Impregnated cathode structure for a CRT and its...

Details Impregnated cathode structure for a CRT and its... Impregnated cathode structure for a CRT and its...

1998-11-25

2001-06-26

Ramsey, Kenneth J. (Department: 2879)

Electric lamp and discharge devices

Electrode and shield structures

Cathodes containing and/or coated with electron emissive...

C445S051000

Reexamination Certificate

active

06252342

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an impregnated cathode structure for a cathode-ray tube (CRT) and its manufacturing method, and more particularly to an impregnated cathode structure for a cathode-ray tube (CRT) which can prevent the deterioration of impregnated electron emitting material due to an effect of the welding heat for securing a pellet to a heater sleeve, and a method of easily manufacturing it.
BACKGROUND OF THE INVENTION
In general, an impregnated cathode for a CRT is manufactured by pressing tungsten powder into a pellet having a certain porosity, sintering the pellet, impregnating electron emitting material into the sintered pellet, and securing the pellet to a pellet sleeve and a heater sleeve, generally using a laser or an electric-resistance welding method or a brazing method. Therefore, since the pellet is secured to the heater sleeve by the welding, the impregnated electron emitting material is deteriorated due to an effect of the welding heat and hot electron emitting decreases, or hot electron is not produced from the cathode, thus deteriorating the whole characteristics of the CRT.
FIGS. 1
to
5
illustrate the improved prior art cathode structures to solve or alleviate the above problems or the like.
Referring to
FIG. 1
, a pellet cup
12
, which is secured to a heater sleeve
13
, has plural projection parts on its base part in an impregnated cathode structure, which is disclosed by Japanese patent laid-open publication No. 61227342 A. Thus, a substantial contact area with a cathode pellet
11
can be kept large even when a pellet cup
12
generates thermal deformation. Thereby, the fitting condition between the cathode pellet
11
and the pellet cup
12
can be stabilized to realize an impregnated cathode having stable electron emitting property at its high operating temperature and thereby improve the temperature property of a cathode.
In
FIG. 2
, a pellet
21
of an impregnated cathode structure, which is disclosed by Japanese patent laid-open publication No. 55143743 A, is obtained by cutting a porous tungsten rod which is sintered after compressing tungsten powder. A pellet assembly is formed by securing tungsten wire mesh
22
tightly through Mo-Ru brazing material
23
mixed with an organic binder to the pellet
21
. Then the outside portion is removed such that the surface portion of the mesh
22
is exposed. Thereafter it is heated under reductive ambient to perform the brazing work. Then said substrate is cut to predetermined shape to produce a cathode member which is welded through resistor welding with a heater sleeve, which is not illustrated herein. This structure can achieve good soldering and stable characteristics.
FIG. 3
a
illustrates the prior art impregnated cathode structure for a CRT, which is disclosed on Japanese patent laid-open publication No. 03155020 and wherein an intermetallic compound bond layer
33
with a main ingredient of Al is formed between a pellet
31
and the bottom surface of a cup
32
to firmly bond them together, then the cup
32
is secured to the upper surface of the a heater sleeve
34
. This provides an impregnated cathode structure showing stabilized electron emitting characteristic even after a long period of use. In
FIG. 3
b
, the intermetallic compound bond layer
33
is formed by placing an aluminum foil
33
′ between the pellet
31
and the bottom surface of the cup
32
followed by heating in vacuum, thus having an advantage of a low manufacturing cost.
Referring to
FIG. 4
disclosed on Japanese patent laid-open publication No. 60165021, many holes
42
are formed on a nickel substrate
43
and are impregnated with the alkaline earth carbonate. Furthermore, the alkaline earth carbonate may be spread on the electron emission layer
41
to such a thickness that coating resistance generates no trouble. In this way, even if the cathode is heated to high temperature during the sealing procedure of the cathode-ray tube in atmosphere, the nickel substrate
43
does not take much oxygen and the cathode-ray tube after completion stably bears high current density operation, thereby reproducing the images with high brightness and high precision.
In
FIG. 5
, which illustrates the prior art impregnated cathode structure disclosed by Japanese patent laid-open publication No. 60047331, brazing material
54
is applied to only the external section of a hollow cylindrical body
55
that is integratedly comprised with a cathode substrate
51
. Since such structure does not require the sealing hole treatment near the central part in which the thickness of the cathode substrate
51
is smallest, the insufficient impregnation of electron emission material can be offset due to the intrusion of brazing material and a cathode with more homogeneous electron emission characteristics can be obtained. In addition, since a heater coil
53
is connected to the inner part of a sleeve
52
and the hollow cylindrical body
55
, thermal conduction efficiency is improved.
However, the above conventional impregnated cathode structures still employ a welding method such as a laser welding method or a brazing method in securing the pellet to a pellet sleeve and a heater sleeve. Therefore, the above conventional impregnated cathode structures have not completely overcome the problem yet that the impregnated electron emitting material is deteriorated due to an effect of the welding heat, which thus causes deterioration of the whole characteristics of the CRT.
SUMMARY OF THE INVENTION
The present invention has been made to overcome the above described problems of the prior arts, and accordingly it is an object of the present invention to provide an impregnated cathode structure in which electron emitting material impregnated in a pellet is free from an effect of the welding heat generated when the pellet is secured to a pellet sleeve and a heater sleeve.
It is another object of the present invention to provide a methode for manufacturing the impregnated cathode structure in which electron emitting material impregnated in a pellet is free from an effect of the welding heat, through a simple process.
To achieve the above objects, the present invention provides an impregnated cathode structure for a cathode ray tube, the impregnated cathode structure comprising: a pellet assembly including a pellet and a pellet fixing sheet, the pellet being attached to a first surface of the pellet fixing sheet, the first surface having a plurality of protuberances, the pellet being manufactured by pressing and sintering tungsten powder, and being impregnated by electron emitting material; a pellet sleeve in which the pellet assembly is inserted and welded with the heater sleeve; and a heater sleeve welded to a second surface of the pellet fixing sheet, the second surface being opposite to the first surface.
Preferably, the pellet fixing sheet is a Molybdenum sheet with a thickness of 48 to 52 m and has pores and protuberance, the pellet fixing sheet being fixed to the upper side of heater sleeve.
The present invention also provides a method for manufacturing an impregnated cathode structure, the method comprising the steps of:
(1) manufacturing a pellet assembly including a pellet and a pellet fixing sheet, the pellet being attached to a first surface of the pellet fixing sheet, the first surface having a plurality of protuberances, the pellet being manufactured by pressing and sintering, and being impregnated by electron emitting material;
(2) welding the pellet assembly to a heater sleeve. It is preferred that the step
1
comprises the steps of:
(a) performing blanking to a fixing sheet material having the protuberances formed on a surface of the fixing sheet material so as to make the pellet fixing sheet, the surface of the fixing sheet material being the first surface of the pellet fixing sheet;
(b) pressing the tungsten powder by the first surface of the pellet fixing sheet to thereby attach a pellet to the first surface of the pellet fixing sheet, the tungsten powder being the pellet attached with sheet; and
(c)

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