Patent Document

CLAIM OF PRIORITY 
     This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for FLUORESCENT SCREEN FOR CATHODE RAY TUBE AND THE FABRICATION METHOD THEREOF earlier filed in the Korean Industrial Property Office on 6 Jul. 2001 and there duly assigned Serial No. 40469/2001. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to cathode ray tubes, and more particularly, to a screen for a cathode ray tube, capable of preventing a metal layer, which is formed on a phosphor film coated inside a panel, from expanding and being separated from the underlying layer during a thermal process, and a method for manufacturing the screen. 
     2. Description of the Related Art 
     In general, a cathode ray tube (CRT) displays an image by excitation of red, green, and blue phosphors of a phosphor film coated inside a panel by electron beams emitted by an electron gun and passed through electron beam apertures of a shadow mask mounted in the bulb structure formed by the panel and a funnel. 
     On the inner front surface of a panel, a phosphor film including a black matrix layer and red, green, and blue (RGB) phosphor layer, which are alternately formed as strips, is formed. A metal layer, for example, an aluminum layer, is formed on the phosphor film. 
     Briefly, a method for manufacturing a screen for the CRT having the structure described above will be described. After cleaning the panel, the black matrix layer and the RGB phosphor layer are sequentially formed inside the panel. Subsequently, a filming layer is formed using an organic material to make the surface of the RGB phosphor layer even. To improve the luminance of the phosphor film and facilitate the emission of excess electrons in the bulb, the aluminum layer is deposited in a vacuum by thermal diffusion. 
     Next, the filming layer is calcinated so that the organic material is thermally decomposed, emitting gas into the air. This is for preventing energy loss as an electron beam emitted from the electron gun hits the filming layer before landing on the phosphor layer. Formation of the screen inside the panel is complete through a series of processes described above. 
     In the conventional CRT, the aluminum layer is formed over the entire inner region of the panel to completely cover the phosphor film. This structure has the following problems. 
     As described above, in forming the filming layer between the fluorescent layer and the aluminum layer to make up fine recessions or air gaps in the phosphor layer, an organic material such as an aqueous emulsion of acrylic resin is evenly spin coated on the phosphor film. The filming layer is removed by means of calcination after the aluminum layer is deposited thereon. 
     In the deposition of the filming layer inside the panel, it is difficult to evenly control the thickness of the filming layer. It is common that the filming layer is thicker at the edge of the panel, particularly at the corners, than the other inner region of the panel. As a result, a large amount of gas is generated from the relatively thicker region of the filming layer as it thermally decomposes during the calcinations process. 
     Also, the aluminum layer deposited on the filming layer expands and is separated from the panel while another process is performed or the CRT is operated, so that particles of the aluminum layer block the electron beam apertures up. As the aluminum layer expands, irregular reflection of light occurs at the screen, thereby lowering the luminance of the CRT. 
     SUMMARY OF THE INVENTION 
     To solve the above-described and other problems, it is an object of the present invention to provide a screen for a cathode ray tube and a method for manufacturing the same, in which a gas exhaust member is selectively formed on the boundary of a metal layer formed on a phosphor film inside a panel to prevent the metal layer from expanding during a thermal process. 
     It is another object to provide a technique and an apparatus for a cathode ray tube that accommodates for light emitted from the phosphor layer to be uniformly reflected toward the front surface of the panel. 
     It is still another object to provide a technique and an apparatus for a cathode ray tube that improves the luminance in the cathode ray tube. 
     To achieve the above and other objects of the present invention, there is provided a screen for a cathode ray tube, including: a phosphor film formed on the inner front surface of a panel where at least one stud pin is mounted, the phosphor film including phosphor layers; a metal layer formed on the phosphor film, which reflects light emitted from the phosphor layers toward the front side of the panel; and a gas exhaust member extended from the metal layer, which provides a path for gas to exhaust, the gas being generated as a filming layer, interposed between the phosphor film and the metal layer to make the thickness of the phosphor film uniform, is decomposed. 
     It is preferable that the gas exhaust member is formed along the boundary of the metal layer in the inner front surface of the panel, except for the corners of the panel. 
     It is preferable that the gas exhaust member is selectively formed on the boundary of the metal layer in the inner front surface of the panel such that at least one recession along the side edges of the panel is exposed. 
     It is preferable that the gas exhaust member is selectively formed on the boundary of the metal layer such that the corners of the panel and at least one recession along the side edges of the panel are exposed. 
     It is preferable that the gas exhaust member additionally extends to the inner sidewall of the panel from the boundary of the metal layer, except for a region where the stud pin is positioned. 
