Abstract:
A panel for use in a cathode ray tube of the present invention includes a face portion, a skirt portion extending from a periphery of the face portion and a blend round portion connecting the face portion and the skirt portion. A mold match line is formed on the skirt portion in a manner that a mold match line height H1 satisfies a first equation: 0&lt;H1≦H×0.47 when mean outer radius of curvature is equal to greater than 10,000 mm, and satisfies a second equation: 0&lt;H1≦H×0.37 when mean outer radius of curvature is less than 10,000 mm, where H is an overall height of the panel.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a cathode ray tube; and more particularly, to a cathode ray tube capable of effectively preventing the failure thereof by way of optimizing the location of a mold match line.  
         BACKGROUND OF THE INVENTION  
         [0002]    As well known, a glass bulb in a cathode ray tube (CRT) used in a TV set or a computer monitor basically includes a panel for displaying picture images, a conical funnel sealed to the back of the panel and a cylindrical neck integrally connected to an apex portion of the conical funnel. The panel, the funnel and the neck are made of glass, wherein particularly the panel and the funnel are formed of predetermined dimensions and shapes by press forming a glass gob.  
           [0003]    Referring to FIG. 1, there is illustrated a cross sectional view of a conventional glass bulb  10 . A panel  20  of the glass bulb  10  is provided with a face portion  21  whose inner surface is covered with an array of dots of fluorescent material (not shown) to display picture images; a skirt portion  23  extending backward from a perimeter of the face portion  21  and having a seal edge  22  on its back edge; and a blend round portion (or corner portion)  24  integrally joining the face portion  21  to the skirt portion  23 . A funnel  30  of the glass bulb  10  can be divided into a body portion  32 , i.e., a fore part thereof, having a seal edge  31  connected to the seal edge  22  of the skirt portion  23 ; and a yoke portion  33 , i.e., a back part thereof, extending backward from the body portion  32 . And a neck  40  of the glass bulb  10  is connected to the yoke portion  33  of the funnel  30 . A tube axis  11  passes through the center of the face portion  21  and coincides with an axis of the neck  40 . Placed by way of the so-called “shrinkage fit” scheme around the outer periphery of the skirt portion  23  is a metallic implosion-proof band  50 , which strengthens the bulb  10  against tensile stress induced in the blend round portion  24  and the skirt portion  23  by evacuating the inner space of the bulb  10 , so that fragments of the glass can be prevented from flying away when the panel  20  is broken or exploded.  
           [0004]    Referring to FIG. 2, there is illustrated a schematic cross-sectional view of a mold set  60  for forming the panel  20 . The mold set  60  is provided with a bottom mold  62  in which a cavity  61  is formed; a middle mold (or shell)  63 , for forming the skirt portion  23  and the seal edge  22 , which is fitted on top of the bottom mold  62 ; and an upper mold  64  (or plunger) which presses a glass gob loaded in the cavity  61  of the bottom mold  62  to form the panel  20 . The upper mold  64  is connected to a press ram  65 , so that it can be lifted or lowered by the ram  65  so as to press the glass gob loaded in the cavity  61  of the bottom mold  62  to form the panel  20 . There exists a parting line  66  between the bottom mold  62  and the middle mold  63 . Therefore, when the panel  20  is formed in the mold set  60  as shown in FIG. 1, a mold match line  25 , which is a flash made by the parting line  66 , is formed on the outer periphery of the skirt portion  23  near the face portion  21 . The peripheral length of the mold match line  25  represents the maximum peripheral length of the panel  20 . And, in general, the position of the parting line  66  and thus the position of the mold match line  25  are set near the face portion  21  rather than the seal edge  22  in order to ease the extraction of the molded panel  20  from the bottom mold  62 .  
           [0005]    Referring to FIG. 3, there is illustrated a schematic cross sectional view of the panel  20  of FIG. 1. Formed on the outer periphery of the skirt portion  23  is a first tapered surface  26 , which extends from the mold match line  25  toward the seal edge  22  with an inward slant of a first slant angle θ1 with respect to the tube axis  11 . And the first slant angle θ1 is set less than 1.5° in order to prevent the band  50  from slipping. There is formed a second tapered surface  27  between the first tapered surface  26  and the seal edge  22 . The second tapered surface  27  has a second slant angle  02  ranging from, e.g., 3° to 4°. The border where the first tapered surface  26  meets with the second tapered surface  27  is referred to as a break line  28 , which is positioned away from a lower end of the implosion-proof band  50 .  
