Implosion proof structure in flat cathode ray tube

Details Implosion proof structure in flat cathode ray tube Implosion proof structure in flat cathode ray tube

2000-12-08

2004-12-21

Glick, Edward J. (Department: 2882)

Electric lamp and discharge devices

Cathode ray tube

Envelope

C313S47700R, C348S821000, C348S822000, C220S00210R, C220S00210A

Reexamination Certificate

active

06833664

ABSTRACT:

This nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application Nos. P1999-56497 filed in Korea on Dec. 10, 1999, P2000-30319 filed in Korea on Jun. 2, 2000, and P2000-32775 filed in Korea on Jun. 14, 2000, which are herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a flat cathode ray tube, and more particularly, to an implosion proof structure in a flat cathode ray tube for preventing implosion of the flat cathode ray tube.
2. Background of the Related Art
Referring to
FIG. 1
, a related art flat cathode ray tube is provided with a planar panel
1
, a funnel
3
smoothly curved from a sealing surface to the panel to a neck portion
3
a
having an electron gun sealed therein, welded to the panel
1
with Frit glass, and an electron gun
4
sealed in the neck portion for emitting red, green and blue electron beams toward the panel. In detail, there is a piece
2
of explosion proof glass attached to a front face of the panel for enhancing an explosion proof property of the panel
1
, and a fluorescent film
5
on an inside surface of the panel for emitting light as electron beams strike the fluorescent film
5
. There is a rectangular rail
6
on an inside surface of the panel, and a shadow mask
7
fitted to the rail
6
in an effective surface of the panel
1
having multiple slits for selecting a color from the electron beams. There is an inner shield
8
fixed at the rear of the rail for protecting the electron beams emitted from the electron gun and travelling toward the panel from geomagnetism, and a deflection yoke
9
on an outer circumferential surface of the neck portion of the funnel for deflecting the electron beams in horizontal and vertical directions. There is a band
11
strapped around the panel
1
for fastening a plurality of lugs
10
to an outer circumference of the panel
1
, for use in fastening the foregoing flat cathode ray tube to a sash of a monitor or a TV receiver.
Accordingly, when power is provided to the electron gun
4
sealed in the neck portion
3
a
, to emit thermal electrons, the emitted electrons are accelerated and focused as they pass through a plurality of electrodes in succession, and are directed toward a screen side while being deflected in a vertical and a horizontal direction by the deflection yoke
9
. The electron beams emitted from the electron gun
4
and directed toward the screen side are involved in color selection as they pass through fine holes in the shadow mask
7
, and strike fluorescent material in the fluorescent film
5
. Eventually, a picture is reproduced as the fluorescent material emits lights resulting from an energy difference occurring when electrons in the fluorescent material is first excited and then dropped down to a base state. In order to enhance the electron emission, the cathode ray tube is passed through an evacuation process during its fabrication for keeping an inside of the cathode ray tube under a vacuum in a 10
−6
~10
−7
Torr range.
The evacuation process for the related art flat cathode ray tube will be explained, briefly.
Once the cathode ray tube having the funnel
3
fitted to the flat panel
1
is subjected to the evacuation process, and vacuumed down to a range of 10
−7
~10
−8
Torr, there is a pressure difference between an inside and outside of the cathode ray tube of at least 10
−6
Torr since outside of the cathode ray tube is at a 760 Torr atmospheric pressure. That is, the cathode ray tube is under a pressure of one atmosphere, i.e., 1.01325×10
5
N/m
2
pressure at all points thereof. Consequently, the panel and the funnel are deformed by the pressure until the outer and inner pressures come to an equilibrium, particularly, the panel
1
collapses in an inward direction of the cathode ray tube in a “c” direction in FIG.
2
. Moreover, as a provision for fixing the cathode ray tube that has been subject to the evacuation process to the sash of the monitor or the TV receiver, if the band assembly of the lugs
10
and the band
1
is strapped around the panel
1
under tension, the inward collapse of the panel becomes more serious. That is, as shown in
FIG. 2
, in the related art implosion proof structure in the cathode ray tube, the strapping of the band
11
around the panel
1
with a tension, having an inward deformation along an axis of the tube of a bulb (the panel plus the funnel) having been through the evacuation process, makes the deformation more serious. Because stress is greater in the vicinity of a sealed surface of the panel
1
and the funnel
3
, breakage of the cathode ray tube may occur in the vicinity of the sealed surface due to permanent stresses coming from the one atmosphere pressure difference caused by the evacuation and the strapping force caused by the band around the panel
1
. Accordingly, the panel is susceptible to an implosion, in which the cathode ray tube may implode even by a small external impact, and may result in poor picture quality since a front face of the panel is not flat.
For preventing such an implosion of the panel, as an example, the panel in the related art flat cathode ray tube has a thickness at a central portion thereof set greater than a thickness the same region of a cathode ray tube with a conventional radius of curvature. However, the thicker panel causes the following problem.
In the evacuation process of the cathode ray tube during fabrication, the bulb is heated to a temperature in a range of approx. 340~360° C. for extracting gas adsorbed in an inside surface of the bulb. A heat generated at a heater in a furnace heats an outer surface of the bulb by means of convection, and the heat at the outer surface of the bulb is transferred to the inside surface of the bulb by conduction. While glass has a thermal conductivity in a range of approximately 0.92×10−3(W/mm°K), the rail, a metal, has a thermal conductivity in a range of approximately 22.8×10−3(W/mm°K), i.e., the thermal conductivity of glass is relatively lower than metal. As heat conduction is inversely proportional to a thickness of the panel, the bulb may be broken by thermal stress resulting from a temperature difference between an inner surface and an outer surface of the bulb which becomes the greater as the thickness of the flat panel
1
increases. On the other hand, in a Frit sealing process in which the panel
1
and the funnel
3
are sealed with Frit glass carried out before the evacuation, when the Frit glass is crystallized to seal the panel
1
and the funnel
2
, the bulb is required to be heated up to approximately 440° C. according to a crystallization characteristic of the Frit glass. Therefore, when the thickness of the panel
1
is great, the bulb may be broken by a temperature difference between the inner surface and the outer surface of the bulb. In order to minimize such breakage, the heating process is required to be prolonged for heating the bulb slowly in an attempt to reduce the temperature difference between the inner surface and the outer surface of the bulb, which deteriorates yield, requires a greater time period for fabrication, and requires an increased amount of heat energy. In a case in which the panel
1
has a thickness equal to, or greater than 18.0 mm, a tint glass application with a light transmittivity of 75% at a thickness of 10.16 mm shows a light transmittivity below 40%, and a dark tint glass application with a light transmittivity of 46% at a thickness of 10.16 mm shows a light transmittivity below 28% (which is actually impossible to apply). Accordingly, there may be a limitation imposed on the design of the bulb in that only a clear glass application with a light transmittivity of 86% at a thickness of 10.16 mm and a semi-clear glass application with a light transmittivity of 82% at a thickness of 10.16 mm are possible. Because the bulb is liable to break when an external impact is applied if the permanent stress caused by the vacuum is excessive, an allowable vacuu

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