparatus comprising the electrostatic spinning nozzle 10 and the collection electrode coated with the dielectric material 75 is used to produce the nanofibers 45, the spinning area of the polymer solution injected from the electrostatic spinning nozzle 10 can be enlarged so as to increase discharge efficiency, and thus, nanofibers with large width can be produced. The polymer used in the present invention which is a raw material compound for the production of nanofibers, can be dissolved in solvents. As the polymer, all kinds of polymers which can be electrostatically spun can be used depending on the use purpose of nanofibers. If the nanofibers 45 are used in industrial applications, particularly air filters, the use of, for example, nylon, polyethylene, cellulose, etc., will be preferred in view of economic efficiency. Since the solvent in the polymer solution which is used in the present invention is sufficient if it is suitable to dissolve the polymer, it is obvious to a person skilled in the art that the solvent may be selected depending on the kind of the polymer. Particularly, the polymer solution preferably has a viscosity of 1000-5000 cps . This is because if the viscosity of the polymer solution is in said range, it will be easy to control the electrostatic spinning and morphology of nanofibers. The polymer solution is fed by a metering pump 35 into the electrostatic spinner 15 including the above-described electrostatic spinning nozzle, and the pressure in feeding the polymer solution can be controlled depending on the magnitude of voltage applied between the nozzle and the collection electrode 20, and generally controlled to 0.4-1.0 kg/cm². The polymer solution is electrostatically spun by the above-described electrostatic spinning method so as to produce the nanofibers 45 where fibers with a fine size of several nanometers are stacked and entangled with each other. In this case, the rotary spinner 15 shown in FIG. 8 rotates by itself so as to spin the nanofibers 45 over a wide range. Also, by the combination of a plurality of the spinners 15 or the left and right movements of the rotary spinner 15 itself, the nanofibers can be spun over a wide range. Also, the nanofibers 45 can be collected on the collection electrode 20 by the rotation of a roller, or heated or heated/pressed to form a film with large width. Alternatively, in order to form a coating layer on a film with large width, the fiber with large width is passed beneath the spinner 15 or the rotary spinner 15 while the nanofibers 45 are spun on the fiber, thus forming a coating on the fiber. As shown in FIG. 8 showing one embodiment of the present invention, the electrostatic spinning apparatus using the electrostatic spinning nozzle comprises, in addition to the nozzle, a storage container 40 for storing the polymer solution, a rotary spinner 15, a metering pump 35 for feeding a given amount of the polymer solution into the spinner, a rotating device 30, a unit 25 for driving the rotating device, a high voltage generator for applying high potential to the polymer solution, an earthed collection electrode 20, and a rotating roller for the continuous production of a fiber film, which is placed around the collection electrode. In this case, a given flow rate of the polymer solution is fed from the storage container by a metering pump 35 into the rotary or non-rotary spinner 15, and when high voltage is applied between the nozzle and the collection electrode 20 by the high voltage generator, the polymer solution can be spun from electrostatic spinning nozzle. If necessary, when the rotating device is driven by the rotating device-driving unit 25, the spinner can be rotated to spin the polymer solution over a wider region, and for the continuous production of a nanofiber film, winding rollers may also be included such that the fiber film can continuously pass over the collection electrode 20. FIG. 8 is a perspective view of the rotary spinner with the needle-type nozzle 10 according to one embodiment of the present invention. The rotary spinner 15 with the right-angled nozzle rotates while spinning the polymer solution, and upon the rotational spinning, the right-angled nozzle of the present invention has the effect of remarkably increasing the spinning area of the polymer solution as compared to the general nozzle. This is because the polymer solution is directed outward by the centrifugal force while the corner of the nozzle and the polymer solution act on each other, so that the polymer solution is directed outward as compared to the case of the general round-type nozzle. Also, the present invention provides a method for producing nanofibers using the electrostatic spinning apparatus, particularly a method for producing nanofibers with large width. Namely, the present invention provides a method for the mass production of nanofibers, which comprises the steps of: (a) feeding a polymer solution into at least two regularly arranged rotary spinners which are rotationally driven by the rotating device 30 and its driving unit 25 and include a plurality of electrostatic spinning nozzle holes at the lower side of each thereof, the nozzle holes being offset from the center of the rotating axis of the spinners; (b) spinning the polymer solution through the electrostatic spinning nozzles which are eccentrically rotated by the rotating device 30 and applied with high voltage; and (c) collecting the spun fibers on the earthed collection electrode 20 placed below the nozzles. As shown in FIG. 8, the rotary spinner 15 comprises the rotating device 30 and the driving unit 25 for driving the rotating device 30. In order to increase the spinning area of the nanofibers 45 formed on the collection electrode 20 by the spinning of the polymer solution, the spinner 15 including a plurality of the nozzles needs to be rotated, and for this purpose, the rotating device 30 capable of rotating the spinner 15, and its driving unit 25, are required. Examples of the rotating device 30 may include a union structure, and as the rotation-driving