           [0006]    When the explosion-proof band  50  is installed around the outer periphery of the skirt portion  23  of the glass bulb  10  after the glass bulb being evacuated, the implosion-proof band  50  expanded by heating is pushed from the side of the face portion  21 , and then is fitted around the skirt portion  23 . At this time, the mold match line  25  is brought into contact with the implosion-proof band  50 , which may incur scratches or/and cracks in the mold match line  25 . Therefore, in a case where the mold match line  25  is formed near the face portion  23 , an area of the inner surface of the implosion-band  50  sweeping or scrubbing the mold match line  25  is comparatively greater and thus, the frequency of the contacts between the mold match line  25  and the implosion-proof band  50  increases. Consequently, a greater number of cracks and scratches are formed in the mold match line  25 . Further, additional cracks are developed in the mold match line  25  by a compressive stress generated by the shrinkage of the expanded implosion-proof band  50 .  
           [0007]    Such cracks formed in the mold match line  25  of the skirt portion  23  are one of the major causes for rendering the breakage or failure of the cathode ray tube occurring when the cathode ray tube is subject to a heat treatment in an annealing lehr for removing remaining stress therefrom, resulting in an increase of the production cost and the deterioration of production yield.  
         SUMMARY OF THE INVENTION  
         [0008]    It is, therefore, an object of the present invention to provide a panel for use in a cathode ray tube (CRT) capable of effectively preventing the failure of the CRT, such as implosion or breakage, during a heat treatment process of the CRT by optimizing the location of the mold match line.  
           [0009]    It has been found by the inventors of the present invention that the cracks and scratches can be effectively prevented from forming in the mold match line by locating the mold match line such that the inner surface area of the implosion-proof band sweeping the mold match line is comparatively less and the mold match line is subject to the comparatively less compressive force produced by the implosion-proof band.  
           [0010]    In accordance with a preferred embodiment of the present invention, there is provided a panel for use in a cathode ray tube, including: a face portion for displaying picture images, whose mean outer radius of curvature is equal to or greater than 10,000 mm; a skirt portion extending from a periphery of the face portion and having a seal edge sealed to a funnel; and a blend round portion connecting the face portion and the skirt portion, wherein a mold match line is formed on the skirt portion in a manner that a mold match line height H1 satisfies a following equation: 0&lt;H1≦H×0.47 where an overall height H is a distance between a first plane passing through the seal edge and a second plane passing through a center of the face portion, and the mold match line height H1 is a distance between the first plane and a third plane passing through the mold match line.  
           [0011]    In accordance with another preferred embodiment of the present invention, there is provided a panel for use in a cathode ray tube, including: a face portion for displaying picture images, whose mean outer radius of curvature is less than 10,000 mm; a skirt portion extending from a periphery of the face portion and having a seal edge sealed to a funnel; and a blend round portion connecting the face portion and the skirt portion, wherein a mold match line is formed on the skirt portion in a manner that a mold match line height H1 satisfies a following equation: 0&lt;H1≦H×0.37 where an overall height H is a distance between a first plane passing through the seal edge and a second plane passing through a center of the face portion, and the mold match line height H1 is a distance between the first plane and a third plane passing through the mold match line.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which:  
         [0013]    [0013]FIG. 1 illustrates a cross sectional view of a conventional glass bulb;  
         [0014]    [0014]FIG. 2 presents a schematic cross-sectional view of a mold set for forming a panel;  
         [0015]    [0015]FIG. 3 depicts a schematic cross sectional view of a panel of FIG. 1;  
         [0016]    [0016]FIG. 4 offers a schematic cross sectional view of a flat panel in accordance with preferred embodiments of the present invention; and  
         [0017]    [0017]FIG. 5 sets forth a schematic cross sectional view of a spherical panel (or regular type panel) in accordance with preferred embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]    Panels for use in a cathode ray tube in accordance with preferred embodiments of the present invention will now be described with reference to accompanying drawings. And like parts will be represented with like reference numerals.  
