Electric lamp and discharge devices – With gas or vapor – Three or more electrode discharge device
Reexamination Certificate
1999-08-26
2001-10-23
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Three or more electrode discharge device
C445S024000, C313S582000, C313S609000, C313S632000
Reexamination Certificate
active
06307318
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method and apparatus for making a back glass substrate for plasma display panels and also relates to the resultant product.
BACKGROUND ART
Plasma display panels are currently expected to replace cathode ray tubes for many uses such as televisions, monitors, and other video displays. One important advantage of plasma display panels is that a relatively large display area can be provided with relatively minimal thickness as compared to cathode ray tubes.
The general construction of plasma display panels includes generally sheet like front and back glass substrates having inner surfaces that oppose each other with a chemically stable gas hermetically sealed therebetween by a seal between the substrates at the periphery of the panel. Elongated electrodes covered by a dielectric layer are provided on both substrates with the electrodes on the front glass substrate extending transversely to the electrodes on the back glass substrate so as to thereby define gas discharge cells or pixels that can be selectively energized by an electrical driver of the plasma display panel. The panels can be provided with phosphors to enhance the luminescence and thus also the efficiency of energizing the panels. The phosphors can also be arranged in pixels having three subpixels or gas discharge cells for respectively emitting the primary colors red, green, and blue to provide a full color plasma display panel.
The conventional construction of back glass substrates for plasma display panels has elongated gas discharge troughs and barrier ribs that space the troughs from each other so as to thus generally isolate each column of pixels within each trough from the columns of pixels on each side thereof and thereby provide good color separation and pixel definition. The gas discharge trough and barrier rib construction can be inexpensively provided by a known thick film printing technique utilizing thick film electrodes typically made of silver, nickel or aluminum paste and covered by dielectric paste for electrical insulation. However, this thick film printing technique, although relatively inexpensive, is difficult to apply to large areas requiring fine patterning due to deformation of print screens and the substrate itself.
Another way in which the back glass substrate gas discharge trough and barrier rib construction can be provided is by first applying thick film electrodes on the substrate and then applying a thick film dielectric glass layer that is typically then fired. A thick film barrier material film frit is then applied and dried. Thereafter, a photoresist film is laminated on the dried frit layer. The photoresist layer is then patterned by a conventional photolithographic process to provide a protecting layer prior to sandblasting that removes material to provide the gas discharge trough and barrier rib construction that is then heated to provide sintering.
DISCLOSURE OF THE INVENTION
One object of the present invention is to provide an improved method for making a back glass substrate for a plasma display panel.
In carrying out the above object, the improved method for making a back glass substrate for a plasma display panel is performed by forming hot sheet glass heated above its annealing point to provide gas discharge troughs spaced by barrier ribs and by thereafter cooling the formed sheet glass to provide the back glass substrate.
Forming of the hot sheet glass while heated above its annealing point to provide the gas discharge trough and barrier rib construction eliminates the need for thick film printing or sandblasting and the resultant problems associated with such conventional processing.
The gas discharge trough and barrier rib forming can be performed on sheet glass that is either a hot sheet glass ribbon or discrete glass sheets.
In one practice of the method, the gas discharge troughs and barrier ribs are formed in the hot sheet glass by rolling engagement with curved projections spaced from each other along a rotational axis of the curved projections. The curved projections can be cooled by a liquid coolant to control temperature. This rolling engagement can also utilize a rotating roll having a smooth outer surface that cooperates with the curved projections in an opposed relationship to provide the gas discharge trough and barrier rib forming in the hot sheet glass.
In another practice of the method, a press member having a generally flat forming face including elongated projections of a straight shape spaced from each other in a parallel relationship and the hot glass sheet are moved relative to each other to provide pressing of the press member against the hot sheet glass to form the gas discharge troughs and barrier ribs. The press member and sheet glass are then disengaged from each other.
After the forming of the gas discharge troughs and barrier ribs, the press member can be cooled by a liquid coolant prior to disengaging the hot sheet glass.
After the forming of the gas discharge trough and barrier rib construction, the back glass substrate can be cooled by pressurized gas to provide compressive stresses that strengthen the substrate.
The gas discharge trough and barrier rib forming can be performed on hot sheet glass having a metal layer that provides electrodes in the gas discharge troughs and also can include removal of the metal layer from the barrier ribs between the troughs.
In addition, the gas discharge trough and barrier rib forming can be performed on hot sheet glass having a metal layer and an outer dielectric layer to provide insulated electrodes within the gas discharge troughs.
The method can also be performed by providing the gas discharge troughs with bottom surfaces formed with an undulating shape along their lengths. This undulating shape of the bottom surfaces of the troughs is formed in one practice by rolling engagement with undulating projections of a generally curved shape on a rotatable forming member. In another practice, the undulating shape of the bottom surfaces of the troughs is formed by engagement with a press member having elongated undulating projections of a generally straight shape spaced from each other in a parallel relationship.
In addition, the method can also be performed by forming the barrier ribs with distal ends of an elongated shape having spaced openings that provide communication between adjacent gas discharge troughs.
In the preferred practice of the method, the gas discharge troughs have bottom surfaces formed with an undulating shape having spaced peaks along their lengths, and the barrier ribs are formed with distal ends of an elongated shape having spaced openings that are located adjacent the peaks of the bottom surfaces and provide communication between adjacent gas discharge troughs.
Another object of the invention is to provide improved apparatus for making a back glass substrate for a plasma display panel.
In carrying out the immediately preceding object, the apparatus for making a back glass substrate for a plasma display panel includes a conveyor for conveying hot sheet glass heated above its annealing point and also includes a forming member that engages the hot sheet glass to form gas discharge troughs and barrier ribs that space the troughs from each other.
In one construction of the apparatus, the conveyor is a ribbon former including a bath for molten tin on which a hot sheet glass ribbon heated above its annealing point is floated and then delivered for the forming of the gas discharge troughs and barrier ribs in the hot sheet glass ribbon.
The forming member of the apparatus is also disclosed as including curved projections spaced along a rotational axis of the forming member and engaged with the hot sheet glass by rolling engagement that provides the gas discharge troughs and barrier ribs. This construction of the apparatus is also disclosed as including a rotatable roll having a smooth outer surface that cooperates with the curved projections in an opposed relationship to provide the forming of the gas discharge troughs and barrier ribs.
The forming
Kaake Steven A. F.
Nicholson Robert D.
Gerike Matthew J.
Marshall & Melhorn LLC
Patel Ashok
Photonics Systems, Inc.
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