Coating apparatus – With means to apply electrical and/or radiant energy to work... – Electrostatic and/or electromagnetic attraction or...
Reexamination Certificate
1999-08-04
2001-08-28
Crispino, Richard (Department: 1734)
Coating apparatus
With means to apply electrical and/or radiant energy to work...
Electrostatic and/or electromagnetic attraction or...
C118S620000, C118S621000, C427S157000
Reexamination Certificate
active
06280524
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to an apparatus and a method for coating a powder material on a flat panel and more particularly, relates to an apparatus and a method for coating a fluorescent powder on a substantially flat, non-electrically conducting panel by an electrostatic coating method in which the panel is heated and negatively charged by a gas flame.
BACKGROUND OF THE INVENTION
In recent years, flat panel display devices have been developed and widely used in electronic applications such as personal computers. One of such devices is a field emission display (FED) device that overcomes some of the limitations of liquid crystal displays and provides significant advantages over the traditional LCD devices. For instance, the field emission display devices have higher contrast ratio, larger viewing angle, higher maximum brightness, lower power consumption and a wider operating temperature range when compared to a conventional thin film transistor liquid crystal display panel.
One of the most drastic difference between a FED and a LCD is that, unlike the LCD, FED produces its own light source utilizing colored phosphor. The FEDs do not require complicated, power-consuming backlights and filters and as a result, almost all the light generated by a FED is visible to the user. Furthermore, the FEDs do not require large arrays of thin film transistors, and thus, a major source of high cost and yield problems for active matrix LCDs is eliminated.
In a FED, electrons are emitted from a cathode and impinge on a fluorescent coating layer, such as a phosphor layer on the back of a transparent cover plate to produce an image. Such a cathodoluminescent process is known as one of the most efficient methods for generating light. Contrary to a conventional CRT device, each pixel or emission unit in a FED has its own electron source, i.e., typically an array of emitting microtips. A voltage difference existed between a cathode and a gate attracts electrons from the cathode and accelerates them toward the phosphor coating. The image produced by the phosphor coating is therefore largely dependent on the quality and the uniformity of the phosphor coating. The process for coating a phosphor layer on a transparent glass plate is therefore an important step in the total fabrication process of a FED.
Conventionally, the coating of a fluorescent powder layer on a flat transparent plate (or on a flat bulb) is accomplished by either a screen printing or a dip coating process. In either process, the screen printing paste or the dip coating emulsion contains a large amount of solvent which is used in forming the paste or the emulsion. After a paste is printed on a glass plate or after a glass plate is dip coated in an emulsion, the glass plate must be oven baked to evaporate all the solvent. The screen printing and the dip coating process are therefore not only complicated fabrication processes, but also processes that generate pollution for the environment for release of evaporated solvent into the atmosphere. The complicated fabrication process further result in a low throughput of the device fabricated.
It is therefore an object of the present invention to provide an apparatus for coating a fluorescent powder on a flat panel that does not have the drawbacks or shortcomings of the conventional apparatus.
It is another object of the present invention to provide an apparatus for coating a fluorescent powder on a flat panel that operates on an electrostatic coating principle.
It is a further object of the present invention to provide an apparatus for coating a fluorescent powder on a flat panel electrostatically that utilizs gas flames for heating the panel and negatively charging the panel.
It is another further object of the present invention to provide an apparatus for coating a fluorescent powder on a flat panel that is capable of rotating a flat panel mounted on a powder spray chamber during the electrostatic coating process.
It is still another object of the present invention to provide an apparatus for coating a fluorescent powder on a flat panel that is capable of heating the panel to a temperature of at least 100° C. and simultaneously charging the panel with a negative voltage of at least 20,000 volts.
It is yet another object of the present invention to provide an apparatus for coating a fluorescent powder on a flat panel that is capable of electrostatically coating the powder on a panel that is electrically non-conductive.
It is still another further object of the present invention to provide a method for coating a fluorescent powder on a flat panel by simultaneously heating a glass panel to a high temperature and negatively charging the panel to a high negative voltage and directing positively charged powder particles at the panel surface.
It is yet another further object of the present invention to provide a method for coating a fluorescent powder on a flat panel by simultaneously heating, rotating and negatively charging the panel and directing positively charged powder particles under a high air pressure toward the panel surface.
SUMMARY OF THE INVENTION
In accordance with the present invention, an apparatus and a method for coating a fluorescent powder on a substantially flat panel are provided.
In a preferred embodiment, an apparatus for electrostatically coating powder on a panel is provided which includes a chamber that has a top opening, a bottom opening and a cavity contained therein, a panel positioned on top of the chamber substantially sealing the top opening, the panel has a bottom surface to be coated which is exposed in the top opening to the cavity, a heating means for heating the panel on a top surface opposite to the bottom surface and for electrically grounding the flat panel, a powder spray nozzle adapted for engaging the bottom opening of the chamber and for receiving a positive voltage forming a closed-loop circuit with the heating means, means for rotating the chamber and the panel positioned on the chamber, and high pressure means for flowing a powder through the spray nozzle and for charging the powder with a positive electrostatic charge such that the powder is attracted toward the negatively charged bottom surface of the panel.
The apparatus for electrostatically coating powder on a flat panel may further include a chamber that has a columnar shape with a diameter at the top larger than a diameter at the bottom. The apparatus may further include a chamber fabricated of glass that is capable of withstanding a temperature of at least 100° C. The panel may be a glass panel for coating a fluorescent powder thereon. The panel may be a glass panel for fabricating a flat panel display device. The apparatus may further include a heating means that includes a plurality of gas nozzles for forming a layer of gas flame when ignited. The apparatus may further include a heating means that includes a plurality of gas nozzles for heating the panel to a temperature between about 100° C. and about 250° C., and preferably between about 100° C. and about 200° C.
The apparatus for electrostatically coating powder on a panel may furter include a heating means that includes a plurality of gas nozzles for heating the panel and for providing electrical conductance to the panel such that the panel may be grounded. The powder spray nozzle may further include a multiplicity of apertures for passing powder therethrough, the multiplicity of apertures may each have a passageway formed at an angle between about 0° and about 45° when measured from a vertical axis. The positive voltage received by the powder spray nozzle is between about 20,000 volts and about 50,000 volts.
The apparatus for electrostatically coating powder on a panel may further include a rotor member engaging the chamber for providing a rotational motion of the chamber at between about 1 RPM and about 20 RPM. The apparatus may further include a gas supply tank for delivering a flammable gas to the heating means. The apparatus may further include a powder recovery unit for recovering powder that
Huang Jen-Yun
Kuang Lung-Tsai
Lin Shieh-Hsien
Crispino Richard
Industrial Technology Research Institute
Tadesse Y.
Tung & Associates
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