METHOD OF MANUFACTURING EXTERNAL ELECTRODE

FLUORESCENT LAMPS HAVING VARIOUS SHAPES AND

SIZES AND GLASS TUBE UNIT STRUCTURE USED FOR THE

METHOD Technical Field [1] The invention relates to a fluorescent lamp, and more particularly to a method of manufacturing external electrode fluorescent lamps having diverse shapes and sizes. Background Art [2] An external electrode fluorescent lamp (EEFL) is a fluorescent lamp having such a structure that a gas is fed into an enclosed glass tube and then electrodes are formed on both external ends of the tube so as to carry out a gas discharge operation without exposing the electrodes to a gas discharge space and thus to generate a plasma in the tube by electric fields of the external electrodes. The gas discharge phenomenon occurring in the tube is same as a general lamp. However, the glass tube itself serves as a dielectric and thus there occurs a voltage gain because wall charges are added by ac¬ cumulations of spatial charges, which occur due to a pre-discharge preceding an external voltage to be applied so as to induce the gas discharge. [3] The external electrode fluorescent lamp is a next-generation illumination lamp having following advantages; since the electrode is positioned outside the lamp and an electron emission method by the electric field is used, there occurs less heat, a life span of the lamp is longer than a general fluorescent lamp by five times or more, a brightness is about ten times higher and it has an energy efficiency higher than a cold cathode fluorescent lamp (CCFL) by five times or more. Further, The EEFL can drive a plurality of tubes with another driving device, so that it is much used in applications requiring a high brightness, such as LCD TV, signboard and the like. [4] In the mean time, a baking process is performed as a process of removing impurities, moisture and other foreign substances during the manufacture of the EEFL. At this time, a heater box is typically used to carry out the baking process. [5] The heater box is useful to manufacture a fixed form of EEFL. However, as uses of the EEFL are diversified, there occur many problems. Specifically, the EEFL is widely used for signboards having various shapes as well as LCD. However, the signboard in character does not have a fixed shape. Instead, it is often desired to express diverse characters or pictures on the signboard depending on the use aspects. Correspondingly, the EEFL should be also manufactured to have diverse shapes and sizes. [6] However, the heater box is adapted to manufacture an external electrode fluorescent lamp having specific shape and size, for example, a linear fluorescent lamp, in succession and performs the baking operation two times. Specifically, for example, impurities of powders are primarily removed at high temperatures of 600~700°C and remaining air, foreign substances, moisture and the like are then removed in a next secondary baking operation. However, the EEFL used for the signboard has various shapes and sizes, so that there are often many bends in the EEFL. In this case, if a shape of a glass tube for the EEFL is not precisely formed to have a same thickness, a thinner part is depressed or a whole shape is distorted during the secondary baking operation of a high temperature, although the secondary high temperature is lower than the temperature of the primary baking operation. In addition, when the glass tube enters the heater box once, it is difficult to prevent the above problems since it is impossible to observe the baking operation for the glass tube from the outside. As a result of that, it is impossible to perform the baking operation with precise control. Ac¬ cordingly, since it is difficult to precisely control the glass tube having entered the heater box, an operator should accurately shape the glass tube of an arbitrary form so that the tube has a regular thickness, before putting the glass tube in the heater box. [7] In addition, since the heater box has a fixed size rather than a variable size, it can treat only a glass tube capable of entering the heater box. Thereby, when manu¬ facturing an external electrode fluorescent lamp having a size larger than the heater box depending on the applications, such as EEFL for the signboard, the heater box c annot be used, so that a heater box adapted to the EEFL having desired shape and size should be separately provided or a size of the EEFL should be adapted to the definite size of the heater box. Accordingly, there is a limitation in the manufacturing of a single EEFL having a desired size. This can cause a manufacturing cost to be increased. [8] Additionally, there is an attempt to use the plasma for the manufacturing of the EEFL without the heater box. However, this method has following disadvantages. [9] An apparatus and a method for carrying out the baking operations using the plasma are adapted to manufacture a linear external electrode fluorescent lamp such as normal fluorescent lamp, so that it is difficult to manufacture EEFLs having various shapes and sizes used for a signboard. [10] In addition, according to the prior art, it should be performed an operation of removing a glass tube including an internal electrode for generating plasma from a main body of the EEFL using heat of a high temperature, such as torch. At this time, expansion and shrinkage are repeated at a welded part of the two glass tubes, so that the glass is depressed into the main body of the EEFL. Additionally, when removing the glass tube, a considerable attention should be paid to the removal operation due to a high pressure difference between the interior and exterior of the glass tube. The shape and thickness of the depressed part are irregular, thereby exerting a bad influence on a durability of the EEFL. In addition, many difficulties are accompanied to remove a trace of the depressed part, so that it is required a high degree of technical skill. As a diameter of the glass main body of the EEFL is increased, the above disadvantages are also increased. Accordingly, it is the real situation that the above prior art is not com¬ mercialized. Disclosure of Invention Technical Problem [11] Accordingly, the present invention has been made to solve the above problems. An object of the invention is to provide a method of manufacturing external electrode fluorescent lamps having diverse shapes and sizes, allowing an operator to easily manufacture the EEFL irrespective of the shape or size of the lamp and being capable of manufacturing the EEFL without adopting