Abstract:
A rail of a flat type cathode ray tube is disclosed, wherein the flat type cathode ray tube comprises a panel having a deposited fluorescent surface therein and of which interior and exterior surfaces are substantially flat, a funnel connected to the panel; a shadow mask arranged with the inner surface of the panel with a predetermined gap, and a rail fixed to the panel and combined with the shadow mask. In the flat type cathode ray tube, if a height of the rail is L, the rail maintains a predetermined gap of 0.1L˜0.3L with the panel and is fixed by a frit glass.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a flat type cathode ray tube (CRT), and particularly, to a rail in a flat type cathode ray tube, wherein stress which occurs between a panel and a rail is reduced, thereby preventing cracks in the panel.  
           [0003]    2. Description of the Background Art  
           [0004]    Generally, cathode ray tube (CRT) is a device to realize a screen by deflecting an electron beam emitted from an electron gun by a deflection yoke, landing on a fluorescent surface formed at an inner surface of a panel by passing through a plurality of electron beam through holes formed on a shadow mask.  
           [0005]    Recently, a flat type CRT having a panel of a flat type is developed and commercialized so as to prevent image distortion, to minimize a reflection by exterior light, and to maximize a visible region.  
           [0006]    The flat type CRT will be explained with reference to attached drawings.  
           [0007]    [0007]FIG. 1 is a schematic view showing flat type cathode ray tube (CRT) in accordance with the conventional art, and FIG. 2 is a frontal view showing a panel in a conventional flat type CRT.  
           [0008]    As shown in FIG. 1, the conventional flat type CRT comprises a funnel  10  corresponding to a rear glass, a panel  20  corresponding to a frontal glass which is combined to the funnel  10  and sealed to be a high vacuum state. Moreover, an electron gun  40  located at an end portion of the funnel  10  for. emitting an electron beam  50 ; a deflection yoke  30  mounted at an outer circumference of a neck portion of the funnel  10  for deflecting the electron beam  50  towards a fluorescent surface formed at an inner side of the panel  20 , a shadow mask  70  disposed at a rear surface of the panel  20  for sorting out colors of the electron beam  50 , and an inner shield  60  prolonged from the panel  20  to the funnel  10  for shielding an external terrestrial magnetism.  
           [0009]    Also, a fluorescent film  22  playing a role of luminescent material is deposited in the panel  20 , and a rail  80  is attached to the panel to fix the shadow mask  70  and the inner shield  60 .  
           [0010]    The rail  80 , as shown in FIG. 2, includes two major side rails  86  and two minor side rails  87 , wherein the major and minor side rails  86  and  87  have different lengths and a same shape, and end portions thereof are cut with 45° respectively and engaged to each other with forming a corner portion  88 .  
           [0011]    At this time, the corner portion  88  is grinded with a predetermined curvature so as to prevent stress from being concentrated.  
           [0012]    The rail  80  is fixed to the panel  20  by a frit glass, wherein one side thereof is formed as a stair shape to fix the shadow mask  70  and the inner shield  60 , and the other side thereof is formed as a plane shape to be attached to the panel  20 .  
           [0013]    A process for attaching the rail  80  to the panel  20  will be explained with reference to FIG. 3.  
           [0014]    [0014]FIG. 3 is a sectional view showing a process for fixing the rail  80  of the flat type CRT to the panel  20 .  
           [0015]    First, a frit glass  90  is deposited on a panel fusion portion  84  of the rail  80  in a furnace of high temperature of 400° C.˜500° C.  
           [0016]    Then, the rail  80  on which the frit glass  90  is deposited is attached to the panel surface  20 , and passes through the furnace of high temperature of 400° C.˜500° C. According to this, the rail  80  is attached to the panel  20  by melting of the frit glass  90 , thereby completing the attachment.  
           [0017]    When the rail  80  is attached to the panel  20  at high temperature by the frit glass  90 , the rail  80  and the panel  20  have thermal expansion and contraction through the furnace process. At this time, since the rail  80  and the panel  20  have different coefficients of thermal expansion and contraction, remained thermal stress exists by the difference. According to this, cracks occur in the panel  20  due to the thermal stress, thereby damaging the panel  20 .  
