Electric lamp and discharge devices – Cathode ray tube – Envelope
Reexamination Certificate
2000-02-24
2003-03-18
O'Shea, Sandra (Department: 2875)
Electric lamp and discharge devices
Cathode ray tube
Envelope
C362S482000, C362S440000
Reexamination Certificate
active
06534908
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a cathode ray tube, and, more particularly, to a shortened cathode ray tube having an envelope which has a sufficient mechanical strength in a narrowed deflection yoke mounting area.
BACKGROUND OF THE INVENTION
In general, a cathode ray tube which is employed as an image display device is constituted by a vacuum envelope which is formed by connecting a panel portion which forms a screen having a phosphor coating on an inner surface thereof, a neck portion which accommodates an electron gun, and a funnel portion having a funnel shape which gradually decreases in diameter in the direction from the panel portion to the neck portion.
In a color cathode ray tube, a color screen formed of a plurality (usually three colors) of phosphors is provided on the inner surface of the panel portion, a shadow mask which operates as a color selection electrode is arranged adjacent to the screen, and an inline-type electron gun which irradiates three electron beams is accommodated in the neck portion.
The color cathode ray tube includes a stem at the end of the neck portion, which stem supports the accommodated electron gun and is provided with stem pins which supply a given voltage or given signals to the electron gun and are mounted in an annular manner, thus sealing the neck portion. A deflection yoke which scans the electron beams on the screen by deflecting the electron beams in both horizontal and vertical directions is mounted on the outer surface of the funnel portion.
A color display tube (CDT) used as a monitor device of an information processing terminal is used with a higher deflection frequency than a conventional cathode ray tube for television, and hence, the deflection power is increased.
In such a cathode ray tube, as a means for reducing the power consumed by the deflection yoke, the outer diameter size of a portion on which the deflection yoke of the funnel is mounted (deflection yoke mounting region) may be reduced in size so as to bring the deflection yoke closer to the electron beams, thus more efficiently applying the deflection magnetic field to the electron beams.
However, in case the outer diameter of the deflection yoke mounting region is simply reduced in size, a portion of the funnel portion connected to the neck portion (smaller diameter portion of the funnel portion) becomes narrow, and hence, at the time that the electron beams are deflected through the maximum deflection angle, the electron beams impinge on the inner surface of the funnel portion, thus giving rise to a region on the phosphor screen where the electron beams do not reach (non-scanned portion).
In view of this problem, Japanese Laid-Open Patent Publication 10-144238 discloses a cathode ray tube in which the outer wall in the deflection yoke mounting region of the funnel portion has a pyramidal shape so as to narrow the distance between the deflection yoke and the electron beams, while also avoiding the occurrence of a non-scanned portion.
Furthermore, in the cathode ray tube having a shortened length in the tube axis direction so as to provide an increased deflection angle, the enlargement angle from the neck portion to the funnel portion is increased. In such a cathode ray tube, a so-called inflection edge is formed, which inverts the curving direction of the inner wall surface toward the panel portion side of the deflection yoke mounting region.
FIG. 10
is a cross-sectional view showing a condition of a panel portion and a funnel portion of a conventional cathode ray tube cut along the short axis of the tube. Numeral
1
indicates the panel portion, numeral
2
indicates a neck portion, numeral
3
indicates the funnel portion, numeral
3
A indicates a portion of a deflection yoke mounting region, and numeral
3
i
indicates an inner wall of the funnel portion
3
. FIG.
10
(
a
) shows an enlarged view of the boundary between the deflection yoke mounting region of the funnel portion
3
and a panel-portion side inner wall, that is, a portion W of the wall including the inflection edge P where the inner surface angle changes from the inner wall of the deflection yoke mounting region to the panel-portion side inner wall of the funnel portion.
In the conventional cathode ray tube, as shown in
FIG. 10
, where the tube axis is represented by the line Z-Z, a straight line in the short axis direction which passes through the inflection edge P and is perpendicular to the tube axis Z-Z is represented as y-y, and a tangent line which passes through a point which intersects the straight line y-y of the inflection edge P is represented as a, an angle &thgr; made by the straight line y-y and the tangent line a is set to a value not less than 11°.
Particularly, in a cathode ray tube having a contour in the deflection yoke mounting region in the form of a pyramidal shape, the vacuum envelope decreases its strength at a connection portion between the funnel portion and the neck portion, and hence, the possibility that a so-called implosion may occur is increased. In the above-mentioned Japanese Laid-Open Patent Publication 10-144238, to prevent the occurrence of an implosion, a reinforcing member is mounted on the connecting region between the pyramidal-shaped deflection yoke mounting region and the panel portion. In the cathode ray tube disclosed in Japanese Laid-Open Patent Publication 10-144238, the cross section of an outer wall thereof perpendicular to the tube axis of the deflection yoke mounting region is formed to have a rectangular shape and the cross section of an inner wall thereof is also formed to have a similar rectangular shape.
Further, in a cathode ray tube disclosed in Japanese Utility Model 44-29152, in case the deflection angle of the electron beams is large, to eliminate the above-mentioned non-scanned portion caused by the opening shape of a connecting portion between the funnel portion and the neck portion (narrow-diameter portion of the funnel portion) and to obviate implosion, the opening shape of the inner wall (cross section of the inner wall perpendicular to the tube axis) of the portion where the diameter of the funnel portion is narrowed is formed such that bulges which protrude inwardly are formed (in a so-called pin-cushion shape) on given portions of all of or two parallel sides out of four sides which form the profile line, and the corners are rounded.
In the conventional cathode ray tube, the angle &thgr; made by the short axis, the long axis or the diagonal axis (of the rectangular cross-section) which are perpendicular to the tube axis, or the above-mentioned straight line y-y of the inner surface of the funnel portion on the respective axes and the tangent line a of the inner surface of the funnel portion, typically exceeds 11°. Therefore, in a cathode ray tube in which the deflection yoke mounting region is formed to have a pyramidal shape, the shape of the inner wall surface of the funnel portion from the large diameter portion of the panel portion side to the front end of the neck portion (small diameter portion of the funnel portion) via the deflection yoke mounting region cannot have a gentle profile. Particularly, an inflection edge where the inner wall surface changes its angle is formed at the side end portion of the panel portion of the deflection yoke mounting region of the funnel portion.
In the case of a cathode ray tube whose deflection yoke mounting region adopts a pyramidal funnel shape, it is necessary to make the angle (&thgr;) of the tangent line at the inflection edge small to assure the mechanical strength of the funnel portion. In case the above-mentioned angle is made smaller, in an internal graphite film coating process, which constitutes one of the cathode ray tube's manufacturing steps, a coating liquid of graphite in the form of a film is settled on the inflection edge or it becomes difficult to smoothly coat the inner surface of the deflection yoke mounting region and the neck portion, and hence, the thickness of the internal graphite film becomes non-uniform due to the unevenness of th
Ito Hiroshi
Kawamata Kenji
Nose Hisashi
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
O'Shea Sandra
Ton Anabel
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