each of heater boxes to correspond the shape and size of each of the lamps. [12] Another object of the invention is to simply manufacture an external electrode fluorescent lamp (EEFL) by providing a glass tube including an internal electrode for generating plasma for a baking operation of the lamp as a single unit structure, as well as not to use the heater box when manufacturing a fluorescent lamp, especially the EEFL. [13] Still another object of the invention is to provide a method of manufacturing an EEFL using plasma without the heater box, capable of manufacturing the EEFLs having diverse shapes and sizes without influencing on shape, thickness and external appearance of a glass main body of the EEFL when removing a separate glass tube including an internal electrode for generating plasma from the main body of the EEFL. Technical Solution [14] The inventor studied means capable of substituting the heater box so as to achieve the objects. As a result of the study, the inventor accomplished the present invention of carrying out a baking operating using a plasma principle rather than the existing heater box and thus manufacturing the EEFL through an existing apparatus without adding a new separate apparatus. [15] In other words, in order to achieve the objects, there is provided a method of manu¬ facturing an external electrode fluorescent lamp (EEFL), the method comprising steps of: (a) providing a glass tube body having both ends opened, formed to have a shape and a size corresponding to a final use of the EEFL, and having an inner wall coated with a fluorescent material except a region to which an external electrode is to be formed; (b) welding second glass tubes to the both ends of the glass tube body, each of the second glass tubes including an internal electrode for generating plasma therein; (c) performing an operation of reducing a tube diameter adjacent to the welded part of the glass tubes; (d) connecting an exhaust pipe to the welded body of the glass tube body and the glass tubes; (e) vacuumizing an inside of the welded body to a certain level through an exhaust apparatus connected to the exhaust pipe; (f) generating plasma in the welded body through a plasma generating apparatus connected to the internal electrodes for generating plasma, thereby baking the inside of the welded body; (g) exhausting air and impurities remaining in the welded body and introducing a pre¬ determined amount of inert gas into the welded body; (h) removing the internal electrode and the exhaust pipe; and (i) forming an external electrode on the glass tube. [16] Accordingly, according to the invention, as the plasma generating apparatus connected to the internal electrodes is operated, the plasma is formed in the glass tube and thus the impurities of the powder and other foreign substances in the glass tube are burned and then exhausted. As a result of that, it is possible to remove the impurities and the foreign substances by the single baking operation only, compared to the prior art, so that the existing heater box is substituted. Accordingly, since it is not necessary to adopt the heater box, it is possible to remove the impurities and the like in the glass tube using the plasma principle, even though the EEFL is formed to have any shapes and sizes. In addition, after the baking operation, only if the internal electrode for generating plasma is removed and the external electrode is formed on the glass tube according to the typical process of manufacturing the EEFL, it is possible to manufacture an EEFL having desired shape and size. Additionally, by performing the operation of reducing a tube diameter, it is possible to prevent the depression of the glass tube due to a pressure difference between the interior and exterior of the glass tube, when separating the glass tube. [17] According to an embodiment of the invention, an inner wall of the second glass tube may be not coated with a fluorescent material or may be coated with a fluorescent material at the inner wall region except the welded part with the glass tube body. [18] According to an embodiment of the invention, the second glass tubes may be welded to both ends of the glass tube body in a manner of welding one of the second glass tubes including the internal electrode for generating plasma therein to one end of the glass tube body, forming an aperture by blowing air through the other opened end of the glass tube body to connect the exhaust pipe to the aperture, and welding the other of the second glass tubes including the internal electrode for generating plasma therein to the other end of the glass tube body. [19] Preferably, the exhaust pipe may be connected to the second glass tube near the position in which the internal electrode for generating plasma is located. [20] According to a preferred embodiment of the invention, the exhaust pipe and the internal electrode may be simultaneously removed from the glass tube body by cutting the shaped part of the reduced diameter. [21] According to another embodiment of the invention, there is provided a method of manufacturing an external electrode fluorescent lamp (EEFL), the method comprising steps of: (a) providing a glass tube body having both ends opened, formed to have a shape and a size corresponding to a use of the EEFL, and having an inner wall coated with a fluorescent material except parts of the inner wall adjacent to the both ends; (b) welding a pair of second glass tubes, each of which having an blind end, to both ends of the glass tube body, respectively, and then bending-forming the second glass tubes to be parallel with the glass tube body; (c) connecting a pair of third glass tubes, each of which including an internal electrode for generating plasma therein and having a connecting part with a diameter smaller than that of the third glass tube, to the second glass tubes in a vertical relation so as to communicate with the second glass tubes, re¬ spectively; (d) connecting an exhaust pipe to any one of the third glass tubes to vacuumize an inside of the welded body of the glass tubes and the tube body to a certain level; (e) generating plasma in the welded body through a plasma generating apparatus connected to the internal electrodes for generating plasma, thereby baking the inside of the welded body; (f) exhausting air and impurities remaining in the welded body; (g) introducing a predetermined amount of inert gas into the welded body through the exhaust pipe; (h) removing the third glass tubes including the internal electrodes and