           [0018]    A distribution of the thermal stress occurring at the panel  20  will be explained with reference to the attached drawings.  
           [0019]    [0019]FIG. 4 is a graph showing a change of stress existing on the panel to which the rail in the conventional flat type CRT is attached according to a location change from a center of the panel to a center of the minor side rail  87 .  
           [0020]    As shown in FIG. 4, stress is increased towards an outer side of the minor side rails (X axis) from a center portion (point O) of the panel  20 , and tensile stress and compression stress are crossed at the fusion portion on which the rail  80  and the panel  20  are fixed.  
           [0021]    At this time, cracks occur at the fusion portion due to unbalance of the stress, and the stress unbalance phenomenon severely occurs at the corner portion  88  of the rail  80 .  
           [0022]    The said phenomenon is resulted from the different thermal expansion ratio between the rail  80  and the panel  20 , resulted from that the rail  80  is in contact with the panel  20  to cause the stress unbalance severely, or resulted from that the frit glass  90  for buffering the stress is not sufficiently inserted between the rail  80  and the panel  20 .  
           [0023]    In the meantime, as another example of the conventional flat type CRT, a receiving groove  102  for receiving the frit glass  90  is formed in the rail  80  so as to buffer the stress occurring by the different thermal expansion ratio between the rail  80  and the panel  20  more efficiently by sufficiently disposing the frit glass  90  between the rail  80  and the panel  20 .  
           [0024]    That is, as shown in FIGS. 5A and 5B, the receiving groove  102  for receiving the frit glass  90  is formed with a half circle or a square sectional shape in a longitudinal direction of the rail  100 .  
           [0025]    Accordingly, the stress is buffered more efficiently by disposing the frit glass  90  in the receiving groove  102 , and the stress due to the different thermal expansion ratio between the rail  100  and the panel  20  is more reduced by reducing a contacted area between the rail  100  and the panel  20 .  
           [0026]    However, as shown in FIG. 6, since the receiving groove  102  is formed, in case of that the corner portion  88  of the rail, that is, a portion where the major side rail  86  and the minor side rail  87  are engaged, has a grinding with a predetermined curvature, the receiving groove  102  is opened towards an outer side of the corner portion  88 , so that the frit glass  90  is leaked to the opened portion of the corner portion  88  and the leaked frit glass  90  causes thermal stress to be concentrated at the corner portion  88 , thereby causing cracks in the panel  20 .  
         SUMMARY OF THE INVENTION  
         [0027]    Therefore, an object of the present invention is to provide a flat type CRT, wherein a rail maintains a predetermined gap with a panel and fixed by a frit glass, so that stress which occurs due to thermal expansion ratio between the rail and the panel is buffered by the frit glass, thereby preventing the panel from being cracked by the stress.  
           [0028]    To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a flat type CRT wherein in case of that a receiving groove is formed in a longitudinal direction of a rail, at least one of an inner leg and an outer leg which are divided as inner and outer sides of the panel by the receiving groove maintains a predetermined gap with the panel, and the legs and the panel are fixed by a frit glass, thereby preventing the panel from being cracked by buffering of the frit glass.  
           [0029]    In the flat type CRT of the present invention comprising a panel having a deposited fluorescent surface therein and of which inner and outer surfaces are substantially flat, a funnel connected to the panel, a shadow mask arranged with a predetermined gap from the fluorescent surface of the panel for sorting out colors, and a rail fixed to the panel and combined with the shadow mask, the rail maintains a predetermined gap with the panel to be fixed by a frit glass.  
           [0030]    Also, in the flat type CRT of the present invention, the rail includes a receiving groove formed therein towards a length direction thereof for inserting the frit glass, an outer leg formed towards an outer direction of the panel by being divided by the receiving groove, and an inner leg formed at an opposite side of the outer leg, wherein at least one of the outer leg and the inner leg is fixed to the panel with a predetermined gap.  
