Electric lamp and discharge devices – With gas or vapor – Three or more electrode discharge device
Reexamination Certificate
1998-11-19
2001-12-25
Patel, Ashok (Department: 2875)
Electric lamp and discharge devices
With gas or vapor
Three or more electrode discharge device
C313S582000, C313S586000
Reexamination Certificate
active
06333600
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a plasma display panel, in particular a plasma display panel with high luminance and high contrast.
2. Description of the Related Art
For improving image quality of a plasma display panel, for example, JP-A 8-287834/1996 has disclosed a technique of forming a photoabsorption layer on the viewing side of the panel.
FIG. 3
shows a schematic sectional view of a cell as an example of a plasma display panel of the prior art.
In a color panel, each fluorescence layer
9
is colored in R(red), G(green) and B(blue) corresponding to luminescent colors of individual cells. UV generated in a discharge space cell is radiated on the fluorescence layer
9
to emit colors assigned to individual fluorescence layers.
In addition, light observed in the viewing side includes external light besides emission light. It is light generated by reflection of incident light into the cell from the outside, on the fluorescence layer
9
and a dielectric layer
11
. It may increase luminance of black display, leading to reduction of contrast ratio. To remove the external light, a photoabsorption layer
15
is formed.
The photoabsorption layer plays a role as a dielectric layer required in AC type drive, i.e., a drive procedure in which voltages with different polarities are alternately applied to a discharge cell for light emission. External light passes through the photoabsorption layer
15
twice, i.e., at incidence and reflection. On the other hand, since emission light passes once, reducing a transmission may allow contrast to be improved.
There has been disclosed, for example in JP-A 8-138559/1996, a technique for effectively taking emission light in which a wavelength-selective reflection film is formed on a rear side for effectively reflecting only emission light. Specifically, a wavelength-selective reflection film is formed on the rear side of the fluorescence layer to reflect emission light from the fluorescence layer to the rear side for effectively utilizing the emission light.
JP-As 3-190039/1991 and 3-246857/1991 have disclosed a technique in which a fluorescence layer is formed on the rear-substrate side and a technique in which a reflection film is further formed on the rear-substrate side.
One problem in the prior art is that a display luminance is reduced due to a photoabsorption layer for improving display contrast. Display luminance may vary depending on a transmission of the photoabsorption layer. A resulting display may be of high contrast and low luminance or of low contrast and high luminance.
An adequately high quality of image cannot be, therefore, displayed because a photoabsorption layer is formed on the viewing-side substrate and a reflectance of the fluorescence layer is high.
SUMMARY OF THE INVENTION
This invention has been achieved, whose objective is to provide a high-luminance and high-contrast plasma display panel without the above problems.
The above problems or objective can be solved or achieved by this invention. This invention provides a plasma display panel comprising a plurality of cells having a fluorescent material between two glass substrates, viewing-side and rear substrates, in which the fluorescent material is excited by UV energy to emit visible light, characterized in that the visible-light reflectance of the fluorescence layer is below 25% and a photoreflection layer which effectively reflects only light with a specific emission wavelength of the fluorescent material of each cell and absorbs the remaining light, is formed between a barrier rib separating cells from each other and/or a cell bottom surface, namely the surface of the rear substrate and the fluorescence layer formed on the inner surface of the cell.
This invention also provides an AC type of plasma display panel comprising a plurality of cells having a fluorescent material between two glass substrates, viewing-side and rear substrates, in which the fluorescent material is excited by UV energy to emit visible light, characterized in that the visible-light reflectance of the fluorescence layer is below 25% and a barrier rib separating cells from each other and/or a dielectric layer on a cell bottom surface, namely the surface of the rear substrate is a photoreflection layer which can effectively reflect only light with a specific emission wavelength of the fluorescent material and absorb the remaining light.
This invention further provides a plasma display panel comprising a plurality of cells having a fluorescent material between two glass substrates, viewing-side and rear substrates, in which the fluorescent material is excited by UV energy to emit visible light, characterized in that a gray photoreflection layer which does not have a wavelength distribution, is formed between a barrier rib separating cells from each other and/or a cell bottom surface, namely the surface of the rear substrate and the fluorescence layer formed on the inner surface of the cell.
This invention further provides an AC type of plasma display panel comprising a plurality of cells having a fluorescent material between two glass substrates, viewing-side and rear substrates, in which the fluorescent material is excited by UV energy to emit visible light, characterized in that a barrier rib separating cells from each other and/or a dielectric layer on a cell bottom surface, namely the surface of the rear substrate is a photoreflection layer which does not have a light distribution and can absorb light.
The plasma display panel of this invention is characterized in that the visible-light reflectance of the fluorescence layer is below 25% and the fluorescence layer has a photoabsorption or photoreflection layer on its rear side for improving contrast ratio.
In the panel of this invention, a photoabsorption layer is placed on the rear side of a fluorescence layer for minimizing reflection of external light, and therefore, a component incident on the viewing side of emission light from the fluorescence layer is displayed without passing through the photoabsorption layer. In a panel of the prior art, a photoabsorption layer is placed on the viewing side in relation to the fluorescence layer and thus the whole emission light from the fluorescence layer is displayed through the photoabsorption layer. Therefore, the plasma display panel of this invention can perform display lighter than that of the prior art.
In this invention, reflectance of a fluorescence layer is below 25%. External light is absorbed by a photoabsorption layer as is in a panel of the prior art to prevent contrast reduction, but external light reflected on the fluorescence layer cannot be removed.
The panel controlling reflectance below 25% can achieve contrast higher than that having a photoabsorption layer on the viewing side.
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patent: 5661500 (1997-08-01), Shinoda et al.
patent: 5757131 (1998-05-01), Tsuchiya
patent: 5932967 (1999-08-01), Chikazawa
patent: 5939826 (1999-08-01), Ohsawa et al.
patent: 5957743 (1999-10-01), Konishi et al.
patent: 6117370 (2000-09-01), Hasegawa et al.
patent: 3-190039 (1991-08-01), None
patent: 3-246857 (1991-11-01), None
patent: 8-138559 (1996-05-01), None
patent: 8-162026 (1996-06-01), None
patent: 8-287834 (1996-11-01), None
patent: 8-329843 (1996-12-01), None
patent: 9-231910 (1997-09-01), None
Haynes Mack
NEC Corporation
Patel Ashok
Sughrue & Mion, PLLC
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