the exhaust pipe. [22] According to an embodiment of the invention, the method may further comprise a step of forming an external electrode on a surface of the second glass tube after the step of (h). [23] According to a preferred embodiment of the invention, the second glass tube may comprise an external electrode on a surface thereof. [24] According to another embodiment of the invention, there is provided a method of manufacturing an external electrode fluorescent lamp (EEFL), the method comprising steps of: (a) providing a glass tube body having both ends opened, formed to have a shape and a size corresponding to a use of the EEFL, and having an inner wall coated with a fluorescent material except parts of the inner wall adjacent to the both ends; (b) welding a pair of second glass tubes, each of which having an blind end, to both ends of the glass tube body, respectively, and then bending-forming the second glass tubes to be parallel with the glass tube body; (c) connecting third and fourth glass tubes, each of which including an internal electrode for generating plasma therein and having a connecting part with a first diameter smaller than those of the third and fourth glass tubes, to the non-coated second glass tubes in a vertical relation so as to communicate with the non-coated second glass tubes, respectively; (d) connecting an exhaust pipe to the third glass tube to vacuumize an inside of the welded body of the tube body and the glass tubes to a certain level; (e) generating plasma in the welded body through a plasma generating apparatus connected to the internal electrodes for generating plasma, thereby baking the inside of the welded body; (f) exhausting air and impurities remaining in the welded body; (g) primarily introducing a predetermined amount of inert gas into the welded body through the exhaust pipe; (h) removing the fourth glass tube having no exhaust pipe connected thereto from the second glass tube and reducing the first diameter of the connecting part of the third glass tube to a second diameter smaller than the first diameter; (i) exhausting the inert gas while keeping only the amount of the inert gas for a lamp discharge; and (j) removing the third glass tube from the second glass tube. [25] According to a preferred embodiment of the invention, the inert gas may be introduced so that an inner pressure of the welded body is smaller than an atmospheric pressure by a few Torr in the step of (g). [26] Preferably, the step of (i) may further comprise steps of further exhausting the inert gas completely and secondarily introducing a predetermined amount of inert gas for a lamp discharge. [27] According to another embodiment of the invention, there is provided a method of manufacturing an external electrode fluorescent lamp (EEFL), the method comprising steps of: (a) providing a glass tube body having both ends opened, formed to have a shape and a size corresponding to a use of the EEFL, and having an inner wall coated with a fluorescent material except parts of the inner wall adjacent to the both ends; (b) welding first and second unit structured glass tubes, each of which comprising a second glass tube including an internal electrode for generating plasma therein and having a connecting part with a first diameter smaller than that of the second glass tube and a third glass tube having a blind end and connected to the second glass tube in a vertical relation so as to communicate with the second glass tube via the connecting part, to both ends of the glass tube body, respectively, and then bending-forming the first and second unit structured glass tubes to be parallel with the glass tube body; (c) connecting an exhaust pipe to any one of the second glass tubes to vacuumize an inside of the welded body of the glass tubes and the tube body to a certain level; (d) generating plasma in the welded body through a plasma generating apparatus connected to the internal electrodes for generating plasma, thereby baking the inside of the welded body; (e) exhausting air and impurities remaining in the welded body; (f) primarily introducing a predetermined amount of inert gas into the welded body through the exhaust pipe; (g) removing the second glass tube having no exhaust pipe connected thereto from the third glass tube and reducing the first diameter of the connecting part of the second glass tube having the exhaust pipe connected thereto to a second diameter smaller than the first diameter; (h) exhausting the inert gas while keeping only the amount of the inert gas for a lamp discharge; and (i) removing the glass tube having the exhaust pipe connected thereto from the non-coated glass tube. [28] According to a preferred embodiment of the invention, the method may further comprise a step of forming an external electrode on a surface of the third glass tube after the step of (i). [29] Preferably, the third glass tube may comprise an external electrode on a surface thereof. [30] According to another embodiment of the invention, there is procvided a method of manufacturing an external electrode fluorescent lamp (EEFL), the method comprising steps of: (a) providing a glass tube body having both ends opened, formed to have a shape and a size corresponding to a use of the EEFL, and having an inner wall coated with a fluorescent material except parts of the inner wall adjacent to the both ends; (b) welding unit structured glass tubes, each of which consisting of a first glass tube section including an internal electrode for generating plasma therein and a second glass tube section to be welded to the glass tube body, to both ends of the coated glass tube body, respectively; (c) connecting an exhaust pipe to any one of the unit structured glass tubes including the internal electrode to vacuumize an inside of the welded body of the glass tubes and the tube body to a certain level; (d) generating plasma in the welded body through a plasma generating apparatus connected to the internal electrodes for generating plasma, thereby baking the inside of the welded body; (e) exhausting air and impurities remaining in the welded body and introducing a pre¬ determined amount of inert gas into the welded body; and (f) removing the first glass tube section including the internal electrode and the exhaust pipe. [31] Preferably, a part between the first and second glass tube sections may be formed to have a reduced diameter. [32] According to a preferred embodiment of the invention, the first glass tube section may be removed by cutting the part of reduced