Patent Application
20050067952
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, at least 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 (TiO2) or barium titanate (BaTiO3). A rear 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 mold into a three dimensional surface, for example. 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.
EL lamps made with polyurethane layers are known; see U.S. Pat. No. 4,297,681 (Dircksen). An EL panel encapsulated in an envelope is known in the art; see U.S. Pat. No. 4,138,620 (Dickson) and U.S. Pat. No. 4,181,925 (Burrows). U.S. Pat. No. 5,856,030 (Burrows) discloses an EL panel having a urethane layer on release paper as a substrate. The release paper provides structural support while other lamp layers are applied. A second layer of urethane is deposited and is attached to the first layer of urethane around the periphery of the panel to enclose the lamp layers in a urethane envelope.
Relatively flexible EL panels are known in the art. 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 difficult to automate the assembly of panels into end products, e.g. a front cover for a cellular telephone.
It is known to mold EL lamps into translucent or transparent articles; e.g. see U.S. Pat. No. 4,619,624 (Kerr III et al.), U.S. Pat. No. 5,565,733 (Krafcik et al.), U.S. Pat. No. 5,780,965 (Cass et al.), PCT published application WO 03/025890 (Nissha Printing Co.), and Japanese patent abstract 11-162633 (Nissha Printing Co.), In general, the molded lamp becomes an internal member of the molded part, restricting needed access to electrical terminals. In addition, it is difficult to predict or control the final shape of the EL lamp, unless the lamp is preformed and includes a relatively stiff (self-supporting) substrate such as the of polyester or polycarbonate substrates described above. Finally, an internal EL lamp may limit the type or extent of graphics applied to a major surface of an article or to the lamp itself.
In view of the foregoing, it is therefore an object of the invention to provide a flexible, moldable EL lamp.
Another object of the invention is to provide a molded article wherein an EL lamp is molded into the article but forms a portion of the outer surface of the article.
A further object of the invention is to provide an EL lamp that simplifies molding the lamp into an article.
Another object of the invention is to eliminate the envelope around a flexible EL panel.
A further object of the invention is to provide an EL lamp that is compatible with a wide range of graphics and textures on the EL lamp.
Another object of the invention is to provide an EL lamp that is compatible with a wide range of graphics and textures in an article containing the EL lamp.
The foregoing objects are achieved in this invention in which a flexible EL lamp is made by depositing successive layers onto a release layer. The lamp is molded into a substantially stiffer article, leaving the lamp as a portion of a surface of the article. In one embodiment of the invention, the lamp emits light through the article. In another embodiment, the lamp emits light from the exposed portion of the surface. The EL lamp, as molded, can be substantially flat or have a three dimensional shape. The lamp is molded with or without the release layer.
A more complete understanding of the invention can be obtained by considering the following detailed description in conjunction with the accompanying drawings, in which:
In
Electrode 23 overlies layer 22 and is a thin, conductive layer of indium tin oxide or indium oxide or a screen printed conductor. Phosphor layer 25 overlies electrode 23 and dielectric layer 26 overlies the phosphor layer. Electrode 27 overlies dielectric layer 26 and is made by screen printing a conductive ink. Polyurethane layer 28 overlies electrode 28 and provides a protective function. Layer 29 is a hard coating, e.g. a UV curable clear coating that provides some scratch resistance and insulates the ink layers (e.g. 25, 26, and 27) from the heat of the injected resin. Suitable materials are commercially available, such as Nazdar 641109PS SPL. In some applications, those not requiring extensive bending, protective layer 28 can be omitted in favor of hard coating 29.
Phosphor layer 35 overlies split electrode 33 and dielectric layer 36 overlies the phosphor layer. Electrode 37 overlies dielectric layer 36. Polyurethane layer 38 overlies electrode 38 and provides a protective function. Layer 39 is a graphics layer that also insulates the ink layers (e.g. 35, 36, and 37) from the heat of the injected resin. Preferably, layer 39 is a layer of polycarbonate, 5-10 mils (0.127-0.254 mm.) thick, having graphics printed thereon. In some applications, those not requiring extensive bending, Protective layer 38 can be omitted in favor of graphics layer 39.
Lamp 20 and lamp 30 are suitable for use in injection molding processes known in the art.
Because the invention is compatible with known lamp manufacturing processes and materials and with known injection molding apparatus and materials, virtually any injection molded product that one wanted to illuminate can benefit from the invention, particularly those with three dimensional luminous surfaces.
The invention thus provides a flexible, moldable EL lamp that forms part of the outer surface of an injection molded article. The stability of the EL lamp on the release layer simplifies molding the lamp into an article, which can eliminate the envelope around a flexible EL panel. An EL lamp constructed in accordance with the invention is compatible with a wide range of graphics and textures on the EL lamp and in an article containing the EL lamp.
As used herein, a “surface” is meant to include substantially flat planes and three dimensional shapes not including sharp breaks or corners; that is, without what would be described mathematically as discontinuities; e.g. an abruptly changing radius of curvature. A mathematical definition of “surface” is not intended here, particularly with regard to thickness. The EL lamp is or intersects the outer surface of the article. As applied to surfaces that are continuous and enclose a volume, e.g. rings, ovoids, or spheroids, a “surface” is what generally faces in one direction or is what can be seen at a normal viewing distance without rotation of the article.
Having thus described the invention, it will be apparent to those of skill in the art that various modifications can be made within the scope of the invention. For example, the procedure described above uses a single “shot” or injection of resin. One can make an article in accordance with the invention in a two shot mold by shaping the mold to protect the electrical leads, to prevent resin from covering the leads during the second injection. The release layer is removed, partially removed, or left in place between injections, as desired.