         [0019]    Referring to FIGS. 4 and 5, there are illustrated schematic cross sectional views of a flat panel  20 ′ and a spherical panel (or regular type panel)  20 ″ in accordance with preferred embodiments of the present invention, respectively. These panels are classified into the flat panel  20 ′ and the spherical panel  20 ″ on the basis of their mean outer radius of curvature R, which is an average of radii of curvature of an outside contour  21   a  passing through a center of a face portion  21  in predetermined radial directions. In addition, the center of the face portion  21  is a point where an axis of a neck  40  (shown in FIG. 1) passes through and is an intersection of the diagonals of the face portion  21 . The reference notation H represents an overall height of the panel  20 ′ or  20 ″, i.e., a distance between a first imaginary plane passing through a seal edge  22  and a second imaginary plane passing through the center of the face portion  21  on the outer contour  21   a  and being parallel to the first plane; H1, a height of a mold match line  25 , i.e., a distance between the first plane and a third imaginary plane passing through the mold match line  25  whose outer peripheral length represents a maximum length of the panel  20 ′ and  20 ″; and H2, a height of a break line  28 , i.e., a distance between the first plane and a fourth imaginary plane passing through the break line  28 .  
         [0020]    In general, the mean outer radius of curvature R of the flat panel  20 ′ is equal to or greater than 10,000 mm, and the mean outer radius of curvature R of the spherical panel  20 ″ is less than 10,000 mm. And it is widely known that the flat panel  20 ′ is more advantageous than the spherical panel  20 ″ in that it causes less image distortion and less eye fatigue, and has wide range of visibility.  
         [0021]    The flat panel  20 ′ shown in FIG. 4 satisfies a design guideline, such as the outer radius of the curvature R being equal to or greater than 10,000 mm and the mold match line height H1 satisfying the following equation:  
         0 &lt;H 1 &lt;H× 0.47  Eq. 1  
         [0022]    In other words, the mold match line  25  is formed at or below a position whose height from the seal edge  22  is 47% of the overall height H.  
         [0023]    Experiment 1  
         [0024]    In Tables 1 and 2, band tensions measured at predetermined points of implosion-proof bands along its widthwise (or axial) direction are listed, wherein the implosion-proof bands were placed around glass panels for televisions of 29 and 32-inch models, respectively, each having a useful screen area of an aspect ratio of 4:3.  
         [0025]    As shown in FIG. 4, Tables 1 and 2, a band zone Z0 represents a reference height, i.e., the seal edge  22 ; a band zone Z1, the height of the lower edge of the implosion-proof band  50  near the seal edge  22 ; and a band zone Z8, the height of the upper edge of the explosion-proof band  50  near the face portion  21 . In addition, band zones Z2 to Z7 correspond to points arranged in the implosion-proof band  50  along the width thereof with predetermined distances therebetween. In Tables 1 and 2, ratios (%) represent percentages of the mold match line height H1, the break line height H2 and heights of the band zones Z1 to Z8 to the overall height H of the panel  20 , respectively, wherein the heights of the band zones Z1 to Z8 are distances between the first plane and planes passing through the band zones Z1 to Z8 and being parallel with the first plane, respectively, and other height hereinafter will also be measured likewise.  
                                                         TABLE 1                                   Flat Panel for           Band Tension           29-inch model   Height (mm)   Ratio (%)   (Mpa)                                        H   97.6   100   —           H1   69.6   71   —           H2   31.6   32   —           Band Zones           Z1   33.1   34   48.4           Z2   45.0   46   91.8           Z3   47.0   48   167.1           Z4   56.1   57   129.8           Z5   63.8   65   111.9           Z6   69.8   72   207.9           Z7   78.3   80   218.1           Z8   86.9   89   132.3                      
 
         [0026]    As indicated in Table 1, a lower edge of the implosion-proof band was positioned 33.1 mm high from the seal edge and 1.5 mm high from break line. Further, the upper edge of the implosion-proof band was positioned 86.9 mm high from the seal edge and 17.3 mm high from the mold match line.  
         [0027]    The band tension at Z3 of 167.1 MPa was dropped sharply to the band tension at Z2 of 91.8 MPa, and the difference therebetween was as large as 75.3 MPa. From this and Table 1, it can be inferred that the band tension declines as the height from the seal edge is lowered below the band zone Z2 whose ratio (%) of the height to the overall height H is 46% and hence, satisfies Eq. 1. Moreover, the height of a middle point between the band zones Z2 and Z3, whose ratio of the height to the overall height H is 47%, satisfies Eq. 1. Accordingly, by forming the mold match line below the middle point, the mold match line will be subject to a comparatively less compressive force as a result of the band tension, and hence a comparatively less number of cracks will be formed therein. Consequently, breakage of glass bulbs made of panels whose mold match lines are formed below the middle point is reduced.  
