Patent Publication Number: US-7211939-B2

Title: External electrode fluorescent lamp and method for manufacturing the same

Description:
This application claims the benefit of the Korean Application No. P2002-87810 filed on Dec. 31, 2002, which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an external electrode fluorescent lamp EEFL for a backlight, and more particularly, to an external electrode fluorescent lamp and a method for manufacturing the same, in which indentations are provided in a surface of a glass tube by etching when forming external electrodes at both ends of a fluorescent lamp. 
     2. Discussion of the Related Art 
     A Cathode Ray Tube (CRT) has been widely used as monitors in televisions, measuring machines, and information terminals. However, the CRT has limitations in size and weight. Accordingly, display devices such as liquid crystal display (LCD) devices using an electro-optics effect, plasma display panels (PDP) using gas discharge, and an electro luminescence display (ELD) devices using an electro-luminescence effect have been developed to replace the CRT. 
     LCD devices have been studied because LCD devices have great picture quality, low power consumption, and low heat dissipation as compared to CRTs. However, an LCD device does not emit light by itself, so that it is necessary to provide an additional light source. One solution is a reflecting-type LCD device using ambient light as a light source, but this has limitations in practical use due to the environment. In response, a transmitting-type LCD device having an additional light source has been developed, in which the additional light source is referred to as a backlight. An LCD device may use one of various light sources such as electro luminescence (EL), a light emitting diode (LED), a cold cathode fluorescent lamp (CCFL), or a hot cathode fluorescent lamp (HCFL). The CCFL having a long lifetime, low power consumption, and a thin profile is generally used for the light source. 
     In transmitting-type LCD devices, the backlight may be classified into a direct-type method and an edge-type method depending on the position of a fluorescent lamp. In the edge-type backlight, a tube-type fluorescent lamp is positioned at a side of the LCD panel, for transmitting the light from the fluorescent lamp to the entire surface of the LCD panel with a transparent light-guiding plate. Meanwhile, the direct-type backlight has been more widely used with large-sized LCD devices of 20-inch or more, in which a plurality of fluorescent lamps are placed below a lower surface of a light-diffusion plate, whereby the entire surface of the LCD panel is directly illuminated by the fluorescent lamps. At this time, the direct-type method, which has greater luminous efficiency as compared with that of the edge-type method, is used for large-sized LCD devices requiring high luminance. For example, the LCD device of the direct-type method is generally used for large-sized monitors or the televisions. 
     Hereinafter, a backlight for an LCD device according to the related art will be described with reference to the accompanying drawings. 
       FIG. 1  is a perspective view schematically illustrating a direct-type backlight according to the related art, and  FIG. 2  illustrates a fluorescent lamp according to the related art. 
     As shown in  FIG. 1 , the direct-type backlight according to the related art includes a plurality of fluorescent lamps  1 , an outer case  3 , and light diffuser  5 . In this example, the plurality of fluorescent lamps  1  are positioned along one direction at fixed intervals, and the outer case  3  maintains and supports the plurality of fluorescent lamps  1  at fixed intervals. Then, the light diffuser  5  is positioned above the plurality of fluorescent lamps  1 . The light diffuser  5  prevents the silhouette of the fluorescent lamps  1  from being displayed on the display surface of the LCD panel (not shown), and for providing a light source having uniform luminance. For improving efficiency in diffusing light, a plurality of diffusion sheets and diffusion plates  5   a,    5   b,    5   c  may be provided. Also, a reflecting plate  7  is provided on an inner surface of the outer case  3  to concentrate the light emitted from the fluorescent lamps  1  to the display surface of the LCD panel, thereby improving the luminous efficiency. Also each fluorescent lamp  1  is fixed to holes provided at both sides of the outer case  3 . 
     As shown in  FIG. 2 , the CCFL  1  is filled with a discharge gas, and electrodes  2  and  2   a  are provided, one electrode of a glass tube for applying power (not shown). Also, wires  9  are connected to the electrodes  2  and  2   a . The wires  9  are also connected to an inverter (not shown) and a driving circuit. Each fluorescent lamp  1  requires an individual inverter. 