           [0031]    The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.  
         [0033]    In the drawings:  
         [0034]    [0034]FIG. 1 is a schematic view showing flat type cathode ray tube (CRT) in accordance with the conventional art;  
         [0035]    [0035]FIG. 2 is a frontal view showing a panel of a conventional flat type CRT;  
         [0036]    [0036]FIG. 3 is a sectional view showing a process that a rail in the conventional flat type CRT is fixed to a panel;  
         [0037]    [0037]FIG. 4 is a graph showing a change of stress existing on a panel of the conventional flat type CRT according to a location change from a center of the panel to a center of a minor side rail;  
         [0038]    [0038]FIGS. 5A and 5B are sectional views showing one embodiment of a rail in the conventional flat type CRT;  
         [0039]    [0039]FIG. 6 is a partial frontal view showing a state that a frit glass is leaked at a corner portion where rails of the conventional flat type CRT are respectively engaged;  
         [0040]    [0040]FIG. 7 is a schematic view showing a flat type CRT of the present invention;  
         [0041]    [0041]FIG. 8 is a perspective view showing a panel of a flat type CRT according to one embodiment of the present invention;  
         [0042]    [0042]FIG. 9 is a sectional view taken along line IX-IX of FIG. 8;  
         [0043]    [0043]FIG. 10 is a partial frontal view showing a jig for fixing a rail in the flat type CRT to a panel according to one embodiment of the present invention;  
         [0044]    [0044]FIG. 11A is a sectional view showing a state that a rail in the flat type CRT is fixed to a panel according to another embodiment of the present invention;  
         [0045]    [0045]FIG. 11B is a partial plane view showing a state that a rail in the flat type CRT is fixed to a panel according to another embodiment of the present invention; and  
         [0046]    [0046]FIG. 12 is a sectional view showing a state that a rail in the flat type CRT is fixed to a panel according to another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0047]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. As shown in FIG. 7, the flat type CRT according to the present invention includes a funnel  110  corresponding to a rear glass and a panel  120  corresponding to a frontal glass which is combined with the funnel  110  and sealed to be a high vacuum state, an electron gun  140  located at an end portion of the funnel  110  for emitting an electron beam  150 ; a deflection yoke  130  mounted at an outer circumference of a neck portion of the funnel  110  for deflecting the electron beam  150  towards a fluorescent surface of inside of the panel  120 , a shadow mask  170  located at a rear surface of the panel 0.120, and an inner shield  160  prolonged from the panel  120  to the funnel  110  for shielding an external terrestrial magnetism.  
         [0048]    Also, a fluorescent film  122  playing a role of luminescent material is deposited at an inner side of the panel  120  of, and a rail  180  is attached to the panel  120  to fix the shadow mask  170  and the inner shield  160 .  
         [0049]    As shown in FIGS. 8 and 9, one side of the rail  180  is formed as a stair shape to fix the shadow mask  170  and the inner shield  160 , and the other side of the rail  180  is formed as a plane shape, so that the rail  180  is fixed to the panel  120  by a frit glass  190  composed of material having a low melting point. The rail  180  includes two major side rails  186  and two minor side rails  187 , wherein the major and minor side rails  186  and  187  have different lengths and a same shape, and end portions thereof are cut with  45 ° respectively and engaged to each other with forming a corner portion  88 .  
         [0050]    At this time, the corner portion  188  is grinded with a predetermined curvature so as to prevent stress from being concentrated.  
         [0051]    The flat type CRT is the same or a similar construction with that of the conventional art.  
         [0052]    However, as shown in FIG. 9, the rail  180  according to one embodiment of the present invention is not in contact with the panel  120 , but fixed and fixed to the panel  120  by the frit glass  190  with a predetermined gap (AL).  
         [0053]    That is, since the rail  180  and the panel  120  are composed of different material each other, cracks occur in the panel  120  by the different thermal expansion ratios when the rail  180  and the panel  120  are fixed. To reduce the cracks, the frit glass  190  is disposed between the rail  180  and the panel  120 .  