         [0028]    Further, although skirt portion&#39;s configuration of panels whose match mold line is formed at or below the middle point is different from that of the panel used in this Experiment 1, the difference can be neglected since the first slant angle θ1 is small and therefore, the distribution of the band tension of the implosion-proof band used in such panels is similar to that of the panel used in this Experiment 1.  
         [0029]    The heights of the band zones Z3 to Z8 do not satisfy Eq. 1. And if the mold match line is formed at one position between the band zones Z3 and Z8, it will be subject to a greater compressive force as a result of the greater band tension, thereby having a higher potential to be scratched and/or crack during and after the installation of the implosion-proof band. Consequently, the glass bulb made of such panel also will have a higher potential to be broken.  
                                                         TABLE 2                                   Flat panel for           band tension           32-inch model   height (mm)   ratio (%)   (Mpa)                                        H   113.0   100   —           H1   82.5   73   —           H2   33.0   29   —           Band Zones           Z1   34.5   31   94.7           Z2   49.0   43   72.9           Z3   54.1   48   218.8           Z4   60.9   54   132.0           Z5   69.7   62   115.7           Z6   82.8   73   309.6           Z7   91.3   81   231.0           Z8   99.8   88   100.0                      
 
         [0030]    As indicated in Table 2, a lower edge of the implosion-proof band surrounding a flat panel for 32-inch model was positioned 34.5 mm high from the seal edge and the 10 upper end thereof was positioned 99.8 mm high from the seal edge. The band tension at the band zone 3 of 218.8 MPa was dropped sharply to the band tension at the band zone 2 of 72.9 MPa, and the difference therebetween was as large as 145.9 MPa. From this and Table 2, it can be inferred that band tension declines as a measuring height is lowered below the band zone Z2 whose ratio of the height to the overall height H is 43% and hence, satisfies Eq. 1. Accordingly, by forming the mold match line below the middle point, the mold match line will be subject to a comparatively less compressive force as a result of the band tension, and hence a comparatively less number of cracks will be formed therein. Consequently, breakage of glass bulbs made of panels whose mold match lines are formed below the middle point will be reduced.  
         [0031]    The band zones Z3 to Z8 do not satisfy Eq. 1. And if the mold match line is formed at one position between the band zones Z3 and Z8, it will be subject to a greater compressive force as a result of the greater band tension and therefore, comparatively more scratches and/or cracks will be formed therein during and after the installation of the implosion-proof band. Consequently, the glass bulb made of a panel whose mold match line is formed between the band zones Z3 and Z8 also will have a higher potential to be broken.  
         [0032]    Further, in Tables 1 and 2, although band stress of the band zone 8 was close to that of the position whose ratio (%) was 47%, it was so near to the face portion that the mold match line could not be formed thereon. And although band stresses of the band zones Z4 and Z5 were also close to that of the position whose ratio was 47%, more cracks and/or scratches were formed during the implosion-proof band installation since the face portion was first entered into the implosion-proof band. In other words, the area of the implosion-proof band sweeping or scrubbing the mold match line was comparatively greater and thus the frequency of contacts between the mold match line and the inner surface of the implosion-proof band.  
         [0033]    The spherical panel  20 ″ shown in FIG. 5 satisfies design guideline, such as outer radius of curvature R being less than 10,000 mm and the height of the mold match line H1 satisfying the following Eq. 2:  
         0&lt; H 1≦ H× 0.37  Eq. 2  
         [0034]    In other words, the mold match line is formed on the spherical panel in a manner that the ratio of the mold match line height H1 to the overall height H is equal to or less than 37%.  
         [0035]    Experiment 2  
         [0036]    Two spherical glass panels for televisions of 28 and 29-inch models, each having a useful screen area of an aspect ratio of 4:3, were prepared. Then, explosion-proof bands were placed around the outer periphery of the skirt portions thereof. Afterwards, band tensions were measured at band zones Z1 to Z8 and listed in Tables 3 and 4. The ratios and heights in Tables 3 and 4 were defined with a same method as in Experiment 1, and therefore, the explanation therefor will be omitted for simplicity.  
