Electric lamp and discharge devices – Cathode ray tube – Screen
Reexamination Certificate
2000-03-03
2003-09-02
Bruce, David V. (Department: 2882)
Electric lamp and discharge devices
Cathode ray tube
Screen
C313S112000, C430S027000
Reexamination Certificate
active
06614160
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fluorescent screen of a color CRT and its fabricating method, and more particularly, to a fluorescent screen structure of a color CRT which is directed to improve contrast characteristics, luminance characteristics and color purity of a screen, and to a fluorescent screen of a color CRT and its fabricating method which is capable of simplifying a fabricating process of the fluorescent screen.
2. Description of the Background Art
Generally, a color CRT is an instrument in which an electronic beam radiated from an electric gun hits a fluorescent screen formed on the inner surface of a panel, to thereby implement a picture. Recently, as the screen is being enlarged in size, it requires more improved luminance characteristics and contrast characteristics, for which research is being done.
For example, in order to obtain favorable contrast characteristics, there has been proposed that using of a dark glass of which light transmittance is approximately 36%-55% as a panel, forming a fluorescent material layer by using a fluorescent with an inorganic pigment of the same color attached on the surface of the particles thereof, or forming a three-color filter layer having the same color as that of the fluorescent material layer between the three-colored fluorescent material layer and a panel where a black matrix is formed to thereby improve a selective permeability.
However, the three methods proposed for improvement of the contrast characteristics respectively include the following disadvantages.
First, in case of the fluorescent screen of a color CRT using the dark glass as a panel, though the contrast characteristics of the screen can be improved by absorbing an external light by means of the dark glass, since the dark glass also absorbs the light emitting of the fluorescent screen, the luminance characteristics of the screen is degraded.
Secondly, in case of the color CRT in which the fluorescent material layer is formed by using a fluorescent material with pigment attached, though the contrast characteristics is improved as the attached pigment absorbs the external light, since the fluorescent material particles are overlapped to various layers to form a fluorescent screen, the light emitting of the fluorescent screen is partially absorbed to the pigment, resulting in that the luminance characteristics of the screen is degraded. In addition, since the pigment prevents electron discharged from the electron beam from colliding with the core of the fluorescent material, the luminance characteristics are degraded.
In order to solve the problem, as shown in
FIG. 1
, there has been o proposed a fluorescent screen where 3 color filter layer is formed which corresponds to the three-color fluorescent material layer.
FIG. 1
shows a fluorescent screen of a color CRT in which three color filter layers are formed in accordance with a conventional an.
In the drawing, the fluorescent screen has a structure in that three-color filter layers (
3
R,
3
G and
3
B) are formed on a panel
1
on which a black matrix
2
was formed, and three color fluorescent material layers (
4
R,
4
G and
4
B) are formed corresponding to the three color filter layers (
3
R,
3
G and
36
).
There are various methods of forming the three color filter layers (
3
R,
3
G and
3
B), of which two representative methods will now be described.
One method:
A black matrix
2
is formed on the inner surface of the panel
1
of which light transmittance is approximately 70%-85% by a conventional method.
Sensitizing solution composed of polyvinyl alcohol PVA and ammonium dichromate ADC and a filter slurry liquid mixed with pigment dispersion liquid are coated and dried on the inner surface of the panel
1
where the black matrix
2
.
The portions where each filter layer is to be formed is exposed by using a shadow mask. For example, in case of forming a green filter layer
3
G, only the portion where the green filter layer
3
G is to be formed is exposed to form a photoresist film, which is then developed by using water. And then, the other region except for a portion where the green filter layer
3
G is to be formed is washed away, and only the green filter layer
3
G remains. In order to form the red filter layer
3
R or the blue filter layer
3
B, the same process is repeatedly performed for the portions where each filter layer is to be formed.
Another method:
A black matrix
2
is formed on the inner surface of the panel
1
of which light transmittance is approximately 70%~85% by a conyentional method.
Sensitizing solution composed of polyvinyl alcohol PVA and ammonium dichromate ADC is coated and dried on the inner surface of the panel
1
where the black matrix
2
.
The portion except for the region where the green filter layer
3
G is to be formed is exposed and hardened to form a photoresist film, and then a green color pigment dispersion liquid is coated and dried on the inner surface of the panel where the photoresist film was formed.
The photoresist film is detached by etching process by using an etching solution such as aqueous hydrogen peroxide (H
2
O
2
) and developed by a strong hydraulic pressure. Then the photoresist film is removed and a green filter layer
3
G is formed. In case of the red filter layer
3
R and the blue filter layer
3
B, the same process is repeatedly performed to thereby form filter layers.
After the three filter layers
3
R,
3
G and
3
B are formed, on which fluorescent material layers
4
R,
4
G and
4
B are formed corresponding to each filter layer, thereby completing a fluorescent screen structure of a color CRT having three color filter layers.
Reference numeral
5
of
FIG. 1
denotes an aluminum film for preventing the electron beam from deviating backward and for rendering the light emitted in the backward direction to be reflected in the forward direction, and reference numeral
6
is a coloration film or a coloration coating layer for improving the contrast characteristics of the screen.
As mentioned above, in case that the three-color filter layers
3
R,
3
G and
3
B are formed on the fluorescent screen of the color CRT, its contrast and luminance can be improved by 10%~20% compared to the color CRT using the fluorescent material attached by the pigment.
A Japanese Open Laid No. 9-27284 discloses that since the three-color filter layers
3
R,
3
G and
3
B has the maximum transmittance for the light having a wave length in the range of approximate ±20 nm of the maximum light emitting wave length region of the three-color fluorescent material layers
4
R,
4
G and
4
B corresponding to each filter layer and have relatively low transmittance for the other wave length region, the contrast characteristics of the color CRT can be improved.
Substantially, as shown in
FIGS. 2A
,
2
B and
2
C, the transmittance of each filter layer
3
R,
3
G and
3
B for the light emitting region of the red, green and blue fluorescent material layers
4
R,
4
G and
4
B is effective in the maximum light emitting region of each fluorescent material layer.
In case of the blue filter layer
3
B, as shown in
FIG. 2A
, it has approximately 70% transmittance at 450 nm, that is, the maximum light emitting region of the blue fluorescent material layer
4
B, while in case of the red filter layer
3
R, as shown in
FIG. 2B
, it has approximately 60% transmittance at 625 nm, that is, the maximum light emitting region of the red fluorescent material layer
4
R. Meanwhile, in case of the green filter layer
3
G, as shown in
FIG. 2C
, it has approximately 70% transmittance at 530 nm, that is, the maximum light emitting region of the green forescent material layer
4
G.
However, the conventional art has the following problems.
Though forming each filter layer for each fluorescent material layer is effective in the aspect of improving the contrast characteristics and the luminance characteristics of the color CRT, since the three filter layers need to be formed, the number of the processes is inevitably increased add
Birch & Stewart Kolasch & Birch, LLP
Bruce David V.
LG Electronics Inc.
Yun Jurie
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