Electric lamp and discharge devices – Electrode and shield structures – Indirectly heated cathodes
Reexamination Certificate
1998-08-20
2001-10-09
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Electrode and shield structures
Indirectly heated cathodes
C313S34600R
Reexamination Certificate
active
06300711
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an indirectly heated cathode used for a television receiver and a computer display, etc., and a cathode ray tube using the same.
BACKGROUND OF THE INVENTION
A conventional indirectly heated cathode comprises a hot cathode emitting electrons at one end and a tubular sleeve comprising a molybdenum material and having a heater inside. In order to enhance the capacity of the tubular sleeve to absorb radiant heat from the heater, an aluminum layer is coated on the inside face of the tubular sleeve and heat-treated in wet hydrogen to form a blackened thermal absorption layer on the inside face of the tubular sleeve (Publication of Japanese Patent Application (Tokkai Sho) No. 56-169778).
However, there are some disadvantages in such an indirectly heated cathode where Al
3
Mo is formed on the thermal absorption layer. One of the disadvantages is that while such an indirectly heated cathode integrated into a cathode ray tube is operated, Al
3
Mo evaporates from the thermal absorption layer of the indirectly heated cathode. The vapor of Al
3
Mo may attach to an electrode located in the vicinity of an indirectly heated cathode, thus causing insulation breakdown. Evaporation of Al
3
Mo may make the black thermal absorption layer less black, preventing the tubular sleeve from efficiently absorbing radiant heat from the heater.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an indirectly heated cathode that can enhance the withstand voltage and the efficiency of radiating heat from a heater to a tubular sleeve, and a cathode ray tube using such a cathode.
According to the present invention, an indirectly heated cathode comprises a hot cathode emitting electrons at one end, a tubular sleeve including a high melting point metal and having a heater inside, and a thermal absorption layer formed on the inside face of the tubular sleeve. The thermal absorption layer contains a boron compound.
Thus, the evaporation of a material from the thermal absorption layer can be inhibited.
Moreover, the cathode ray tube of the present invention comprises a faceplate portion having a fluorescent screen on its inner face; a funnel portion provided behind the faceplate portion; a neck portion, which is formed behind the funnel portion, having an electron gun that emits electron beams; and an indirectly heated cathode that is provided inside the electron gun, the indirectly heated cathode comprising a hot cathode emitting electrons at one end, a tubular sleeve including a high melting point metal and having a heater inside and a thermal absorption layer formed on the inside face of the tubular sleeve. The thermal absorption layer contains a boron compound.
Thus, the attachment of a material to the electrode portion in the tube is prevented and the deterioration of blackening in the thermal absorption layer of the tubular sleeve is inhibited.
It is preferable that the boron compound is a boride.
It is preferable that the boron compound contains at least one element selected from the group consisting of W, Mo, Nb, Sr, Hf, Ta, Ti and Zr.
It is preferable that the boron compound has a melting point of 2000° C. or more.
It is preferable that the thickness of the thermal absorption layer is in the range of 0.5 &mgr;m to 10 &mgr;m.
It is preferable that the tubular sleeve is formed from a substrate including the high melting point metal and having the thermal absorption layer on the substrate.
REFERENCES:
patent: 4364780 (1982-12-01), Blanken
patent: 4637042 (1987-01-01), Braun
patent: 5543682 (1996-08-01), Hara et al.
patent: 5841222 (1998-11-01), Heuvelmans et al.
Yamamoto Yoji
Yamashita Katsuyuki
Guharay Karabi
Matsushita Electronics Corporation
Merchant & Gould P.C.
Patel Nimeshkumar D.
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