Electric lamp and discharge devices – Cathode ray tube – Screen
Reexamination Certificate
2001-10-26
2004-02-10
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Screen
C313S47700R
Reexamination Certificate
active
06690106
ABSTRACT:
The present invention relates to a color cathode ray tube of the type which is used in a color television set for personal use and to a color display monitor for an information terminal; and, more particularly, the invention relates to a color cathode ray tube which has a faceplate panel of improved curved shape.
BACKGROUND OF THE INVENTION
The glass envelope of a cathode ray tube generally comprises a panel portion having a curved faceplate, a neck portion with a reduced diameter, and an approximately funnel-shaped portion which connects the panel portion and the neck portion. The cathode ray tube further includes a phosphor screen formed over the inner surface of the faceplate, an electron gun installed inside of the neck portion, and a deflection yoke mounted on an outer periphery of the funnel portion. Here, the glass envelope of the cathode ray tube has a near vacuum in its interior, with atmospheric pressure being impressed on it, outer side at all times, so that the glass envelope is required to have a mechanical strength that is higher than a predetermined level. For this reason, various parts of the glass envelope are formed to a sufficient thicknesses to be able to provide the corresponding required mechanical strengths.
In a known cathode ray tube, the faceplate of the glass envelope normally has a construction in which the peripheral section of the faceplate is made thicker than the central section of the faceplate.
FIG. 11
is a cross-sectional view showing one example of the constitution of the faceplate portion of a glass envelope of the type used in a known cathode ray tube.
In
FIG. 11
, numeral
31
indicates a faceplate, numeral
31
(
1
) indicates an inner surface of the faceplate, numeral
31
(
2
) indicates an outer surface of the faceplate, tpc indicates the thickness of a central section of the faceplate
31
, tpa indicates the thickness of a peripheral section of the faceplate
31
, Rpi indicates the radius of curvature of the inner surface
31
(
1
) of the faceplate with a deflection center point O of the electron beam taken as its center, and Rpo indicates the radius of curvature of the outer surface
31
(
2
) of the faceplate with the deflection center point O of the electron beam taken as its center.
As shown in
FIG. 11
, the faceplate
31
is constructed such that the thickness tpa of the peripheral section is greater than the thickness tpc of the central section so as to provide the required mechanical strength as described above. As a result, the radius of curvature Rpi of the inner surface
31
(
1
) of the faceplate is smaller than the radius of curvature Rpo of the outer surface
31
(
2
) of the faceplate, that is, tpc<tpa and Rpi<Rpo.
In the above-described known cathode ray tube, the thickness tpc of the central section of the faceplate
31
is thin and the thickness tpa of the peripheral section is thick so that when an image is displayed on the phosphor screen formed on the inner surface of the faceplate
31
, light irradiated outwardly from the phosphor screen through the faceplate
31
becomes attenuated more at the peripheral section of the faceplate
31
having the large thickness tpa than at the central section of the faceplate
31
having the small thickness tpc. That is, if we let Tpc stand for the light transmittivity at the central section of the faceplate
31
and Tpa for a light transmittivity at the peripheral section, then Tpc>Tpa and the brightness of the displayed image is lower at the peripheral section of the faceplate
31
than at the central section of the faceplate
31
, thus giving rise to a problem that the brightness of a displayed image cannot be ensured at a sufficient level at the peripheral section. The brightness at the peripheral section is further degraded by the fact that the weight of the phosphor is smaller at the peripheral section of the screen than at the central section of the screen.
To correct the brightness of the displayed image at the peripheral section of the faceplate
31
so that it will match the brightness of the displayed image at the central section, when the brightness of the displayed image at the peripheral section of the faceplate
31
is lowered compared with the brightness of the displayed image at the central section, the intensity of the electron beam projected onto the peripheral section of the phosphor screen needs to be stronger than the intensity of the electron beam projected onto the central section of the phosphor screen. Such a means for correcting the electron beam intensity, however, cannot be easily obtained.
To cope with such a problem, an applicant of the present invention filed an application (Japanese Laid-open Patent Publication 18547/1998), in which the curved shape of the faceplate of a cathode ray tube is formed such that the radius of curvature of the inner surface thereof is larger than the radius of curvature of the outer surface, and the thickness of the peripheral section is made thin compared with the thickness of the central section of the faceplate, so that the brightness of a displayed image at the peripheral section of the faceplate is increased, and the brightness of the displayed image at the peripheral section is approximated to the brightness of the displayed image at the central section.
However, in the above-mentioned cathode ray tube, since the radius of curvature of the inner surface of the faceplate is larger than that of the outer surface of the faceplate, the radius of curvature of a shadow mask, which is arranged to face the phosphor screen formed on the inner surface of the faceplate in an opposed manner and performs color selection, becomes large as a whole. In a cathode ray tube having such a constitution, since the molding retaining strength of the curved surface of the shadow mask becomes weak, the curved surface is easily deformed, so that the electron beams which pass through apertures formed in the shadow mask do not normally impinge on the phosphor screen (making it impossible to perform normal color selection) whereby there arises a new problem in that a deterioration of the color purity of the displayed image is induced.
Particularly, at the peripheral section of the screen along the minor axis direction, the shadow mask is liable to be easily influenced by vibrations or an impact at the time of dropping; and, hence, when the radius of curvature of the shadow mask is increased, the mechanical strength of the curved surface becomes weak, so that the curved surface is liable to be easily deformed in that area.
Further, the inside of the glass bulb is approximately in a vacuum state and atmospheric pressure is always applied to the outside of the glass bulb. Accordingly, in view of the geometric structure of the glass bulb for a cathode ray tube, a stress strain is liable to be concentrated on the peripheral section of the screen, along the minor axis direction in particularly; and, hence, when the glass thickness of the peripheral section along the minor axis direction becomes thin by increasing the radius of curvature of the inner surface of the faceplate, the mechanical strength of the glass bulb (panel portion) becomes weak in that area.
Further, at the peripheral section of the screen along the diagonal direction, the distance from the center of the screen becomes longest; and, hence, when the radius of curvature of the shadow mask becomes large, the molding retaining strength of the curved surface is decreased, so that the curved surfaces are liable to be easily deformed between the center and the peripheral section along the diagonal direction.
The present invention has been made to solve the foregoing problems, and it is an object of the present invention to provide a color cathode ray tube in which the brightness of a displayed image at a peripheral section of a faceplate will match the brightness of a displayed image at a central section of the faceplate using means having a simple constitution and, at the same time, can prevent the degradation of the color purity of the displayed image and the lowering of the mec
Hosotani Nobuhiko
Itou Hiroshi
Watanabe Mitsuru
Yoshida Haruhiko
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Patel Nimeshkumar D.
Zimmerman Glenn D.
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