     To further achieve the above and other objects of the present invention, there is also provided a method for manufacturing a screen for a cathode ray tube, the method includes: forming a phosphor film on the inner front surface of a panel; forming a filming layer of an organic material on the phosphor film; fitting a guide block into the panel and evacuating a processing space where the panel is loaded, the guide block having a mask pattern corresponding to a pattern of a metal layer and gas exhaust member to be formed as a single body inside the panel; on the filming layer, simultaneously forming the metal layer to cover the phosphor film and forming the gas exhaust member to selectively extend from the boundary of the metal layer as a pattern, by heating a precursor of the metal layer to evaporate, the gas exhaust member providing a path for gas generated during decomposition of the filming layer to exhaust; restoring the processing space to normal pressure; and thermally processing the panel to decompose and remove the filming layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein: 
         FIG. 1  is a sectional view showing a conventional screen having a metal layer on a panel; 
         FIG. 2  is a plan view of the conventional screen of  FIG. 1 ; 
         FIG. 3  is a sectional view showing a first embodiment of a screen for a cathode ray tube according to the present invention in which a metal layer formed on a panel is shown; 
         FIG. 4  is a plan view of the screen of  FIG. 3 ; 
         FIG. 5  is a perspective view of the screen of  FIG. 4 ; 
         FIG. 6  illustrates a panel of  FIG. 3  coupled to an apparatus to form a metal layer and a gas exhaust member on the panel; 
         FIG. 7  is a partially cutaway perspective view of  FIG. 6 ; 
         FIG. 8  is a perspective view of a guide block of  FIG. 7 ; and 
         FIG. 9  is a perspective view showing a second embodiment of the screen according to the present invention in which a metal layer and gas exhaust members formed on the panel are shown. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in  FIG. 1 , on the inner front surface of a panel  11 , a phosphor film  14  including a black matrix layer  12  and red, green, and blue (RGB) phosphor layer  13 , which are alternately formed as strips, is formed. A metal layer, for example, an aluminum layer  15 , is formed on the phosphor film  14 . 
     Briefly, a method for manufacturing a screen for the CRT having the structure described above will be described. After cleaning the panel  11 , the black matrix layer  12  and the RGB phosphor layer  13  are sequentially formed inside the panel  11 . Subsequently, a filming layer is formed using an organic material to make the surface of the RGB phosphor layer  13  even. To improve the luminance of the phosphor film  14  and facilitate the emission of excess electrons in the bulb, the aluminum layer  15  is deposited in a vacuum by thermal diffusion. 
     Next, the filming layer is calcinated so that the organic material is thermally decomposed, emitting gas into the air. This is for preventing energy loss as an electron beam emitted from the electron gun hits the filming layer before landing on the phosphor layer  13 . Formation of the screen inside the panel is complete through a series of processes described above. 
     As shown in  FIG. 2 , in the conventional CRT, the aluminum layer  15  is formed over the entire inner region of the panel  11  to completely cover the phosphor film  14 . This structure has the following problems. 
     As described above, in forming the filming layer between the fluorescent layer  14  and the aluminum layer  15  to make up fine recessions or air gaps in the phosphor layer  13 , an organic material such as an aqueous emulsion of acrylic resin is evenly spin coated on the phosphor film  14 . The filming layer is removed by means of calcination after the aluminum layer  15  is deposited thereon. 
     In the deposition of the filming layer inside the panel  11 , it is difficult to evenly control the thickness of the filming layer. It is common that the filming layer is thicker at the edge of the panel  11 , particularly at the corners, than the other inner region of the panel  11 . As a result, a large amount of gas is generated from the relatively thicker region of the filming layer as it thermally decomposes during the calcinations process. 
     Also, the aluminum layer  15  deposited on the filming layer expands and is separated from the panel while another process is performed or the CRT is operated, so that particles of the aluminum layer  15  block the electron beam apertures up. As the aluminum layer  15  expands, irregular reflection of light occurs at the screen, thereby lowering the luminance of the CRT. 
     A sectional view of a first embodiment of a screen for a cathode ray tube according to a first embodiment of the present invention is shown in FIG.  3 . Referring to  FIG. 3 , a phosphor film  34  is formed on the inner front surface of a panel  31 , and a metal layer, for example, an aluminum layer  35 , is deposited on the phosphor film  34 . 
     The phosphor film  34  includes a black matrix layer  32  formed inside the panel  31  as strips spaced a predetermined distance apart and a phosphor layer  33  of red, green, and blue phosphors, which are alternatively interposed between each of the strips of the black matrix layer  32 . To prevent color purity degradation by successive emission of adjacent phosphors, the black matrix layer  32  is formed of a non-luminescent, light-absorbing material, such as graphite. 
