Electric lamp and discharge devices – Cathode ray tube – Screen
Reexamination Certificate
1999-08-23
2001-07-31
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Screen
C313S486000
Reexamination Certificate
active
06268691
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to red emitting phosphor for cathode ray tubes such as color Braun tubes and cathode ray tubes using the same.
2. Description of the Related Art
A phosphor layer of a color cathode ray tube is generally fabricated in the following way. That is, first, into water solution that contains polyvinyl alcohol (PVA), ammonium dichromate and a surfactant, phosphor is dispersed to prepare a phosphor slurry. This phosphor slurry is coated on a glass panel to form a phosphor layer. Then, onto this phosphor layer, ultra-violet rays are irradiated through a shadow mask to cure the PVA of irradiated portion. By developing, the phosphor layer other than the cured portion is removed. In this way, the phosphor layer is formed in stripe or in dot.
Upon forming a phosphor layer by the use of the aforementioned coating method, the following characteristics are demanded for the phosphor. That is, the phosphor (1) is capable of forming a phosphor layer of closely disposed stripe or dot, (2) does not mingle with another phosphor of different color, (3) sticks strongly to a panel, and (4) can form a phosphor layer of sufficient thickness. Further, in the case of pigmented phosphor being employed, the pigment is required not to peel off the phosphor in the slurry solution.
So far, in order to satisfy the aforementioned requirement on phosphor, a variety of kinds of surface treatments of phosphor have been implemented to improve and develop. For instance, Japanese Patent Laid Open Publication No. (KOKAI) Sho 54-102299 and Japanese Patent Publication (KOKOKU) No. Sho 59-8310 disclose methods in which by letting contact the pigmented phosphor with a solution of water soluble organic compound, dispersion ability of the phosphor is improved.
In addition, Japanese Patent Publication (KOKOKU) Nos. Sho 60-21675, Sho 61-46512 and Sho 62-39186 disclose method that improves dispersion property of phosphor by sticking an inorganic compound on the surface of phosphor. Further, Japanese Patent Laid-Open Publication (KOKAI) No. Hei 2-178387 discloses a method in which by sticking an inorganic compound and an organic compound on the surface of phosphor, settling property of phosphor in a slurry solution is improved.
As described above, so far, by the use of the surface treatment in which an inorganic compound or an organic compound is stuck on the phosphor, quality of the phosphor layer has been improved to some degree. However, accompanying the recent enlargement of the computer market, color cathode ray tubes are demanded to satisfy higher performance that the computer display terminal demands. Accordingly, the phosphor layer thereof is also demanded to satisfy requirement of higher performance. In particular, demand for higher contrast is strong. In addition, also in cathode ray tubes for color television, upon making the screen larger and finer, the phosphor layer of higher quality, particularly of higher contrast, is being demanded.
As a method for attaining the higher contrast, an improvement of the brightness of phosphor layer can be cited. In order to improve the brightness of the phosphor layer, the phosphor itself is required to improve the brightness thereof, or by forming a denser phosphor layer than ever, the phosphor layer can improve the brightness thereof.
Now, the present inventors have paid attention to a method that materialize densification of the phosphor layer to improve the brightness thereof and accordingly the contrast of color cathode ray tubes. With the above intention, the inventors have studied in detail the quality of the phosphor layer of the existing color cathode ray tube. As a result of this, it is found that denseness of the red emitting phosphor layer is remarkably poor in contrast with those of green and blue emitting phosphor layers. The low denseness of the red emitting phosphor layer does have no relation with the order by which each phosphor of three colors is coated.
Thus, through improvement of the denseness of the red emitting phosphor layer, the brightness of the red emitting phosphor layer can be improved, as a result of this higher contrast of a color cathode ray tube can be realized. However, the existing red emitting phosphor can not form such dense red emitting phosphor layer.
Further, Japanese Patent Laid-Open Publication (KOKAI) No. Hei 3-220286 discloses a red emitting phosphor (phosphor that has yttrium oxysulfide as a phosphor base material) of which content of particles of particle diameter coarser than 8.01 &mgr;m is 10% or less. However, only by reducing the ratio of the coarser particles, the denseness of the red emitting phosphor layer can not be sufficiently heightened.
Further, in Japanese Patent Laid-Open Publication (KOKAI) No. Hei 8-41453, a fabrication method is disclosed in which rare earth oxide raw material is mixed with alkali metal carbonate, aluminum compound and sulfur raw material, and the mixture thereof is fired to fabricate a rare earth oxysulfide phosphor. In the embodiment of this publication, as criteria of particle size distribution, −log (d
84
/d
50
) and +log (d
16
/d
50
) are disclosed. However, the red emitting phosphor having the disclosed particle distribution can not sufficiently improve the denseness of the phosphor layer.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a red emitting phosphor for cathode ray tubes that enables to obtain a phosphor layer of very high denseness with reproducibility. Another object of the present invention is to provide, by employing such a red emitting phosphor, a cathode ray tube in which the brightness of the phosphor layer is improved and accordingly the higher contrast is realized.
A first red emitting phosphor for cathode ray tube of the present invention is a red emitting phosphor for cathode ray tube that comprises phosphor powder of which base material is yttrium oxysulfide, wherein the phosphor powder has such a particle size distribution that the content of a component of a particle diameter of less than 4.0 &mgr;m is 15% or less, that of a component of a particle diameter of 4.0 &mgr;m or more and less than 8.0 &mgr;m is 75% or more, and that of a component of a particle diameter of 8.0 &mgr;m or more is 10% or less.
The first red emitting phosphor for cathode ray tube stipulates that the particle size distribution of the red emitting phosphor of medium particle size has a 50% D value of cumulative particle size distribution of for instance 5.0 &mgr;m or more and 6.5 &mgr;m or less. Such a red emitting phosphor of medium particle size is suitable for cathode ray tubes for computer display use.
A second red emitting phosphor for cathode ray tube of the present invention is a red emitting phosphor for cathode ray tube that comprises phosphor powder of which phosphor base material is yttrium oxysulfide, wherein the phosphor powder has a particle size distribution in which the content of a component of a particle diameter of less than 5.04 &mgr;m is 20% or less, that of a component of a particle diameter of 5.04 &mgr;m or more and less than 10.079 &mgr;m is 70% or more, and that of a component of a particle diameter of 10.079 &mgr;m or more is 10% or less.
The second red emitting phosphor for cathode ray tube stipulates that the particle size distribution of red emitting phosphor of large particle size has the 50% D value of cumulative particle size distribution of for instance 6.5 &mgr;m or more and 8.0 &mgr;m or less. Such a red emitting phosphor of larger particle size is suitable for cathode ray tubes for color television use.
A first cathode ray tube of the present invention comprises a panel that constitutes an envelope, a phosphor layer that is formed on an internal surface of the panel and contains the first red emitting phosphor for cathode ray tube of the present invention, and an electron source that emits electron beams onto the phosphor layer. The first cathode ray tubes are suitable for computer display use.
A second cathode ray tube of the pres
Mikami Akira
Oyaizu Tsuyoshi
Shimizu Yohe
Sugano Satoshi
Takemura Hirofumi
Foley & Lardner
Kabushiki Kaisha Toshiba
Patel Vip
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