Cathode ray tube neck glass

Electric lamp and discharge devices – Cathode ray tube – Envelope

Reexamination Certificate

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C501S060000, C501S062000

Reexamination Certificate

active

06218775

ABSTRACT:

FIELD OF THE INVENTION
Cathode ray tubes and, more particularly, a neck glass that is compatible with other glass components of a tube envelope.
BACKGROUND OF THE INVENTION
The envelope for a conventional cathode ray tube is composed of a faceplate, a funnel, a neck and an electron gun mount. These several components are commonly formed separately and hermetically sealed together to form a completed tube envelope. Other tube components, such as a mask and a phosphor screen, are assembled within the envelope to form a functional tube after the envelope is evacuated and sealed.
The neck portion of a cathode ray tube is customarily drawn from a glass melt as tubing. It is conventional practice to draw such tubing by a Vello or a downdraw process. The tubing is drawn continuously from the forehearth and bowl of a continuous, glass tank. Such a process is depicted and described, for example, in U.S. Pat. Nos. 2,009,326 and 2,009,793 (Vello) and at pages 210-211 of the glass text,
Glass: The Miracle Maker
, C. J. Phillips, Pitman Publishing Corporation (1941).
A continuous length of glass tubing, thus drawn, is cooled and cut into short lengths to form neck members for cathode ray tube envelopes. U.S. Pat. No. 5,192,718 (Danielson) describes a family of lead silicate glasses particularly well adapted to drawing neck glass tubing for use in cathode ray tube envelopes. The Danielson glasses were designed to provide a low liquidus value. This avoided a troublesome, devitrification problem that developed in the forehearth/bowl outlet as tubing was drawn through the outlet.
A glass, based on Example 12 of the Danielson patent, was developed for production of neck glass tubing. This glass provided generally satisfactory sealing results in cathode ray tube production. However, the glass was recognized as being a relatively hard glass. This meant that the glass had a relatively high temperature-viscosity curve. For sealing purposes, good results were obtained with a burner having a strong, hot flame. However, variations in burners, and consequent variations in flame temperatures, could result in poor seals. This created the possibility of cracks developing in the seal.
It became desirable, then, to provide a neck glass that would be universally acceptable. Such glass would be able to accommodate to different sealing processes without risk of cracks developing in the seal. At the same time, other requisite properties of the current, commercial glass would have to be maintained, or preferably improved upon.
The basic purpose of the present invention is to provide an improved, tubular, neck glass.
A further purpose is to provide an improved, tubular, neck component for sealing in a cathode ray tube.
Another purpose is to provide a tubular, neck component that can be compatibly sealed between a funnel member and an electron gun mount to produce a cathode ray tube envelope.
A still further purpose is to provide a tubular, neck glass that can accommodate to different, flame sealing processes and burners while avoiding cracks in the seals produced.
These purposes, and others, are achieved through practice of the invention hereafter disclosed and claimed.
SUMMARY OF THE INVENTION
The invention resides in part in a cathode ray tube comprising a glass funnel member, a glass gun mount, and an improved tubular, glass, neck member sealed to, and connecting the gun mount and the funnel member, the improved tubular neck member having a softening point in the range of 640-650° C., an annealing temperature in the range of 460-472° C., a strain point in the range of 420-425° C., a coefficient of thermal expansion in the range of 94-97×10
−7
/° C., and a linear X-ray absorption value of at least 100 cm
−1
and a composition, as calculated in weight % on an oxide basis, consisting essentially of 46.5-49.5% SiO
2
, 1.5-2% Al
2
O
3
, 0.5-1.5% Na
2
O, 10-12% K
2
O, 2-3% SrO, 1-1.8% BaO, 32-34% PbO, 1-1.5% ZnO and a fining agent.
The invention further resides in a length of glass tubing drawn from a lead silicate glass melt, the glass having a softening point in the range of 640-650° C., an annealing temperature in the range of 460-472° C., a strain point in the range of 420-425° C., a coefficient of thermal expansion in the range of 94-97×10
−7
/° C., and a linear X-ray absorption value of at least 100 cm
−1
and a composition, as calculated in weight on an oxide basis, consisting essentially of 46.5-49.5% SiO
2
, 1.5-2% Al
2
O
3
, 0.5-1.5% Na
2
O, 10-12% K
2
O, 2-3% SrO, 1-1.8% BaO, 32-34% PbO, 1-1.5% ZnO and a fining agent.
Another aspect of the invention is a family of lead silicate glasses having a softening point in the range of 640-650° C., an annealing temperature in the range of 460-472° C., a strain point in the range of 420-425° C., a coefficient of thermal expansion in the range of 94-97×10
−7
/° C., and a linear X-ray absorption value of at least 100 cm
−1
and a composition, as calculated in weight % on an oxide basis, consisting essentially of 46.5-49.5% SiO
2
, 1.5-2% Al
2
O
3
, 0.5-1.5% Na
2
O, 10-12% K
2
O, 2-3% SrO, 1-1.8% BaO, 32-34% PbO, 1-1.5% ZnO and a fining agent.


REFERENCES:
patent: 5192718 (1993-03-01), Danielson

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