Patent Publication Number: US-6710530-B2

Title: Cathode ray tube having shadow mask with improved shock absorption effect

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Application No. 2001-68306, filed Nov. 2, 2001, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present invention relates to a cathode ray tube and, more particularly, to a cathode ray tube with a shadow mask which is free of deformation while involving improved shock absorption effect. 
     (b) Description of the Related Art 
     Generally, as shown in FIG. 11, a cathode ray tube includes a panel  101  with an inner phosphor screen  102 , a funnel  103  sealed to the panel  101  while facing the phosphor screen  102 , and a neck  105  sealed to the rear of the funnel  103  while mounting an electron gun  107  to emit electron beams  106  therein. A deflection yoke  109  externally surrounds the funnel  103 . 
     A color selection member  121  called the “shadow mask” is mounted within the panel  101  such that it faces the phosphor screen  102 . The electron beams emitted from the electron gun  107  are deflected by the deflection yoke  109 . The electron beams then pass through the shadow mask  121 , and land on the phosphor screen  102 . 
     The shadow mask  121  has a rectangular-shaped hole formation portion  121   a  with a plurality of beam-guide holes, a non-holed portion  121   b  surrounding the hole formation portion  121   a  in the shape of a rectangular frame, and a skirt  121   c  bent from the outer periphery of the non-holed portion  121   b  to the rear of the panel  101 . The respective components of the shadow mask  121  are formed in a body by way of press formation. 
     The skirt  121   c  of the shadow mask  121  is inserted into a mask frame  123  to thereby form a mask assembly. The mask assembly is internally suspension-fitted to the panel  101 . 
     When the skirt  121   c  of the shadow mask  121  is inserted into the mask frame  123  while being sealed thereto, stress is made at the borderline area between the shadow mask  121  and the mask frame  123  due to the outstretching of the skirt. The stress is transmitted to the hole-formation portion  121   a  of the shadow mask  121  via the skirt  121   c  and the non-holed portion  121   b.    
     With the stress, as illustrated in FIG. 12, the relatively weak periphery of the hole-formation portion  121   a  (the borderline area between the hole-formation portion  121   a  and the non-hole portion  121   b ) is sunken, and this results in curvature deformation of the shadow mask  121 . 
     Even though such a curvature deformation of the shadow mask is not visible, it greatly affects the strength of the final product against impact, and hence, it is preferable to reduce the stress transmitted to the hole-formation portion as much as possible. 
     In order to prevent such a curvature deformation, it has been proposed that a plurality of notches and bead-shaped expansions should be provided in the skirt, or slits should be provided below the non-holed portion, thereby preventing the stress from being generated at the boundary of the mask frame. However, with this method, the effect of preventing the curvature deformation is not so great. 
     Furthermore, as the outstretching is made at the bottom of the skirt, the length of the skirt may be reduced to decrease the degree of outstretching, thereby preventing the curvature deformation. In this case, the welding point of the mask frame to the mask is heightened so that the flexibility relation between the skirt and the welding point at the possible impact of dropping is deteriorated, and this is disadvantageous in the shock absorption. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a cathode ray tube which enhances the stress prevention effect at the boundary of the mask frame as well as at the welding point thereof to the shadow mask where two or more half etchings differentiated in the etching roughness are made. 
     Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     The foregoing and other objects of the present invention may be achieved by providing a cathode ray tube including: a panel with an inner phosphor screen; a funnel sealed to the panel while facing the phosphor screen, the funnel being externally mounted with a deflection yoke; a neck sealed to the rear of the funnel while mounting an electron gun to emit electron beams therein, a shadow mask placed within the panel, the shadow mask having a hole-formation portion with a plurality of beam-guide holes, a non-holed portion externally surrounding the hole formation portion while being shaped with a rectangular frame, and a skirt bent from the outer periphery of the non-holed portion to the rear of the panel, the skirt having a basic etching portion half-etched at a predetermined roughness, the components of the shadow mask being integrated into one body; a welding portion is formed at the bottom of the skirt with a plurality of welding points; and a mask frame internally suspension-fitted to the panel while being welded to the skirt to support the shadow mask, wherein the skirt of the shadow mask has a subsidiary etching portion placed between the welding portion and the basic etching portion while being half-etched at a roughness greater than the roughness of the basic etching portion. 
     In another aspect of the present invention, the subsidiary etching portion is formed at the central bottom portion of the skirt. 