diameter. [33] The exhaust pipe may be preferably connected to the first glass tube section. [34] According to another embodiment of the invention, there is provided a method of manufacturing an external electrode fluorescent lamp (EEFL), the method comprising steps of: (a) providing a glass tube body formed to have a shape and a size cor¬ responding to a use of the EEFL and having an inner wall coated with a fluorescent material; (b) arranging unit structured glass tubes, each of which consisting of a first glass tube section including an internal electrode for generating plasma therein, a second glass tube section to be welded to the coated glass tube body and a third glass tube section serving as an exhaust pipe, to be parallel with the coated glass tube body and then welding the second glass tube sections to parts adjacent to both ends of the coated glass tube body, respectively; (c) vacuumizing an inside of the welded body of the unit structured glass tubes and the tube body to a certain level through an exhaust apparatus connected to the third glass section; (d) generating plasma in the welded body through a plasma generating apparatus connected to the internal electrodes for generating plasma, thereby baking the inside of the welded body; (e) removing the first glass tube section; (f) exhausting air and impurities remaining in the welded body and introducing a predetermined amount of inert gas into the welded body; and (g) removing the third glass tube section. [35] Preferably, parts between the first and second glass tube sections and between the second and third glass tube sections may be formed to have a reduced diameter. [36] According to a preferred embodiment of the invention, a diameter of the reduced part between the first and second glass tube sections may be larger than a diameter of the reduced part between the second and third glass tube sections. [37] According to another aspect of the invention, there is provided a unit structured glass tube to be connected to a glass tube coated with a fluorescent material used for an external electrode fluorescent lamp, the unit structured glass tube comprising a first glass tube section including an internal electrode for generating plasma in a connected body after connecting the unit structured glass tube to the coated glass tube and an exhaust pipe for vacuumizing an inside of the coated glass tube, removing impurities and foreign substances of the fluorescent material and introducing an inert gas; and a second glass tube section to be connected to the coated glass tube so as to communicate with it wherein a part between the first and second glass tube sections is formed to have a reduced diameter. [38] According to still another aspect of the invention, there is provided a unit structured glass tube to be connected to a glass tube coated with a fluorescent material used for an external electrode fluorescent lamp, the unit structured glass tube comprising a first glass tube section including an internal electrode for generating plasma in a connected body after connecting the unit structured glass tube to the coated glass tube; a second glass tube section to be connected to the coated glass tube so as to communicate with it; and a third glass tube section serving as an exhaust pipe for vacuumizing an inside of the coated glass tube, removing impurities and foreign substances of the fluorescent material and introducing an inert gas wherein parts between the first and second glass tube sections and between the second and third glass tube sections are formed to have a reduced diameter. [39] According to a preferred embodiment of the invention, an external electrode may be formed on a surface of the second glass tube section during the manufacture of the external electrode fluorescent lamp. [40] Preferably, the second glass tube section may comprise an external electrode on a surface thereof. [41] According to a preferred embodiment of the invention, a diameter of the reduced part between the first and second glass tube sections may be larger than a diameter of the reduced part between the second and third glass tube sections. Brief Description of the Drawings [42] The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: [43] FlG. 1 is a flow chart showing a process of manufacturing an external electrode fluorescent lamp according to an embodiment of the invention; [44] FlG. 2 is a schematic view illustrating each of procedures of manufacturing an external electrode fluorescent lamp according to a preferred embodiment of the invention; [45] FlG. 3 is a schematic view illustrating a process of manufacturing an external electrode fluorescent lamp according to another preferred embodiment of the invention; [46] FlG. 4 is a flow chart showing a process of manufacturing an external electrode fluorescent lamp according to another embodiment of the invention; [47] FlG. 5 is a view showing a process of manufacturing an external electrode fluorescent lamp using a unit structured glass tube including an internal electrode for generating plasma therein, according to an embodiment of the invention; [48] FlG. 6 is a view showing a process of manufacturing an external electrode fluorescent lamp using a unit structured glass tube including an internal electrode for generating plasma therein, according to another preferred embodiment of the invention; [49] FlG. 7 is a view showing an exemplified structure of a unit structured glass tube including an internal electrode for generating plasma and an exhaust pipe; [50] FlG. 8 is a view showing another exemplified structure of a unit structured glass tube including an internal electrode for generating plasma and an exhaust pipe; and [51] FlG. 9 is a schematic view illustrating an example of an external electrode fluorescent lamp having a certain shape to which the invention is applied. Best Mode for Carrying Out the Invention [52] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the invention is not limited to the embodiment. In the following description of the present invention, a manufacture process known to those skilled in the art of an external electrode fluorescent lamp, an operation capable of being conventionally performed, and structures and operations of a known apparatus will be omitted. In addition, although the invention will be described with regard to the external electrode fluorescent lamp, it should be understood that the invention can be applied to a neon signboard using a glass lamp having no fluorescent material coated thereto. [53] [54] 1. A first