         [0054]    At this time, as shown in FIG. 10, a jig  200  is provided to fix the rail  180  to the panel  120  with a predetermined gap.  
         [0055]    The jig  200  includes an insertion groove  202  having a shape corresponding to the stair shape of the rail  180  at one side thereof for inserting the rail  180 , and a gap settlement member  204  formed at one side of the insertion groove  202  and engaged to the insertion groove for maintaining a gap between the panel  120  and the rail  180 .  
         [0056]    A processor for fixing the rail of the flat type CRT to the panel according to one embodiment of the present invention will be explained.  
         [0057]    First, the rail  180  is inserted to the insertion groove  202  of the stair shape formed at the jig  200 , and the frit glass  190  is deposited on the fusion portion  184  of the rail  180  in a furnace of high temperature.  
         [0058]    Then, the rail  180  on which the frit glass  190  is deposited is transported towards the panel  120  by a movement of the jig  200 , and passes through the furnace of high temperature of 400° C.˜500° C., thereby fixing the rail  180  to the panel  120  by melting of the frit glass  190 .  
         [0059]    At this time, the gap settlement member  204  of the jig  200  maintains a gap between the rail  180  and the panel  120  when the jig  200  is transported towards the panel  120 .  
         [0060]    Herein, when the gap between the panel  120  and the rail  180  is under 10% of the length (L) of the rail  180 , it is difficult to obtain an effect, and when above 30%, a transformation can occur by tensile stress of the shadow mask  170 . Accordingly, it is preferable that the rail  180  and the panel  120  maintain a gap corresponding to 10%˜30% of a total height (L) of the rail  180 . The gap between the panel  120  and the rail  180  is 0.4 mm˜1.3 mm when calculated as a real length. In the rail of the flat type CRT according to one embodiment of the present invention, since the rail is not in contact with the panel but fixed by the frit glass by maintaining a predetermined gap, stress due to a difference of the thermal expansion ratio between the rail and the panel can be reduced when compared with the related art in which the rail and the panel are in contact with each other.  
         [0061]    Also, thermal stress between the rail and the panel is buffered by the frit glass, so that cracks in the panel by the thermal stress can be prevented.  
         [0062]    Also, whereas a rail composed of material having a thermal expansion coefficient similar to the thermal expansion coefficient of the panel as much as possible is used in the related art, in the present invention, the rail can have various selections for material since the cracks by the different thermal expansion ratio can be prevented, and a fabricating cost of the rail can be reduced since the rail can be constructed with a low cost and commercialized material.  
         [0063]    That is, in the related art, as material of the rail, expensive material (28% chrome steel) corresponding to 0.97˜1.03 times of the thermal expansion coefficient (105*10 −7  mm/° C.) of the panel is used. However, in the present invention, since cracks in the panel can be prevented, it is possible to use a rail of a low cost and commercialized material corresponding to 1.03˜1.15 times of the thermal expansion coefficient (105*10 −7  mm/° C.) of the panel.  
         [0064]    The rail of a flat type CRT according to the present invention will be explained with reference to the attached drawings. Hereinafter, the same components with the one embodiment of the present invention will be endowed the same reference numerals and explanations will be omitted.  
         [0065]    [0065]FIGS. 11A and 11B are sectional views showing a rail in a flat type CRT according to another embodiment of the present invention.  
         [0066]    That is, as shown in FIGS. 11A and 11B, the rail  280  in the flat type CRT according to another embodiment of the present invention is composed of two major side rails  286  and two minor side rails  287 , and provided with a receiving groove  281  for inserting a frit glass  290  as a length direction of the rail  280  at a panel fusion portion where the rail is fixed to the panel  220 .  
         [0067]    That is, the receiving groove  281  is formed so as to insert the frit glass  290  sufficiently between the rail  280  and the panel  220  to reduce cracks which occur in the panel  220  due to a difference of thermal expansion ratio when the rail  280  is fixed to the panel  220 .  