     In another aspect of the present invention, the volume reduction rate per unit volume of the subsidiary etching portion by way of the half etching is greater than the volume reduction rate per unit volume of the basic etching portion. The volume reduction rate per unit volume of the subsidiary etching portion by way of the half etching is established to be in the range of 40-60%. 
     In yet another aspect of the present invention, a plurality of longitudinal slit-typed etching grooves are formed at the subsidiary etching portion while horizontally proceeding parallel to each other. Further, the etching grooves may be partitioned into two or more columns. In this case, it is preferable that the distance P c  between the etching groove columns is established to be in constant proportion to the vertical pitch P v  of the etching grooves. 
     In yet another aspect of the present invention, the subsidiary etching portion is formed either at the external surface of the skirt, or at the internal surface thereof. In yet another aspect of the present invention, the subsidiary etching portion may be formed both at the external surface of the skirt and at the internal surface thereof. In the latter case, the central axes of the etching grooves correspondingly formed at the internal and the external surfaces of the skirt agree to each other, or are deviated from each other by a predetermined distanced. In yet another aspect of the present invention, a width of each groove on one surface of the mask skirt may be narrower than that of the other surface of the mask skirt. 
     The foregoing and other objects of the present invention may also be achieved by providing a cathode ray tube including: a panel with an inner phosphor screen; a funnel sealed to the panel while facing the phosphor screen, the funnel being externally mounted with a deflection yoke; a neck sealed to the rear of the funnel while mounting an electron gun to emit electron beams therein; a shadow mask placed within the panel, the shadow mask having a hole-formation portion with a plurality of beam-guide holes, a non-holed portion externally surrounding the hole-formation portion while being shaped with a rectangular frame, and a skirt bent from the outer periphery of the non-holed portion to the rear of the panel, the components of the shadow mask being integrated into one body, and a mask frame internally suspension-fitted to the panel while being welded to the skirt to support the shadow mask, wherein the skirt of the shadow mask is formed using two or more half etchings differentiated in the etching roughness. 
     In an aspect of the present invention, the skirt of the shadow mask may be formed by way of the half etching such that the etching roughness at the bottom side of the skirt is greater than the etching roughness at the top of the skirt. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
     FIG. 1 is a cross sectional view of a cathode ray tube with a shadow mask according to an embodiment of the present invention; 
     FIG. 2A is a perspective view of the shadow mask illustrated in FIG. 1; 
     FIGS. 2B and 2C are enlarged views of the welding portion and the basic etching portion of the skirt illustrated in FIG. 1; 
     FIG. 3 is a partial side view of a shadow mask skirt illustrating a slit-type half etching; 
     FIG. 4 is a partial side view of a shadow mask skirt illustrating another slit-type half etching; 
     FIG. 5 is a partial sectional view of the shadow mask skirt taken along the V—V line of FIG. 3; 
     FIGS. 6 to  9  are partial sectional views of shadow mask skirts illustrating various types of half etchings; 
     FIG. 10 is a side view of a shadow mask according to another embodiment of the present invention; 
     FIG. 11 is a cross sectional view of a conventional cathode ray tube with a shadow mask; and 
     FIG. 12 is a partial amplified view of the cathode ray tube illustrated in FIG. 11 where the shadow mask is fitted to a mask frame. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
     FIG. 1 is a cross sectional view of a cathode ray tube with a shadow mask according to an embodiment of the present invention, and FIG. 2A is a perspective view of the shadow mask illustrated in FIG.  1 . 
     As illustrated in FIG. 1, the cathode ray tube includes a panel  10  with an inner phosphor screen  12 , a funnel  14  sealed to the panel  10  while facing the phosphor screen  12 , and a neck  16  sealed to the rear of the funnel  14  while mounting an electron gun  18  therein. 
     A mask frame  25  is internally suspension-fitted to the panel  10 , and a shadow mask  23  is welded to the mask frame  25  by way of a bottom welding portion  26  with a plurality of welding points. The shadow mask  23  is provided with a hole-formation portion  23   a , a non-holed portion  23   b , and a skirt  23   c . The respective components of the shadow mask  23  are formed in a body of the shadow mask  23 . 
     As illustrated in FIG. 2A, the skirt  23   c  of the shadow mask  23  is bent from the outer periphery of the non-holed portion  23   b  to the rear of the panel  10 . The skirt  23   c  has a basic etching portion  24  half-etched at a predetermined roughness, and a subsidiary etching portion  27  placed between the welding portion  26  and the basic etching portion  24 . 