     The aluminum layer  35  is deposited on the phosphor film  34 . The aluminum layer  35  reflects a scanning electron beam diverging by hitting the fluorescent layer  33  after having been emitted by an electron gun (not shown), toward the front side of the panel  31 , thereby improving the luminance. The aluminum layer  35  acts to enhance the potential for the screen by guiding the flow of electrons hitting the phosphor layer  33 , which is an insulating layer, out of the phosphor layer  33  to prevent a potential drop therein. To end this, the aluminum layer  35  is electrically connected to a stud pin  31   a  in a subsequent process, which is formed inside the panel  31  using a conductive material such as graphite. As a result, once electrons reach the screen, the electrons can migrate to the anode through the aluminum layer  35 , the stud pin  31   a , a shadow mask assembly, an electron shield, and then an interior graphite layer. 
     A feature of the present invention lies in that a gas exhaust member is formed as an extension of the aluminum layer  35 . 
       FIG. 4  is a plan view of the screen of  FIG. 3 , and  FIG. 5  is a perspective view of the screen of FIG.  3 . Referring to  FIGS. 4 and 5 , the aluminum layer  35  is deposited on the phosphor film  34  (see FIG.  3 ), which is formed as an image forming layer on the inner front surface of the panel  31 . 
     Gas exhaust members are formed inside the panel  31 . In particular, the aluminum layer  35  is formed to completely cover the phosphor film  34 . A first gas exhaust member  310  is selectively formed on the boundary of the aluminum layer  35 . A second gas exhaust member  320  is formed on the inner sidewall of the panel  31 , extending from the first gas exhaust member  320 . The first and second gas exhaust members  310  and  320  are formed of substantially the same material and at the same time as the aluminum layer  35  by vacuum deposition. 
     In detail, in the manufacture of a screen, an intermediate filming layer is formed of an organic material on the phosphor film  34  to make the surface of the phosphor layer  32  even. However, the filming layer deposited on the phosphor film  34  has a localized thickness variation. As a result, when the organic material of the filming layer is thermally decomposed and vaporized during a subsequent calcination process following deposition of the aluminum layer  35  thereon, a large amount of gas is generated from the relatively thicker region of the filming layer so that the aluminum layer  35  expands much at the thicker region. To prevent this phenomenon, according to the present invention, the aluminum layer  35  is not deposited on the region of the filming layer having a relatively large thickness. 
     To end this, after the aluminum layer  35  is formed to completely cover the phosphor film  34 , gas exhaust members are selectively formed on the boundary of the aluminum layer  35 . In particular, at the corners or at the long-side and/or short-side edges of the panel  31 , an aluminum layer is not formed such that gas generated during removal of the filming layer easily exhausts. Meanwhile, the first gas exhaust member  310  is formed along the remaining edge region, extending from the aluminum layer  25 , thereby resulting in an uneven pattern along the boundary of the aluminum layer  25 . 
     On the inner sidewall of the panel  31 , the second gas exhaust member  320  is selectively formed, extending from the first gas exhaust member  310 . One end of the second gas exhaust member  320  is connected to the stud pin  31   a  by a conductive material such as graphite. 
     An example of the process of manufacturing the screen having the structure described above will be described. 
     After cleaning the inner surface of the panel  31 , the black matrix layer  32  is formed on the inner front surface of the panel  31 . The black matrix layer  32  is formed as strips by means of photoresist deposition, exposure, development, graphite deposition, and etching processes. 
     The phosphor layer  33  is formed between the strips of the black matrix layer  32  by a precipitation, photolithography, or slurry method, but the slurry method is widely used. The phosphor layer  33  is spin coated on the inner surface of the panel  31 , dried using an infrared heater, exposed to an ultra high vacuum mercury lamp while a shadow mask is fit into the bulb, and developed using water, thereby forming a phosphor pattern. By repeating these processes for R, G, B phosphors, a RGB phosphor pattern is formed. As a result, the formation of the phosphor film  34  is complete. 
     Next, to make the surface of the phosphor layer  33  even, an organic material is deposited on the entire surface of the phosphor film  34  to form the filming layer. After formation of the filming layer is complete, a metal layer having a high reflectivity, for example, the aluminum layer  35 , is deposited on the filming layer. 
     The aluminum layer  35  is deposited using a vacuum deposition apparatus, as shown in  FIGS. 6 and 7 . In particular, the panel  31  is coupled to the vacuum deposition apparatus  60 . When the vacuum deposition apparatus  60  is applied to deposit the aluminum layer  35 , intermolecular bombardment of aluminum is less likely to occur and thus, improving the evaporation rate of aluminum. Also, the vacuum condition, which almost free from oxygen or nitrogen, prevents oxidation and nitrification reactions from taking place therein. 
