Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
2000-06-16
2002-08-13
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
Reexamination Certificate
active
06433468
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an aperture-grill type, color-selection mechanism and a color cathode-ray tube using the color-selection mechanism.
A color cathode-ray tube used for a television receiver, a display for a monitor of a computer and the like has a structure as shown in FIG.
1
. In this figure, reference numeral
1
designates a panel,
2
is a color selection electrode,
3
is a phosphor,
4
is a funnel, and
5
is an electron gun.
FIG. 2
is a perspective view showing an aperture-grill type, color-selection electrode
2
, which includes tapes
6
, slits
7
, and a frame
8
.
FIG. 3
is a sectional view showing a panel
1
and a color selection electrode
2
of a related art color cathode-ray tube.
Referring to
FIG. 3
, an electron beam
9
emitted from an electron gun passes through one slit
7
of the color-selection electrode
2
and further through an aluminum film
10
, and it collides with a phosphor
3
a
to make phosphor
3
a
luminous.
The color-selection electrode
2
is generally produced by forming a patterned mask film on the surface of a steel sheet having a specific thickness and etching the steel sheet using the mask film as a mask to form a large number of slits
7
, each of which extends in a stripe-shape between adjacent tapes
6
. Each tape
6
has the cross-sectional shape shown in
FIG. 3
, in which the width of the portion on the electron gun side of tape
6
is different from the width of the portion on the panel side, of the tape
6
, and, more specifically, the width of the flat portion
6
a
, nearest to the panel side of tape
6
is narrowest.
To be more specific, the cross-sectional shape of the tape
6
is designed such that a portion on the electron gun side, which is in a thickness range being several tens percent of the total thickness of the tape
6
, has a width which is constant and widest, the flat portion
6
a
nearest to the panel side has the narrowest width, and a portion therebetween has a width which becomes narrower when nearing to the panel side. Reference numeral
6
c
designates a tilt portion formed by making the width of the tape
6
narrower toward the panel side. The reason why each tape
6
has such a cross-sectional shape is that the electron beam
9
(generally, electron beam for red or blue), having obliquely passed through the slit
7
, is allowed to be made incident on the corresponding phosphor
3
a
as much as possible while not being shielded by the tapes
6
positioned on both sides of the slit
7
.
According to the related art color-selection electrode
2
, with the arranged pitch of slits (hereinafter referred to as “a slit pitch”) set in a range of 0.310 to 0.221 mm, the width of the flat portion
6
a
nearest to the panel side of tape
6
is set to be 0.25 to 0.30 times the slit pitch.
By the way, the related art color cathode-ray tube has the problem that it is difficult to improve the color purity. The reason for this is as follows: namely, a color cathode-ray tube used for a display obtaining a high-definition image quality requires a finer arranged pitch of slits; however, such a finer arranged pitch of slit causes the phenomenon that electrons having collided with a desired phosphor are partially reflected therefrom and scattered, and the scattered electrons collide with an undesired phosphor to make the undesired phosphor luminous.
To be more specific, as shown in
FIG. 3
, when the electron beam
9
, having obliquely passed through one slit
7
, collides with the corresponding phosphor
3
a
, all of the beam
9
having thus collided with the phosphor
3
a
is not necessarily made incident on the phosphor
3
a
; that is, it does not necessarily contribute to generation of luminescence of the phosphor
3
a
. That is to say, there may occur the phenomenon that part
9
a
of the electron beam
9
is reflected from the phosphor
3
a
and collides with the flat portion
6
a
on the panel side of tape
6
of the color selection electrode
2
, and the electron beam
9
a
having thus collided with the flat portion
6
a
is scattered, and part of the scattered beam is made incident on an undesired phosphor
3
b
to generate luminescence of the undesired phosphor
3
b
. As a result, a color mixture occurs, and thereby the color purity is degraded.
An effort has been directed to make the color deviation due to reflection of an electron beam as small as possible by improving the materials of the phosphors
3
and the color selection electrode
2
; however, at the present condition, the requirement toward improvement of the color purity has been made larger, and it has been difficult to meet such a requirement.
The related art color-selection mechanism has another problem that the color purity is uneven between a central portion of the screen and right and left sides thereof because the tilt angle at which an electron beam collides with a phosphor differs between the central portion of the screen and the right and left sides thereof.
To be more specific, the electron beam
9
emitted from an electron gun passes through one slit
7
of the color selection electrode
2
, and part of the electron beam
9
is reflected from the aluminum film
10
and the phosphor
3
; and, it is known that the reflectance of the electron beam differs depending on the tilt angle at which the electron beam
9
collides with the aluminum film
10
and the phosphor
3
, and, more specifically, the reflectance of the electron beam
9
becomes larger as the above tilt angle becomes larger. On the other hand, as described above, the tilt angle at which the electron beam collides with the aluminum film
10
and the phosphor
3
differs between the central portion of the screen of the color cathode-ray tube and the right and left sides thereof. As a result, unevenness of the color purity occurs due to the difference in reflectance among positions in the horizontal scanning direction on the screen.
The present inventor has found that the evenness of the color impurity on the screen can be obtained by suitably changing the width of the flat portion
6
a
, on the panel side of each tape of the color selection mechanism in accordance with the tilt angle at which an electron beam collides with the aluminum film
10
and the phosphor
3
. As the result of examining the change in width of the flat portion
6
a
on the panel side of each tape of the related art color selection mechanism depending on the position on the horizontal scanning direction, it was found that the above width is changed as shown by the data (“related art”) in FIG.
6
.
The present inventor has repeatedly made experiments and found that the evenness of color purity can be significantly enhanced by changing the above width as shown by the data (“present invention (third embodiment)”) in
FIG. 6
, and has accomplished a third invention to be described later on the basis of such knowledge.
SUMMARY OF THE INVENTION
The first object of the present invention is to provide a color-selection mechanism capable of suppressing the degradation of color purity due to the fact that an electron beam, which has passed through a slit and has been reflected from the inner surface of a panel, is reflected from a surface on the panel side of each tape of a color-selection electrode and is made incident on another phosphor different from a desired phosphor, and to provide a color cathode-ray tube using the color-selection mechanism.
The second object of the present invention is to provide a color-selection mechanism capable of reducing the unevenness of color purity caused depending on the position in the horizontal scanning direction on the screen and to provide a color cathode-ray tube using the color-selection mechanism.
According to a first aspect of the present invention, there is provided a color-selection mechanism with an aperture-grill type, color-selection electrode which includes tapes constituting the matrix of the electrode and slits each that are disposed between the tapes, the arranged pitch of the slits are in the range of 0.310 to 0.221 mm,
Kananen, Esq. Ronald P.
Patel Ashok
Rader & Fishman & Grauer, PLLC
Sony Corporation
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