unit, various driving units such as DC or AC motors may be used. Also, in order to control the rotational speed of the rotating device, the electrostatic spinning system may further comprise a driving control unit. The rotating device 30 is connected to the rotary spinner 15 such that the spinner 15 can be rotated on itself. Namely, by the centrifugal force generated by the rotating movement of the rotary spinner, the polymer solution spun from the nozzle is spun over a wider range, thus achieving the above purpose. For the greatest possible utilization of the centrifugal force, position of the nozzle is preferably spaced as far as possible from the central axis of the rotary spinner 15. Thus, to maximize the generation of the centrifugal force, the lower side of the rotary spinner 15 preferably has a circular shape. Through the lower circular end of the rotary spinner 15, a plurality of nozzle holes may be formed. Particularly the number of the nozzle holes formed through the lower end may be 4-16 in view of spinning area and uniform spinning. It will be understood that, for the nozzle on the lower end of the spinner 15, the integral-type nozzle as shown in FIG. 5 or the needle-type nozzle as shown in FIG. 4, and in addition to this, the wire-containing nozzle or the right-angled section nozzle as described above, may be applied. Also, the rotary spinners 15 may be arranged in various configurations so as to increase production efficiency. Namely, if a plurality of the rotary spinners 15 are arranged in one row, a nanofiber film with large width can be formed, and if a plurality of the rotary spinners 15 are arranged in a plurality of rows, the formation of nanofibers can be made in a faster time, such that the speed of rollers adjacent the collection electrode 20 can be increased, thus increasing productivity. In one embodiment of the arrangement of plural rows, the rotary spinners 15 are arranged two rows in which, in the first row, N rotary spinners are arranged at a constant interval, and in the second row, N-l rotary spinners are arranged alternately with those of the first row. Alternatively, N-l rotary spinners are arranged in the first row and N rotary spinners are arranged in the second row. As this embodiment, FIG. 10 shows that five rotary spinners are arranged alternately with each other. This arrangement has advantages in that the spinning of the polymer solution can be made uniformly over the entire area, and a process can be performed in a short time. In addition to the one row or plural row arrangement of the rotary spinners 15, the electrostatic spinning apparatus comprises, as shown in FIG. 11 showing an alternative to the arrangement of a plurality of the rotary spinners 15, a left and right movement device for moving the rotary spinner in the left and right directions, and a unit for driving the left and right movement device, such that the rotary spinner can move in the left and right directions while spinning the polymer solution. This makes it possible to form a fiber layer with large area, and to control the span of movement stroke of the rotary spinner, thus producing a fiber layer or film with necessary area. It will be understood that this movement device can be applied also in the electrostatic spinning apparatus comprising a plurality of the rotary spinners. For this purpose, the electrostatic spinning apparatus may be constructed by use of a conventional left and right movement device . Also, the rotary spinner 15 shown in FIG. 8 can utilize either the combination of a plurality of the spinners or the left and right movements of the rotary spinner itself, and also utilize the combination of plural spinners along with the left and right movement of the rotary spinner itself, thus spinning the nanofibers 45 over a wide range. In addition to the construction as described above, the electrostatic spinning apparatus may comprise, as shown in FIG. 8 showing one embodiment thereof, a storage container 40 for storing the polymer solution, a metering pump 35 for feeding a given amount of the polymer solution into the spinner, a high voltage generator for providing high potential to the polymer solution, and rotating rollers for the continuous production of fibers, which are placed near the collection electrode. Also, for the uniform and wide spinning of the nanofibers 45, the electrostatic spinning apparatus may further comprise a dielectric layer 75 as a discharge barrier on the collection electrode. Namely, by adding the dielectric layer, an electric field in the form of arc discharge in a case with no dielectric layer is changed to an electric field in the form of barrier discharge, thus making the uniform and wide spinning of fibers possible . It is to be understood that the dielectric layer used in the present invention may be made of a conventional dielectric material. The dielectric layer may preferably be made of urethane resin, heat-resistant synthetic resin, ceramic, silicone, polyimide resin or glass fiber. More preferably, the dielectric layer may be made of urethane resin. The dielectric material is preferably coated on the surface of the collection electrode to a thickness of 0.1-5 mm, and preferably 1-3 mm. The electrostatically spun nanofibers 45 are collected on the earthed collection electrode 20 disposed below the nozzle, and for the production of a fiber film, the nanofibers 45 collected on the collection electrode 20 is collected by the rotation of rollers, and the collected film can be heated or heated/pressed so as to form a fabric with large width. Also, to form a coating layer on a fiber with large width, the large- width fabric is passed beneath the rotary spinner at a constant speed by rollers while the nanofibers 45 are spun on the fabric, thus forming a coating layer on the fabric. In addition, the present invention provides nanofibers produced by the above-described method for producing nanofibers. Thus, large-width nanofibers, nanofiber-coated layers or nanofiber non-woven fabrics may be obtained with excellent quality.

