Patent Publication Number: US-6657374-B1

Title: Cathode ray tube

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a cathode ray tube having a lightweight funnel and a lightweight panel. 
     2. Description of the Related Art 
     A schematic appearance of a cathode ray tube is shown in 
     FIG.  6 . In FIG. 6, D (mm) shows a diagonal axis length which is an effective dimension of a diagonal axis defined in EIAJ ED-2136A of the Standard of Electronic Industries Association of Japan. 
     FIG. 7 is a view showing a method of setting a diagonal axis length D of the cathode ray tube. In FIG. 7, a method  1  and a method  2  are shown. The method  1  can provide an effective shape (W, H, D: effective lengths of a major axis, a minor axis, and a diagonal axis shown in FIG. 6 respectively) by adding a 30-degree length of an blend R of an inner wall surface to the center position of the blend R of the inner wall surface, while using an R shape of a corner portion and a center position of the R shape of the panel inner wall surface (IL, IS, ID: center positions of the blend R of the panel inner wall surface in respective sectional shapes along the major axis, the minor axis, and the diagonal axis shown in FIG. 6 respectively). The method  2  can provide an effective diameter by using a contact point P of an inner curved surface Z=f(x,y) and the blend R, as shown in the right side in FIG.  7 . 
     A sectional shape taken along an A-A′ line in FIG. 6 is shown in FIG.  8 . In FIG. 8,  1   a  denotes a panel;  11 , a face surface which is formed on the panel  1   a  and has a substantially square outer shape and on which the image is displayed;  12 , a blend R portion of an outer wall surface;  13 , a skirt portion which extends substantially vertically from all areas of an outer peripheral portion of the face surface  11  to the face surface  11 ;  1   b , a funnel which has a funnel shape whose outer shape of a widest open portion of the funnel shape has the same outer shape as the skirt portion  13  of the panel  1   a ;  14 , a sealing portion for connecting the panel  1   a  and the funnel  1   b ;  121 , an F 0  point which is located in the neighborhood of a joint between the blend R portion  12  and the face surface  11 ;  122 , an F 1  point which is located in the neighborhood of a joint between the blend R portion  12  and the skirt portion  13 ;  18 , a neck portion which is a part of the funnel  1   b  and into which the electron gun is installed;  17 , a yoke portion which is a part of the funnel  1   b  and onto which a deflection yoke for deflecting electron beams is fitted;  15 , a body portion which is a part of the funnel  1   b  as shown in FIG.  8  and extends to the sealing portion  14  connected to the panel; and  16 , a TOP OF ROUND which is an inflection point on a boundary line between the yoke portion  17  and the body portion  15  and is located at a position remote from a yoke reference line by 40 to 50 mm in the sealing portion direction. In this case, the yoke reference line is a reference line in a tube axis of the funnel, which is set forth in EIAJ ED-2134B. 
     As for the shape of the funnel  1   b , respective dimensions of the sectional shape of the funnel  1   b  shown in FIG. 9 are given in Table 1 as an example. 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Funnel Outer Shape 
                 [mm] 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Diagonal axis length 
                 D 
                 410 mm 
                 460 mm 
                 510 mm 
               
               
                 Minor axis outer length 
                 L1 
                 147.09 
                 164.14 
                 184.44 
               
               
                 Major axis outer length 
                 L2 
                 182.44 
                 205.74 
                 227.24 
               
               
                 Diagonal axis outer length 
                 L3 
                 220.64 
                 246.49 
                 274.54 
               
               
                 Sealing portion to 
                 L4 
                 154.1 
                 183.7 
                 198.7 
               
               
                 Reference line 
               
               
                 Reference line to Neck 
                 L5 
                 43.4 
                 43.4 
                 43.4 
               
               
                 portion 
               
               
                 Reference line to Top of 
                 L6 
                 43.4 
                 45.03 
                 45.03 
               
               
                 Round 
               
               
                 Total length (Reference 
                 L7 
                 324.5 
                 354.1 
                 369.1 
               
