Electric lamp and discharge devices – Cathode ray tube – Envelope
Reexamination Certificate
1999-09-20
2001-08-14
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Envelope
C313S461000, C313S408000
Reexamination Certificate
active
06274977
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a cathode ray tube (CRT) and, more particularly, to a flat-panel CRT which can minimize raster distortion of electron beams while maintaining structural strength of a shadow mask.
(b) Description of the Related Art
Generally, a faceplate panel for CRTs is shaped like a convex lens. Both sides of the faceplate panel, an inner phosphor-coated side and an outer viewing screen side, have a curved shape. This is because the convex-shaped panel has advantages in various aspects such as convenience of formation, stability in strength, and adaptability for shadow mask application.
However, to the eyes of the viewer, it is desirable that the screen image should be displayed as substantially flat. For this reason, several attempts have been made to form both sides of the faceplate panel with a flat shape while maintaining the normal display characteristics of the CRT. It is found that when a flat panel is used for the display screen problems occur in the convergence characteristics of electron beams and in the strength of a shadow mask. For example, when the surface of the phosphor-coated side is flat-shaped, it becomes difficult to deflect three electron beams of red R, green G and blue B correctly on a suitable convergence point. Furthermore, because the shadow mask facing the inner side of the panel should be correspondingly flat-shaped, the desired strength of the shadow mask cannot be achieved through the common shadow mask forming technique.
In addition, there is a problem with the flat-panel CRT from the standpoint of the viewer. When the viewer watches a monitor with the flat-shaped faceplate panel, they feel that the screen image is sunken at its center portion while protruded at its peripheral portion.
Therefore, it is preferable in the shadow mask-formation typed CRTs that the outer viewing screen side is formed with a flat shape and the inner phosphor-coated side with a curved shape.
In such a faceplate panel, as an inner curvature radius becomes smaller, the formation characteristics of the panel can be improved and the corresponding shadow mask can be formed with a stable structure capable of reducing a doming phenomenon. However, when the inner curvature radius of the panel falls below a minimum value, the peripheral portion of the panel is undesirably thick and this results in poor production efficiency as well as high production cost. Furthermore, the large thickness of the peripheral portion has a poor transmission rate and ultimately causes brightness failure.
In order to overcome such problems, various techniques are proposed for the one-sided flat panel CRT application. For example, these kinds of techniques are disclosed in Japanese Patent Laid Open Publication Nos. Hei 36710 and Hei 6-44926. However, they do not specify technical details for preserving the structural strength of the shadow mask which should be redesigned pursuant to the curvature radii varied at the inner side of the panel.
Furthermore, they do not calibrate the desired thickness ratios of a diagonal portion of the panel to the peripheral portion for minimizing distortion of the screen image. Therefore, when the CRT panel is manufactured on the basis of the above-identified techniques, the aforementioned problems remain.
In the usual sized flat-panel CRTs of 21-inch, 25-inch and 29-inch, it turns out that the thickness ratios of the peripheral portion of the panel to the center portion are 3.13, 2.91 and 2.72, respectively. These ratios are so high that they result in bad production efficiency as well as brightness failure.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a CRT which can minimize raster distortion of electron beams while maintaining structural strength of a shadow mask.
This and other objects may be achieved by a CRT provided with a panel having an inner phosphor-coated side with a curved shape, an outer viewing screen side with a substantially flat shape, and a rectangular-shaped effective screen area ranged through the inner phosphor-coated side and the outer viewing screen side. A shadow mask faces the phosphor-coated side of the panel. The shadow mask is formed to be adapted to the curved shape of the phosphor-coated side. The panel is sealed to a funnel which is in turn connected to a neck having an electron gun therein.
The rectangular-shaped effective screen area of the panel has two horizontally parallel long sides meeting a vertical axis V
1
, two vertically parallel short sides extended perpendicular to the horizontal sides, and four boundary corners formed between the neighboring horizontal and vertical sides. The vertical sides meet a horizontal axis H
1
and each of the boundary corners meet a diagonal axis D
1
.
The meeting point of the horizontal long side and the vertical axis V
1
has a thickness Tv. The meeting point of the vertical short side and the horizontal axis H1 has a thickness Th. The meeting point of the boundary corner and the diagonal axis D
1
has a thickness Td. The thickness ratio of Tv to Td is in the range of 0.75≦Tv/Td≦0.93, whereas the thickness ratio of Th to Td is in the range of 0.75≦Th/Td≦0.85.
REFERENCES:
patent: 6157124 (2000-12-01), Wakasono
patent: Hei 6 36710 (1994-02-01), None
patent: Hei 6 44926 (1994-02-01), None
Kim Chan-Yong
Kim Wan
Pyun Do-houn
Berck Ken A.
Christie Parker & Hale LLP
Patel Nimeshkumar D.
Samsung Display Devices Co. Ltd.
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