Funnel structure of cathode ray tube

Details Funnel structure of cathode ray tube Funnel structure of cathode ray tube

2002-12-11

2004-08-17

Patel, Nimeshkumar D. (Department: 2879)

Electric lamp and discharge devices

Cathode ray tube

Envelope

C313S440000, C313S441000, C313S634000, C335S210000, C335S213000

Reexamination Certificate

active

06777866

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cathode ray tube, and more particularly, to a funnel structure of a cathode ray tube in an optimum funnel horn shape that is capable of improving a sensitivity of a deflection yoke and capable of satisfying a beam shadow neck margin of an electron beam.
2. Description of the Background Art
As shown in
FIG. 1
, a conventional cathode ray tube includes a fluorescent face
4
is formed with R (red), G (green) and B (blue) fluorescent material coated thereon, a panel
1
formed at a front portion with an explosion-proof unit fixed thereon, a funnel
2
melt at a rear end of the panel
1
, an electron gun (no reference numeral given) inserted into a neck portion
13
of the funnel
2
and emitting electron beam
6
, a deflection yoke
5
for deflecting the electron beam
6
, a shadow mask
3
mounted to have a certain interval with an inner face of the panel
1
and having a plurality of holes for passing the electron beam
6
, a main frame
7
and a sub-frame
8
fixedly supporting the shadow mask
3
so that the shadow mask
3
can be maintained with a certain interval with the inner face of the panel
1
, a corner spring
9
for connecting and supporting the main frame
7
and the panel
1
, an inner shield
10
for shielding the cathode ray tube so that the cathode ray tube can be less influenced by an external earth magnetism, and a reinforcing band
12
installed around the side portion of the panel
1
and preventing an external impact.
A magnet
11
made of 2, 4 and 6 poles is provided to correct a proceeding trajectory of the electron beam so that the electron beam can accurately hit the fluorescent material is provided, by which a color purity defect can be prevented.
A rug
14
is welded at a corner portion of the reinforcing band
12
and coupled with an outer case of a television set or a monitor.
The overall fabrication process of the CRT can be divided into a former process and a latter process. In the former process, step of coating the fluorescent face
4
onto the inner surface of the panel
1
, while the latter process includes the following several steps.
First, the fluorescent face
4
is formed, and the panel
1
having a mask assembly in which the shadow mask
3
and the frames
7
and
8
are coupled inserted therein and the funnel
2
having a sealing face with a frit glass coated thereon are sealed at a high temperature through an envelop process. Thereafter, the electron gun is inserted into the inner side of the neck portion
13
of the funnel
2
through an encapsulating process, and the inside of the CRT is vacuumized through an exhausting process and then enclosed.
When the inside of the CRT is vacuumized through these processes, the CRT is compressed or receives a tensile stress according to a shape of the CRT due to an atmosphere pressure.
If a surface area is reduced as a depth of the panel
1
or the funnel
2
becomes considerably small compared to that of the conventional art, the force applied per unit area is increased. Thus, there is shown such a stress distribution that a relatively high stress is concentrated thereto.
As a matter of course, after the exhausting process, the stress concentration occurring at the panel
1
and the funnel
2
can be distributed by attaching the reinforcing band
12
at an outer circumferential surface of the panel
1
so as to make an effect of reducing its absolute value. But such an effect is made little in case of a slim type CRT.
Meanwhile, as shown in
FIG. 2
, the funnel
2
of a general CRT is divided into a funnel body portion
2
a
, a funnel yoke portion
2
b
where the deflection yoke
5
is positioned, and a neck portion
2
c
where the electron gun is positioned.
A boundary line at which the funnel body portion
2
a
and the funnel yoke portion
2
b
meet is defined as a top of round
21
, a boundary line at which the funnel yoke portion
2
b
and the neck portion
2
c
meet is defined as a neck seal line
23
, and, a reference line, though not shown with an actual object but always defined in designing, in measuring a depth of the CRT is defined as a reference line
22
.
Provided that a region of the screen actually shown is an effective screen and diagonal ends of the four corners of the effective screen are effective surface end
25
, when the point at which the tube axis
24
and the reference line
22
intersect is connected to the effective surface end
25
, an angle with the tube axis
24
is defined as a deflection angle
26
.
The CRT is mainly used for a television set, a computer monitor, or the like, and recently, it is also applied to a high quality product such as an HDTV.
In order for the CRT to be applied to the high quality television or a monitor, or in order to improve a quality itself such as improvement of a brightness of the screen, a deflection frequency of the deflection yoke
5
needs to be heightened. In this respect, however, heightening of the deflection frequency causes problems that a leakage magnetic field is generated due to an increase in a deflection power and a power consumption is increased.
Meanwhile, when the CRT is adopted as a computer monitor, the leakage magnetic field leaked from the product is regulated by a related agency. If a compensation coil is mounted at the deflection yoke
5
in order to reduce the leakage magnetic field, the effect of reducing the leakage magnetic field may be expected to a degree but a power consumption is increased according to the use of the compensation coil which results in an increase in an expense.
And recently, as the CRT is in the trend toward being slim, a distance between the electron gun and the fluorescent material coated at the inner surface of the panel
1
becomes short, and accordingly, as the deflection angle of deflecting the electron beam
6
becomes large, a power consumption of the deflection yoke
5
for controlling the deflection angle is increased.
In an effort to solve the problem, these days, the funnel
2
to which the deflection yoke
5
is mounted has such an outer circumference shape that it is changed from a circular form to an oval form as it goes from the neck portion
2
c
of the funnel
2
toward the panel
1
, or an almost rectangular funnel yoke portion
2
b
, not the circular funnel yoke portion
2
b
, is used so that a horizontal or vertical coil of a deflection coil (no reference numeral given) comes near the region where the electron beam
6
formed inside the funnel
2
, thereby resultantly reducing power required for the deflection.
However, if the CRT is made slim, even though the rectangular yoke portion is used, the amount of increase in the deflection power is meager compared with the CRT with the existing deflection angle. In addition, due to the structural characteristics of the rectangular shape, the stress concentration is more severe to the diagonal portion of the rectangular yoke portion.
FIG. 3
is a sectional view of the funnel yoke portion
2
b
of the conventional art.
The deflection yoke
5
is attached to the funnel yoke portion
2
b
to control the electron beam
6
emitted from the electron gun to reach the fluorescent material coated at the inner surface of the panel
1
. In this respect, if the rectangular yoke portion of the funnel
2
is designed to come closer to the tube axial direction in order to reduce the deflection power, the electron beam
6
collides with the inner surface of the funnel
2
, causing a problem of a BSN phenomenon that it is shown black in an actual screen, as shown in FIG.
4
.
Moreover, after the CRT is completely fabricated, there needs to be a margin of about 3~4 mm back and forth along the tube axis
24
of the CRT so as for the deflection yoke
5
to be movable for a screen adjustment such as an ITC. If there is no margin between the electron beam
6
and the inside of the funnel
2
, the electron beam
6
would easily collide with the inside of the funnel
2
.
The position with which the electron beam
6
collides differs depending on the deflect

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