Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
1999-12-17
2002-08-20
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S403000, C313S404000, C313S407000, C313S408000, C313S409000
Reexamination Certificate
active
06437496
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color cathode ray tube (CRT), and more particularly, to a tensioned shadow mask with a color selection function, which has dummy bridges with an improved structure, and a color CRT adopting the same.
2. Description of the Related Art
Color CRTs for televisions and computer displays employ a shadow mask (hereinafter, simply referred to as a mask) for accurate landing of three electron beams emitted from an electron gun on each phosphor of a phosphor screen. The mask includes a dot mask with substantially circular apertures a slot mask with parallel elongated apertures, and a tensioned mask to which tension is applied from opposite sides thereof, and having series of parallel strips separated by slits through which electron beams pass.
FIG. 1
shows an example of a tensioned mask. As shown in
FIG. 1
, the tensioned mask formed of a foil includes a plurality of strips
12
separated by slits
11
having a predetermined interval, and a plurality of tie bars
13
which interconnect the adjacent strips to define the slits
11
at predetermined intervals.
In the mask, the tie bars
13
which interconnect the adjacent strips
12
can reduce a howling phenomenon, which occurs due to mask vibration from external impact, and unacceptable Poisson's contraction. However, if the vertical pitch PV of the tie bars
23
is too large, that is, if the vertical pitch PV of the tie bars
23
is twice or more the horizontal pitch PH thereof, a reflection image of the tie bars
13
is shown on the screen, which is unpleasant to viewers.
To avoid this problem, U.S. Pat. No. 4,926,089 discloses a tensioned mask as shown FIG.
2
. As shown
FIG. 2
, a tensioned mask
20
includes a plurality of strips
21
separated by slits
22
having a predetermined interval, and tie bars
23
which interconnect the adjacent strips
21
. Also, dummy bridges
24
, which extend partially between but not interconnecting adjacent strips, are disposed between the adjacent tie bars
23
to separate each slit
21
into sub-slits having a predetermined interval.
In the tensioned mask, due to a technical problem in mask pattern formation, the width WI of the dummy bridges
24
is smaller than the width W
2
of the tie bars
23
. Thus, the reflection images by the dummy bridges
24
and the tie bars
23
have a slight difference in intensity of light. This difference raises the problem of tie bar visibility, thus deteriorating display image and making viewing unpleasant.
In formation of the phosphor screen on the inner side of a faceplate, as shown in
FIG. 3
, a tensioned mask and frame assembly is secured to a faceplate
100
, and then subjected to an exposure process for forming a phosphor screen
101
, wherein an exposure lamp
102
for use in the exposure process is long enough to irradiate a region corresponding to the vertical pitch between adjacent tie bars
23
or that of adjacent dummy bridges
24
of the tensioned mask
20
. However, in the phosphor screen formation using the exposure lamp
102
, red phosphor, blue phosphor and green phosphor are not completely excited, resulting in black matrix pattens in the nonexcited regions, as shown in FIG.
4
. This problem is associated with the offset configuration of the dummy bridges
24
of the tensioned mask
20
. In particular, as shown in
FIG. 2
, the dummy bridges
24
of the tensioned mask
20
extend from a strip
21
′ toward the adjacent strip
21
″, to define gaps near the strip
21
″. Accordingly, regions of the phosphor patterns that correspond to the offset protrusions of the dummy bridges
24
, except for regions that correspond to the gaps between the dummy bridges
24
and the strip
21
″, are not excited by the electron beams emitted from the electron gun, so that the black matrix remains therein. Such intrusion of the black matrix into the red, blue and green phosphor patterns reduces the emission area of the phosphors, and regions, which are not excited due to the dummy bridges
24
are also shown in a screen, thereby lowering appearance uniformity.
SUMMARY OF THE INVENTION
An object of the present is to provide a tensioned shadow mask and a color cathode ray tube (CRT) adopting the same, capable of eliminating intrusion of a black matrix into phosphor patterns during phosphor screen formation, due to dummy bridges.
Another object of the present invention is to provide a tensioned mask and a color CRT adopting the same, capable of eliminating the problem of tie bar visibility.
According to an aspect of the present invention, there is provided a tensioned shadow mask for a cathode ray tube (CRT), comprising: a series of parallel strips separated by slits having a predetermined interval; a plurality of tie bars interconnecting adjacent strips to define a plurality of slits at predetermined intervals; and a plurality of dummy bridges disposed between adjacent tie bars, the dummy bridges extending between the adjacent strips and facing each other, but not interconnecting the adjacent strips.
Preferably; the area of the dummy bridges is equal to that of the tie bars, or the area difference between the dummy bridges and the tie bars is in a predetermined range.
According to another aspect of the present invention, there is provided a color cathode ray tube (CRT) including a faceplate having on the inner side thereof a phosphor screen, a tensioned mask and frame assembly secured into the faceplate, which is an assembly of a tensioned mask and a frame, a funnel connected to the faceplate, the funnel having a neck portion and a cone portion, an electron gun inserted in the neck portion of the funnel, and a deflection yoke installed in the cone portion of the funnel, wherein the tensioned mask comprises: a series of parallel strips separated by slits having a predetermined interval; a plurality of tie bars interconnecting adjacent strips to defines a plurality of slits at predetermined intervals; and a plurality of dummy bridges disposed between adjacent tie bars, the dummy bridges extending between the adjacent strips and facing each other, but not interconnecting the adjacent strips.
REFERENCES:
patent: 3973965 (1976-08-01), Suzuki et al.
patent: 4296189 (1981-10-01), Kuzminski
patent: 4727280 (1988-02-01), Fujimura
patent: 4926089 (1990-05-01), Moore
patent: 4942332 (1990-07-01), Adler et al.
patent: 5030881 (1991-07-01), Marks et al.
patent: 5583391 (1996-12-01), Good et al.
patent: 6057640 (2000-05-01), Aibara
patent: 487106 (1992-05-01), None
patent: 2702881 (1994-03-01), None
patent: 57-065650 (1982-04-01), None
Kang Gwang-soo
Kim Wan
Shin Soon-Chul
Leydig , Voit & Mayer, Ltd.
Patel Nimeshkumar D.
Roy Sikha
Samsung SDI Co., LTD
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