Patent Publication Number: US-5293096-A

Title: Cathode ray tube device having insulator coating

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a cathode ray tube device (hereinafter abbreviated as CRT) for picture display in a television set or the like. 
     Two desirable qualities for CRTs are high mechanical strength and lightweight. For this purpose, CRTs with funnels made of metal instead of glass are disclosed, for example, in Japanese Patent Kokai Publication 86033/1990. In these CRTS, a high voltage of 25 KV is applied to a thin metal film that covers the phosphor screen of the faceplate, while the metal funnel is grounded. Unfortunately, factors such as dirt on the inside surface of the faceplate and ambient electrons have caused serious problems of creeping discharge between the metal film and the metal funnel. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a lightweight CRT that can avoid creeping discharge between the metal film and the metal funnel. 
     A CRT according to the present invention has a glass faceplate forming an image display surface, and a metal funnel connected to a peripheral part of the faceplate and forming a side wall. The inside surface of the glass faceplate has a phosphor screen covered by a metal film. The CRT also has an insulating layer covering mutually adjacent inside areas of the funnel and the faceplate. 
     A method for manufacturing a CRT comprises the steps of preparing a glass faceplate having a phosphor screen covered by a metal film, and preparing a metal funnel. The method also comprises the steps of applying a first glass solder paste to a peripheral surface of the glass faceplate and an edge part of the funnel, and placing the faceplate and the funnel on a supporting stand so that the surface and part coated by the first glass solder paste are in contact. The method further comprises a step of applying a second glass solder paste mutually adjacent inside areas of the funnel and faceplate, and a single step of heating the above components, thereby sintering both the first and second glass solder pastes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional side view of an embodiment of the present invention. 
     FIG. 2 is an enlarged view of part A in FIG. 1. 
     FIG. 3 is a diagram for explaining a method for manufacturing the CRT of FIG. 1. 
     FIG. 4 is a partial sectional side view of an another embodiment. 
     FIG. 5 is a partial sectional side view of a still another embodiment. 
     FIG. 6 is a sectional view of a yet another embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will now be described with reference to the drawings. 
     As shown in FIGS. 1 and 2, the CRT of the first embodiment comprises a glass faceplate 1 forming an image display surface and a metal funnel 2 joined to the peripheral part 1a of the faceplate 1 and forming a side wall. The faceplate 1 is made of a glass such as the H8602 material specified by the Electronic Industries Association of Japan (EIAJ). The funnel 2 is made of a steel such as SUS410 which has a very low rate of outgassing in a vacuum and a thermal expansion coefficient close to that of the glass faceplate 1. The funnel 2 has an edge part 2a adjacent to the peripheral part 1a of the faceplate 1, a side wall 2c, and a bent part 2b connecting the edge part 2a to the side wall 2c. The edge part 2a of the funnel 2 is joined to an inside surface of the peripheral part 1a of the faceplate 1 by glass soldering using frit glass 11. The edge part 2a and the bent part 2b are thicker than the side wall 2c, because large tensile stress occurs in the bent part 2b. The extra thickness increases the mechanical strength of the bent part 2b, thus protecting the CRT against implosion. Because only the bent part 2b and the edge part 2a are thickened, the CRT is lightweight. 
     The CRT also comprises a glass cone part 2e connected at the rear extremity of the funnel 2, and a deflection yoke (not shown in the drawings) which is mounted externally around the cone part 2e and deflects an electron beam. 
     The CRT also comprises a glass neck 3 connected at the rear extremity of the cone part 2e and an electron gun 3a contained in the neck 3 and facing the faceplate 1. 
     The CRT furthermore comprises a phosphor screen 4 coating part of the inside surface of the faceplate 1 and a metal film 5 covering the phosphor screen 4. The metal film 5 is made, for example, by evaporation deposition of aluminum. In the CRT, a high voltage of 25 KV is applied to the metal film 5, while the metal funnel 2 is grounded. 
     A novel feature of this CRT is an insulating layer 6 that covers mutually adjacent inside portions of the faceplate 1 and the funnel 2. The funnel portion 2d covered by the insulating layer 6 includes, in FIG. 2, the entire edge part 2a and a portion of the bent part 2b. The insulating layer 6 is made of a frit glass, preferably a heat-resistant material. The insulating layer 6 lengthens the distance between the metal film 5 and the exposed surface of the funnel 2, thereby preventing dirt on the inside surface of the faceplate 1 or ambient electrons from causing creeping discharge from the metal film 5 to the funnel 2. 
     A method for manufacturing the CRT of FIG. 1 will be described below with reference to FIG. 3. FIG. 3 shows a supporting stand 10 which contains and supports the components such as the faceplate 1 and funnel 2 at fixed and desired positions. 
     First, the phosphor screen 4 is applied to an inside surface of the glass faceplate 1 and coated by the metal film 5, and the metal funnel 2 is prepared. Next, a first glass solder paste 11 is applied to at least one surface of the peripheral part 1a of the faceplate 1 and the edge part 2a of the funnel 2 and allowed to dry. The first glass solder paste 11 is a mixture of frit glass and solvent, the solvent being a mixture of nitrocellulose and iso-amylacetate. Next, the faceplate 1 and the funnel 2 are placed at a desired position on the supporting stand 10 so that portions covered by the first glass solder paste 11 are in contact. Next, a second glass solder paste is applied to an inside area 2d of the funnel 2 and the adjacent part of the faceplate 1, to form an insulating layer 6. The second glass solder paste comprises the same mixture of frit glass and solvent as the first glass solder paste. Next, the above components fixed on the supporting stand 10 are heated to a temperature of 430° C. for one hour, thereby sintering the first glass solder paste 11 and the second glass solder paste forming the insulating layer 6. 
     An advantage of this method is that one heating step performed, thereby simplifying the manufacturing process. 
     FIG. 4 is a partial sectional side view of an another embodiment. Elements in FIG. 4 corresponding to elements in FIG. 2 have the same reference numerals. In this CRT, the edge part 2a of the funnel 2 is joined to the outside surface of the faceplate 1. Except for this difference, the CRT in FIG. 4 is the same as in FIG. 2. 
     FIG. 5 is a partial sectional side view of still another embodiment. Elements in FIG. 5 corresponding to elements in FIG. 2 have the same reference numerals. In this CRT, the peripheral part 1a of the faceplate 1 has a groove 12 in its edge surface extending around the circumference of the faceplate 1, and the edge part 2a of the funnel 2 fits into the groove 12. Except for this difference, the CRT in FIG. 5 is the same as in FIG. 2. 
     FIG. 6 is a sectional side view of yet another embodiment. FIG. 6 is a diagram schematically showing the flat-type CRT disclosed for example in Japanese Patent Kokai Publication 181028/1986. Elements in FIG. 6 corresponding to elements in FIG. 2 have the same reference numerals. In FIG. 6, numeral 7 denotes a cathode for emitting electrons, 8 denotes means for passing the electrons, 9 denotes a group of electrodes, and 13 denotes a rear wall connected to the rear end of the funnel 2. 
     In the embodiments of FIGS. 4 to 6, creeping discharge between the metal film 5 and the funnel 2 resulting from dirt on the inside surface of the faceplate 1 or ambient electrons can be prevented for the same reason as in the embodiment of FIG. 2.