     As shown in FIGS. 2A through 2C, the etching roughness of the subsidiary etching portion  27  is established to be higher than that related to the basic etching portion  24 . The subsidiary etching portion  27  is placed at the central bottom of the skirt  23   c . The basic etching portion  24  and the subsidiary etching portion  27  have etching grooves, and the depths of the etching grooves in the two different etching portions  24  and  27  are indicated by R 1  and R 2 . The difference in the etching roughness may be represented by the relation of R 2 &gt;R 1 . 
     The etching roughness may be defined by the volume reduction rate per unit volume by way of the etching while being determined dependent upon the shape, width, depth and pitch of the etching groove or slit. 
     Particularly, the skirt  23   a  is formed such that the volume reduction rate per unit volume of the subsidiary etching portion  27  by way of the half etching is greater than that of the basic etching portion  24 . Preferably, when the volume reduction rate per unit volume by way of the usual half etching is assumed to be in the range of 4-15%, the volume reduction rate per unit volume of the subsidiary etching portion  27  is established to be in the range of 40-60%. 
     When the volume reduction rate per unit volume of the subsidiary etching portion  27  is 40% or less, it becomes difficult to achieve the desirable effect compared to other portions. When the volume reduction rate is 60% or more, the shadow mask is liable to be broken during the formation. 
     In the case of a dot-type half etching, the volume reduction rate per unit volume by way of the half etching can be expressed by the mathematical formula 1.                  (       4   3        π                   r   3       )     /   2         P   h   2     ×   t             (   1   )                         
     where r indicates the dot radius, P h  the pitch, and t the thickness of the shadow mask. 
     For instance, in the case of a 17″ CDT, when r=0.075 mm, P h =0.15 mm and t=0.12 mm, the volume reduction rate per unit volume is established to be about 14.7%. 
     With the embodiments of present invention, the subsidiary etching portion  27  of the skirt  23   c  is negatively affected in the half etching where the volume reduction rate per unit volume is increased up to the level of not bearing the breakage problem during the formation so that it can work as a shock absorption region for the skirt  23   a.    
     FIG. 3 is a partial side view illustrating a slit-type half etching applied to the skirt of the shadow mask, and FIG. 4 illustrates another slit-type half etching applied thereto. 
     As illustrated in FIG. 3, the slit-type half etching may be applied particularly to the subsidiary etching portion  27  of the skirt. With the half etching, a plurality of longitudinal slit-type etching grooves are formed while horizontally proceeding parallel to each other. 
     As illustrated in FIG. 3, a plurality of mono slit-type etching grooves  23   d  are formed while proceeding parallel to each other with a predetermined vertical pitch P v . As illustrated in FIG. 4, it is possible that a plurality of slit-type etching grooves  23   f  may be formed parallel to each other while being partitioned into two or more columns. It is preferable that the inter-column distance P c  should be established to be in constant proportion to the vertical pitch P v . 
     FIG. 5 is a cross sectional view of the shadow mask skirt taken along the V—V line of FIG. 3, and FIGS. 6 to  9  are partial sectional views of shadow mask skirts where various kinds of slit-typed half etchings are applied. 
     As illustrated in FIG. 5, the etching grooves  23   d  may be formed at the external surface of the shadow mask skirt  23   c  with a predetermined vertical pitch P v . Particularly, it is preferable that a subsidiary etching portion where the etching roughness is greater than that of the basic etching portion is positioned between the welding portion of the skirt  23   c  and the basic etching portion. 
     Alternatively, as illustrated in FIG. 6, the etching grooves  31   d  by way of the half etching may be formed at the internal surface of the skirt  31   c  with a predetermined vertical pitch P v . Particularly, it is preferable that a subsidiary etching portion where the etching roughness is greater than the basic etching portion is formed between the welding portion of the skirt  31   c  and the basic etching portion. 
     Furthermore, as illustrated in FIGS. 7 to  9 , the etching grooves by way of the half etching may be formed at the internal surface of the skirt as well as at the external surface thereof with a predetermined vertical pitch P v . Particularly, it is preferable that a subsidiary etching portion where the etching roughness is greater than that of the basic etching portion is formed between the welding portion of the skirt and the basic etching portion. 
     As illustrated in FIG. 7, the etching grooves  34   d  and  34   f , formed at the external and internal surfaces of the skirt  34   c  while corresponding to each other, are established such that the central axes thereof agree with each other. 
     As in FIG. 8, the etching grooves  35   d  and  35   f  formed at the external and internal surfaces of the skirt  35   c , while corresponding to each other, are established such that the central axes thereof are deviated from each other by a predetermined distance d. 
