Compositions: coating or plastic – Coating or plastic compositions – Inorganic materials only containing at least one metal atom
Reexamination Certificate
2000-11-16
2003-12-09
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic materials only containing at least one metal atom
Reexamination Certificate
active
06660074
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
1. Field of the Invention
The present invention relates to the field of cold electrodes for gas discharge electrical devices, especially to emission coatings on such electrodes, and the manner of making the same. The invention most particularly relates to such electrodes for use in gas discharge lamps such as neon lights and signs.
2. Background of the Invention
Gas discharge electrical devices, especially neon lamps and signs have been commercially available for decades. Typically, such a device is made up of a phosphor or fluorescent material coating a transparent or translucent material generally tubular in shape and having an electrode at each end. The interior of the device is filled with a conductive gas and is under reduced pressure. On application of a voltage across the electrodes, the current arcs through the gas to the opposing electrode, causing the emission of radiation for perception by a viewer. An intermediary activating material such as mercury may also be involved, as in many so-called neon lamps. In that variation, the current excites the mercury to emit radiation, which radiation excites the fluorescent or phosphor coating. As is generally known, “neon” lamps need not contain neon, but any rare gas of Group VIIIA of the Periodic Table is acceptable.
The electrodes for these devices are made of metal (frequently nickel plated steel) and typically contain an emission coating. They may also contain a ceramic collar. Both the emission coating and the ceramic collar help to reduce sputtering and extend electrode life. See particularly Strattmen: Neon techniques: Handbook of Neon Signs and Cold Cathode Lighting 4
th
Ed., 1997, pages 29 and 31. The emission coating is made up of a mixture of metal carbonates and/or peroxides where the metal is typically selected from barium, strontium, and calcium, although carbonates and/or peroxides of other metals may be present as well. These coatings are typically formed by applying solutions or suspensions of these compounds to the proper surfaces of the electrodes and, on construction of the device, firing it up well above normal operating current, which causes extensive heating of the electrodes whereby the carbonates and/or peroxides are converted to the corresponding oxides (sintering), with release of the carbon (of the carbonate). The release of the carbon (of the carbonate) tends to foul the electrodes resulting in an inelegant appearance and customer dissatisfaction.
To insure that the electrodes are sufficiently heated to result in the conversion, the electrodes are generally viewed visually with a recognition that the entire electrode needs to be “red-hot”. Glass temperature of the lamp may also be monitored in standard fashion as known in the art. In typical fashion, more than one lamp is fired up simultaneously, so that all the electrodes in the firing need to be completely “red-hot” for assurance that the required conversion takes place on all of the electrodes.
It has been noted that if an electrode does not turn “red hot” completely, that electrode has a significantly shorter life or requires greater power consumption. Similarly, if the process is continued to assure the slower heating electrode turns “red hot”, the other electrodes may be “overcooked” resulting in product failures as well.
In addition, the process described above results in the release of carbon, which typically deposits on the surfaces of the electrode, the ceramic cap of the electrode (where a ceramic cap is present), and/or the device inner surface. These “black spots” appear to the device user as defects in the ultimate product, regardless of whether there is in fact any defect.
Thermal emissive electronics and electrodes therefor are discussed in a number of references including U.S. Pat. Nos. 3,625,759; 3,615,901; 5,847,497, 3,760,218; 4,810,926; 4,135,117; 3,766,423; 4,097,762; 4,303,848; 4,052,634; 4,748,375; 5,754,002; and 6,033,924; all of which are incorporated herein by reference.
U.S. Pat. No. 3,625,759 discusses electrodes for thermal emissive electronics and improvements in the electrodes by coating the emission coating carbonate particles with metal salts prior to applying the emission coating to the substrate electrode body. The metal salts are soluble salts. This insures that the metals being introduced remain more uniformly dispersed with the carbonates than merely mixing in metal powders with the carbonates. The metal salts are salts of nickel, cobalt, and iron. Specific iron salts which are mentioned are the nitrate, acetate, formate, and stearate. No specific cobalt compound is mentioned and no oxide ofany of the metals as the metal salt is disclosed.
U.S. Pat. No. 3,615,901 mentions nickel
ickel oxide mixtures with the typical alkaline earth oxide emission coatings for making plastically shapeable cathodes. After sintering, the sintered material on the nickel substrate is then compacted into an appropriate shape.
U.S. Pat. No. 5,847,497 relates to multiple layer electrodes and mentions incorporation of the Group VIIIB metals (free metal) with the further incorporation of sintering aids such as lithium oxide or titanium oxide.
U.S. Pat. No. 3,760,218 includes cobalt oxide or manganese oxide into the emission coating of barium oxide/calcium oxide used in gas discharge electrodes. No carbonates are referred to in that reference.
U.S. Pat. No. 4,810,926 includes transition metals, but says nothing about the oxides. The specific transition metals discussed do not include iron or cobalt.
U.S. Pat. No. 4,135,117 mentions using iron oxide on a conductive segmented phosphor electrode, an electrode very different from the present invention.
U.S. Pat. No. 3,766,423 mentions including iron and/or nickel metal into mixtures of the standard emission coatings. The corresponding oxides are not mentioned.
U.S. Pat. No. 4,097,762 relates to xenon discharge lamps and the problem of electrode material depletion. The solution of this patent is to include aluminum oxide so as to prevent the “evaporation” of electrode materials. Neither iron oxides nor cobalt oxides are mentioned.
U.S. Pat. No. 4,303,848 relates to the problem of blackening. The solution there is to add Yttrium Oxide, Zirconium Oxide, and/or Aluminum Oxide. Neither iron oxides nor cobalt oxides are mentioned.
U.S. Pat. No. 4,052,634 mentions using rare earth metal oxides. Neither iron oxides nor cobalt oxides are mentioned.
U.S. Pat. No. 4,748,375 refers to including indium tin oxide.
U.S. Pat. No. 5,754,002 includes ferrous oxide or cuprous oxide in mercury gas discharge lamps, but those oxides are kept segregated from the emission coating and from the mercury in the lamps until such time as the lamp is discarded and crushed in the course of disposing of the lamp in landfill. The oxides mentioned are asserted to be antioxidants to prevent the mercury from being converted to soluble form by ferric ions, among others.
U.S. Pat. No. 6,033,924, while limited to field emission devices, mentions barium-copper-oxides at Col. 4.
While the art refers to oxides in electrode emission coatings, none of the references teach or suggest inclusion of an iron oxide or a cobalt oxide in the carbonate pre-sintering formulation of the emission coating formulation. None of the references teach or suggest the resulting electrodes of the invention or the electrical devices that incorporate the electrodes of the present invention.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to provide an emission coating for a gas discharge electrode that improves the appearance of the post treatment (firing to convert the carbonates to oxides) electrodes.
It is a further object of the invention to provide an emission coating for a gas discharge electrode that improves the appearance of the gas discharge electrical device constructed from such electrodes.
It is still another object of the invention to provide a gas discharge electrode that has reduced carbo
Adams Thomas L.
Brunsman David
EGL Company, Inc.
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