     However, the direct-type backlight according to the related art has the following disadvantages. In the direct-type backlight according to the related art, the silhouette of the CCFL may be displayed on the display surface of the LCD panel. Therefore, it is necessary to maintain a predetermined distance between the LCD panel and the CCFL. When using the direct-type backlight according to the related art, there are limitations as to how thin the LCD device may be. Also, hot cathode or cold cathode type electrodes are provided at the both ends of the glass tube in the related art fluorescent lamp. However, the process for providing the electrodes inside the fluorescent lamp is complicated, and each fluorescent lamp is driven with an individual inverter, thereby increasing manufacturing cost and the lifetime of the fluorescent lamp. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to an external electrode fluorescent lamp and a method for manufacturing the same that substantially obviates one or more problems due to limitations and disadvantages of the related art. 
     An advantage of the present invention is to provide an external electrode fluorescent lamp and a method for manufacturing the same, wherein external electrodes are provided at both ends of a glass tube for a fluorescent lamp, thereby obtaining a long lifetime of the fluorescent lamp, and simplified manufacturing process steps. 
     Another advantage of the present invention is to provide an external electrode fluorescent lamp and a method for manufacturing the same, wherein indentations are provided in a surface of a glass tube by etching, thereby realizing close adhesion between an external electrode and the glass tube. 
     Additional objects and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, an external electrode fluorescent lamp includes a glass tube filled with a discharge gas, wherein the glass tube has plurality of indentations in a surface thereof; and external electrodes at both ends of the glass tube. 
     Also, the external electrode fluorescent lamp further includes an electrode connection wire being connected to each external electrode, for applying an external power thereto; and an insulator surrounding the external electrode and the electrode connection wire for a complete connection therebetween. 
     In another aspect, a method for manufacturing an external electrode fluorescent lamp includes preparing a glass tube filled with a discharge gas; forming indentations in a glass tube filled with a discharge gas by selectively etching a surface of the glass tube up to about 30% of an entire thickness of the glass tube at both ends of the glass tube; and forming external electrodes at both ends of the glass tube having the indentations. 
     It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
         FIG. 1  is a perspective view schematically illustrating a direct-type backlight according to the related art; 
         FIG. 2  illustrates a fluorescent lamp according to the related art; 
         FIG. 3  is a cross-sectional view illustrating an external electrode fluorescent lamp according to the present invention; and 
         FIG. 4  is an expanded cross-sectional view of “A” portion in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     Hereinafter, an external electrode fluorescent lamp according to the present invention and a method for manufacturing the same will be described with reference to the accompanying drawings. 
       FIG. 3  is a cross-sectional view illustrating an external electrode fluorescent lamp according to the present invention; and  FIG. 4  is an expanded cross-sectional view of a portion denoted “A” in  FIG. 3 . 
     As shown in  FIG. 3 , in the external electrode fluorescent lamp according to the present invention, a glass tube  25  is filled with a discharge gas  21 , and external electrodes  22  are provided at both ends of the glass tube  25  to apply an electric field to the discharge gas  21 . An electrode connection wire  23  is connected to each external electrode  22  to apply power (not shown). 
     To completely and securely connect the electrode connection wire  23  to the external electrode  22 , an insulator  24  surrounds the external electrode  22  and the electrode connection wire  23 , together. The insulator  24  is formed of a contracting tube resulting in a complete connection and close adhesion between the external electrode  22  and the electrode connection wire  23  when heated. Further, as shown in  FIG. 4 , an uneven surface having a plurality of indentations  26  is formed in a surface of the glass tube  25  corresponding to the external electrode  22  for realizing complete adhesion between the external electrode  22  and the glass tube  25 . 
     More specifically, a method of manufacturing the external electrode of the external electrode fluorescent lamp will be described in detail. 