Industrial Applicability According to the present invention, by the nozzle with a right angle cross section, the generation of arc can be minimized even under a high voltage applied between the nozzle and the collection electrode, and also a polymer solution can be spun stably even upon the movement or rotation of the nozzle. Also, according to an increase in spinning area and a reduction in arc generation by the use of the right-angled nozzle, the application voltage between the nozzle and the collection electrode can be further increased such that the distance therebetween can be increased so as to enlarge the spinning area of the polymer solution, and thus, nanofibers with large width can be produced. Accordingly, the rate of inferior products in mass production can be reduced and production cost can be saved. Moreover, by the construction of the electrostatic spinning nozzle including the wire, the distance between the polymer solution and the nozzle can be minimized without influencing a process, so as to supply sufficient electric force to the polymer solution and to maximize a repulsive force between the polymer solution and the nozzle. Thus, the problems of a reduction in fiber formation and difficult mass production can be solved, and the application of nanofibers with uniform thickness is possible by linearly arranged fine holes so as to produce an excellent nanofiber film. Also, the generation of arc can be minimized even under a high voltage applied between the nozzle and the collection electrode, and the polymer solution can be spun stably even upon the movement or rotation of the nozzle. Moreover, according to an increase in spinning area and a reduction in arc generation by the use of the right-angled nozzle, the application voltage between the nozzle and the collection electrode can be increased such that the distance therebetween can be extended so as to enlarge the spinning area of the polymer solution, and thus, a nanofiber film with large width can be produced. Accordingly, the rate of inferior products in mass production can be reduced and production costs can be saved. In addition, the collection electrode comprising the dielectric layer enables discharge efficiency to be increased so as to maximize the spinning area of the polymer solution injected from the electrostatic spinning nozzle, thus forming a nanofiber film with large width. Also, the generation of arc can be minimized under a high voltage applied between the nozzle and the collection electrode, and a repulsive force between the polymer solution and the nozzle can be maximized so as to make mass production possible, and also a nanofiber film with large width can be formed. Furthermore, in the electrostatic spinning apparatus according to the present invention, the distance between the polymer solution and the nozzle can be minimized without influencing a process, so as to supply sufficient electric force to the polymer solution, and a repulsive force between the polymer solution and the nozzle can be maximized. Also, the problems of a reduction in fiber formation and difficult mass production caused by a reduction in electric force can be solved to facilitate mass production, and the application of nanofibers with uniform thickness is possible by linearly arranged fine holes, thus producing an excellent nanofiber film. Moreover, the generation of arc can be minimized even under a high voltage applied between the nozzle and the collection electrode, and the polymer solution can be spun stably even upon the movement or rotation of the nozzle, and according to an increase in spinning area and a reduction in arc generation by the use of the right-angled nozzle, the application voltage between the nozzle and the collection electrode can be increased such that the distance therebetween can be increased so as to enlarge the spinning area of the polymer solution, thus producing a nanofiber film with large width. Accordingly, the rate of inferior products in mass production can be reduced and production cost can be saved. Also, while a prior nozzle shape is used without an increase in the spinning area of each of the nozzles, the spinning area of the polymer solution can be increased by the combination of the centrifugal force according to rotation and a plurality of dischargers, so that a film with large width can be formed or a fiber layer with large width can be coated. Also, if the inventive method is used for the production of large-width fiber films, the problem of the prior method in that spinning operation must be performed in several steps while moving a spinner in a little each step will be eliminated and a large-width film can be produced in one step. Thus, in the inventive method, since the film is produced in one-step operation, no overlapped portions exist in the film so as to make the film thickness uniform and to make the control of the film thickness easy, and production cost and fixed expenditure are very low. This makes the inventive method suitable for mass production. Also, by the right-angled nozzle, the generation of arc can be minimized even under a high voltage applied between the nozzle and the collection electrode, and the polymer solution can be spun stably even upon the movement or rotation of the nozzle. In addition, according to an increase in spinning area and a reduction in arc generation by the use of the right-angled nozzle, the application voltage between the nozzle and the collection electrode can be increased such that the distance therebetween can be increased so as to enlarge the spinning area of the polymer solution, and thus, a nanofiber film with large width can be produced. Accordingly, the rate of inferior products in mass production can be reduced and production cost can be saved. Although a preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

