Electroluminescent (EL) panels are found in many electronics applications, particularly as backlighting for LCD displays, keypads, watches, and other areas requiring uniform, low-power illumination. While relatively flexible, when EL panels made from plastic are bent too sharply, fractures and a severely diminished output usually result. As a result, EL panels have generally been restricted to flat or slightly curved surfaces. However, researchers from Karlsruhe Institute of Technology (KIT) and Franz Binder GmbH & Co have now developed a new manufacturing process to print EL panels directly onto the surface of almost any convex and concave shape. Even, apparently, onto spheres.
In essence, the new technique involves printing electroluminescent layers directly onto an object without any intermediate carrier layer (the plastic material mentioned earlier). In this way, convex and concave surfaces of various materials can be made to glow when an electric current is applied.
"By means of the innovative production process we developed together with our industry partner, any type of three-dimensional object can be provided with electroluminescent coatings at low costs," said Doctor Ing. Rainer Kling, associate professor at the Light Technology Institute of KIT.
Electroluminescent panels are a very popular way to backlight a screen, particularly as they provide an even glow across their entire face, use very little power, and generate almost no heat. And they have been around for longer than you might think. Believe it or not, General Electric has had patents on them since 1938, and EL panels have been in use in automobiles since at least 1960 when Chrysler used them in their prestige models.
Essentially the equivalent of a capacitor when used in an AC (Alternating Current) circuit, EL panels encase their light-emitting material between two electrodes. In standard panels, one electrode is generally clear glass or plastic coated with a transparent conductive coating, while the opaque rear electrode is generally made from a reflective metal foil.
In the KIT/Binder EL panel, however, the production process sees different components of the coating (specifically the electroluminescent and electrically conductive ingredients) applied using a new and unique pad printing process. The printing machine is furnished with an elastic rubber pad that deforms when applying the coatings, thereby being able to conform to uneven or complex 3D shapes.
"In this way, it is possible to provide surfaces and even spheres with homogeneous coatings at low costs," said Elodie Chardin, an engineer working on the project. "Homogeneity of the coating of about one tenth of a millimeter in thickness was one of the challenges of this project."
Though Saarland University announced a prototype EL printing method earlier this yearusing ink-jet printers, the KIT/Binder version seems to be the first to produce such coatings on a commercial scale. The process also only requires very few production steps, which saves money and resources, and a large range colors may be applied to the same surface, thereby providing more versatility to the 3D EL panels.
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