Electric lamp and discharge devices – Cathode ray tube – Envelope
Reexamination Certificate
2000-06-15
2003-09-02
Day, Michael H. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Envelope
C313S318050, C445S004000, C445S045000, C220S00210A, C065S034000, C065S155000
Reexamination Certificate
active
06614164
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-169217, filed Jun. 16, 1999; and No. 2000-170145, filed Jun. 7, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a cathode-ray tube such as a color picture tube and, more particularly, to a cathode-ray tube in which a stem is welded to the end of a neck, and relates to a method of manufacturing the same.
Generally, a color cathode-ray tube has an envelope which is constituted by a glass panel having an inner surface formed with a phosphor screen, a glass funnel bonded to the panel, and a cylindrical glass neck continuously connected to the smaller end of the funnel. To the end of the neck is welded the outer peripheral portion of a flare of the stem. An electron gun is arranged in the neck. The electron gun has three cathodes lined up in line, heaters for heating the cathodes, and a plurality of electrodes sequentially adjoining the cathodes.
In the color cathode-ray tube, three electron beams emitted from the electron gun and traveling in one flat plane in line are deflected by a deflection yoke mounted on the outer surface of the funnel to scan the phosphor screen horizontally and vertically through a shadow mask, thereby displaying a color image.
Usually, the stem is comprised of a circular plate-like glass flare, an exhaust pipe extending vertically from the center of the flare outside the neck end, a plurality of stem pins extending through the flare hermetically and lined up on a circle coaxial with the center of the flare, and fillets surrounding those inner leads of the stem pins extending in the neck, which are on the flare side. The plurality of stem pins support the cathode side of the electron gun to guide a voltage applied to the heater, cathodes, and plurality of electrodes.
In an ordinary stem, of the stem pins, outer leads extending outside the neck and inner leads extending in the neck are located on a common circle. The diameter of a pin circle defined by the plurality of stem pins is determined by the outer diameter of the neck. For example, when the outer diameter of the neck is 29.1 mm, the diameter of the pin circle is 15.24 mm.
As another stem, one disclosed in Jpn. Pat. Appln. KOKAI Publication No. 58-32327 is known. In this stem, a pin circle defined by the inner leads of a plurality of stem pins is made smaller than a pin circle defined by the outer leads, and the inner and outer leads are connected to each other through Dumet wires sealed in a flare. With this arrangement, the pin circle defined by the outer leads is kept identical with that of a stem in which the outer and inner leads are located on the common circle, so that this stem can be welded to a small-diameter neck.
As an electron gun sealing method, a cullet method and a butt seal method are known.
According to the cullet method, an electron gun supported by a stem through stem pins is inserted to a predetermined position in a neck. In this process, the whole stem is inserted in the neck, and the circumference of the flare is set to oppose the inner circumferential surface of the neck. The outer peripheral portion of the flare and the opposing neck portion are welded by heating with the flame of a gas burner. Furthermore, the extra neck portion located closer to the exhaust pipe of the stem than the welded portion is sealed by burning it off with the flame of the gas burner. This method is not suitable for a small-diameter neck, since the stem must be inserted in the neck.
According to the butt seal method, a neck is cut to a predetermined size in advance. An electron gun supported by a stem through stem pins is inserted in the neck, and the end of the neck and the flare of the stem are abutted against each other or opposed to each other at a short distance. In this state, the neck end and the flare are welded by heating with the flame of a gas burner.
With the butt seal method, the stem is not inserted in the neck, so that the neck diameter can be decreased. Since the neck diameter is decreased, a deflection coil can be arranged close to electron beams, and the deflection power can be decreased. As described in Jpn. Pat. Appln. KOKAI Publication No. 58-32327, the exhaust pipe can be made thick to improve the exhaust efficiency.
As described above, the electron gun of the cathode-ray tube is arranged in the neck with its cathode side being supported by the stem, and is sealed in the neck as the neck and stem are welded to each other. This sealing structure of the electron gun is, however, sensitive to a heat shock.
Generally, the neck of a cathode-ray tube is made of glass containing 30% to 34% of PbO, which has a high electrical resistance and breakdown voltage, and having a thermal expansion coefficient &agr;(N) given by
&agr;(
N
)=95 to 96.5×10
−7
/°C. (0° C. to 300° C.)
to match a thermal expansion coefficient &agr;(F)=98 to 98.5×10
−7
/°C. (0° C. to 300° C.) of a funnel to which the neck is to be continuously connected.
The flare of the stem is made of glass having a thermal expansion coefficient &agr;(S) given by
&agr;(
S
)=91.5×10
−7
/°C. (0° C. to 300° C.)
to match a thermal expansion coefficient &agr;(DU)=approximately 90×10
−7
/°C. (30° C. to 400° C.) of the Dumet wire.
Therefore, when the neck and stem are welded to each other by the butt seal method, the glass of the neck and the glass of the flare form a boundary in the lateral direction perpendicularly intersecting the tube axis (Z axis) of the envelope. When heat is applied to the welded portion, the neck expands more than the flare of the stem because of the difference between the thermal expansion coefficient &agr;(N) of the neck and the thermal expansion coefficient &agr;(S) of the flare of the stem, that is,
&agr;(
N
)−&agr;(
S
)=3.5 to 5.0×10
−7
/°C. (0° C. to 300° C.)
so cracking occurs at the boundary.
The heat shock applied to the welded portion of the neck and stem is produced by heat radiated from a heater that heats cathodes while the cathode-ray tube is operated. In a color cathode-ray tube in which a high voltage of about 20 kV to 30 kV is applied to some electrodes of the electron gun, when cracking occurs in the welded portion to decrease the vacuum degree in the envelope, electric discharge occurs in the tube to make the cathode-ray tube defective.
In order to prevent cracking in the welded portion as described above, after the neck and stem are welded to each other, the welded portion must be annealed, or positional displacement between the neck and stem after the electron gun is sealed must be regulated strictly. When annealing the welded portion, to sufficiently remove stress strain generated in the welded portion, a long-time process is required, leading to a decrease in production efficiency.
Since the neck and stem are welded to each other by using a gas burner, an electron gun sealing apparatus is heated to a high temperature. To regulate the positional displacement strictly, the sealing apparatus must be checked and maintained frequently.
BRIEF SUMMARY OF THE INVENTION
The present invention has been made in view of the above problems, and has as its object to provide a cathode-ray tube in which a neck and stem can be welded to each other without decreasing the production efficiency, so that the welded portion is resistant against a heat shock, and a method of manufacturing the same.
In order to achieve the above object, according to the present invention, there is provided a cathode-ray tube comprising: a glass envelope having a panel with an inner surface formed with a phosphor screen, and a cylindrical neck extending substantially coaxially with a tube axis; an electron gun arranged in the neck, for emitting an electron beam toward the phosphor screen; and a stem welded to an end of the neck. The stem has a substantially circular disk-like flare made of gl
Hoshino Fumitaka
Okamoto Hisakazu
Sugawara Shigeru
Day Michael H.
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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