               
                 value) 
               
               
                   
               
            
           
         
       
     
     The outer shape of the funnel  1   b  shown in FIG. 9 is connected smoothly from the neck portion  18 , which is formed as a pipe shape of less than φ40 mm in parallel with the tube axis direction, to the cone-shaped yoke portion  17 , to which the deflection yoke is fitted and which is formed smoothly by using several R-shapes, and then connected to the sealing portion  14  via the TOP OF ROUND  16 . 
     Normally, if the glass bulb consisting of the panel  1   a  and the funnel  1   b  is designed, a maximum tensile vacuum stress which is generated when an inside of the glass bulb is made vacuous is decided from a viewpoint of reliability, especially a viewpoint of the delayed fracture performance, and then a thickness is decided by using the stress as a threshold value. In addition, portions at which the vacuum stress is generated to cause the reduction of the reliability are located in the neighborhood of the blend R portion  12  of the face surface  11  of the panel, and in many cases such vacuum stress is generated mainly on the F 0  point  121  or the F 1  point  122  which is located within a width of 20 mm from both end positions of the blend R. 
     First, thicknesses at the F 0  point  121  and the F 1  point  122  are decided in view of the maximum vacuum stress. Then, a thickness distribution of the skirt portion  13  is decided such that the crack of the glass, etc. are not generated in the heating process step contained in manufacturing steps of the glass bulb. Accordingly, thicknesses up to the sealing portion  14  are decided, whereby the thickness design of the panel  1   a  can be completed. 
     Then, a thickness of the funnel  1   b  is decided based on the thickness of the sealing portion  14 , whereby the shape design of the funnel  1   b  can be completed. That is, thicknesses of the body portion  15  and the yoke portion  17  are decided according to the thickness of the sealing portion  14  to be connected smoothly to the neck portion  18 . 
     For example, as for the aperture grille type cathode ray tube which has the panel  1   a  whose diagonal axis length D is 410 mm and to which a physically reinforcing layer is applied, and in which the maximum value of the stress generated on a surface of the panel  1   a  when the inside of the glass bulb is made vacuous is less than 8.85 MPa, and in which an outer shape R of the face surface  11  is about more than R 30000 mm, the center thickness of the panel  1   a  is set to about 12 mm, the width of the sealing portion  14  is set to about 9 mm, and the thickness of the body portion  15  is set to about 5.4 mm at the lowest minimum in the range from the B-B′ sectional shape to the C-C′ sectional shape of the body portion  15  shown in FIG.  8 . 
     In this case, the B-B′ sectional shape is located at a position which is a half of the funnel body portion in the height direction. Also, a sectional shape which is located just in the middle of the B-B′ sectional shape and the TOP OF ROUND to divide the height into two parts is set as the C-C′ sectional shape. 
     Thickness data of the glass bulb shape every diagonal axis length D are set forth in Table 2. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                 Example 1 
                 Example 2 
                 Example 3 
               
               
                   
                 (D) 
                 (410 mm) 
                 (460 mm) 
                 (510 mm) 
               
               
                   
                   
               
             
            
               
                   
                 Center thickness 
                 12.0 mm  
                 13.0 mm  
                 14.0 mm  
               
               
                   
                 Sealing surface 
                 9.0 mm 
                 9.0 mm 
                 9.2 mm 
               
               
                   
                 thickness 
               
               
                   
                 Body portion center 
                 5.4 mm 
                 5.5 mm 
                 5.5 mm 
               
               
                   
                 thickness 
               
               
                   
                   
               
            
           
         
       
