Electric lamp and discharge devices – Plural unit – Cathode ray tube
Reexamination Certificate
2000-05-10
2003-05-06
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Plural unit
Cathode ray tube
C313S403000
Reexamination Certificate
active
06559575
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cathode ray tube (CRT) used as, for example, a color television or a display device for an information processing terminal device, and a method of manufacturing the CRT. The present invention also relates to a color selecting member for a CRT, for ensuring that an electron beam strikes a predetermined position in a phosphor pattern, and a method of manufacturing the color selecting member.
2. Description of the Related Art
A CRT is used as a usual type of color television receiver of the related art or a display device for an information processing terminal device. For the purpose of achieving a CRT of high picture quality by solving problems such as a chromatic blur of neighboring color pixels, there is provided a color selecting member such as an aperture grille or a shadow mask. Such a color selecting member is used for exposure to form patterns for respective color phosphors in a self aligning manner. Based on the patterns formed by exposure, phosphor patterns corresponding to respective color pixels are formed by photolithography or the like.
In recent years, the size of a screen, especially in a color television receiver, has been increasing. On the other hand, a color television receiver adapted to a high definition display system, what is called a HDTV (high definition television) system, is being developed and put into practical use. Enlarging the entire screen in such a color television receiver involves an increase in the size of the entire CRT.
In the case of a CRT for HDTV, since its screen is further widened especially in the lateral direction (horizontal scan direction), the size of the CRT in the lateral direction is remarkably increased. The CRT for HDTV has to therefore provide for upsizing especially in the lateral direction (horizontal direction). On the other hand, since the CRT for HDTV is a display device for the purpose of higher picture quality in a high definition display system, the CRT for HDTV requires higher picture quality while upsizing.
In such a CRT of the related art, especially a color selecting member and a phosphor layer are manufactured in the following manufacturing process.
FIG. 5
is a schematic diagram showing a process of exposure to form a phosphor layer in a process of manufacturing a usual single-gun type of CRT of the related art. The Description given below relates to the case of a CRT using a phosphor pattern in vertical stripes and a color selecting member (that is, aperture grille) of the related art.
Referring to
FIG. 5
, a photosensitive agent (not shown) such as resist is applied to the inside of a front panel
1
. A color selecting member
2
is mounted just behind the front panel
1
. The color selecting member
2
has narrow slits or a number of rectangular holes arranged in a slot pattern or in a dot pattern. Then, the front panel
1
is exposed through the color selecting member
2
so as to form a pattern for carbon stripes having predetermined widths and pitches in predetermined positions. After that, carbon is applied and dried, and the stripes of the photosensitive agent are removed with a chemical (or a solvent) such as hydrogen peroxide, thereby forming carbon stripes.
A film made of a mixture of each color phosphor, namely, for example, R (Red), G (Green) and B (Blue), and the photosensitive agent is formed and exposed with the exposure position shifted so as to form a pattern in vertical stripes having predetermined widths and pitches in predetermined positions. The pattern formed by exposure is used to form stripes (not shown) of each color phosphor by photolithography. Thus, a phosphor layer is completed.
When the CRT is used as a completed product in practice, an electron beam emitted from an electron gun strikes accurately its intended area in the phosphor layer formed as mentioned above. Thereby, the color phosphor at the intended position emits light and is observed as a pixel. In order to attain high picture quality, the phosphor has to be formed in an exact position where the electron beam strikes. In other words, a deviation of the phosphor from the exact positioning causes defective display such as misregistration, which deteriorates picture quality severely. The demands on exact positioning of the phosphors are becoming even severe in order to cope with higher definition attained in recent years.
For the purpose of accurate positioning of the light for exposing a phosphor and the electron beam, provided is a correction lens system
4
between a light source
3
of a projection aligner and the front panel
1
(more concretely, the phosphor layer). Thereby, a deviation between the locus of the electron beam and that of the light for exposure is corrected. The correction lens system
4
has an uneven shape in cross section as shown in FIG.
5
.
In recent years, while the size of the screen is increasing as described above, reduction in a depth dimension has been strongly demanded in the outer shape of the entire television receiver. Since there is a tendency that the size of the entire CRT has to be increased as the size of the screen increases, the depth dimension of the CRT tends to increase. That is, it goes counter to the demand on reduction in a depth dimension of the outer shape.
Particularly in the case of a CRT adapted to a large screen, especially a CRT for HDTV of a wider screen, further reduction in a depth dimension of the CRT is almost impossible in the single-gun type of CRT. Thus, as shown in
FIG. 6
, there has been a proposal for a CRT in which two or more electron guns
5
are arranged side by side in the lateral direction. The electron guns
5
are housed in the respective necks
7
of the respective rear funnels
6
. Deflection yokes
8
are provided around the respective necks
7
in correspondence with the respective electron guns
5
.
The use of a plurality (two in this case) of electron guns
5
in side-by-side arrangement as mentioned above enables an electron beam emitted from each electron gun
5
to move across only about half of the screen. This enables an electron beam to strike especially in the peripheral areas of the screen at a reasonable angle, even if a depth dimension is reduced by shortening the distance between the electron gun
5
and the front panel
1
. Thus, a depth dimension of the outer shape is reduced while being adapted to the large screen. In addition, high picture quality can be achieved throughout the entire large screen.
Since a usual type of CRT of the related art has one electron gun
5
, a projection aligner used in the manufacturing process also adopts a system in which one light source corresponds to one front panel.
FIG. 7
shows a CRT for large HDTV, as an example of a large CRT having an extremely wide screen, during the process of exposure to form a phosphor layer by using a usual type of projection aligner of the related art having only one light source system
3
in only one place. The portion in
FIG. 7
denoted by reference character A is shown in
FIG. 8
in enlarged dimension. As seen from
FIG. 8
, the use of a usual type of projection aligner of the related art causes a considerable deviation of the locus of light
9
for exposure and that of an electron beam
10
from each other.
The reason is as follows. The number of electron guns for emitting the electron beam
10
is two while there is provided one light source system
3
. This causes a large difference between the incident angle of the electron beam
10
and that of the light
9
, which pass through the same single hole
11
in the color selecting member
2
. As a result, there is a considerable deviation of the position of each color phosphor or each pixel phosphor formed in the photolithography process including the exposure process using the light
9
from the position where the electron beam
10
strikes. This produces problems of deterioration in picture quality and occurrence of display failure.
One possible method to cope with the problem may be, as shown in
FIG. 9
, to modify the
Inoue Takahiro
Muraguchi Shoichi
Ohno Katsutoshi
Okada Masamichi
Sakata Atsushi
Maioli Jay H.
Patel Ashok
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