Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Patent
1998-02-06
1999-12-21
Patel, Ashok
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
313414, 313450, 445 34, 445 36, H01J 914, H01J 2948, H01J 2958
Patent
active
060053380
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a cathode ray tube for projection type and direct viewing type in which a spiral high-resistor is used as a main focusing lens, and also to a method of producing it.
BACKGROUND OF THE INVENTION
It is known that an electron gun in which a main focusing lens is configured by a spiral high-resistor can attain high resolution in a cathode ray tube produced by using the same.
As a method of producing such a main focusing lens of an electron gun for a cathode ray tube, as shown in Japanese patent publication (Kokai) No. HEI6-275211, there is a method using a paste containing ruthenium oxide (RuO.sub.2) and glass. In this method, a resistance material consisting of the ruthenium oxide and a glass paste is formed into a spiral shape on the inner face of a cylindrical tube of insulative ceramics or the like. In another method, after a resistance material consisting of the ruthenium oxide and the glass paste was uniformly applied to the inner face of a cylindrical tube, it is formed into a spiral resistor member by trimming method or other method. Thereafter, firing is conducted at 850 deg. C. for 10 minutes, with the result that a spiral high-resistor having a resistance of 100 M.OMEGA. to 10 T.OMEGA. is obtained. In order to electrically connect the thus formed main focusing lens to other electrode, a cylindrical holder made of a metal such as stainless steel is fitted into the inner face of an end portion of the cylindrical tube. In the cylindrical holder, pairs of projections which are opposed to each other are disposed in three portions. Among the projections, inner ones are contacted with the spiral high-resistor formed on the inner face of the cylindrical tube.
Another method of producing a main focusing lens is disclosed in Japanese patent (Kokoku) No. HEI4-23402. In the method, a resistor layer is formed on the inner face of a hollow tube which is made of glass and to which a metal part is welded, by applying a suspension containing ruthenium hydroxide (Ru(OH).sub.3) and glass particles and then drying it. Thereafter, the resistor layer on the inner face of the hollow tube is machined into a spiral shape, and then heated to 400 to 600 deg. C., so that ruthenium hydroxide is changed to ruthenium oxide, and a spiral resistor of a composition in which ruthenium oxide fuses with glass particles in the resistor layer is obtained.
However, the above-mentioned methods of the prior arts have several problems in formation of a spiral high-resistor having uniform properties.
First, the resistance material used in the method disclosed in the Japanese patent publication (Kokai) No. HEI6-275211 is a thick-film resistor material for a chip resistor which is conventionally used in an electronic circuit board or the like. Therefore, the firing temperature is considerably high or 850 deg. C., and a glass tube or a ceramic tube which can withstand the temperature must be used. Although a kind of such a glass tube is a quartz glass tube, a quartz glass tube has a very small coefficient of thermal expansion as described later, thereby producing a problem in connection with other member having a large coefficient of thermal expansion. In the case where a ceramic tube is used, since a molding accuracy is inferior to that of a glass tube, a working process must be done during or after a process of molding the ceramic tube in order to improve the accuracy, resulting in a high cost.
Specifically, in the method disclosed in the Japanese patent (Kokoku) No. HEI6-275211, ruthenium oxide is used as the high resistance material. Since the firing temperature is 850 deg. C., quartz glass is used; but the quartz glass is expensive. The coefficient of thermal expansion is 5.5.times.10.sup.-7 /deg. C. and very smaller in comparison with the coefficient of thermal expansion of usual glass for the cathode ray tube. By contrast, in the case where the ceramic tube is used, since the surface roughness is so large as 1 to 2 .mu.m, it is difficult to form a spiral with high accuracy on the inner face of
REFERENCES:
patent: 4713879 (1987-12-01), Vrijssen
patent: 5489229 (1996-02-01), Muti et al.
patent: 5521464 (1996-05-01), Vrijssen et al.
Hirabayashi Kazuaki
Konda Masahiko
Nakatera Shigeo
Omae Hideharu
Otani Mitsuhiro
Matsushita Electric - Industrial Co., Ltd.
Matsushita Electronics Corporation
Patel Ashok
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