Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
1999-03-02
2002-08-27
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S403000, C313S408000, C313S407000
Reexamination Certificate
active
06441545
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a color cathode ray tube, and relates, more particularly, to a color cathode ray tube capable of reducing displacement of beam landing attributable to deformation of a shadow mask or oscillation and capable of reducing howling of a phosphor screen, by setting in suitable conditions the curvature of an effective surface of the shadow mask and electron beam through hole rows formed by a plurality of electron beam through holes.
In general, a color cathode ray tube has a vacuum envelop composed of an almost rectangular panel
3
provided with a skirt
2
at the periphery of an effective portion
1
having a curved surface, and a funnel
4
connected to the skirt
2
, as shown in
FIG. 1. A
phosphor screen
5
is provided on the inner surface of the effective portion
1
of the panel
3
. At the inside of the phosphor screen
5
, there is disposed an almost rectangular shadow mask
9
, composed of a mask main body
7
having a large number of electron beam through holes or apertures on an effective surface
6
formed in an almost rectangular curved surface opposite to the phosphor screen, and an almost rectangular mask frame
8
fitted to the periphery of the mask main body
7
. In the mean time, within a neck
11
of the funnel
4
, there is disposed an electron gun assembly
13
for discharging three electron beams
12
B,
12
G and
12
R. The three electron beams
12
B,
12
G and
12
R emitted from this electron gun assembly
13
are deflected by a magnetic field generated from a deflector
14
mounted on the outside of the funnel
4
. These three electron beams
12
B,
12
G and
12
R are then selected by the shadow mask
9
and are directed to the phosphor screen
5
. When the phosphor screen
5
is scanned both horizontally and vertically by the three electron beams
12
B,
12
G and
12
R, a color image is displayed on the phosphor screen
5
.
In this color cathode ray tube, the holes or apertures formed on the effective surface
6
of the shadow mask
9
, through which the electron beams pass, are arranged as follows. A plurality of electron beam through holes are laid out in one line along a short axis (Y axis) direction of the shadow mask, and a plurality of these electron beam through hole array or aperture array composed of the plurality of electron beam through holes in the short axis direction are arranged in a long axis (X axis) direction of the shadow mask. Corresponding to this arrangement of the electron beam through holes, the phosphor screen
5
is structured by black strip layers, i.e., non-light emitting layers extending in the short axis direction, and three-color phosphor layers buried between the black non-light emitting layers. The color cathode ray tube having this structure is called an in-line type, and has been in practical use.
Generally, in order to achieve a display of an image without any color purity degradation on the phosphor screen of a color cathode ray tube, it is essential that each of the three electron beams passing through the electron beam through holes of the shadow mask makes a correct landing on the three color phosphor layer of the phosphor screen. In order to perform a correct landing of the three electron beams, it is necessary that a distance (q value) between the inner surface of the effective portion of the panel and the effective surface of the shadow mask is set at a value within a predetermined permissible range.
In recent years, in order to improve the visibility of an image, color cathode ray tubes have been designed to have a flat surface or almost a flat surface, with a smaller curvature, for the external surface of the effective portion of the panel. These color cathode ray tubes need to have a smaller curvature for the internal surface of the effective portion of the panel, for obtaining good visibility of an image and from the viewpoint of forming the panel. In this case, the effective surface of the shadow mask needs to have a small curvature corresponding to the curvature of the internal surface of the effective portion of the panel, in order to obtain a suitable distance from the internal surface of the effective portion of the panel.
However, the reduction in the curvature of the effective surface of the shadow mask involves such risks that the strength of the curved surface becomes weak, that a local deformation occurs in the shadow mask and the color cathode ray tube at the manufacturing stage, and that color purity is deteriorated. Further, when the color cathode ray tube is built into the image receiver, a howling occurs by the sound from the speaker, which lowers the color purity.
On the other hand, if the curvature of the effective surface of the shadow mask is set large in an attempt to prevent deterioration of the color purity attributable deformation or oscillation of the shadow mask, and if the curvature of the internal surface of the effective portion of the panel is set to correspond to this curvature of the effective surface, then the curvature of the internal surface becomes larger for the shape of the external surface of the effective portion. This not only makes it difficult to form the panel, but also has a risk of a reduction in the visual field angle due to a total reflection and a deterioration in the visibility due to a reflected image on the internal surface of the panel.
There has already been made a proposal for preventing the deterioration of color purity attributable to deformation or oscillation of the shadow mask. According to this proposal, as shown in
FIG. 2
, the internal surface of an effective portion
1
of a panel
3
has a curvature in its short axis direction, and a radius of curvature in the long axis direction is set as infinite in its long axis direction from the center to an intermediate portion of the panel. The radius of curvature in the long axis direction near the periphery of the short side is formed in a larger curved surface than the radius of curvature in the long axis direction from the center to the intermediate portion. The effective surface of the shadow mask is formed in a similar curved surface corresponding to the internal surface shape of the effective portion
1
of the panel
3
.
When the effective portion
1
of the panel
3
and the effective surface of the shadow mask are set in the curved shapes as explained above, it becomes possible to improve the strength of the curved surface of the shadow mask
9
and to increase the atmospheric pressure strength of the vacuum envelop at the same time. However, even in this, the curved surface strength of the shadow mask
9
is insufficient at portions near the center of the effective surface
6
. Further, the phosphor screen formed on the internal surface of the effective portion
1
of the panel
3
is degraded.
In general, the phosphor screen of the color cathode ray tube is formed based on a photo-lithographic method, according to which the black non-light emitting layer is formed first and then the three-color phosphor layer is formed, for the phosphor screen that is composed of the non-light emitting layer and the three-color phosphor explained above.
According to this photo-lithographic method, at first, a photosensitive material is coated on the internal surface of an effective portion
1
of a panel
3
, to form a photosensitive film
15
, as shown in FIG.
3
A. This photosensitive film
15
is exposed by utilizing a shadow mask
9
. After the photosensitive mask
15
has been developed, a resist
17
in a striped pattern corresponding to an electron beam through hole
16
of the shadow mask shown in
FIG. 3A
, is formed as shown in FIG.
3
B. Then, a black non-light emitting coating is coated on the internal surface of the effective portion
1
of the panel
3
on which the resist
17
has been formed. Thereafter, the coating is dried, and a black non-light emitting coated layer
18
is formed, as shown in FIG.
3
C. After that, the black non-light emitting coated layer on the resist
17
is separated together with the resist
17
, and a stripe
Inoue Masatsugu
Mashimo Takuya
Nakagawa Shinichiro
Shimizu Norio
Guharay Karabi
Kabushiki Kaisha Toshiba
Patel Nimeshkumar D.
LandOfFree
Color cathode ray tube having particular arrangement of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Color cathode ray tube having particular arrangement of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Color cathode ray tube having particular arrangement of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2890696