Panel for use in a cathode ray tube

Details Panel for use in a cathode ray tube Panel for use in a cathode ray tube

2003-05-16

2004-11-02

Patel, Vip (Department: 2879)

Electric lamp and discharge devices

Cathode ray tube

Envelope

C313S461000

Reexamination Certificate

active

06812633

ABSTRACT:

FIELD OF THE INVENTION
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
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.
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.
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
.
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 &thgr;
1
with respect to the tube axis
11
. And the first slant angle &thgr;
1
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 &thgr;
2
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
.
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
.
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
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.
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.
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<H
1
≦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 H
1
is a distance between the first plane and a third plane passing through the mold match line.
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 H
1
satisfies a following equation: 0<H
1
≦H×0.37 where a

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