embodiment [55] Fig. 1 is a flow chart showing a process of manufacturing an external electrode fluorescent lamp according to an embodiment of the invention, and Fig. 2 is a schematic view visually showing the process of Fig. 1. Hereinafter, a preferred first embodiment of the invention will be described with reference to Figs. 1 and 2. [56] [57] 1 - 1. A coated glass tube body [58] Firstly, it is prepared a glass tube for manufacturing an external electrode fluorescent lamp (EEFL). In Fig. 2, although a linear glass tube is shown for convenience sake, the glass tube may be formed to have a shape and a size cor¬ responding to uses of the EEFL in advance. An inner surface of the glass tube is coated with a fluorescent material according to a typical process usually carried out during the manufacture of the EEFL (Fig. 2a). In Fig. 2a, although it is shown that the whole inner wall of the glass tube is coated with a fluorescent material, it can be easily understood by those skilled in the art that a part of the inner wall, to which an external electrode will be formed, may be not coated with the fluorescent material. Before coating the fluorescent material, an operation for washing foreign substances on the inner wall of the glass tube is typically performed. The prepared glass tube 10 is introduced in the manufacturing process (SlOl). [59] [60] 1-2. Connections of an internal electrode for generating plasma and an exhaust pipe and reduction of a tube diameter [61] To the glass tube 10 prepared according to the above process is connected a second glass tube 20 including an internal electrode 22 for generating plasma therein (S 102). When connecting the tubes 10, 20, the coated glass tube 10 having a shape as shown in Fig. 2 is connected with the second glass tube 20 including the internal electrode 22 connected with a lead-in 24, using a torch. According to a preferred embodiment of the invention, an aperture is perforated near the region in which the internal electrode 22 is provided and an external electrode 40 will be formed, and an exhaust pipe 30 is connected to the aperture (S 103). As it can be easily understood by those skilled in the art, it should be noted that the steps of S 102 and S 103 may be carried out in reverse order according to connected positions of the exhaust pipe and the glass tube. Spe cifically, in case of connecting the exhaust pipe 30 to the coated glass tube 10, the exhaust pipe 30 may be connected to the coated glass tube 10 before the second glass tube 20 including the internal electrode 22 for generating plasma therein is connected to the coated glass tube 10. [62] The internal electrode 22 for generating plasma is connected to a plasma generating apparatus (not shown) via the lead-in 34. When the apparatus is operated, plasma is generated in the connected body through the internal electrode. Since the structures of the plasma generating apparatus and the internal electrode for generating plasma and a plasma generating operation and the like have been already known to the related field of the invention, detailed descriptions thereof will be omitted. In addition, it should be noted that the structure of the internal electrode is shown to be simplified. [63] According to a preferred embodiment of the invention, the second glass tube 20 including the internal electrode for generating plasma is connected to one end of the coated glass tube 10 using a torch and an aperture is formed at a predetermined position by blowing air through the other opened end of the coated glass tube 10. The exhaust pipe 24 is connected to the aperture and then the other second glass tube 20 including the internal electrode for generating plasma is connected to the other opened end of the coated galss tube 10. Figs. 2a and 2b show a state that the internal electrode and the exhaust pipe are connected to the glass tube. The internal electrode for generating plasma will be later removed since it is not required for an external electrode fluorescent lamp (EEFL). According to a preferred embodiment of the invention, the exhaust pipe may be provided to a position adjacent to the internal electrode 22 for generating plasma so that the exhaust pipe can be removed together with the internal electrode when removing the internal electrode. [64] In the mean time, it may be difficult to remove the internal electrode and the exhaust pipe depending on diameters of the glass tube. In other words, in case of a glass tube having a large diameter, when the welded part of the second glass tube 20 including the internal electrode and the coated glass tube 10 is separated using the torch, a coated glass tube adjacent to the cut part may be depressed into the inside thereof due to a pressure difference between the interior and exterior of the glass tube, thereby deteriorating an external appearance thereof. Accordingly, it is required a precise operation to refine the depressed part. Considering this problem, according to a preferred embodiment of the invention, as shown in Fig. 2d, it is performed a forming operation (reduction shaping) for reducing a diameter of a part of the glass tube so that the separation operation of the glass tube will be more easily carried out later. In the mean time, when the forming operation is performed with the exhaust pipe being connected to the glass tube, the forming operation may be complicated or it may be difficult to perform the operation. Accordingly, it is preferred to perform the forming operation before connecting the exhaust pipe to the one end of the glass tube. [65] [66] 1-3. Vacuumizing and baking operations [67] As described above, after connecting the second glass tube 20 including the internal electrode 22 and the exhaust pipe 30 to the coated glass tube 10, the inside of the glass tube is vacuumized to a certain level in which current can flow, by driving a vacuum pump (P) connected with the exhaust pipe 30 (S 104). After that, when both terminals of the internal electrodes for generating plasma are connected to the plasma generating apparatus and then high current and voltage are applied to discharge the inside of the glass tube, electrons are emitted in the glass tube under plasma state. Accordingly, impurities in the powders and other foreign substances are burned due to the generated plasma and a degree of vacuum is also increased (S 105). Like this, contrary to the prior art using a heater box so as to remove the impurities in the powders and other foreign substances and to easily exhaust them, according to the