Color cathode ray tube

Details Color cathode ray tube Color cathode ray tube

2001-04-16

2003-11-18

O'Shea, Sandra (Department: 2875)

Electric lamp and discharge devices

Cathode ray tube

Shadow mask, support or shield

C313S408000, C313S47700R

Reexamination Certificate

active

06650034

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a color cathode ray tube, and more particularly to a so-called flat panel type color cathode ray tube which is provided with a panel whose inner surface is coated with a phosphor layer and whose outer surface has the radius of curvature extremely larger than that of an inner surface thereof.
Recently, color cathode ray tubes called the flat face type or the flat panel type have been widely adopted as picture tubes for television receivers or monitor display tubes of personal computers or the like.
Generally, a glass-made envelope of a color cathode ray tube is composed of a panel which forms a display part (screen), a narrow-diameter neck and a funnel in a funnel shape which connects the panel with the neck. A phosphor screen (phosphor film) coated with a phosphor in three colors is formed on the inner surface of the panel and a shadow mask which works as a color selection electrode is disposed close to this phosphor screen.
Further, an electron gun which emits three electron beams arranged in in-line is accommodated in the inside of the neck and three electron beams emitted from the electron gun are made to pass through beam apertures formed on the shadow mask and are impinged on respective phosphors to reproduce color images.
Recently, this type of color cathode ray tube has an outer surface of the panel thereof flattened so as to enhance the visibility thereof. Particularly, this flattening of the panel is widely adopted with respect to color cathode ray tubes having large screens. The color cathode ray tubes having such flattened panels are called the flat panel type color cathode ray tubes or the flat-surface panel type color cathode ray tubes.
As literatures which disclose conventional techniques on this kind of flat panel type color cathode ray tube, Japanese Laid-open Patent Publication 45667/1999 and Japanese Laid-open Patent Publication 238475/1999 can be named.
SUMMARY OF THE INVENTION
FIG. 6
is a schematic cross-sectional view showing a structural example of an essential-part of a flat panel type color cathode ray tube. In the drawing, a panel
1
is joined to a periphery of a large diameter which constitutes one end of a funnel
3
and the other end of the funnel
3
which gradually narrows its diameter in a funnel shape is connected to a neck not shown in the drawing.
An outer surface PO of the panel
1
which forms a phosphor screen (screen) having an approximately rectangular shape and coated with a phosphor layer
4
on an inner surface thereof has a curved surface which is substantially a flat surface, wherein the radius of curvature of a curved surface of the inner surface PI is set to be smaller than the radius of curvature of the outer surface PO for maintaining the mechanical strength of a glass-made envelope.
A shadow mask
6
which constitutes a color selection electrode is disposed in the vicinity of this phosphor layer
4
. A large number of electron beam passing apertures
6
a
are formed in the shadow mask
6
. The shadow mask
6
is welded to a mask frame
7
and is held to the inner surface of a side wall of the panel
1
by way of a suspension mechanism not shown in the drawing.
In view of the manufacturing cost and the easiness of manufacturing, with respect to the above-mentioned flat panel type color cathode ray tube, the outer surface (also called “face”) of the panel is set to have a large radius of curvature, that is, the outer surface is set to an approximately flat surface, while the inner surface on which a phosphor layer is formed is set to have a relatively small radius of curvature to a degree that the feeling of a flatness of a displayed image is not spoiled when the display screen is seen from the outer surface.
In manufacturing the flat panel type color cathode ray tube, it is easy to approximate the shape of the outer surface of the panel to the flat surface. However, to approximate the inner surface of the panel to the flat surface, the thickness of the whole panel must be considerably increased to increase the mechanical strength of the glass-made envelope. Therefore, this is not practical in view of the increase of the weight of the cathode ray tube, the increase of cost and the like.
Further, on the other hand, with respect to the shadow mask which is not a color selection electrode of a so-called tension type, it is necessary to form a mask surface thereof with a certain degree of curvature while eliminating a completely flat surface to make the shadow mask stand by itself. Since the manufacturing of a shadow mask having large radius of curvature by a press molding is technically limited, it is necessary to give a given curvature to the shadow mask and simultaneously to give a given curvature to the inner surface of the panel.
As shown in
FIG. 6
, the curvature of the inner surface Pl of the panel
1
is larger than the curvature of the outer surface PO (the radius of curvature of PI being smaller than the radius of curvature of PO) and the shadow mask
6
approximately follows the shape of the curved surface (warp) of the inner surface Pl of this panel so that the flatness is deteriorated at the peripheries in the long axis side (X axis) on the phosphor layer
4
.
In the flat panel type which largely warps the inner surface, there has been a problem that the larger the panel size of the color cathode ray tube (equal to or more than ‘nominal 17 inches’ (effective screen diagonal diameter being 41 cm)) becomes, the feeling of flatness in the short sides of the screen (end portions in the X axis direction) is worsened due to the aspect ratio of the screen.
Particularly, when the radius of curvature of the outer surface of the panel along the diagonal axis of the screen is not less than 10000 mm and the radius of curvature of the inner surface of the panel along the diagonal axis of the screen is not more than 7000 mm, the peripheries of the effective surface of the phosphor layer which is coated on the inner surface of the panel is made geometrically straight. In such a case, when it is viewed from a viewing position (limited position) which is slightly away from the panel of the color cathode ray tube, the peripheries of the effective surface appears in a barrel shape and hence, the feeling of flatness of the screen is damaged. To cope with such a problem, it is effective to form the shape of the effective region of the phosphor layer in a geometrically pincushion (bobbin) shape. Further, due to such a measure, even when the effective diameters of the screen in the X-axis direction and in the Y-axis direction are fixed, it becomes possible to increase the effective diameter in the diagonal direction. However, the realization of such a measure has problems which will be explained hereinafter.
FIG. 7
is an explanatory view of the shape of the phosphor screen showing the coated shape of the approximately rectangular phosphor layer when the side portions are formed in a linear shape or a pincushion shape. In the drawing, numeral
4
indicates the phosphor layer, numeral
4
a
indicates a contour of the effective region of the linear-shaped phosphor layer, and numerals
4
b
and
4
b
′ indicate the contours of the effective regions of the pincushion-shaped phosphor layer.
FIG. 8
is a cross-sectional view showing a corner portion B of the effective region of the linear-shaped or pincushion-shaped phosphor layer shown in
FIG. 7
in an enlarged form. In the effective region of the phosphor layer shown in
FIG. 7
, an axis which is extended in the main scanning direction (in-line arrangement direction of electron beams) and passes the tube axis is set as an X axis, an axis which is extended in the direction perpendicular to the main scanning direction and passes the tube axis is set as a Y axis and an axis which is extended in the diagonal direction and passes the tube axis is set as a D axis.
The contour
4
a
of the effective region of the linear-shaped phosphor layer is approximately accommodated in a front region of the panel
1
. However, with respect to the

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