Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2002-04-24
2004-08-17
McPherson, John A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S270100, C430S281100
Reexamination Certificate
active
06777165
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photopolymerization type photosensitive flourescent paste composition and a method for forming a fluorescent film by using the same, and more particularly, to a photopolymerization type photosensitive phosphor paste composition useful for formation of a fluorescent film in a plasma display panel which is one of flat panel display, and a method for forming a fluorescent film in a plasma display panel by using the same.
2. Background of the Related Art
Being one of flat panel displays utilizing a phenomenon in which a vacuum UV ray(a wavelength approx. 147 nm) emitted from plasma formed at discharge of an inert gas is tuned into red, green and blue lights within a visible light range when the UV ray makes collision onto red, green and blue flourescent films, the plasma display panel(called as ‘PDP’ hereafter) is paid attention as one of the net generation displays, such as HDTV, in view that the PDP can make a full color display, has a fast response and a wide angle of view, and is easy to realize a large sized display over 40″. The fluorescent film in the PDP has thin films of fluorescent materials which can emit red, green, and blue colors respectively coated inside of space surrounded by a barrier with a height 150 &mgr;m at every 200 nm~300 nm formed on a lower glass substrate of the PDP; makes the full color of the PDP available, and is an important component which fixes a quality of the PDP as the flourescent film controls a luminance of the panel. The PDP fluorescent film is to be formed by screen printing and photolithgraphy. However, the screen printing has a problem in that a small contact area between a screen mask and the glass substrate makes it difficult that a uniform thickness is obtained on the barrier sides and the glass substrate unless a special care is taken for controlling a fluidity of the flourescent paste. Particularly, in a case of an HDTV PDP with a size larger than 40″, it is very difficult to apply a uniform coat of flourescent paste between barrier precisely throughout the glass substrate by the screen printing. Eventually, a photolithography using a liquid photosensitive flourescent paste is suggested as a screen printing method suitable for a large sized HDTV PDP.
As a material for forming the PDP flourescent film by the photolithography, a PVA-ADC type photosensitive flourescent paste is suggested in U.S. Pat. No. 5,086,297 in 1989, which is prepared by dissolving ammonium dichromate(call as ‘ADC’ hereafter) in a water solution of polyvinyl alcohol(call as ‘PVA’ hereafter) used in formation of a flourescent film in a color TV CRT, and dispersing flourescent material therein. However, since a structure and materials of the PDP are different from the TV CRT, the dichromate residue degrades the PDP flourescent material and drops a luminance during operation of the PDP. And, U.S. Pat. No. 5,136,207 in 1990 and U.S. Pat. No. 5,601,468 in 1996 suggest use of a PVA-DAST type photosensitive flourescent paste in formation of the PDP flourescent film, which is prepared by dissolving 4,4′-diazidostilbene-2,2′-disulfonic acid sodium salts, one of water soluble photosensitive agents, in PVA water solution and dispersing flourescent material. However, as developments of the PDP advance, there have been problems in that formation of a uniform flourescent film is difficult because, not only formation of a reflection type flourescent film on a PDP panel with a non-flat structure, of a photo cross-linking photosensitive paste, such as PVA-ADC and PVA-DAST is difficult, but also the photo cross-linking photosensitive paste has a weak adhesive force. And, a photopolymerization type photosensitive flourescent paste using acrylate group polymer having carboxyl group as a binder is known, the paste has disadvantages in that a high baking temperature is required after formation of the flourescent film, residual inorganic alkali metals gives an influence to the flourescent material after the development, and the alkali development solution causes environmental pollution.
The foregoing related art photo cross-linking type photosensitive flourescent paste will be explained in more detail.
FIG. 1
illustrates a photoreaction mechanism of the related art photo cross-linking type photosensitive flourescent paste of PVA-ADC, schematically.
FIG. 2
illustrates a photoreaction mechanism of the related art photo cross-linking type photosensitive flourescent paste of PVA-DAST, schematically.
The related art photo cross-linking type photosensitive flourescent paste of photosensitive polymer composition, such as PVA-ADC and PVA-DAST, is prepared by dissolving PVA-ADC or PVA-DAST which induces a photo cross-linking reaction in water, a solvent, and dispersing one of red, green, and blue flourescent material powder therein, wherein the flourescent material powder is included in the photosensitive flourescent paste by 20~30 wt %, the water, a solvent, by 20~30 wt %, with balance of PVA-ADC or PVA-DAST. Upon coating and drying the photosensitive flourescent paste on the glass substrate having the barriers formed-thereon, most of the water, a solvent, is vaporized, and the photosensitive polymer composition of PVA-ADC or PVA-DAST encapsulate the flourescent powder, to form micron grains of diameters ranging 3 &mgr;m~6 &mgr;m, which are stacked to form a composite membrane of flourescent material photosensitive polymer of a thickness ranging approx. 20~30 &mgr;m. Upon directing an UV ray to the composite membrane of flourescent material/photosensitive polymer with a mask placed thereon, an exposed portion is altered into megapolymer groups of three dimensional network structure by a photo cross-linking reaction of a mechanism as shown in
FIGS. 2 and 3
, and becomes insoluble in water, to remain during the development, while portions not exposed are removed permitting to form a desired flourescent material pattern. In this instance, as shown in
FIG. 1
, in the PVA-ADC group photoreaction mechanism, a Cr(VI) ion included in the ADC is altered into Cr(III) ion by the UV ray to form a complex with an —OH in PVA, resulting to form a megapolymer group which is not soluble in water, which is a solvent. And, as shown in
FIG. 2
, in the PVA-DAST group photoreaction mechanism, DAST which is a water soluble photosensitive agent is decomposed by an UV ray, to for nitrene groups, which makes a hydrogen abstraction reaction with PVA, a polymer, to form a photo cross-linked polymer, to become insoluble in water, a development liquid. Though the photo cross-linking photosensitive flourescent paste of a photosensitive polymer composition, such as PVA-ADC or PVA-DAST is applicable in formation of flourescent film in a color TV CRT with a thickness ranging 10 &mgr;m, the paste is not applicable in formation of the PDP flourescent film having a thickness ranging 20~30 &mgr;m before exposure due to a poor adhesive force coming from a difference of cross-linking densities. This is because the cross-linking density is varied with a number of chrome ions in DAST or ADC, a photosensitive agent, in the photo cross-linking photosensitive flourescent paste, which makes a direct bonding with PVA, a polymer, and such reaction can be occurred only when an UV ray is directed onto photosensitive agents, such as DAST and Cr(VI), directly.
Therefore, as a photo energy of an UV ray becomes the less due to absorption and reflection by the flourescent material grains as the film goes the thicker, the cross-linking may not be occurred or inadequate due to lack of the photo energy of the UV ray at a portion the film is required to make bonding to the substrate. Therefore, the contact portion, which is the deepest portion of the film, between the glass substrate and the flourescent film remained in a state not being cross-linked is bulged or dissolved by a development liquid during a development, leading to lost an exposed flourescent portion which should be remained.
SUMMARY OF THE INVENTION
Accordingly, the pr
Oh Hyun Shik
Park Lee Soon
Fleshner & Kim LLP
LG Electronics Inc.
McPherson John A.
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