invention, it is possible to perform the baking operation with one time operation only using the plasma method, without providing heater boxes to correspond to each of shapes and sizes of the EEFLs having diverse shapes and sizes. [68] [69] 1-4. Introducing and removing operations of an inert gas [70] In the mean time, after the baking operation, the remaining air and the substances removed through the baking operation are exhausted to increase the degree of vacuum and then an inert gas is introduced in a predetermined amount for a later discharge of the EEFL (S106). [71] Subsequently, the exhaust pipe 30 is removed. In addition, the internal electrode, i.e., the second glass tube 20 including the internal electrode 22 is cut since the internal electrode 22 has performed its purpose of baking the inside of the glass tube and is not required in the EEFL (S 107). Such removal operation is typically performed using the torch. [72] As shown in Fig. 2d, when the exhaust pipe 30 is connected to the glass tube near the region of the internal electrode 22, it is possible to remove the internal electrode 22 and the exhaust pipe 30 at a time by cutting the second glass tube 20 including the internal electrode 22. Alternatively, it may be possible to separately remove the exhaust pipe 30 and the internal electrode 22 depending on the connected positions. [73] [74] 1-5. Formation of an external electrode [75] After removing the internal electrodes and the exhaust pipe, the external electrode 40 is formed near the region in which the internal electrode for generating plasma and the exhaust pipe are formed (S 108). The external electrode fluorescent lamp having the external electrode 40 formed thereon is shown with a reference numeral 50 in Fig. 2e. [76] [77] 2. A second embodiment [78] Fig. 3 schematically shows a second preferred embodiment of the invention. In the following descriptions, explanations of structures or manufacturing processes overlapped with the first embodiment will be omitted. [79] Firstly, it is prepared a glass tube 100 having both ends opened and having a shape and a size corresponding to a final use of an external electrode fluorescent lamp. As shown, an inner wall of the glass tube 100 is coated with a fluorescent material, except parts of both ends thereof for a ease welding with a separate glass tube which will be described later. [80] Subsequently, a pair of non-coated second glass tubes 200, each of which having a blind end, are welded to each of the ends of the coated glass tube 100. Then, the non- coated glass tubes 200 are bending-formed to be parallel with the coated glass tube 200. That is, the non-coated glass tube will be formed with the external electrodes. At this time, if the external electrode formation region is structured into a linear shape continuing on the coated glass tube, a whole size of the lamp is increased. In addition, since the emission of light does not occur at the external electrode formation region, there occurs a shade. Accordingly, considering this, it is preferred to bending-form the external electrode formation region to be parallel with the coated glass tube 100. In addition, although the inner wall of the second glass tube 200 is not coated with the fluorescent material, it should be noted that an inner wall part except the welded region with the coated glass tube 100 may be coated with the fluorescent material. Also in other embodiments, this is the same. [81] Subsequently, a third glass tube 300 including an internal electrode 300 for generating plasma connected with a lead-in 320 is welded to the second glass tube 200 to communicated with it. At this time, the third glass tube 300 is not directly connected to the second glass tube 200 but indirectly connected to the second glass tube via a connecting part 360 having a smaller diameter. Specifically, the third glass tube 300 including the internal electrode for generating plasma should be removed after ac¬ complishing the purpose of the baking operation. However, as described above, according to the prior art, the glass tube such as the third glass tube 300 is welded to an opened end of the coated glass tube and then removed using heat of the torch. At this time, the welded part is inevitably depressed due to the pressure difference between the interior and exterior of the glass tube, so that the end of the glass tube should be re¬ processed and such re-processing requires a high degree of skill. As the diameter of the glass tube is increased, the problems are also increased. According to the first embodiment of the invention, the problems are solved through the forming operation (reduction shaping). According to this second embodiment of the invention, the glass tube including the internal electrode for generating plasma therein is not directly connected to an opened end of the EEFL, but connected to a part of the glass tube in a vertical relation, at which an external electrode will be formed. That is, as shown in Fig. 3, the third glass tube 300 is connected to the non-coated glass tube 200 in a vertical relation. At this time, since the third glass tube 300 is provided with the connecting part 360 having a diameter smaller than that of the third glass tube, the glass tubes 200, 300 are connected to communicate with each other via the connecting part 300. Accordingly, when removing the glass tube 300 after the baking operation, it has only to cut the connecting part 360 having the smaller diameter. As a result of that, it is possible to easily perform the removal operation while preventing the depression of the glass tube. [82] Next, although it is not shown in Fig. 3, an exhaust pipe is connected to a part of one of the third glass tubes 300 including the internal electrode so as to perform an operation of vacuumizing the inside of the glass tube to a certain level. After that, it is performed the baking operation of the glass tube through the plasma generating apparatus. Then, by successively carrying out the operations of the exhaustion of the remaining air and foreign substances, the introduction of inert gas, the removal of the third glass tube 300 and the exhaust pipe and the formation of the external electrode on a surface of the non-coated glass tube 200, an external electrode fluorescent lamp having desired shape and size is finally completed. [83] In the mean time, according to another preferred embodiment of the invention, there is provided means for performing the removal operation of the glass tube including the internal electrode