Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2002-08-28
2004-11-16
Garrett, Dawn (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S917000, C313S511000, C313S512000, C313S506000, C455S566000
Reexamination Certificate
active
06818326
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the combination of a thick film, inorganic, electroluminescent (EL) panel and, in particular, to the construction of an EL panel having relatively thin luminous areas.
As used herein, an EL “panel” is a single sheet including one or more luminous areas, wherein each luminous area is an EL “lamp.” An EL lamp is essentially a capacitor having a dielectric layer between two conductive electrodes, one of which is transparent. The dielectric layer can include a phosphor powder or there can be a separate layer of phosphor powder adjacent the dielectric layer. The phosphor powder radiates light in the presence of a strong electric field, using relatively little current.
A modern (post-1990) EL lamp typically includes transparent substrate of polyester or polycarbonate material having a thickness of about 7.0 mils (0.178 mm.). A transparent, front electrode of indium tin oxide or indium oxide is vacuum deposited onto the substrate to a thickness of 1000 Å or so. A phosphor layer is screen printed over the front electrode and a dielectric layer is screen printed over phosphor layer. A rear electrode is screen printed over the dielectric layer. It is also known in the art to deposit the layers by roll coating.
The inks used for screen printing or roll coating include a binder, a solvent, and a filler, wherein the filler determines the nature of the printed layer. A typical solvent is dimethylacetamide (DMAC). The binder is typically a fluoropolymer such as polyvinylidene fluoride/hexafluoropropylene (PVDF/HFP), polyester, vinyl, epoxy or Kynar 9301, a proprietary terpolymer sold by Atofina. A phosphor layer is typically screen printed from a slurry containing a solvent, a binder, and zinc sulphide particles. A dielectric layer is typically screen printed from a slurry containing a solvent, a binder, and particles of titania (TiO
2
) or barium titanate (BaTiO
3
). A rear (opaque) electrode is typically screen printed from a slurry containing a solvent, a binder, and conductive particles such as silver or carbon. Because the solvent and binder for each layer are chemically the same or similar, there is chemical compatibility and good adhesion between adjoining layers.
A panel constructed in accordance with the prior art is relatively stiff, even though it is typically only seven mils thick, making it difficult to combine the lamp with a membrane switch, for example, because the EL lamp adversely affects the actuation of the switch. Making an EL lamp as part of a switch has not proven practical, largely for the same reason. There is not a good solution among the many competing trade-offs, including diameter of the bump, height of the bump, stiffness, and tactile feedback. Whether a separate element or part of a membrane switch, an EL panel does not back light the entire area of a key in a keypad. Typically, there is a dark area in the middle of the key.
Layer thickness and stiffness are not directly related. The material from which the layer is made affects stiffness. Typically, EL lamps are made from the materials listed above, which produces an undesirable stiffness. Simply reducing thickness does not provide the desired flexibility.
Relatively flexible EL panels are known in the art. U.S. Pat. No. 5,856,030 (Burrows) discloses a panel made from a urethane layer on a release paper. The release paper provides substantial structural support for the substrate while other layers are applied. Unlike panels made on substrates that are seven mils thick, or so, EL panels made on thin substrates from flexible materials, e.g. urethane one to five mils thick, do not keep their shape but bend or curl. This makes it extremely difficult to automate the assembly of panels into end products, e.g. with a keypad for a cellular telephone.
In view of the foregoing, it is therefore an object of the invention to provide a flexible, self-supporting EL lamp.
Another object of the invention is to provide a relatively thin, self-supporting EL panel.
A further object of the invention is to provide a flexible EL panel that does not affect the actuation of membrane switches located above or below the panel.
Another object of the invention is to provide a flexible EL panel that is compatible with automated assembly equipment.
A further object of the invention is to provide a flexible EL panel that lights the entire area of a key in a keypad overlying the panel.
SUMMARY OF THE INVENTION
The foregoing objects are achieved in this invention in which an EL panel includes a substrate 1-5 mils (0.25-1.26 mm) thick supported by a reinforcing frame printed, coated, deposited or otherwise formed in or on the panel.
REFERENCES:
patent: 4730146 (1988-03-01), Maser et al.
patent: 5856030 (1999-01-01), Burrows
patent: 2002/0041153 (2002-04-01), Burrows
patent: 2003/0048074 (2003-03-01), Ni et al.
patent: 2003/0062518 (2003-04-01), Auch et al.
Durel Corporation
Garrett Dawn
Wille Paul F.
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