                                             TABLE 3                       Spherical Panel           Band Tension       for 32-inch model   Height (mm)   Ratio (%)   (Mpa)                                H   99.6   100   —       H1   53.1   53   —       H2   25.1   25   —       Band Zones       Z1   15.0   15   110.5       Z2   36.8   37   150.2       Z3   40.0   40   364.5       Z4   44.5   45   394.1       Z5   48.5   49   387.3       Z6   51.0   51   336.3       Z7   55.0   55   250.0       Z8   60.0   60   157.6                  
 
         [0037]    As indicated in Table 3, a lower edge of the explosion-proof band placed around the glass panel for TV of 28-inch model was positioned 15 mm high from the seal edge and an upper edge of the explosion-proof band was positioned 60 mm high from the seal edge. The band tension at the band zone 3 of 364.5 MPa was dropped to the band tension at the band zone 2 of 150.2, and the difference therebetween was as large as 214.3 MPa. From this and Table 3, it can be inferred that band tension declines phenomenally below the band zone Z2 whose the ratio of the height to the overall height H is 37%, thereby satisfying Eq. 2.  
         [0038]    Accordingly, by forming the mold match line below the band zone Z2, the mold match line will be subject to a less compressive force as a result of the less band tension, hence comparatively less number of cracks will be formed therein. Consequently, breakage of the bulb made of a panel whose mold match line is formed below the middle point can be reduced.  
         [0039]    The band zones Z3 to Z8 do not satisfy Eq. 2. And if the mold match line is formed at one position between the band zones Z3 and Z8, it will be subject to a comparatively greater compressive force as a result of the comparatively greater band tension and therefore, more cracks and scratches will be formed therein during and after the installation of the implosion-proof band. Consequently, the glass bulb made of a panel whose mold match line is formed between the band zones Z3 and Z8 will have a higher potential to be broken.  
         [0040]    Further, although the band tension of the band zone Z8 was close to that of the band zone Z2 whose ratio was 37%, the band zone Z8 was so near to the face portion that the mold match line was formed thereon.  
                                             TABLE 4                       Spherical Panel           Band Tension       for 32-inch model   Height (mm)   Ratio (%)   (Mpa)                                H   113.7   100   —       H1   50.7   45   —       H2   25.7   23   —       Band Zones       Z1   10.0   9   100.6       Z2   20.0   18   125.5       Z3   41.0   36   150.8       Z4   43.0   38   322.9       Z5   45.0   40   260.9       Z6   48.7   43   214.8       Z7   52.6   46   150.0       Z8   55.3   49   110.0                  
 
         [0041]    As indicated in Table 4, a lower edge of the implosion-proof band surrounding the spherical glass panel for a TV of 32-inch model was positioned 10 mm high from the 10 seal edge and an upper edge thereof was positioned 55.3 mm high from the seal edge. The band tension at the band zone  4  of 322.9 MPa was sharply dropped to the band tension at the band zone 3 of 150.8 MPa, and the difference therebetween was as large as 172.1 MPa. From this and Table 4, it can be inferred that band tension declines phenomenally as a measuring height is reduced below the band zone Z3 whose ratio of the height to the overall height H is 36%, thereby satisfying Eq. 2. Accordingly, by forming the mold match line at or below the band zone Z3, the mold match line will be subject to a comparatively less compressive force as a result of the comparatively less band tension, and hence comparatively less number of cracks will be formed therein. Consequently, breakage of the bulb made of a panel whose mold match line is formed below the band zone Z3 can be reduced.  
         [0042]    The band zones Z4 to Z8 do not satisfy Eq. 2. And if the mold match line is formed at one position between the band zones Z4 and Z8, it will be subject to a comparatively greater compressive force as a result of the comparatively greater band tension and therefore, comparatively more cracks and scratches will be formed therein during and after the installation of the implosion-proof band. Consequently, the glass bulb made of a panel whose mold match line is formed between the band zones Z4 and Z8 also will have a higher potential to be broken.  
         [0043]    Further, in Table 4, although the band stresses of the band zone Z7 and Z8 were close to that of the band zone Z3, the band zones Z7 and Z8 were so near to the face portion that the mold match line could not be formed therein.  
         [0044]    As described above, if the mold match line is formed at a position near the seal edge where the band tension is comparatively less, the mold match line will be subject to the comparatively less compressive force and will not contact with the implosion-proof band as many times as the mold match line formed near the face portion during the implosion-proof band installation. Accordingly, the formation of scratches and cracks in the mold match line of the flat or spherical glass panels for a cathode ray tube in accordance with the preferred embodiments of the present invention can be effectively reduced, and therefore, the glass bulb made of the panel of the present invention will have a less potential to be broken in the annealing lehr or other process, resulting in an improvement in productivity thereof and reduction in the economic loss.  
         [0045]    While the invention has been shown and described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.