Electric lamp and discharge devices – Cathode ray tube – Ray generating or control
Reexamination Certificate
2001-08-29
2003-09-23
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Ray generating or control
Reexamination Certificate
active
06624561
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a color cathode ray tube, and in particular to a color cathode ray tube provided with an internal voltage-dividing resistor for applying a plurality of different voltages to a plurality of electrodes constituting an electron gun housed in its neck portion, and a conductor for increasing a withstand voltage disposed in a space between the internal voltage-dividing resistor and the inner wall of the neck portion.
A color cathode ray tube used in TV receivers or monitors of information terminals has an electron gun housed within a neck portion of its vacuum envelope for projecting plural electron beams and a phosphor screen (a viewing screen) formed of phosphor elements coated on an inner surface of its panel portion for emitting light of plural colors. A deflection yoke is mounted around the outside of the vacuum envelope for scanning the electron beams from the electron gun on the phosphor screen two-dimensionally to produce a desired image.
In many color cathode ray tubes, a shadow mask serving as a color selection electrode is closely spaced from the phosphor screen such that each of the plural electron beams emitted from the electron gun impinges upon the phosphor elements of its intended color to produce a color image.
For the purpose of improving the quality of a color image over the display screen formed on the phosphor screen, a color cathode ray tube is known which employs an electron gun of the type applying a plurality of high voltages other than its anode voltage to a plurality of electrodes focusing the electron beams.
FIG. 6
is a partially cut-away side view of an essential part of a color cathode ray tube incorporating an electron gun provided with an internal voltage-dividing resistor, and
FIG. 7
is a partially cut-away side view of the essential part of the color cathode ray tube of
FIG. 6
as viewed in the direction of an arrow A in FIG.
6
.
The electron gun for projecting three in-line electron beams is housed within a neck portion
32
of a vacuum envelope
10
of the color cathode ray tube. This electron gun comprises an anode (the sixth grid electrode) supplied with a highest voltage (an anode voltage)
1
, an intermediate grid electrode
2
supplied with a voltage obtained by dividing the anode voltage using the internal voltage-dividing resistor, cathodes K for emitting the electron beams, a fifth grid electrode group
3
comprised of plural electrodes constituting a lens for focusing the electron beams emitted from the cathodes K, the fourth grid electrode
4
, the third grid electrode
5
, the second grid electrode
6
, and the first grid electrode
7
. The electrodes
1
to
7
are fixed in the specified order with specified respective spacings therebetween by embedding portions of peripheries of the respective electrodes into a pair of insulating support rods
9
.
A shield cup
8
is attached to the sixth grid electrode
1
, and ends of electrically conductive springs
11
are welded to a sidewall of a front end of the shield cup
8
. A portion of the inner wall of the vacuum envelope
10
is coated with an internal conductive film
10
a
made of material such as graphite and extending from the funnel portion toward the neck portion. The other ends of the electrically conductive springs
11
press on the internal conductive film
10
a
such that the anode voltage is supplied to the sixth grid electrode
1
via a high-voltage terminal embedded in the funnel portion.
An internal voltage-dividing resistor
12
of a configuration explained subsequently is attached to an outside surface of one of the insulating support rods
9
facing an inner wall
32
a
of the neck portion. The internal voltage-dividing resistor
12
is provided with terminals
13
,
14
and
15
for electrical connection, the terminal
13
is electrically connected to the sixth grid electrode
1
to be supplied with the anode voltage, the terminal
14
is connected to the intermediate grid electrode
2
, and the terminal
15
is connected to ground.
The terminal
13
is provided with a connecting tab
13
a
projecting perpendicularly to the longitudinal axis of the electron gun, and the connecting tab
13
a
is connected to the sixth grid electrode
1
. A connecting tab
14
a
projects from the terminal
14
, and is connected to the intermediate grid electrode
2
to supply thereto a high voltage obtained by dividing the anode voltage by a factor of the ratio of the resistors of the internal voltage-dividing resistor. The terminal
15
is connected to one of stem pins
45
by using an extension of a connecting tab
15
a
or another member such that the terminal
15
is connected to a potential such as ground potential (hereinafter ground potential) outside the cathode ray tube.
A conductor
16
made of a metal wire is disposed to pass through a space between the inner wall
32
a
of the neck portion
32
and the internal voltage-dividing resistor
12
and surround the internal voltage-dividing resistor
12
and one of the insulating support rods
9
mounting the resistor
12
, and is welded to one electrode of the fifth grid electrode group
3
on opposite sides of the one of the insulating support rods
9
.
The conductor
16
is made of nickel or stainless steel. A portion of metal contained in the conductor
16
is evaporated by heating the conductor
16
using an external high-frequency induction heater after the completed electron gun assembly has been sealed into the neck portion
32
so as to form a metal thin film
16
a
on the inner wall
32
a
of the neck portion, the insulating support rod
9
and the internal voltage-dividing resistor
12
and thereby to produce stable electric potential on the inner wall of the neck portion during operation of the cathode ray tube. Another type of a conductor
16
is also known which uses an extension of a metal wire for connecting together electrodes to be supplied with the same voltage within the cathode ray tube, and still another type of a conductor
16
is also known which has only one of its two ends fixed to the electrode with the other end being not fixed to the electrode.
Reference numeral
17
denotes a conductive film for preventing spark, and the conductive film
17
is a sputtered film of Au—Pd, or Cr, for example, is formed on the surface of the internal voltage-dividing resistor
12
facing the inner wall of the neck portion, and enhances the effects of spot knocking by preventing spark between the conductor
16
and its neighboring electrodes during the spot knocking procedure described subsequently.
FIGS. 8A
to
8
C are illustrations of the internal voltage-dividing resistor
12
employed in the electron gun of
FIG. 7
,
FIG. 8A
is a plan view of the internal voltage-dividing resistor as viewed from its resistance pattern side, and
FIGS. 8B and 8C
are its side and rear views, respectively.
In the internal voltage-dividing resistor
12
, a resistance layer
19
is formed on one surface of an insulating substrate
18
which is preferably made of ceramic by initially printing a resistance material having desired resistance characteristics such as metal oxide including ruthenium oxide in the form of a desired pattern, and then drying and firing the resistance material. Then a first insulating film
20
a
made of glass, glass of a borosilicate lead system, for example, is formed to cover the pattern of the resistance layer
19
(hereinafter the resistance pattern). Similarly a second insulating film
20
b
is formed over the approximately entire area of the rear surface of the insulating substrate
18
except for regions formed with terminals, and further, a spark-preventing conductive film
17
is coated on the specified portion of the second insulating film
20
b
. The spark-preventing conductive film
17
is somewhat displaced toward the high-voltage terminal
13
from the position of the conductor
16
. The spark-preventing conductive film
17
is formed by bombarding a target made of Au—Pd or Cr with ions and thereby sputtering Au—Pd or Cr onto the secon
Koizumi Sachio
Nakamura Hisao
Suzuki Kenji
Patel Nimeshkumar D.
Phinney Jason R
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