     As illustrated in FIG. 9, the etching groove  37   d  formed at the external surface of the skirt  37   c  is established to bear a first width d 0 , and those  37   f  formed at the internal surface of the skirt  37   c  to bear a second width d l , narrower than the first width d 0  such that a one-to-many correspondence relation is made between the internal and the external etching grooves  37   f  and  37   d . Alternatively, the one to many correspondence relation may be made in a reverse order, that is, between the external and the internal etching grooves  37   d  and  37   f  while being differentiated in the width thereof. 
     In the drawings, the reference numeral Tm indicates the thickness of the shadow mask skirt. 
     Meanwhile, in case the slit-type half etching is applied to the subsidiary etching portion of the skirt, the basic etching portion may suffer a slit-type half etching where the etching roughness is smaller than that of the subsidiary etching portion. Alternatively, the etching grooves may be formed by way of a dot-type half etching. 
     FIG. 10 is a side view of a shadow mask according to another preferred embodiment of the present invention. 
     As illustrated in FIG. 10, the shadow mask skirt  43   c  is provided with a subsidiary etching portion  47  positioned at the bottom side thereof where the etching roughness is greater than that of the top. 
     A longitudinal slit-type etching groove  43   d  may be formed at the bottom side of the skirt  43   c  by way of the slit-type half etching. For instance, a plurality of mono slit-type etching grooves are formed while proceeding parallel to each other by a predetermined vertical pitch, or a plurality of slit-type etching grooves are formed parallel to each other while being partitioned into two or more columns. In the latter case, the inter-column distance may be established to be in constant proportion to the vertical pitch. 
     Furthermore, the etching groove  43   d  may be formed either at the internal or at the external surface of the skirt  43   c , or both at the internal and at the external surfaces thereof. In the latter case, the central axes of the etching grooves correspondingly formed at the internal and external surfaces of the skirt may agree with each other, or deviate from each other by a predetermined distance. 
     As with the bottom side of the skirt  43   c , the slit-type half etching may be applied to the top thereof to form a longitudinal slit-type etching groove there. Alternatively, a dot-type half etching may be applied thereto to form a dot-type etching groove there. It is preferable that the etching roughness related to the top side of the skirt should be established to be relatively small compared to that related to the bottom thereof. 
     An impact test was made with respect to 19″ color display tubes (CDTs), and the result is illustrated in Table 1. In the test, the slit-type half etching illustrated in FIG. 9 was applied to the subsidiary etching portion of the shadow mask skirt. The volume reduction rate per unit volume by way of the half etching is established to be about 56.8%. 
     In Table 1, G indicates the acceleration degree corresponding to the degree of impact. For instance, when the terrestrial gravitation close to the earth surface is indicated by 1G, at least a gravitation of 20G is required for the 19″ CDT. As the value of G is increased, the strength of the target object against impact is enhanced. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Prior art 
                 Present invention 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Example 1 
                 21.5 G&#39;s 
                 31.1 G&#39;s 
               
               
                   
                 Example 2 
                 22.5 G&#39;s 
                 29.8 G&#39;s 
               
               
                   
                 Example 3 
                 22.3 G&#39;s 
                 30.4 G&#39;s 
               
               
                   
                 Example 4 
                 21.9 G&#39;s 
                 30.7 G&#39;s 
               
               
                   
                 Average 
                 22.1 G&#39;s 
                 30.5 G&#39;s 
               
               
                   
                   
               
            
           
         
       
     
     It can be estimated from Table 1 that the strength of the target object against impact in Examples 1 to 4 under the application of the half etching is very high compared to the prior art-based cases. 
     As described above, with the cathode ray tube having a half-etched shadow mask, a subsidiary etching portion is provided between the welding portion of the skirt and the basic etching portion. The subsidiary etching portion involves an etching roughness greater than that related to the basic etching portion so that the possible stress at the boundary of the mask frame as well as at the welding portion thereof to the mask is prohibited, thereby preventing deformation in the curvature of the hole-formation portion of the shadow mask. 
     In addition, the curvature at the borderline area between the hole-formation portion of the shadow mask and the non-holed portion thereof is stabilized, thereby enhancing the strength thereof against impact such as dropping. 
     Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.