     
     Here, the center thickness means a center thickness of the panel  1   a , the sealing surface thickness means a thickness of the sealing portion  14 , and the body portion center thickness means a minimum value of the thickness (here, the thickness on the minor axis) in the range from the B-B′ sectional shape to the C-C′ sectional shape (positions corresponding to 50 to 75% of the length of the funnel body portion  15  along the tube axis direction) of the body portion  15  shown in FIG.  8 . 
     In the structure of the cathode ray tube in the related art, since the design is carried out in light of several points such as the blend R portion  12 , etc., such design depends largely upon the experience of the designer and thus the cathode ray tube has the unnecessary thickness which is naturally unnecessary. In particular, the cathode ray tube having a flat panel face tends to increase the thickness, and thus a weight of the cathode ray tube becomes heavy. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to overcome the above subjects, and it is an object of the present invention to provide a lightweight cathode ray tube by detecting an optimal thickness of a funnel portion. 
     In order to achieve the above object, according to the present invention, there is provided a cathode ray tube comprising: a panel having a face surface whose outer shape is a substantial rectangle and a skirt portion which extends substantially vertically from all areas of an outer peripheral portion of the face surface to the face surface; a funnel which has a funnel shape whose outer shape of a widest open portion of the funnel shape has a same outer shape as the skirt portion of the panel; and a sealing portion for connecting the panel and the funnel, wherein the funnel comprises a body portion having a sealing surface which is connected to the sealing portion, a yoke portion connected to the body portion, and a neck portion connected to the yoke portion, and wherein the cathode ray tube includes a portion whose thickness becomes 
     
       
         (2.78+0.0038 ×D )≦ t   1 ≦(3.7+0.0038 ×D )[mm] 
       
