Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
1999-01-21
2001-11-06
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C445S047000
Reexamination Certificate
active
06313573
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority of Korean Patent Application No. 98-1852, filed Jan. 22, 1998.
FIELD OF THE INVENTION
The present invention relates to a shadow mask for a cathode ray tube (CRT) and a method of manufacturing the same. More particularly, the present invention relates to a shadow mask having improved tensile strength, thereby preventing what is called a spring back phenomenon.
BACKGROUND OF THE INVENTION
A conventional CRT comprises an evacuated envelope having a viewing screen coated with an array of phosphor elements of three different emission colors arranged in a cyclic order, means for producing three convergent electron beams directed towards the screen and a color selection structure or shadow mask comprising a thin multi-apertured metal sheet precisely disposed between the screen and the beam-producing means. The shadow mask shadows the screen and the differences in convergence angles permit the transmitted portions of each beam to selectively excite phosphor elements of the desired emission color.
The conventional CRT shadow mask is typically manufactured by first coating a photoresist on a thin metal plate made of Invar or aluminum-killed steel. The plate is then exposed to light, and developed and etched to form a plurality of holes therein. Thereafter, the plate formed with the holes is annealed using a heat treating process in a hydrogen atmosphere at a high temperature, thereby removing residual stress and providing softness to the plate. The plate is then formed into a predetermined mask shape by the use of a press, after which the plate is cleaned to remove all contaminants from its surface such as fingerprints, dust and other foreign substances. Finally, a blackening process is performed on the shaped plate to prevent doming of the same, thereby completing the manufacture of the shadow mask.
The shadow mask acts as a bridge between electron beams emitted from three electron guns (means for producing three convergent electron beams) and red, green and blue phosphor pixels formed on the screen because it ensures that the electron beams land on the correct phosphor pixels. Accordingly, any deviation of the shadow mask from its original position acts to mis-direct the electron beams to excite unintended phosphor pixels.
The shadow mask can be moved away from its originally-set position in the CRT if it receives external shock or vibrations such as by the loud audio from speakers in the TV set. As the resut electron beams passing through moved shadow mask will land on the wrong phosphor pixel causing deteriorated color purity. This will be described in more detail hereinbelow.
FIG. 1
shows a partial sectional view of a conventional CRT. It shows a shadow mask
6
mounted to a side wall of the panel
1
. More specifically a mask frame
5
joined to a periphery of the shadow mask
6
is coupled to a spring
4
, which is in turn connected to a stud pin
3
protruding from the side wall of the panel
1
. When the CRT receives a substantial external shock or vibrations, the shadow mask
6
is shaken and moves away from its initial position to a deviated position
7
. As the result the electron beams
10
emitted from the electron gun
11
will pass through an unintended aperture of the shadow mask
6
resulting in the excitation of the wrong phosphor pixel. This is perceived as shaking of a displayed picture and thus causes a reduction in color purity and other picture quality problems.
Furthermore, in the case where the CRT receives an extreme shock, such as when it is dropped, it is possible for the shadow mask
6
to be deformed. An example of this is shown in
FIG. 2
in which a deformed area
12
is illustrated. Needless to say, spurious colors would appear.
In an attempt to solve the above problem, the mask was heat-treated to improve its tensile strength and softness. However, since the heat-treating of a shadow mask increases its modulus of elasticity in the skirt portion of the shadow mask, an angle of the bend in the skirt portion made while press-forming the metal plate used to make the shadow mask is not the intended &thgr; degrees, but rather a &thgr;+&Dgr;&thgr; degrees as a result of the spring back phenomenon of the skirt portion.
SUMMARY OF THE INVENTION
The present invention has been made in an effort to solve the above problems.
It is an object of the present invention to provide a shadow mask for a cathode ray tube (CRT) and a method of manufacturing the same in which only an aperture portion of the shadow mask is heat-treated to increase its tensile strength and modulus of elasticity, thereby preventing the occurrence of the spring back phenomenon in a skirt portion of the shadow mask.
To achieve the above object, the present invention provides a shadow mask for a CRT and a method of manufacturing the same. The shadow mask includes an aperture portion having a plurality of apertures formed therein, the aperture portion being formed over a predetermined area in the shadow mask; and a non-aperture portion, formed adjacent to the aperture portion, defining the periphery of the shadow mask. Only the aperture portion is selectively heat-treated so that the tensile strength of the aperture portion is 1.2 to 3 times greater than that of the non-aperture portion, and the modulus of elasticity of the aperture portion is 1.5 to 3 times greater than that of the non-aperture portion.
According to a feature of the present invention, the selective heat-treating of the aperture portion is performed in a gaseous atmosphere including at least one gas selected from the group consisting of RX, propane, ammonia, B
2
H
6
and BCl
3
.
According to another feature of the present invention, the shadow mask is made of a material having a low thermal expansion rate, preferably of aluminum-killed (AK) steel or Invar.
The method includes the steps of selectively performing a heat-treating process on only the aperture portion of the shadow mask by mounting a separating cover on the non-aperture portion, the separating cover preventing contact of the non-aperture portion with the gaseous atmosphere present during the heat-treating process; and press forming the shadow mask.
According to a feature of the present invention, the heat-treating process is performed in a gaseous atmosphere including at least one gas selected from the group consisting of RX, propane, ammonia, B
2
H
6
and BCl
3
.
According to another feature of the present invention, the shadow mask is made of a material having a low thermal expansion rate, preferably AK steel or Invar.
According to yet another feature of the present invention, the separating cover is mounted simultaneously on the top and bottom of the shadow mask.
According to still yet another feature of the present invention, the separating cover is suitably sized and shaped to fully cover the non-aperture portions while exposing the aperture portion of the shadow mask.
REFERENCES:
patent: 4210843 (1980-07-01), Avadani
patent: 4859901 (1989-08-01), Thompson-Russell
patent: 4942333 (1990-07-01), Knox
patent: 4964828 (1990-10-01), Patt et al.
patent: 5451833 (1995-09-01), Tong
patent: 5928047 (1999-07-01), Ishibashi et al.
Han Dong-hee
Han Seung-kwon
Moon Sung-hwan
Christie Parker & Hale LLP
Patel Nimeshkumar D.
Samsung Display Devices Co., Ltd
Santiago Mariceli
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