     The panel  31  is tightly sealed from the outside by a seal member  61  mounted at the binding site between the panel  31  and the vacuum evaporation apparatus  60 . A guide block  62  having a mask pattern corresponding to the pattern of the aluminum layer  35  and the gas exhaust members to be deposited on the panel  31  is attached to the seal member  61 . A boat  64 , in which an aluminum pellet  63  as a source material of the aluminum layer  35  is contained, is located below the guide block  62 . Both ends of the boat  64  are electrically connected to a positive electrode rod  65   a  and a negative electrode rod  65   b , respectively, each having a predetermined length. 
     The vacuum deposition apparatus  60  having the configuration described above is pre-evacuated using a rotary pump and then evacuated to an ultra high vacuum using a diffusion pump, not to exceed a critical vacuum level. 
     The boat  64  is heated by applying a predetermined power across the positive and negative electrode rods  65   a  and  65   b . As the boat  64  is heated, the aluminum pellet  63  contained in the boat  64  melts and the aluminum molecules start to evaporate. The aluminum molecules thermally diffuse at an angle of θ toward the inner front surface of the panel  31  on which the phosphor film  34  has been formed, thereby forming the aluminum layer  35  and the gas exhaust members as a predetermined pattern. 
     The guide block  62  having a mask pattern for the aluminum layer  35  and the gas exhaust members to be deposited is fit into the panel  31 . The guide block  62  is formed as a rectangular frame having a center hole  62   a . The guide block  62  has a recession and projection portion  81  along one edge facing the panel  31 , which has a pattern corresponding to the pattern of the gas exhaust members. 
     As aluminum molecules evaporate and diffuses through the center hole  62   a  of the guide block  62 , the aluminum layer  35  (see  FIG. 5 ) is deposited on the inner front surface of the panel  31 . The first and second gas exhaust members  310  and  320  are formed as a predetermined pattern on the edge of the inner front surface and the inner sidewall of the panel  31  as the evaporated aluminum molecules diffuse into the recession  82  of the guide block  62 . The diffusion of the vaporized aluminum molecules is blocked by the projection  83  of the guide block  62 , so that the first gas exhaust member  310  is not formed at an edge region of the panel  31  covered by the projection  83 . 
     As a result, the first and second gas exhaust members of a recession and projection pattern are formed along the edge of the inner front surface of the panel  31 . By blocking a region of the inner front surface of the panel  31 , where the filming layer is formed to be thick, with the guide block  62 , the first and second gas exhaust members  310  and  320  are not formed at the relatively thick region of the inner front surface. 
     After deposition of the aluminum layer  35  and the first and second gas exhaust members as a predetermined pattern is complete, the panel  31  is calcinated. The filming layer is thermally decomposed during calcination and removed from the screen. 
     Through the processes described above, the phosphor film  34 , the aluminum layer  35 , and the first and second gas exhaust members  310  and  320  are completely formed on the inner front surface of the panel  31 . 
       FIG. 9  is a perspective view of a second embodiment of the screen according to the present invention. In this embodiment, only features of the screen will be described. Referring to  FIG. 9 , a phosphor film (not shown), as described above, is formed on the inner front surface of the panel  31 , and an aluminum layer  95  is formed as a predetermined pattern to cover the phosphor film. A first gas exhaust member  910  is selectively formed on the boundary of the aluminum layer  95 , and a second gas exhaust member  920  is formed on the inner sidewall of the panel  31 . 
     The first gas exhaust member  910  extends from the aluminum layer  95 . Also, the first gas exhaust member  910  is formed to protrude from the boundary of the aluminum layer  95 . The first gas exhaust member  910  is selectively formed on the edge of the inner front surface of the panel  31 . 
     The second gas exhaust member  920  is formed on the inner sidewall of the panel  31 , extending from the first gas exhaust member  910 . Unlike the first embodiment described above, the second gas exhaust member  920  is deposited on the inner sidewall of the panel  31 , extending to a height at which the stud pin  31  is positioned. The second gas exhaust member  920  is not deposited near the stud pin  31   a . The second gas exhaust member  920  may be not formed in a region of the inner sidewall of the panel  31  adjacent to the region where the first gas exhaust member  910  is not formed. The area of deposition in the panel  31  is increased by the first and second gas exhaust members  910  and  920  formed as extending from the aluminum layer  95 , so that the potential of the screen is increased. 
     The screen for a CRT and the method for manufacturing the same according to the present invention described above provide the following effects. 
     The gas exhaust member is formed as an extension of the metal layer formed on the phosphor film in the inner front surface of a panel, extending from the boundary of the metal layer as a predetermined pattern. As a result, in removing the filming layer interposed between the phosphor layer and the metal layer to manufacture a screen, expansion of the metal layer due to the non-uniform thickness of the filming layer can be prevented so that light emitted from the phosphor layer can be uniformly reflected toward the front surface of the panel, thereby improving the luminance of the CRT. 
     While this invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Technology Category: 5