Electric lamp and discharge devices – Cathode ray tube – Screen
Reexamination Certificate
2000-07-19
2003-04-29
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Screen
C313S466000, C313S478000, C313S479000, C313S474000, C220S00210A, C220S00210R
Reexamination Certificate
active
06555953
ABSTRACT:
BACKGROUND OF THE INVENTION
In recent years, color cathode ray tubes of the so-called flat face type or flat panel type are widely employed in television receiver sets and personal computer monitors. From a viewpoint of manufacturability and manufacturing cost, such flat panel type color cathode ray tubes are generally designed so that the outer surface of a display panel is formed into a substantially flat plane through increase of a radius of curvature (equivalent radius of curvature) thereof while forming on an inner panel surface a phosphor screen into a curved plane having a relatively small radius of curvature (equivalent radius of curvature) that is as small as possible not to spoil the flatness of display images. Due to this panel design, a peripheral portion of such panel is greater in thickness than a central portion thereof, which leads to the risk of multi-reflection of externally incident rays of light at the thick panel peripheral portion resulting in a degradation of quality of display images.
See
FIG. 36
, which is a diagram for explanation of an image quality degradation occurring when external light rays are reflected off at a panel of the flat panel color cathode ray tube. In
FIG. 36
, reference numeral “
1
” is used to designate a panel;
1
a
denotes a display screen section of the panel;
1
b
indicates a skirt section;
1
c
is a non-glare anti-static layer; line segment Z—Z shows a tube phosphor screen. As shown in
FIG. 36
, externally incident light rays L
i
are reflected off at an outer panel surface while at the same time behaving to reflect at an inner panel face to thereby outgo as reflected light L
r
from the outer panel face, which would result in a decrease in viewability of picture images as visually displayed on the panel screen. Furthermore, the thick panel peripheral portion might also experience occurrence of multireflection in association with inner face reflection, which results in overlapping or “superposition” of multiple reflection image components onto a display image, thereby further reducing the viewability. It should be noted that although the discussion in conjunction with
FIG. 36
was done while neglecting any possible influence of reflection on the outer panel face, such outer face reflection will hardly be precluded completely even when employing the nonglare antistatic layer
1
c.
A cathode ray tube with an optical selection/absorption layer provided between the inner panel face and phosphor screen has been disclosed in Japanese Patent Application Laid-Open Hei 4-345737/1992. The optical select/absorb layer as taught from this Japanese document is comprised of a mixture of more than two materials including organic or inorganic pigment or dye materials, wherein these pigment/dye materials are in the form of fine powdery grains or particles with a grain size of 1.0 micrometer (&mgr;m) or less and also with two or more maximal spectral absorption peaks while forming on the outer panel face a mixture layer of a conductive material and a binder, or a single-layered antireflection layer that is lower in refractivity than a glass panel, or alternatively a multilayer antireflection film including two to four layers of different refractivities, or still alternatively a film with conductive particles made of ATO or ITO or else mixed into this multilayered antireflection film.
Another cathode ray tube is disclosed in Japanese Patent Application Laid-Open Hei 5-182604/1993, wherein in order to let its panel be uniform in optical transmissivity, a chosen coloring agent is mixed into a silica binder and is then spray-coated on an outer panel surface with the resultant coat density being variable so that a density value is high at a central portion and low at a peripheral portion; then, a conductive agent with no coloring agents added thereto is spray coated thereon to form a convex-concave surface configuration having its glossiness (gloss value) that is adjustable with a change in amount of ethylene glycol being added to a coating liquid used.
A color cathode ray tube is disclosed in U.S. Pat. No. 4,815,821, wherein the cathode ray tube includes a glass panel having on its inner surface a first transparent layer that is higher in refractivity than the panel glass, a black matrix (BM) formed thereon, and a second transparent layer overlying the black matrix to have reflectivity less than that of the first transparent layer, and wherein the refractivity of the first transparent layer is designed to fall within a range of 1.7 to 2.0 while letting each transparent layer be set at a quarter of the wavelength of visible light.
With flat panel color cathode ray tubes, it is required to lessen the radius of curvature of an inner panel surface to the extent that the lack of flatness is avoided when viewing on-screen display images by human eyes, thereby offering increased manufacturability and enhanced surface flatness of a tube bulb (evacuated envelop). As currently available color cathode ray tubes are typically designed to add a significant difference in radius of curvature to the panel's inner surface and outer face in the way discussed above, the resulting plate thickness becomes greater at the periphery than at the center part thereof, which in turn results in occurrence of a problem that those display images at the panel periphery are made darker than an image being displayed at the center of such panel.
One prior known approach to reducing a difference in brightness or luminance intensity between the panel center and periphery is to employ a panel made of certain glass materials with increased optical transmissivities. Unfortunately this approach is encountered with problems which follow: the higher the optical transmissivity, the lower the contrast of display images; and, the operability of letting a glass material per se absorb for attenuation multireflection light rays at the panel's inner and outer surfaces might likewise decrease resulting in a decrease in color purity.
Furthermore, in addition to improving the display image quality, it is also a must for color cathode ray tubes to meet the strict need for satisfying ergonomics design requirements including, but not limited to, preclusion of extraneous electromagnetic radiation and external attendant light prevention.
SUMMARY OF THE INVENTION
The present invention is to provide a flat panel color cathode ray tube excellent in panel face flatness and image contrast plus extended color reproduction range. To this end, the color cathode ray tube in accordance with this invention is specifically arranged to employ an inside light absorption layer containing therein inorganic pigment at a selected portion lying adjacent to a panel than a light absorption matrix (black matrix) on an inner panel surface or adversely providing an inside light absorption layer containing such inorganic pigment on or over the light absorption matrix (on an electron gun assembly side) to thereby suppress unwanted creation of multireflection on both the inner panel surface and outer surface, thus correcting or compensating for any possible difference in light absorption amount which can occur due to the presence of a plate thickness difference between a central portion and a peripheral portion of the panel. Another principal concept of the invention lies in forming on the outer panel surface an outside light absorption layer which consists essentially of a conductive micro-particle layer that offers light absorbability by itself and a low refractivity layer overlying this microparticle layer with this layer being less in refractivity than the microparticle layer. The conductive microparticle layer is such that a binder is permeated into gaps defined among neighboring microparticles, wherein the former is less in refractivity than the latter. This outside light absorption layer is expected to function also as an antistatic nonglare layer.
Still another principle of the color cathode ray tube of the invention is that the inside light absorption layer being formed on the inner panel surface is speci
Nishizawa Masahiro
Odaka Yoshiyuki
Tojo Toshio
Yoshioka Hiroshi
Guharay Karabi
Hitachi , Ltd.
Milbank Tweed Hadley & McCloy LLP
Patel Nimeshkumar D.
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