         [0068]    The fusion portion where the rail  280  is fixed to the panel is divided by the receiving groove  281  and composed of an outer leg  284  formed towards outside of the panel  220  and an inner leg  282  formed towards inside of the panel. In the meantime, to sufficiently fill the receiving groove  281  in the rail  280  with the frit glass  290 , widths of the outer and inner panel fusion portions of the rail  280  have to be reduced. At this time, if a width of the outer leg  284  is too reduced, when the corner portion  288  of the rail  280  is rounded as a predetermined curvature radius (R), the receiving groove  281  is opened outwardly towards the corner portion  288 , so that the frit glass  290  is leaked to cause cracks in the panel  220 . Therefore, a width of the outer leg  284  has to be set lest the receiving groove  281  should be opened outwardly even if the corner portion  288  of the rail  280  is rounded.  
         [0069]    Accordingly, a relationship among the rounding curvature radius (R) of the corner portion  288  of the rail  280 , a width of the outer leg (W 1 ), and a width of the inner leg (W 2 ) is preferably set as follows.  
           W 1 /R≧ 0.3  (1)  
           W 2 /W 1&lt;1  (2)  
         [0070]    That is, in case that a ratio between the curvature radius (R) of the corner portion  288  of the rail  280  and the width of the outer leg  284  (W 1 ) of the panel  220  is under 0.3, the receiving groove  281  is opened towards the corner portion  288 , so that the frit glass  290  is leaked to cause cracks in the panel  220 .  
         [0071]    Also, since the width of the outer leg  284  is set to be large, a hole does not occur at the time of a rounding process of the corner portion  288 , and since an area of the receiving groove  281  is set to be wider than that of the related art, the frit glass  290  is more deposited, thereby dispersing the stress and lowering a crack occurrence.  
         [0072]    However, in the flat type CRT having the said structures, since the width of the outer leg  284  (W 1 ) is wider than that of the inner leg  282  (W 2 ), when the rail  280  is fixed to the panel  220 , the frit glass  290  has a lowered flow towards the outer leg  284  than the inner leg  282 . Accordingly, as shown in FIGS. 11A and 11B, a phenomenon that a width of the frit glass  294  (L 1 ) dispersed at an outer side of the rail  280  is reduced than that of the frit glass  290  (L 2 ) dispersed at an inner side of the rail  280  occurs.  
         [0073]    Therefore, unbalanced thermal stress occurs by a difference of a dispersed amount between the frit glass  292  at the inner side of the rail  280  and the frit glass  294  at the outer side of the rail  280 .  
         [0074]    Also, since the width (W 2 ) of the inner leg  282  is narrower than that (W 1 ) of the outer leg  284  of the rail  280 , the receiving groove  281  is formed with a bias from a vertical center (C) of the rail  280  to an inner side, thereby increasing the unbalance stress dispersion between the inner side and the outer side of the rail  280 .  
         [0075]    Since the said unbalanced thermal stress cause cracks, a length (Lo) of the outer leg  384  is formed to be shorter than that (Li) of the inner leg  382 , and a space is obtained between the outer leg  384  and the panel  320 , thereby increasing a flow of the frit glass  390  towards an outer side direction.  
         [0076]    In case that the length (Lo) of the outer leg  384  is formed to be shorter than that (Li) of the inner leg  382 , the frit glass  390  flows outwardly in a smooth state and an amount of the frit glass at the inner side  392  and the frit glass at the outer side  394  is formed uniformly, thereby preventing the unbalanced thermal stress which occurs at the inside and outside of the rail  380 .  
         [0077]    Also, in case that the length (Lo) of the outer leg  384  is formed to be shorter than that (Li) of the inner leg  382 , when the rail  380  is attached to the panel  320 , the inner leg  382  of the rail  380  is in contact with the panel  320 , but the outer leg  384  is not in contact with the panel  320 , and the frit glass  390  is inserted therebetween. According to this, thermal stress between the rail  380  and the panel  320  is buffered by the frit glass  390 , thereby preventing cracks in the panel  320  due to the thermal stress.  
         [0078]    As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalence of such metes and bounds are therefore intended to be embraced by the appended claims.