Electric lamp and discharge devices – Cathode ray tube – Ray generating or control
Reexamination Certificate
1998-12-23
2001-02-06
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Ray generating or control
Reexamination Certificate
active
06184616
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a resistor the surface of which is coated with an overcoat glass to cover its resistor pattern, an electron gun for a cathode-ray tube using the same and a method of manufacturing the resistor.
2. Description of the Related Art
In recent years, demand has increased for a high resolution in a television, a display and the like.
To this end, as shown in
FIG. 1
, for example, an electron gun
31
having a common electric field extended lens i.e. an Extended Field Elliptical Aperture Lens referred to as “EFEAL” structure was developed and has become commercial. See SID '97 DIGEST p347-350 (1997).
This electron gun
31
is comprised of, though not shown, three cathodes K for generating electron beams corresponding to three colors or a red R, a green G and a blue B; respective electrodes, that is, a first electrode G
1
, a second electrode G
2
, a third electrode G
3
, a fourth electrode G
4
, a fifth electrode G
5
, an intermediate electrode GM which will be explained later, a sixth electrode G
6
and a convergence cup
35
for accelerating and controlling the electron beams. The gun
31
is attached with a resistor
32
substantially parallel to a longitudinal direction of the electron gun
31
. In
FIG. 1
, reference numeral
33
designates a stem and reference numeral
34
denotes a stem pin.
This electron gun
31
with the EFEAL structure needs a new electrode for applying an intermediate voltage (for example, 14 kV) between a conventional focus voltage (for example, 6 kV) and an anode voltage (for example, 27 kV).
To this end, the intermediate electrode GM is provided between the sixth electrode G
6
on an anode side and the fifth electrode G
5
, or the focus electrode. The electron gun
31
having the EFEAL structure is such that the fifth electric electrode G
5
, the intermediate electrode GM and the sixth electrode G
6
have, though not shown, electric field correcting electrode boards therein, each of which has beam penetration apertures corresponding to the three electron beams, and each of the electrodes G
5
, GM, and G
6
is shaped like a cylinder which is cross-sectionally elliptical.
Then, by applying the above-mentioned intermediate voltage of, for example, 14 kV to the intermediate electrode GM, the penetration of the electric field to the beam penetration apertures of the electric field correcting electrode board (not shown) of the intermediate electrode GM controls the shape of the electron beams and the convergence thereof, thereby making it possible to optimize them.
Here, a voltage which can be applied through the stem pin
34
to the electron gun from the outside of the cathode-ray tube is limited to about 10 kV or so due to a withstand voltage characteristic between the pins.
Therefore, in order to apply the intermediate voltage of, for example, 14 kV and the like to the intermediate electrode GM, the resistor
32
becomes indispensable for connecting the low voltage from the stem pin
34
with the high voltage on the anode side and then driving the same.
FIGS. 2A and 2B
show the resistor
32
of the electron gun
31
in FIG.
1
. The cross-sectional view of resistor
32
is shown in FIG.
2
A and the plan view thereof is shown in FIG.
2
B. The resistor
32
is formed in such a manner that a conductive film is coated on one surface of a ceramic substrate
36
made of, for example, alumina and the like with a predetermined pattern, printed and fired to form a resistor pattern
37
.
Then, an overcoat glass
38
is formed on the resistor pattern
37
and on the rear surface of the ceramic substrate
36
in order to protect the resistor pattern
37
. Thus, the resistor
32
is formed.
The resistor
32
thus formed is fitted to the electron gun
31
with its surface of the ceramic substrate
36
, on which the resistor pattern
37
is formed, being on the side of the electron gun
31
and its surface on the opposite side being outside, that is, on the neck-glass side of the cathode-ray tube.
An anode voltage, for example, a high voltage of 25-32 kV or so is applied to a high voltage electrode portion
39
at the left end of the resistor
32
and an earth electrode portion
41
at the right end thereof is grounded or is connected to an outer-fitted resistor outside the cathode-ray tube.
In the electron gun
31
of
FIG. 1
, the high voltage electrode portion
39
is connected to the convergence cup
35
, the earth electrode portion
41
is grounded through the stem pin
34
and an intermediate electrode portion
40
of the resistor
32
is connected to the intermediate electrode GM.
The above-mentioned resistor
32
comprises, for example, a so-called inner dividing resistor (IBR: Inner Breeder Resistor), an IMR (Inner Middle voltage breeder Resistor), an IFR (Inner Focus breeder Resistor) and the like, and is used for applying a convergence voltage to obtain a convergence characteristic of the electron gun for the cathode-ray tube, applying a focus voltage of the electron gun for the cathode-ray and further, is used as a focus controller of a television receiver and the like other than for applying the intermediate voltage to the above-mentioned intermediate electrode GM.
However, in the case of such a resistor
32
, there generates a growth of dendrite due to ion migration of natrium while it is in operation, resulting in a phenomenon that a portion between the resistor pattern
37
is electrically conducted.
For example, as shown in
FIG. 2B
, on the interface between the overcoat glass
38
and the ceramic substrate
36
, there generates a growth of a dendrite
42
from an edge portion of the overcoat glass
38
toward the resistor pattern
37
.
The growth of the dendrite
42
can be explained as follows.
As shown in
FIG. 3
, a natrium atom is ionized from Na
2
O which is contained in the overcoat glass, the ceramic substrate and the resistor pattern as an impurity, and hence there is generated a natrium ion Na
+
. This natrium ion Na
+
causes the ion migration along an electric potential gradient and moves to a cathode side (a low electric potential side) K.
Further, on the cathode side K, it absorbs oxygen from oxides in surrounding portion and precipitates as a layer of sodium oxide Na
2
O with the result that the dendrite
42
made of sodium oxide Na
2
O grows from the cathode side K to the anode side (a high electric potential side) A.
When the growth of the dendrite
42
progresses while the cathode-ray tube is in operation, there occurs the above-mentioned electrical conductivity among the neighboring portions of the resistor pattern
37
. For example, in the case of
FIG. 2B
, originally, the intermediate electrode portion
40
applies 14 kV, but because a substantial resistor becomes short due to the short-circuit of the resistor pattern
37
on the low voltage side, the electric potential at the intermediate electrode GM rises up to a voltage of 15 kV and the like, thereby giving rise to a defective focus.
Particularly in recent years, there is a growing demand that a resistor be used under electrically and mechanically severe conditions like the above-mentioned FEEAL-type electron gun
31
and the like, thereby making the conductivity problem among the resistor pattern
37
serious.
Also, when miniaturization of the electron gun
31
is implemented, because the space among the resistor pattern
37
becomes narrow and the short-circuit tends to occur easily, it has been difficult to miniaturize the electron gun
31
.
SUMMARY OF THE INVENTION
In order to solve the above-mentioned problem, it is an object of the present invention to provide a resistor which has a long life span and is capable of being miniaturized by restraining a short circuit among a resistor pattern, and an electron gun equipped with this resistor for a cathode-ray tube as well as a manufacturing method of the resistor.
According to an aspect of the present invention there is provided a resistor which makes the natrium concentration of overcoat glass covering the resistor patter
Amano Yasunobu
Endo Naruhiko
Kajiwara Kazuo
Nakayama Kazutaka
Yodokawa Katsuyuki
Hopper Todd Reed
Kananen Ronald P.
Patel Vip
Rader Fishman & Grauer
Sony Corporation
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