Electric lamp and discharge devices – Cathode ray tube – Envelope
Reexamination Certificate
2002-09-25
2004-11-02
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Envelope
C220S00210A
Reexamination Certificate
active
06812631
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
The entire disclosure of Japanese Patent Application No. 2001-291803 filed on Sep. 25, 2001, the foreign priority Application, including specification, claims, drawings and summary is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a glass bulb for a cathode ray tube to be used for e.g. a display for a television broadcast receiver (hereinafter referred to as a television) or a computer, and to a cathode ray tube employing said bulb.
2. Description of Related Art
A face portion
5
of a cathode ray tube has a substantially rectangular shape as illustrated in
FIG. 10
, as viewed from the direction of the tube axis
19
(arrow A in FIG.
2
), and has two long sides
21
and two short sides
22
. Further, the axis passing through the center
23
of the face portion
5
in parallel with the long sides
21
, is referred to as the long axis
24
, and the axis in parallel with the short sides
22
is referred to as the short axis
25
.
As illustrated in
FIG. 11
, the panel
2
, like the face portion
5
, has four sides comprising two long sides
30
and two short sides
31
at its seal edge portion
7
, and its outer profile has a shape substantially the same as the profile of the face portion
5
.
Further, as illustrated in
FIG. 12
, the seal edge portion
8
of the funnel
3
likewise has two long sides
32
and two short sides
33
, and has a shape substantially congruent with that of the seal edge portion
7
of the panel
2
, as described above. Then, the seal edge portion
7
of the panel
2
and the seal edge portion
8
of the funnel
3
are joined and sealingly bonded by means of e.g. a solder glass, to form a sealing portion
34
(shown in FIG.
2
).
In the cathode ray tube having a construction as described above in detail, inside of the bulb
1
is maintained to be in high vacuum in order to have the electron beam radiated to display picture images. However, the bulb
1
having an asymmetrical shape, as is different from a spherical shell, is loaded with a pressure difference of 1 atm between its inside and outside, whereby it is in an unstable state due to a high strain energy thus formed. Therefore, even when a very small crack is formed in the glass constituting the panel
2
or the funnel
3
, it is likely that the crack grows to release the strain energy, which may lead to a destruction. Further, when a high tensile stress is formed on the outer surface of the panel
2
or the funnel
3
, a delayed fracture may take place due to the effect of moisture in the atmosphere, which may cause decrease in the reliability of the cathode ray tube.
In recent years, liquid crystal displays and plasma displays have been developed and put into practical use, and when these are compared with a display employing a cathode ray tube, the large depth of the cathode ray tube is regarded as a demerit. Therefore, it has been tried to reduce the depth (the length in the direction of the tube axis
19
) of a bulb to be employed in cathode ray tubes, and as a result, the asymmetricity of the shape of the bulb has further increased and the tensile stress formed on the outer surface of the bulb has increased.
The body portion
9
of the funnel
3
is formed to have a substantially truncated pyramid shape which has a large opening towards the panel
2
, and accordingly, when the inside of the bulb
1
is vacuumed, the body portion
9
tends to be deformed as it is depressed towards the panel
2
in the direction of the tube axis
19
. And, the face portion
5
of the panel
2
, is formed to be most flat in the bulb
1
in order to display picture images, and thus is very likely to be deformed, and tends to be deformed so as to be depressed towards the funnel
3
in the direction of the tube axis
19
. As a result, to the sealing portion
34
and the skirt portion
6
continuous therefrom, a force will be exerted to expand them outward (in the direction departing from the tube axis
19
).
FIG. 13
shows an example of the distribution of the stress formed on the outer surface of the bulb
1
. Here, when the distribution curve (indicated by a chain double-dashed line in the FIG.) is outside of the profile of the bulb
1
, it indicates that a tensile stress is formed, and when the distribution curve is inside of the profile of the bulb
1
, it indicates that a compressive stress is formed.
The left half of the solid line in
FIG. 13
represents the outer profile line of the cross section when the bulb is cut along the long axis
24
, and its right half represents the outer profile line of the cross section when the bulb is cut along the short axis
25
. Further, in the following description, the tensile stress formed on the bulb surface when its inside is vacuumed, will be referred to as a “tensile vacuum stress”.
As illustrated in
FIG. 13
, a high tensile vacuum stress is formed at the end of the face portion
5
of the panel
2
and at the body portion
9
of the funnel
3
. Accordingly, on the outer surface of the sealing portion
34
where the seal edge portion
7
of the panel
2
and the seal edge portion
8
of the funnel
3
are bonded, strains formed on both the panel
2
and the funnel
3
, are propagated and concentrated to form an extremely high tensile vacuum stress. Especially, at the end portions of the short axis
25
of the face portion
5
, namely in the vicinity of the center portions of the long sides
21
, a high tensile vacuum stress is formed.
As a result, it may cause lowering of the safety due to destruction of the cathode ray tube, or lowering of the reliability due to the delayed fracture caused by moisture in the atmosphere. Further, if the wall thickness of the glass of the body portion
9
or of the seal edge portions
7
and
8
, is increased in order to solve the problem of such a high tensile vacuum stress, there will be a problem of an increase of the mass, which is a major demerit for a cathode ray tube, as well as the problem of the depth.
It is an object of the present invention to prevent the increase of the tensile vacuum stress formed at the sealing portion without increasing the wall thickness of the glass at the body portion of the funnel or at the sealing portion of the panel and the funnel, and thereby to provide a glass bulb for a cathode ray tube, being light in weight and having a small depth and high safety, and to provide a cathode ray tube employing such a bulb.
SUMMARY OF THE INVENTION
FIG. 2
is a schematic view illustrating the cross section of a cathode ray tube. The cathode ray tube employs a glass bulb (hereinafter, a glass bulb for a cathode ray tube will be referred to simply as “a bulb”)
1
as an envelope, and the bulb
1
is constituted by a panel
2
and a funnel
3
. The panel
2
comprises a face portion
5
having a screen
4
for displaying picture images, and a skirt portion
6
constituting a sidewall of the face portion
5
. The skirt portion
6
has a seal edge portion
7
at its end.
Further, the funnel
3
has a seal edge portion
8
having a shape substantially congruent with the shape of the seal edge portion
7
of the panel
2
, and the other opening portion is connected to a cylindrical neck portion
10
, and a yoke portion
11
is integrally connected between the body portion
9
and the neck portion
10
to form a substantially funnel shape.
An electron gun
12
is housed in the neck portion
10
, and an electron beam radiated from the electron gun
12
is deflected by a deflecting yoke
13
put around the yoke portion
11
, and lets a phosphor screen
14
emit a light.
Besides these, an aluminum film
15
for reflecting the light emitted from the phosphor screen
14
forward, a shadow mask
16
for regulating the position of electron beam irradiation on the phosphor screen
14
, stud pins
17
for fixing the shadow mask
16
to the inside of the panel
2
, and an anode button
18
for preventing high electrostatic potential of the shadow mask
16
due to the electron beam and for conductiv
Asahi Glass Company Limited
Guharay Karabi
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Patel Nimeshkumar D.
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