Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
2001-10-04
2003-06-10
Day, Michael H. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S479000
Reexamination Certificate
active
06577048
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color CRT, and more particularly, to an inner shield of a color CRT that is capable of improving a shielding effect by enhancing a structure of an inner shield and capable of preventing a color spread phenomenon due to color mixture when an image is reproduced by reducing a variation degree in landing of an electron beam according to an external magnetic field variation according to the improved shielding effect.
2. Description of the Background Art
FIG. 1
is a partially-cut side view showing an internal construction of a color CRT having an inner shield in accordance with a conventional art, and
FIGS. 2A and 2B
are a rear view and a plan view showing the inner shield in accordance with the conventional art.
As shown in
FIG. 1
, a color CRT is formed with its external appearance by a panel
10
coated with a red, green and blue color fluorescent material
11
on the inner face thereof, and a funnel
20
sealed at the rear side of the panel
10
by a frit glass and maintaining an internal pressure in a high vacuum state of about 10-7 Torr.
A shadow mask
40
having fine slits serving for color selection is mounted at the inner side of the panel
10
through the medium of a frame
30
, and the frame
30
is supported at the inner face of the panel
10
by means of the spring
50
.
An inner shield
60
for shielding a magnetic field such as an earth magnetic field so that an electron beam
71
injected from an electron gun
80
is not influenced by the magnetic field is mounted at a rear side of the frame
30
.
A neck portion
70
is installed at a rear side of the funnel
20
, and the electron gun
80
for injecting the electron beam
71
is mounted at an inner side of the neck portion
70
.
A deflection yoke
90
for deflecting the electron beam
71
injected from the electron gun
80
to the entire fluorescent surface coated with the fluorescent material
11
is mounted at a boundary portion positioned between the rear side of the funnel
20
and the neck portion
70
.
Reference numeral
25
denotes a safety band for reinforcing the coupling portion of the panel
10
and the funnel
20
.
Accordingly, when the electron gun
80
irradiates the electron beam
71
, the electron beam
71
passes through holes
41
formed at the shadow mask
40
and collides with the fluorescent material
11
formed at the inner surface of the panel
10
, radiating the fluorescent material
11
, and according, an image is reproduced through the panel
10
.
Especially, the inner shield
60
includes a vertical portion
62
extended in parallel to a tube central axis (X) and a slope portion
63
integrally formed at the rear portion of the vertical portion
62
and extended to be sloped toward the tube central axis (X).
As shown in
FIG. 1
, a front opening (Bf) is formed in front of the vertical portion
62
, and a bent portion is formed bent vertically to the vertical portion
62
so that the inner shield
60
can be fixed with a clip (C) to the frame
30
.
A rear opening (Br) relatively smaller than the front opening (Bf) is formed at a rear side of the slope portion
63
.
The inner shield
60
of a color CRT of the conventional art, however, has several problems.
That is, for example, with reference to
FIG. 2B
, since the height (h
1
) of the vertical portion
62
is too small for the entire height (H) of the inner shield
60
constituted by the vertical portion
62
and the slope portion
63
, the slope portion
63
is away from the funnel
20
with the big distance (d) therebetween, resulting in that efficiency in shielding the earth magnetic field is degraded.
In case where the inner shield
60
is adopted to a product of a color CRT and used for some periods, since the shielding efficiency of the earth magnetic field is degraded, the variation degree that the electron beam is landed becomes great according to the variation of an external magnetic field, causing a problem of occurrence of a color spread due to a color mixture when an image is reproduced.
When the color spread occurs due to such factors, the product of the color is CRT purchasing a high image quality is devaluated, and a reliability of the product is accordingly degraded.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide an inner shield of a color CRT that is capable of improving a shielding effect by enhancing a structure of an inner shield and capable of preventing a color spread phenomenon due to color mixture when an image is reproduced by reducing a variation degree in landing of an electron beam according to an external magnetic field variation according to the improved shielding effect.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a color CRT having an inner shield being mounted at a frame inside a panel and a funnel to shield an earth magnetic field, the inner shield having a vertical portion formed in parallel to the central axis of the CRT and mounted at the frame, a slope portion extended slanted against the central axis of the CRT at a rear side of the vertical portion and a notch with its central portion formed concave at the end portion of the slope portion, the opposite of the frame, and under the assumption that the entire height of the inner shield constructed with the vertical portion and the slope portion is ‘V’, a height (V
1
) of the vertical portion satisfies the relational expression of 0.18≦V
1
/V≦0.25, and on the assumption that the shortest height from a starting point of the vertical portion to the notch is V
2
, the height V
1
of the vertical portion satisfies a relational expression of 0.40≦V
1
/V
2
≦0.54.
On the assumption that a sectional area of a front opening formed by the vertical portion, the frame side, is ‘Af’ and a sectional area of a rear opening formed by the slope portion, the opposite side of the frame, is ‘Ar’, the inner shield is designed to satisfy a relational expression of 0.56≦Ar/Af≦0.78.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 5103132 (1992-04-01), Van Der Bolt et al.
patent: 5530316 (1996-06-01), Haga et al.
patent: 5763990 (1998-06-01), Kwak
patent: 5804912 (1998-09-01), Park
patent: 6310433 (2001-10-01), Youn et al.
patent: 6448702 (2002-09-01), Kamada et al.
Day Michael H.
LG Electronics Inc.
Perry Anthony
LandOfFree
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