     
     where D is a diagonal axis length [mm] between rectangular corner portions of an effective screen of the panel, and t 1  is a thickness [mm] at positions which occupy 75% of a length of the body portion extending from the sealing surface of the body portion to the yoke portion along a tube axis direction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a flowchart showing an optimally analyzing approach according to the present invention. 
     FIG. 2 is a view showing sectional shapes of a conventional glass bulb and a glass bulb according to the present invention for the sake of comparison. 
     FIG. 3 is a graph showing actually measured values of a thickness of a funnel body portion in a C-C′ sectional shape of the cathode ray tube in FIG.  8 . 
     FIG. 4 is a graph showing minimum thickness values of the funnel body portion in a range from a B-B′ sectional shape to the C-C′ sectional shape of the cathode ray tube in FIG.  8 . 
     FIG. 5 is a graph showing a thickness ts of the funnel body portion and a thickness w of a sealing portion of the cathode ray tube for the sake of comparison. 
     FIG. 6 is a schematic perspective view showing an appearance of the cathode ray tube. 
     FIG. 7 is a view showing a method of setting a diagonal axis length D of the cathode ray tube. 
     FIG. 8 is a sectional view showing a sectional shape of the cathode ray tube taken along an A-A′ line in FIG.  6 . 
     FIG. 9 is a sectional view showing a shape of the funnel portion of the cathode ray tube. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In order to obtain a cathode ray tube according to the present invention, the design approach which has been disclosed in Japanese Patent Application No. Hei. 10-159674 is employed. Then, the design approach will be described hereinbelow. 
     This design approach is an optimization analytic approach in which the unique improvement is added to the existing genetic algorithm (abbreviated as “GA” hereinafter). This design approach executes the analysis by using thicknesses of the glass bulb as parameters to obtain the glass bulb which can have optimal thicknesses. 
     FIG. 1 is a flowchart showing an optimally analyzing approach according to the present invention. In FIG. 1, 
     (1) Initial plate thicknesses (thicknesses) of respective elements of the analysis model for n individuals (referred to as “individuals” hereinafter) are decided based on the random numbers. The n individuals are analyzed by the FEM to calculate the maximum stress. Also, four parameters of α, β, γ, δ are defined every individual, and 0.0 to 1.0 values of respective parameters are expressed 8-bit genes. That is, the expression of 8-bit genes signifies that the values of respective parameters are divided equally into 256 equal parts in the domain and then expressed by 8-place binary digits. 
     (2) The maximum stress and the weight are calculated by FEM-analyzing respective individuals to calculate a degree of adaptation based on Equation (c) described later. 
     (3) The convergence decision is performed. 
     (4) The individuals (models) with the low degree of adaptation are selected (rejected) and the individuals with the high degree of adaptation are multiplied (the number of models is increased). Thus, life groups are evolved. 
     (5) The values of parameters of α, β, γ, δ are changed. As a method of changing, neighborhood values of the parameters some two individuals (models) may be selected (this is referred to as the crossing), or completely different values may be adopted by using the random number (this is referred to as the mutation). 
     (6) The plate thickness (thickness) is changed based on Equation (a) described in the following.                  th   i     g   +   1       =           σ   j       σ   o         ×     1   β     ×     th   i   g                     (       if                     σ   j       σ   o         &lt;   α     )              
            th   i     g   +   1       =           σ   j       σ   o         ×     1   δ     ×     th   i   g                     (       if                     σ   j       σ   o         &lt;   γ     )                 Equation                   (   a   )                 P   =       ∑     i   =   1     n                     {           (         σ   j       σ   o       -   1     )             (       if                     σ   j       σ   o         &gt;   1.0     )                          0         (       if                     σ   j       σ   o         &lt;   1.0     )           }               Equation                   (   b   )                 Fit   =     1   -     W     W   o       -     C   ×   P               Equation                   (   c   )                 C   =     g   ×     g   /   G               Equation                   (   d   )                           
     In other words, if a stress ratio σ j /σ a  is smaller than α, the plate thickness (thickness) is changed as indicated by the first equation of Equation (a). Also, if the stress ratio σ j /σ a  is larger than γ, the plate thickness (thickness) is changed as indicated by the second equation of Equation (a). In this case, the case where the bending stress is dominant is considered, (σ j /σ a ) ½  is employed as the plate thickness changing parameter. 
     Here, β and δ are parameters associated with increase and decrease of the plate thickness. In Equation (a), th g , is the plate thickness of the element j in the generation g, σ j  is the maximum stress (absolute value) of the element j, and σ a  is the allowable stress of the member. 
     Also, in the case of the constrained optimization problem, there has been proposed such an approach that, when the constraint is not satisfied, the penalty term is added to the evaluation value to lower a degree of adaptation. However, there is such a possibility that the resolution to satisfy the constraint cannot be obtained if a weight coefficient of the penalty term is small, but it is difficult to obtain the wide area optimal solution if the weight coefficient is large. Hence, in the above Application, an solution searching efficiency can be improved by setting the penalty term as a function of the number of generation. 
     As the result of the FEM analysis, if the element stress is in excess of the allowable stress, the penalty value P is decided against the excess stress, as indicated by Equation (b), and also the penalty term in which P is multiplied by C is added to the non-dimensional weight in the degree of adaptation, as indicated by Equation (c). Where C≈0 is set in the stage that the number of generation is small, as indicated by Equation (d), and the individuals which cannot satisfy the constraint are ready to be selected by increasing C with the increase of the number of generation to thus increase the penalty. 
     In Equation (c), Fit denotes the degree of adaptation; W, the weight; Wo, a reference weight; P, the penalty value; C, the weight constant; σ j , the element stress of the element j; and g, the number of generation. Also, in the above Application, the number of generation is used as the calculation closing condition, G denotes the final number of generation, and n denotes the number of element. 
     In this case, as characteristic values, the elastic modulus E (GPa)=71.5, the Poisson&#39;s ratio ν=0.21, the density r (kg/mm 3 )=2.5×10 −6  are applied to the panel  1   a . Also, the elastic modulus E (GPa)=69.2, the Poisson&#39;s ratio ν=0.19, the density r (kg/mm 3 )=3.0×10 −6  are applied to the funnel  1   b.    
     Embodiment 1 
     As a cathode ray tube according to the present invention, if such a cathode ray tube is employed that the glass which has a physically reinforcing layer thereon is used, the maximum value of the stress generated on the panel outer surface when the inside of the bulb is made vacuous is set to 10.2 MPa, an aspect ratio of the panel face surface is set as 3:4, the panel face surface has an almost flat shape having about R30000 mm or more, and the color selection electrode is of the aperture grille type, for example, is employed, the thickness of the body portion  15  can be thinned up to about 4.4 mm along the minor axis, and accordingly the thickness of the sealing portion  14  can be thinned up to about 7.5 mm, and the center thickness of the face portion of the panel  1   a  can be thinned up to about 10 mm when a diagonal axis length D of 410 mm, for example, is selected. For the sake of comparison, sectional shapes of the conventional glass bulb and the glass bulb according to the present invention, both have the diagonal axis length D of 410 mm, are shown in FIG.  2 . 
     Since a width of the sealing portion  14  on the funnel  1   b  side must be given appropriately with respect to a width of the sealing portion  14  on the panel  1   a  side, a thickness in the vicinity of the sealing portion  14  of the funnel  1   b  cannot be thinned independently with the thickness of the sealing portion  14  on the panel  1   a . For example, even if the thickness of the body portion  15  is optimal at 4.4 mm, the thickness in the neighborhood of the sealing portion  14  of the body portion  15  cannot be set immediately to 4.4 mm since a smooth distribution of the thickness from 7.5 mm as the thickness of the sealing portion  14  of the panel  1   a  must be attained. However, for example, reduction in the thickness can be achieved at locations from the B-B′ sectional shape to the C-C′ sectional shape of the body of the funnel shown in FIG.  8 . 
     Embodiment 2 
     As the cathode ray tube according to the present invention, results of the glass bulb shape are given in Table 3. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                   
                 Example 1 
                 Example 2 
                 Example 3 
               
