1. Field of the Invention
This invention relates to a plasma display panel (hereinafter referred to as PDP) for color display, which is a flat display of a self-emission of light type utilizing a gas discharge.
2. Description of the Related Art
Plasma display panels (PDPs) are generally so configured that electrodes in pairs are regularly arranged in two opposing glass substrates with gases mainly containing Ne, Xe and the like enclosed therebetween. A discharge of electricity is then caused in minute cells around the electrodes by applying voltage across the electrodes to make each cell give off light emissions for displaying purposes. In order to have information displayed, the cells regularly disposed are selectively made to give off light emissions. The PDPs are classified into two types: namely, a DC type in which electrodes are exposed to a discharge space; and an AC type in which electrodes are covered with insulating layers.
FIG. 7 shows an example of the structure of an AC type PDP 50 in such a state that the front plate has been set apart from the back plate. As shown in FIG. 7, two sheets of glass substrates 1 and 6 are disposed in parallel and opposite to each other, and both of them are maintained by barriers 7 with a predetermined space held therebetween, the barriers 7 being provided in parallel to each other on the backside glass substrate 6.
On the back side of the glass substrate 1 as the front side of the PDP 50 are parallel row electrodes X and Y, the row electrodes X and Y comprising transparent electrodes 2 and metallic electrodes as bus electrodes 3, respectively. There are also formed a dielectric layer 4 covering the row electrodes, and a protective layer 5 (MgO layer) formed on the dielectric layer 4. Further, each of parallel column electrodes 8 is formed between the barriers 7 on the front side of the glass substrate 6 as the back side so that the column electrodes 8 may intersect the row electrodes X and Y at right angles. Fluorescent materials 9 are provided in such a way as to cover the wall surfaces of the barriers 7 and the base s of cells, respectively. Moreover, the glass substrates 1 and 6 are disposed opposite to each other and a discharge gas containing a mixture of neon, xenon and the like is injected into and enclosed within a discharge space 10 between the barriers 7.
This AC type PDP 50 is of a superficial discharge type and so structured that an AC voltage is applied across the row electrodes X and Y on the glass substrate 1 to make a discharge with an electric field leaked in a space. In this case, the direction of the electric field varies with the frequency because the AC voltage is applied. The fluorescent materials 9 are caused to emit light by the ultraviolet rays of light generated by the discharge, and the light transmitted through the glass substrate 1 as a display side is visually recognized by an observer.
Such a PDP 50 is manufactured by forming the column electrodes 8 on the backside glass substrate 6, the dielectric layer 4 in such a way as to cover the column electrodes 8 as occasion demands and the barriers 7 and then providing each of the fluorescent material layers 9 between the barriers 7. There are known methods of forming the column electrodes 8 including a method comprising the steps of forming films of an electrode material on the backside glass substrate 6 by vacuum evaporation, sputtering, plating, thick film processing and the like and then subjecting the films thus formed to lithography for patterning purposes, and a screen printing method for patterning using a thick film paste. The dielectric layer 4 is formed by the screen printing method or the like. Further, the barriers 7 are formed by double printing through the screen printing, a sandblasting or the like. The fluorescent material layer 9 is formed by the screen printing or the like in which fluorescent paste of three colors of red (R), green (G) and blue (B) is selectively filled in between the barriers 7 or by lithography using photosensitive fluorescent paste.
Incidentally, the luminance of the fluorescent materials of the three colors for use in making color display are different and therefore, the chromaticity of white light (white balance) is normally adjusted by adjusting the level of an input signal for each color. When the levels of input signals for green and red colors are reduced relative to the level of an input signal for blue color, for example, a discharge cell for blue color display is such that up to 256 gradations of the maximum luminance can be displayed but in the case of discharge cells for green and red color display, the luminance of emission of light up to gradations lower than those of the maximum luminance is only obtainable. Therefore, the display gradations in the luminescence display of the discharge cells differ with the color and the problem is that the gradation display quality becomes greatly deteriorated.
An object of the present invention intended to solve the foregoing problem is to provide a plasma display panel capable of properly adjusting the chromaticity of white light without lowering the gradation level of each color.
In order to achieve the above object, according to the present invention, there is provided a plasma display panel comprising: a pair of substrates disposed opposite to each other through a discharge space; a plurality of pairs of row electrodes disposed on an inner surface of one of the pair of substrates; a dielectric layer for covering the pairs of row electrodes from the discharge space; a plurality of column electrodes extended in a direction of intersecting the pairs of row electrodes on an inner surface of the other of the pair of substrates in order to form a discharge cell in each intersecting portion; and fluorescent material layers for covering the column electrodes and giving off blue, green and red color light emissions, wherein an area of the pair of row electrodes within at least a discharge cell for one color display out of the discharge cells for the color display is made different from areas of the pairs of row electrodes within the discharge cells for other color display.