     First, the glass tube  25  is filled with the discharge gas  21 . Then, the glass tube  25  is selectively etched to form the indentations  26  in predetermined portions at both ends of the glass tube  25 , whereby the irregular indentations  26  are formed in the surface of the glass tube  25 . After that, the external electrodes  22  are formed at both ends of the glass tube  25  having the irregular indentations  26 . 
     Herein, the method for forming the external electrode on the glass tube  25  having the indentations  26  may be classified into plating and sintering methods. 
     In the plating method, the external electrode  22  is formed of a metal material such as nickel Ni. In this method, before forming the external electrode  22 , a physical and chemical etching process is performed on the surface of the glass tube  25  to improve adhesion efficiency. Then, the external surfaces of both ends of the glass tube  25  having the indentations  26  are thinly plated with a metal material such as an non-electrolytic nickel, thereby forming the external electrodes  22  at the both ends of the glass tube  25 . The irregular indentations  26  are formed in the external surfaces at both ends of the glass tube  25  by etching, so that the external electrodes  22  adhere to the glass tube  25 , completely and easily. Then, each external electrode  22  is electrically connected to the electrode connection wire  23 , and a voltage applied to the electrode connection wire  23  passes through the external electrode  22  of the fluorescent lamp, thereby generating the electric field inside the fluorescent lamp. According to the aforementioned process, the fluorescent lamp emits the light. 
     In the sintering method, powdered metal such as Ag is dispersed in a thermoplastic binder (not shown), thereby making a melting conductive paste. Then, the melting conductive paste is injected into a socket (not shown) in a small amount, where the socket forms the external electrode  22 . Subsequently, after dipping the glass tube having the indentations  26  into the socket (not shown) containing the conductive paste, the glass tube is heated to a high temperature to form the external electrode  22 . At this time, the appropriate temperature may vary according to the kind of the conductive paste. In case of a fluorescent lamp, it is preferable to maintain the glass tube at a temperature of 150° C. In the sintering method for the external electrode  22 , the external electrode  22  is formed of the conductive paste such as Ag. Also, like the plating method, the sintering method performs the physical and chemical etching process on the surface of the glass tube to improve the adhesion efficiency before forming the external electrode  22 . 
     In addition to the plating and sintering methods, various methods may be used for forming the external electrode of the fluorescent lamp. For example, a taping method may be used, in which the external electrode is formed of Al or Cu tape. Or, the external electrode  22  may be formed using a method of covering both ends of the glass tube  25  with metal capsules (not shown). 
     Among the methods for forming the external electrode  22 , the aforementioned method for forming the external electrode  22  by etching the surface of the glass tube  25  results in great adhesion between the glass tube  25  and the external electrode  22  because the plurality of indentations  26  are formed in the surface of the glass tube  25  by etching. 
     When forming the indentations  26  in the surface of the glass tube  25 , if a predetermined portion of the glass tube  25  is etched excessively, it may result in a pinhole in the surface of the glass tube  25  when applying a high voltage to the external electrode  22 . Accordingly, in the case of forming the indentations  26  in the surface of the glass tube  25  by etching, the depth of each indentation  26  is about 30% or less of the thickness of the glass tube  25 . That is, after completing the etching process, the thickness of the glass tube  27  after forming the indentations is at 70% or more of an initial thickness thereof. By controlling the etching thickness, it is possible to have complete adhesion between the glass tube  25  and the external electrode  22 , and to prevent a pinhole from forming in the glass tube  25  when applying a high voltage to the external electrode  22 . 
     As mentioned above, the external electrode fluorescent lamp for the backlight and the method for manufacturing the external electrode according to the present invention have the following advantages. 
     In the method for forming the external electrode, the indentations are formed in the surface of the glass tube by etching, whereby the external electrode completely adheres to the glass tube. Especially, when etching the surface of the glass tube, the etching depth of the indentation is controlled within a predetermined limit, so that it is possible to prevent a pinhole from forming in the surface of the glass tube when applying a high voltage to the external electrode, thereby realizing a long lifetime of the fluorescent lamp according to the present invention. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.