               
                   
                 (D) 
                 (410 mm) 
                 (460 mm) 
                 (510 mm) 
               
               
                   
                   
               
             
            
               
                   
                 Center thickness 
                 10.0 mm  
                 11.0 mm  
                 12.0 mm  
               
               
                   
                 Sealing surface 
                 7.5 mm 
                 8.0 mm 
                 8.5 mm 
               
               
                   
                 thickness 
               
               
                   
                 Body portion center 
                 4.4 mm 
                 4.4 mm 
                 4.8 mm 
               
               
                   
                 thickness 
               
               
                   
                   
               
            
           
         
       
     
     The body portion center thickness set forth in this example is a value on the minor axis. According to the above configuration, a lightweight cathode ray tube which is able to omit an amount of useless glass can be obtained. 
     Embodiment 3 
     Respective dimensions of the conventional cathode ray tubes and the cathode ray tubes according to embodiments of the present invention at this time are given in Table 4. Numeral values (⋆ mark) in Table 4 correspond to the embodiments at this time. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 [mm] 
               
            
           
           
               
               
               
               
            
               
                 Diagonal axis 
                 Minor axis 
                 Major axis 
                 Diagonal axis 
               
               
                 length D 
                 thickness ts 
                 thickness tl 
                 thickness td 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 410 
                 6.40 
                 6.70 
                 6.90 
               
               
                 410 
                 5.45 
                 5.98 
                 6.60 
               
               
                 ⋆410   
                 4.40 
                 4.65 
                 4.90 
               
               
                 410 
                 5.50 
                 5.87 
                 6.50 
               
               
                 460 
                 5.50 
                 6.10 
                 6.60 
               
               
                 ⋆460   
                 4.40 
                 4.70 
                 4.90 
               
               
                 500 
                 5.88 
                 6.50 
                 6.75 
               
               
                 500 
                 5.88 
                 6.50 
                 6.75 
               
               
                 510 
                 5.80 
                 6.13 
                 6.45 
               
               
                 ⋆510   
                 4.78 
                 5.00 
                 5.56 
               
               
                   
               
            
           
         
       
     