and the exhaust pipe more easily. Specifically, when carrying out the operations of baking and exhausting the glass tube, forces that the glass tube can endure are different. That is, since a high heat occurs when the baking operating is performed using the plasma, the glass tube having a smaller diameter may be used during the exhausting operation, compared to the baking operation using the plasma. In addition, since the inside of the glass tube is highly vacuumized during the plasma operation, the diameter of the connecting part 360 of the glass tube 300 should endure the baking treatment using the plasma although it is smaller than that of the third glass tube 300 as in the above embodiment. Accordingly, there is a limitation in the reduction of the diameter. As a result, since the connecting part 360 has a relatively large diameter, it may be difficult to remove the connecting part 360 during the removal operation of the third glass tube 300. In addition, the removal operation of the third glass tube 300 should be elaborately carried out, considering the depression problem of the glass tube due to the pressure difference between the interior and exterior of the glass tube. Accordingly, according to the invention, considering these problems, the diameter of the connecting part 360 is made to be smaller than that of the third glass tube 300. In addition, the diameter of the connecting part is made to be sufficient enough to endure the plasma operation and to easily perform the removal operation of the glass tube. Further, it is introduced a process for relieving the difficulty of the removal operation due to the pressure difference between the interior and exterior of the glass tube. [84] More specifically, after performing the baking operation with the plasma and then exhausting the air, foreign substances and the like remaining in the glass tube, a pre¬ determined amount of inert gas is primarily introduced into the glass tube. Preferably, the inert gas is introduced so that an inner pressure of the glass tube is smaller than an atmospheric pressure by a few Torr, thereby reducing the pressure difference between the interior and exterior of the glass tube at the utmost. Subsequently, the glass tube including the internal electrode for generating plasma and having no exhaust pipe connected thereto is removed from the second glass tube 200. At this time, since the pressure difference between the interior and exterior of the glass tube is reduced at the utmost, it is possible to easily carry out the removal operation of the glass tube including the internal electrode. Next, the connecting part 360 of the third glass tube 300 including the internal electrode and having the exhaust pipe connected thereto is formed to have a diameter smaller than its original diameter using the torch. Sub¬ sequently, the introduced inert gas is exhausted from the exhaust pipe while keeping the amount of the inert gas for a lamp discharge and the other third glass tube 300 is removed from the second glass tube 200. Like this, according to this embodiment, the removal operation of the glass tube including the internal electrode is divided into two steps. Firstly, one of the third glass tubes is easily removed by reducing the pressure difference and then the diameter of the connecting part 360 of the other third glass tube is further reduced so as to easily perform the removal operation of the other glass tube. In the mean time, the exhaust operation of the inert gas may consist of completely exhausting the inert gas so as to completely remove the foreign substances and the like and then secondarily introducing an inert gas for a lamp discharge. [85] Finally, an external electrode is formed on the second glass tube 200. Meanwhile, the external electrode may be previously formed on the second glass tube so as to simplify the manufacturing process depending on the embodiments. In other words, carbon, silver paster and the like may be coated on a surface of the second glass tube and the coated part is dried and then heat-treated or subject to a taping treatment by adhering an aluminum tape and the like so as to form an external electrode. Like this, a second glass tube having the external electrode formed through the process may be prepared in advance and then subject to the above described manufacturing process. Also in other embodiments, this is the same. [86] [87] 3. A third embodiment [88] According to the first and second embodiments, a glass tube on which an external electrode will be formed and a glass tube including an internal electrode are re¬ spectively provided through separate operations. However, according to this embodiment, a unit structured glass tube including a region at which an external electrode will be formed is directly welded to a coated glass tube, thereby simplifying the manufacturing process. Fig. 4 is a flow chart showing this embodiment. As shown in Fig. 4, this embodiment is generally similar to the embodiment shown in Fig. 1, except that a unit structured glass tube is provided. Accordingly, detailed descriptions of the manufacturing steps overlapped with those shown in Fig. 1 will be omitted. [89] As shown in Fig. 5, a unit structured glass tube 400, which comprises a first glass tube 420 having a blind end and a second glass tube 440 including an internal electrode 444 having a lead-in 442 connected thereto and connected to the first glass tube 420 via a connecting part 446 in a vertical relation so as to communicate with the first glass tube, is welded to each of both ends of a coated glass tube body 500. Accordingly, in the manufacturing process of the EEFL, it is possible to simplify the procedures of separately providing a glass tube to which an external electrode will be formed and a glass tube including an internal electrode and then welding the two separate glass tubes and thus to mass-produce a glass tube required to manufacture the EEFL as a unit structure, thereby making it possible to perform the manufacturing process more ef¬ ficiently. Other procedures, except that the glass tube 440 including the internal electrode and the glass tube 420 to which an external electrode will be formed are provided as the unit structured glass tube 400 and then the glass tube 400 is welded to the coated glass tube body 500, can be performed as described in the above em¬ bodiments. Accordingly, detailed descriptions thereof will be omitted. In the mean time, although it is not specifically shown in Fig. 5, it should be noted that the unit structured