Electric lamp and discharge devices – Cathode ray tube – Screen
Reexamination Certificate
1998-12-17
2001-08-14
Patel, Ashok (Department: 2875)
Electric lamp and discharge devices
Cathode ray tube
Screen
C313S463000, C313S473000, C313S461000
Reexamination Certificate
active
06274976
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a cathode ray tube, and, specifically, the invention relates to an improvement in a metal film which is formed over a phosphor layer in the fluorescent screen of the cathode ray tube.
In a cathode ray tube, electron beams from electron guns are scanned on a fluorescent screen, which constitutes a display surface, to form an image on the fluorescent screen, according to the intensity of the electron beams. An evacuated envelope of a cathode ray tube typically comprises a panel portion where the fluorescent screen is formed of a number of phosphor, a neck portion housing the electron guns, and a funnel portion smoothly connecting the panel portion and the neck portion. A deflection yoke for deflecting the electron beams is arranged around the funnel portion.
The fluorescent screen formed on the inner side of the panel portion has a metal film coated thereover so as to cover the fluorescent screen. This metal film improves the brightness of the displayed image by the action of reflection and is supplied with a voltage to attract three electron beams. Normally, the metal film is called a metal reflection film or a metal back film. The metal film is formed by evaporation over an organic film resin which has been applied to the entire fluorescent screen, and then the organic film resin is removed by baking, so that the metal film remains, covering the fluorescent screen. Normally, aluminum is used for the metal film. The organic film resin is used to prevent molecules of the metal film from diffusing into the phosphor layer during the formation of the metal film, as would occur if the metal film was formed directly over the fluorescent screen.
With a cathode ray tube of the above-described construction, however, it has been pointed out that the luminance of displayed images is reduced because (1) the metal film is largely fractured, (2) the metal film as formed floats over the fluorescent screen, and (3) the metal film is not formed over a large enough area to fully cover the fluorescent screen. Our investigation into the cause of this trouble has resulted in a finding that, although an increase in the amount of organic film resin formed over the fluorescent screen results in the formation of a flat metal film without cracks or pin holes caused by degassing (generally referred to as cracks), a large amount of decomposed gas generated during the organic film resin baking process partially raises the metal film or breaks it over a wide area (hereinafter referred to as a “blister phenomenon”).
Further, the organic film resin soaks into the phosphor layer. So, if the amount of the organic film resin is reduced, the organic film resin cannot cover the entire fluorescent screen. Although reducing the amount of the organic film resin can prevent the blister phenomenon in the metal film, it is found that this tends to degrade the state. of the formed metal film, leading to a reduced brightness.
The present invention has been directed to these circumstances and its objective is to provide a cathode ray tube having a metal film which is capable of preventing the blister phenomenon and reduced brightness.
Examples of a conventional cathode ray tube designed to prevent the blister phenomenon include Japanese Patent Laid-Open Nos. 191932/1982, 35834/1983 and 225723/1991.
Japanese Patent Laid-Open No. 191932/1982 discloses a technology that makes the metal film porous at corner portions and skirt portions to prevent blisters at these locations where there is no phosphor film. This publication also discloses that the drying temperature of the emulsion is differentiated between the fluorescent screen and the corner and skirt portions to make the metal film at the corner and skirt portions porous. This method, however, does not consider the prevention of blisters on the effective surface where the phosphor film is formed.
Japanese Patent Laid-Open No. 35834/1983 describes that, for the prevention of blisters, the organic film is formed by applying over the fluorescent screen a filming liquid which contains 10-20 wt% of acrylic emulsion, 0.05-0.3 wt% of propylene glycol alginate, 1-3 wt% of silicone and the remaining percentage of water, and by drying the filming liquid. It is also described that during this process the acrylic resin and the alginate separate like islands and that dislocations occur in the boundaries between the acrylic resin and the alginate, forming gaps. This technology, however, stops short of controlling the locations where the gaps occur.
Japanese Patent Laid-Open No. 225723/1991 describes that an inorganic pigment layer is formed which has relatively large raised and recessed portions in a light absorption matrix and that a part of the raised portions pierces the metal back film to form pin holes. However, it does not take into consideration the pin holes and cracks in the phosphor layer.
SUMMARY OF THE INVENTION
Representative aspects of this invention may be briefly summarized as follows.
The cathode ray tube of the present invention comprises a metal film formed to cover a phosphor layer on an inner wall of a panel portion of an envelope, wherein the metal film is formed over an organic film resin applied to the phosphor layer, the organic film resin is baked and removed so that the metal film covers the phosphor layer, and cracks are formed in the metal film in a greater number on side portions of the phosphor areas of the phosphor layer than on an upper portion of the phosphor areas. In a cathode ray tube with this construction, decomposed gases generated during the process of baking the organic film resin are released through the many cracks formed in the metal film on the side portions of the phosphor areas of the phosphor layer. Hence, the blister phenomenon can be prevented without degrading the formed state of the metal film.
The cathode ray tube of the present invention comprises: a panel portion having a black matrix layer, a phosphor layer and a metal film, all formed over the inner surface thereof, a neck portion housing electron guns for emitting electron beams; and a funnel portion connecting the panel portion and the neck portion; wherein the metal film is formed above the phosphor layer and has holes in a part thereof, with the total area of the holes on the side surface portions of phosphor areas of the phosphor layer being larger than that of those on the upper surface portion thereof.
The cathode ray tube of the present invention comprises: a plurality of openings demarcated by a black matrix layer on an inner surface of a panel; and a phosphor layer having phosphors laminated in each area of the plurality of openings; wherein a metal film having holes formed in a part thereof is formed above the phosphor layer having phosphor areas provided in the openings of the black matrix layer and the holes in the metal film are larger on side surface portions of the phosphor areas than on an upper surface side thereof.
This invention provides a cathode ray tube that requires no additional layers to prevent blisters and which can prevent a reduction in brightness of a display image.
REFERENCES:
patent: 4651053 (1987-03-01), Katao et al.
patent: 5489816 (1996-02-01), Lee
patent: 6094005 (2000-07-01), Aibara
patent: 6140758 (2000-10-01), Matsuda et al.
patent: 01286236-A (1989-11-01), None
Ishigaki Toshimasa
Nishizawa Masahiro
Suzuki Tetsuo
Takahashi Fumio
Antonelli Terry Stout & Kraus LLP
Hitachi Ltd
Patel Ashok
Santiago Mariceli
LandOfFree
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