Explosives Emboss Holograms
PFINZTAL, Germany, March 31, 2008 -- Hear the word "explosives" and images might spring to mind of an old building being demolished, or an avalanche being triggered. But now a more precise, delicate task has been found for explosive materials-- embossing holograms in steel.
Holograms -- colorful, iridescent interference images -- can protect currency, tickets, drivers' licenses and other items from forgery because they take a great deal of effort to produce and are almost impossible to copy. This is because the image is created not only by the interaction of different colors and contrasts, but also by the surface structure. Different pictures can be seen, depending on the direction from which the light is shining.
Mold insert with explosive-stamped holographic structures in its inner ring (Image © Fraunhofer ICT)
Holograms are normally produced with the aid of laser beams, starting by creating a prototype from photosensitive material. However, this template is too soft to be able to act as an embossing or injection-molding tool for holograms. Consequently, the filigree relief-pattern is copied onto a harder material, such as nickel, through electroplating. Mounted on a roller, this nickel shim transfers the hologram onto a plastic film for use on items such as credit cards and concert tickets.
But now researchers at the Fraunhofer Institute for Chemical Technology (ICT) in Pfinztal have come up with the more radical method of using sheet explosives to impress holograms into steel. With the right dosage, explosives enable a template to be copied with far greater accuracy than by conventional methods, they said. The "explosive embossing" method achieves a resolution in the two-figure nanometer range.
“Nobody believed such a thing could be possible,” said ICT project manager Günter Helferich. Almost any structure, such as those made from wood, leather and textiles, can be rapidly and accurately impressed on metal in perfect detail with the aid of a sheet explosive, he said.
The scientists are now working with industrial partners to create steel tools with holographic structures as a "stamp" for applying holograms to plastic parts. The challenge is tremendous: The structures that have to be imprinted into the steel are so tiny that they cannot even be discerned under an optical microscope. The experts have optimized the method to the desired image sharpness through numerous series of experiments.
The advantage of this method over electroplating is that it does not produce a soft nickel piece that quickly wears out, but a hard steel stamp. Steel treated in this way is also in demand in the plastics industry, where many plastic parts now must look attractive, particularly if they are placed in elegant surroundings.
For more information, visit: www.fraunhofer.de/EN
- An interference pattern that is recorded on a high-resolution plate, the two interfering beams formed by a coherent beam from a laser and light scattered by an object. If after processing, the plate is viewed correctly by monochromatic light, a three-dimensional image of the object is seen.
- The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
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