glass tube may be provided as a unit structure comprising an exhaust pipe. In this case, the exhaust pipe may be integrated with the second glass tube 440. Al¬ ternatively, the exhaust pipe may be connected to a part of the second glass tube 440 through a separate process. [90] [91] 4. A fourth embodiment [92] According to the above embodiments, the glass tube including the internal electrode is vertically connected to the glass tube to which an external electrode will be formed via the connecting part, so that the glass tube including the internal electrode, which is not necessary for the EEFL, can be easily removed. However, according to this embodiment, there is provided means for easily removing the glass tube, without the glass tube comprising the connecting part having a smaller diameter. [93] More specifically, as shown in Fig. 6, according to a preferred embodiment of the invention, a glass tube 600 including an internal electrode 640 having a lead-in 620 connected thereto is welded to an opened end of a coated glass tube 700 to communicate with it. The glass tube 600 consists of a unit structure comprising a first glass tube section 660 including an internal electrode for generating plasma therein, and a second glass tube section 680 to be welded to the opened end of the coated glass tube 700. As shown in Fig. 6, the first and second glass tube sections 660, 680 are continued through a forming-shaped part 690 having a reduced diameter between them. Accordingly, it is possible to easily cut the first glass tube section 660 including the internal electrode and the like that is not necessary for the EEFL, without depressing the glass tube. After welding such unit structured glass tube 600 to each of the opened ends of the coated glass tube 700, it is possible to manufacture the EEFL through the procedures as described above with regard to the first to third em¬ bodiments. Although it is not shown in Fig. 6, an exhaust pipe may be connected to a part of the first glass tube section 660 so that it can be removed with the first glass tube section 660 through one removal operation, or may be connected to the glass tube 600 in advance so as to provide it as a unit structure (refer to Fig. 7). [94] In the mean time, according to another preferred embodiment of the invention, a same effect can be provided using a simple unit structure without providing a separate exhaust pipe. As shown in Fig. 8a, a unit structured glass tube 800 to be welded to a coated glass tube 700 consists of three sections, unlike the embodiment shown in Fig. 7. Specifically, the glass tube 800 comprises a first glass tube section 820, a second glass tube section 840 and the a third glass tube section 860. The first glass tube section 820 includes an internal electrode 824 having a lead-in 822 connected thereto, the second glass tube section 840 is a section that is welded to the coated glass tube section 700 and an external electrode will be later formed on a surface thereof, and the third glass tube section 860 serves as an exhaust pipe and is connected to an outside vacuum pump (P). Parts between the first and second glass tube sections 820, 840 and between the second and third glass tube sections 840, 860 are also forming-shaped to have a reduced diameter. At this time, higher heat is applied to the glass tube and thus the glass tube may be deformed when the plasma operation is carried out, compared to the exhaust operation. Accordingly, it is preferred that the part between the first and second glass tube sections 820, 840 is forming-shaped to have a larger diameter than that of the forming-shaped part between the second and third glass tube sections 840, 860. According to a preferred embodiment of the invention, the glass tube 800 having such structure is welded to the coated glass tube 700 as shown in Fig. 8b to perform the baking operation. After that, when the first glass tube section 820 including the internal electrode is removed, the vacuumizing operation and the introduction of the inert are performed through the third glass tube section 860 and then the third glass tube section 860 is removed and only the second glass tube section 840 is remained as it is welded to the coated glass tube 700. An external electrode is then formed on a surface of the second glass tube section 840. Mode for the Invention [95] Fig. 9 is a schematic view illustrating an example of an external electrode fluorescent lamp having a character as shown used for a signboard. According to the prior art, a heater box corresponding to the shape and size of the character should be separately provided and the shape of the glass tube should be constantly maintained. However, according to the invention, it has only to connect the internal electrodes and the exhaust pipe to the glass tube having been formed into the shown shape and to operate the plasma generating apparatus connected to the electrodes so as to generate plasma in the glass tube, thereby burning the foreign substances and the like except the fluorescent material, without using the heater box. Then, after completing the exhaust operation, the internal electrodes and exhaust pipe are removed and then an external electrode is formed according to a conventional method. Through the process, it is possible to obtain an external electrode fluorescent lamp having desired shape and size. [96] While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made thereto without departing from the spirit and scope of the invention as defined by the appended claims. Industrial Applicability [97] As described above, according to the invention, the impurity removing operation, i.e., baking operation for the external electrode fluorescent lamp is performed using a plasma principle without using the heater box, contrary to the prior art. Accordingly, when it is manufactured an external electrode fluorescent lamp (EEFL) having diverse shapes and sizes, it is not required to separately provide a heater box correspondingly to it. In addition, since the EEFL can be manufactured with an existing system, it is possible to easily manufacture the fluorescent lamp and to considerably reduce the manufacturing cost. [98] In addition, since it has only to provide a glass tube including the internal electrode for generating plasma and the exhaust pipe as a separate unit structure and to weld the unit structure to the glass tube body and then to remove it after the baking operation, it is possible to perform the manufacturing process of the EEFL more easily in general.