Electric lamp and discharge devices – Cathode ray tube – Ray generating or control
Reexamination Certificate
2000-03-13
2003-03-11
Day, Michael H. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Ray generating or control
C313S447000
Reexamination Certificate
active
06531813
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a cathode ray tube having an improved cathode structure, and particularly to a cathode ray tube having an electron gun having a plurality of cathodes supported within respective eyelets of a glass-bonded cathode support assembly which is in turn fixed within and to a cup-shaped first grid electrode, and capable of retaining the insulation strength of the glass-bonded cathode support assembly for a long period of time.
Generally, color cathode ray tubes such as a color picture tube and a color display tube comprise a phosphor screen formed on an inner surface of a faceplate of a panel portion of an evacuated envelope, a shadow mask having a multiplicity of electron beam apertures and spaced from the phosphor screen within the panel portion, an electron gun of the in-line type housed within a neck portion of the evacuated envelope, and a deflection yoke mounted around a funnel portion of the evacuated envelope.
In the operation of the color cathode ray tube, three electron beams emitted from the electron gun are deflected by the deflection yoke and thereafter are projected onto picture elements of the corresponding colors of the phosphor screen through the electron beam apertures of the shadow mask to display a desired color image on the phosphor screen.
FIGS. 6A and 6B
are constitutional views showing an example of the constitution of an electron gun used for a conventional color cathode ray tube,
FIG. 6A
being a side view thereof, and
FIG. 6B
being a top view thereof.
In
FIGS. 6A and 6B
, reference numeral
30
designates a cathode;
31
a cup-shaped first grid electrode (G
1
);
32
a second grid electrode (G
2
);
33
a third grid electrode (G
3
);
34
a fourth grid electrode (G
4
);
35
a fifth electrode (G
5
);
36
a sixth grid electrode (G
6
);
37
a shield cup;
38
multiform glass rods;
39
a stem; and
40
an electron gun. In this case, only one cathode
30
is shown, but actually there are three electron guns arranged in a line.
The cathodes
30
, the cup-shaped first grid electrode
31
, the second grid electrode
32
, the third grid electrode
33
, the fourth grid electrode
34
, the fifth grid electrode
35
, the sixth grid electrode
36
, and the shield cup
37
are mounted, in order named from the stem
39
, in spaced relationship between the pair of multiform glass rods
38
spaced from each other and arranged parallel with each other. This beaded assembly is supported on the stem
39
.
The cathodes
30
, the cup-shaped first grid electrode
31
, the second grid electrode
32
, the third grid electrode
33
, the fourth grid electrode
34
, the fifth grid electrode
35
, the sixth grid electrode
36
, and the shield cup
37
are supported on and secured to the pair of multiform glass rods
38
through electrode supports. The electron gun
40
is held in place within the neck portion in such a manner that the stem
39
mounting the electron gun
40
thereon is heat-sealed to the open end of the neck portion of the color cathode ray tube, and bulb spacer contacts
200
welded to the shield cup
37
hold the forward end of the electron gun
40
centered in the neck portion.
FIGS. 7A and 7B
are a plan view and a sectional view, respectively, showing the constitution of a portion supporting cathodes of an electron gun
40
proposed in Japanese Patent Application Laid-Open No. 56-109429 Publication. Cathodes
30
B,
30
G and
30
R composed of a cathode cap
150
provided with an electron-emissive surface, a cathode sleeve
151
, and a skirt portion
152
are secured to an insulating substrate
120
b
by metal supports
170
. The insulating substrate
120
b
is secured within the cup-shaped first grid portion
31
(
FIG. 6A
) by a metal member
110
.
Normally, when the color cathode ray tube is operated for a long period of time, metal components are evaporated from cathodes
30
G,
30
B and
30
R, and the evaporated metal deposit on the constituent parts arranged in proximity to the cathodes. It has been known that, where the cathodes
30
G,
30
B and
30
R are, for example, oxide cathodes, evaporated metals are magnesium mg from a cap-shaped base metal
150
containing Mg serving as a reducing agent, a chrome (Cr) from a metal sleeve
151
. These metals deposit on the surface of the insulating substrate
120
b
with time of operation and deteriorate the insulation strength.
In
FIG. 7B
, in order to prevent the insulation strength of the electron gun from deteriorating, the top surface of the insulating substrate
120
b
is made slightly little higher than the upper open end of the metal member
110
, and a step
130
is provided between the top surface of the insulating substrate
120
b
and the edge of the opening of the metal member.
With the above described constitution, even if the metals evaporated from the three cathodes
30
G,
30
B and
3
OR fall on the top surface of the insulating substrate
120
b
beyond the metal support
170
and contaminate the top surface of the substrate
120
b
with time of operation, the vertical part of the step
130
provided between the top surface of the substrate
120
b
and the upper open end of the metal member
110
is a shadow zone not irradiated by the evaporated metals such that the contamination by metals do not develop in the step
130
, and the insulation strength is secured between the metal support
170
and the metal member
110
.
Further, in the constitution described in Japanese Patent Application Laid-open No. 56-109429 Publication, there is provided the following arrangement for preventing the deterioration of the electric insulation characteristics caused by the evaporation or sputtering of material constituting the cathode. In
FIG. 7A
, a line-of-sight passing through the upper end of the metal support
170
from the edge of the cathode cap
150
is designed so as to strike a point A as illustrated in
FIG. 7A
which is on the edge of the opening of the metal member
110
and is equidistant from the two adjacent cathodes
30
B and
30
G. The following is a relationship required in this case:
H=
(
L−LA
)×
HA÷
(
L−LB
)
where H is a protruding height of the metal support
170
beyond the insulating substrate
120
b,
L={
(
S/
2)
2
+LL
2
}
0.5
≈S/
2
0.5
,
LL is a distance from the center of the cathodes
30
B,
30
G and
30
R to the edge of the opening of the metal member
110
,
LA is a radius of the metal support
170
, and
LB is a radius of the cathode cap
150
.
However, the invention described in Japanese Patent Application Laid-open NO. 56-109429 Publication does not take into account a prevention of occurrence of a leakage path between the adjacent metal supports
170
on the insulating substrate
120
b
formed directly by the sputtering or evaporation from the two adjacent cathodes
30
B and
30
G.
SUMMARY OF THE INVENTION
The present invention eliminates those problems as noted above, and an object of the invention is to provide a color cathode ray tube having a constitution for preventing the deterioration of the insulation strength between a plurality of cathodes and a first grid electrode or between a plurality of cathodes.
For achieving the aforesaid object, a color cathode ray tube of the present invention comprises at least an evacuated envelope comprising a panel portion having a phosphor screen formed on an inner surface thereof, a neck portion, and a funnel portion connecting the panel portion and the neck portion, a shadow mask spaced from the phosphor screen and suspended within the panel portion, an electron gun housed in the neck portion comprising at least a plurality of cathodes, a cup-shaped first grid electrode spaced from the plurality of cathodes and a plurality of electrodes spaced between the first grid electrode and the shadow cask for generating and directing a plurality of electron beams toward the phosphor screen, and a deflection yoke mounted in the vicinity of the junction between the neck portion and the funnel portion, the plurality of cathodes bein
Koizumi Sachio
Komiya Toshifumi
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