     FIG. 3 shows measured values of the thickness of the funnel body portion as a graph by plotting Table 4. Where an abscissa denotes the diagonal axis length D of the effective screen of the panel, and an ordinate denotes a smallest thickness ts of the thickness t 1  in the C-C′ sectional shape of the body portion on the minor axis. In this case, FIG. 3 is depicted to confirm a level to which the cathode ray tube according to the present invention at this time can be improved rather than the conventional cathode ray tube. 
     In FIG. 3, points encircled with a circle indicate embodiments according to the present invention at this time, and other points indicate conventional examples. Out of two straight lines in the graph, a lower straight line is obtained by a linear approximation based on the method of least squares in order to get a relationship between the thickness ts of the body portion  15  on the minor axis of the cathode ray tube according to the present invention at this time and the diagonal axis length D. Since it may be supposed that a lower limit value of the thickness is changed according to the diagonal axis length D and thus the minimum thickness value becomes thick as the diagonal axis length D is increased, this relationship can be approximated by a right-upward inclined straight line. 
     An approximate expression ts of the lower straight line can be given as 
     
       
           ts =2.78+0.0038 ×D [mm]. 
       
     
     It is possible to reduce the thickness ts into this value. 
     While, an upper straight line in FIG. 3 can be depicted by lifting the lower straight line up to a level of the conventional cathode ray tube while keeping a gradient 0.0038 of the lower straight line. The upper straight line has an approximate expression ts 
     
       
           ts =3.7+0.0038 ×D [mm]. 
       
     
     This is because, if predetermined constraints are given, the thickness of the funnel body portion has a linear relationship, which has the same gradient 0.0038 as the above approximate expression, relative to the bulb size. 
     Here, ts is the thickness on the minor axis to provide the thinnest portion of t 1 . Since the lower limit value of ts means a lower limit value of the thinnest portion of t 1 , such lower limit value may be said in other words as a lower limit value of t 1 . 
     Accordingly, such a shape can be obtained that contains a portion whose thickness t 1  becomes 
     
       
         (2.78+0.0038 ×D )≦ t   1 ≦(3.7+0.0038 ×D )[mm] 
       
     
     at positions which occupy 75% of the length of the body portion  15  extending from the sealing surface of the body portion  15  to the yoke portion  17  along the tube axis direction. 
     In addition, Table 5 indicates a relationship between the minimum value t 2  [mm] of the thickness of the body portion, which extends from the B-B′ sectional shape to the C-C′ sectional shape, and the diagonal axis length D of the effective screen. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 [mm] 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Diagonal axis 
                 Minimum 
                 Maximum 
                   
               
               
                   
                 length D 
                 thickness t2 
                 thickness 
                 Difference 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 410 
                 6.40 
                 7.10 
                 0.70 
               
               
                   
                 410 
                 5.40 
                 6.80 
                 1.40 
               
               
                   
                 ⋆410   
                 4.40 
                 5.10 
                 0.70 
               
               
                   
                 410 
                 5.50 
                 6.70 
                 1.20 
               
               
                   
                 460 
                 5.50 
                 6.80 
                 1.30 
               
               
                   
                 ⋆460   
                 4.40 
                 5.90 
                 1.50 
               
               
                   
                 500 
                 5.80 
                 6.80 
                 1.00 
               
               
                   
                 500 
                 5.80 
                 6.80 
                 1.00 
               
               
                   
                 510 
                 5.50 
                 6.60 
                 1.10 
               
               
                   
                 ⋆510   
                 4.78 
                 5.10 
                 0.32 
               
               
                   
                   
               
            
           
         
       
     
     FIG. 4 shows measured minimum thickness values of the funnel body portion as a graph by plotting Table 5. Such a shape can be obtained that contains a portion whose thickness t 2  becomes 
     