What Is Claimed Is :

1. An electrostatic spinning nozzle in which the shape of the nozzle end is at a right angle to the nozzle hole.

2. The electrostatic spinning nozzle of Claim 1, which is a needle-type nozzle.

3. The electrostatic spinning nozzle of Claim 1, which comprises: a given volume of a body whose upper side is connected to the lower side of a spinner and whose lower side is blocked; and a fine hole which is formed in the lower side of the body and communicates the inside and outside of the body with each other.

4. An electrostatic spinning nozzle comprising a wire charged by the application of voltage.

5. The electrostatic spinning nozzle of Claim 4, which comprises: a given volume of a body whose upper side is connected to the lower side of an electrostatic spinner and whose lower side is blocked, the body including linearly arranged fine holes passed through the lower side thereof; and a wire which is in parallel with the arrangement of the fine holes and spaced upwards from the fine holes by a given distance, both ends of the wire being fixed to the inner wall side of the body.

6. The electrostatic spinning nozzle of Claim 4, which comprises: a given volume of a body whose upper side is connected to the lower side of an electrostatic spinner and whose lower side is blocked, the body including linearly arranged fine holes passed through the lower side thereof; and a wire which is in parallel with the arrangement of the fine holes and downwards spaced apart from the fine holes by a given distance, both ends of the wire being fixed to a protrusion extending downwards from the circumferential edge of the lower side of the body.

7. The electrostatic spinning nozzle of Claim 5 or 6, wherein the shape of the nozzle end is at a right angle to the nozzle hole.

8. The electrostatic spinning nozzle of Claim 3, 5 or 6, wherein the fine holes are 0.7-1.0 mm in diameter, and 4-6 mm spaced apart from the inner edge of the body, and the thickness of the lower side of the body is 4-6 mm.

9. The electrostatic spinning nozzle of Claim 5 or 6, wherein the wire has a thickness of 0.05-0.2 mm.

10. An electrostatic spinning apparatus comprising an electrostatic spinning nozzle and a collection electrode, wherein the surface of the collection electrode is coated with a dielectric material.

11. The electrostatic spinning apparatus of Claim 10, wherein the dielectric material is at least one selected from the group consisting of urethane resin, heat-resistant synthetic resin, ceramic, silicone, polyimide resin, and glass fiber .

12. The electrostatic spinning apparatus of Claim 10, wherein the dielectric material is coated on the surface of the collection electrode to a thickness of 0.1-5 mm.

13. The electrostatic spinning apparatus of Claim 10, wherein the electrostatic spinning nozzle is the electrostatic spinning nozzle of any one of Claims 1 to 9.

14. A method for producing nanofibers using the electrostatic spinning nozzle of any one of Claims 1 to 9.

15. A method for producing nanofibers using the electrostatic spinning apparatus of any one of Claims 10 to 13.

16. A method for producing nanofibers with large width, which comprises the steps of: a) feeding a polymer solution into at least two regularly arranged rotary spinners which are rotationally driven by a rotating device and its driving unit and include a plurality of electrostatic spinning nozzle holes in the lower side of each thereof, the nozzle holes being offset from the center of the rotating axis of the spinners; b) spinning the polymer solution through the electrostatic spinning nozzle which eccentrically rotates by the rotating device and is applied with high voltage; and c) collecting the spun fibers on an earthed collection electrode placed below the nozzle.

17. The method of Claim 16, wherein the upper side of the rotary spinner is circular in shape, the nozzle holes consist of 1-16 nozzle holes which are spaced apart inwards from the edge of the lower side of the spinner by a given distance.

18. The method of Claim 16, wherein the electrostatic spinning nozzle is the electrostatic spinning nozzle of any one of Claims 1 to 9.

19. The method of Claim 16, wherein the rotary spinners are arranged in two rows in which in the first row, N rotary spinners are arranged at a constant interval, and in the second row, N-l rotary spinners are arranged alternately with the spinners of the first row.

20. The method of Claim 16, which further comprises, in the step b) , moving the rotary spinners in the left and right directions .

21. The method of Claim 16, wherein, in the electrostatic staining of the step b) , the collection electrode further comprises a dielectric layer formed thereon.