       
         (2.78+0.0038 ×D )≦ t   2 ≦(3.5+0.0038 ×D )[mm] 
       
     
     in a range between the B-B′ sectional shape and the C-C′ sectional shape, i.e., at positions which occupy 50% to 75% of the length of the body portion  15  extending from the sealing portion  14  to the neck portion  18  along the tube axis direction. 
     Accordingly, the thickness of the body portion  15  can be reduced as a whole between the B-B′ sectional shape and the C-C′ sectional shape. 
     Embodiment 4 
     Table 6 indicates a sum of a thickness w of a shielding portion and the thickness ts of the funnel body portion relative to the diagonal axis length D of the effective screen of the panel, in the conventional cathode ray tube and the cathode ray tube according to the present invention. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 [mm] 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                   
                 Sealing 
                   
               
               
                   
                 Diagonal axis 
                 Minor axis 
                 portion 
               
               
                   
                 length D 
                 thickness ts 
                 thickness w 
                 (ts + w) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 410 
                 6.40 
                 9.0 
                 15.40 
               
               
                   
                 410 
                 5.45 
                 9.0 
                 14.45 
               
               
                   
                 ⋆410   
                 4.40 
                 7.5 
                 11.90 
               
               
                   
                 410 
                 5.50 
                 9.0 
                 14.50 
               
               
                   
                 460 
                 5.50 
                 9.0 
                 14.50 
               
               
                   
                 ⋆460   
                 4.40 
                 8.0 
                 12.40 
               
               
                   
                 500 
                 5.88 
                 9.2 
                 15.08 
               
               
                   
                 500 
                 5.88 
                 9.2 
                 15.08 
               
               
                   
                 510 
                 5.80 
                 9.2 
                 15.00 
               
               
                   
                 ⋆510   
                 4.78 
                 8.5 
                 13.28 
               
               
                   
                   
               
            
           
         
       
     
     FIG. 5 shows measured numerical values in Table 6 as a graph in the conventional cathode ray tube and the cathode ray tube according to the present invention, wherein an abscissa denotes the diagonal axis length D of the effective screen of the panel and an ordinate denotes the sum of the thickness w of the shielding portion and the smallest thickness ts of the thickness t 1  of the funnel body portion on the minor axis. The points encircled with a circle indicate examples of the cathode ray tube according to the present invention at this time. If the sectional shape of the funnel portion extending from the sealing portion to the body portion is assumed as a trapezoid having an upper base and a lower base, the weight can become lighter as an area of the funnel is reduced more and more. Therefore, if a height from the sealing portion to the body portion thickness ts is assumed constant, the lightweight funnel can be obtained by reducing a value of (ts+w) 
     As for two straight lines in the graph in FIG. 5, a lower straight line is obtained by the linear approximation based on the method of least squares in order to get a correlation between the sum (ts+w) of the thickness ts of the body portion  15  and the thickness w of the sealing portion of the cathode ray tube according to the present invention at this time and the diagonal axis length D. Such approximated straight line can give the sum 
     
       
         ( ts+w )=(6.2+0.0138 ×D )[mm] 
       
     
     under a limitation w≧ts≧4.4 [mm] in the method of manufacturing the panel glass and the funnel glass by the present press machine. Thus, it is possible to reduce the sum (ts+w) up to the above value. 
     Here, ts is a thickness on the minor axis to provide the thinnest portion of the thickness t 1 . Hence, since the lower limit value of ts means the lower limit value of the thinnest portion of t 1 , such lower limit value may be said in other words as the lower limit value of t 1 . Since the lower limit value of (t 1 +w) becomes (ts+w), (6.2+0.0138×D)≦(w+t 1 ) can be derived within the range of w≧t 1 ≧4.4. In this case, the upper straight line in the graph in FIG. 5 can be depicted by lifting the lower straight line up to a level of the conventional cathode ray tube while holding a gradient of the lower straight line. 
     As a result, a relationship of 
     
       
         (6.2+0.0138 ×D )≦( w+t   1 )≦(7.9+0.0138 ×D )[mm] 
       
     
     where w≧t 1 ≧4.4 can be derived. 
     Since the present invention is constructed as described above, it is possible to form the glass bulb of the cathode ray tube into a useful shape, and therefore the reduction in cost and the improvement in handling property can be achieved because of the reduction in weight of the glass bulb per se.