Mirror Mirror, on the… Note
Micro-mirrors have been in use for banknote security features by Louisenthal, a subsidiary of G+D Currency Technology, for several years now. About 4 million microscopic mirrors per square centimetre are aligned and shaped in such a way that the collective impact of their reflections results in an image that moves dynamically when the banknote is tilted. It even enables 3D effects such as reliefs or the shifting and floating of objects.
"The combination of micro-mirrors with a security coating provides excellent protection against counterfeiting", explains Dr Stefan Bichlmeier, Louisenthal´s Head of Product Management. "In addition, it opens up a whole new world for banknote design. The unique optical effects created by micro-mirror technology on security threads and foils, such as incredibly deep and convincing 3D-effects and the extremely brilliant colours and colour shift effects, are a designer’s dream."
There is a difference in using holograms or using micro-mirror technology when creating 3D-effects: with micro-mirrors the light is reflected by the millions of tiny mirrors. Holograms, on the other hand, are based on light diffraction which, according to Bichlmeier, results in a far more diffuse and darker-seeming image. "The highly efficient light reflection of tiny mirrors achieves an outstanding degree of contrast and contour sharpness even in poor lighting." Micro-mirrors are built by first creating an original based on the design template. The origination process involves a highly specific software calculating the size, viewing angle, and arrangement of the individual mirrors. Then, over several processing stages, a tool is created which is used for production. Micro-mirrors are encapsulated in a layered structure, which prevents them from wearing. The effect is preserved over the lifetime of the banknote and is not harmed by coatings or dirt.
The highly efficient light reflection of tiny mirrors achieves an outstanding degree of contrast and contour sharpness even in poor lighting
Dr. Stefan Bichlmeier, Louisenthal’s Head of Product Management
Attractive and recognisable effects
Louisenthal further reinforces the security of micro-mirror features by sophisticated combinations. "We use special coatings such as for the RollingStar® security threads, which pair micro-mirror technology with multiple, metallic thin film layers in order to create a unique colour switch," says Bichlmeier. "Controlling the thickness of each thin film layer at nano-scale is essential to obtain a precise colour shift effect." In addition to Rollingstar, the technology is utilsied for varifeye® ColourChange foil, the special coating of which causes a motif to be displayed in premium gold in direct light and turns into brilliant blue in transmitted light. "In both cases, the combination of micro- mirrors and special coating ensures not only brilliant appearance and dynamics but also a very high anti-counterfeiting security, a result which has also been proven by independent studies," he notes. Another security feature that works in combination with micro-mirrors is a magnetic signature that ranges from simple yes/no recognition to complex coding.
Increasing demand drives innovation
Banknote series with security threads using micro-mirror technology by Louisenthal have now been in circulation for eight years, in more than 40 denominations. "Over 50 additional denominations are in the pipeline. In addition, the first notes featuring security foils which are applied on to the paper are already in circulation. They include the Armenian 500 dram commemorative note which won the Best Regional Banknote for the EMEA region this year. Further issues of entire series with micro-mirror foils are on the agenda and currently in production – the level of demand is staggering," says Bichlmeier. Louisenthal has increased capacity and continues to invest heavily in R&D to further advance the technology. Progress in data processing means that new effects are constantly being developed in terms of both threads and foils, explains Bichlmeier. Louisenthal is also working on new add-ons and new combination options, with the objective of further enhancing the anti- counterfeiting security of banknotes and unlocking new potential for design.
Further Reading
Galaxy® Security Threads
Clear authentication, high dynamics and 3D effects – Louisenthal has rolled all these properties into an innovative security thread technology. Galaxy is based on tiny microscopic mirrors plus ColourShift, a technology which provides a brilliant visual experience and extreme protection against counterfeiting.
varifeye® ColourChange (Stripe)
The interplay between the translucent window and the changing image is a thing of fascination – but also builds a high barrier for counterfeiters. Synchronizing the window motif with the print image of the note enables fast authentication by the public.
varifeye® ColourChange Patch
Louisenthal’s state-of-the-art patch technology saves space on the banknote while enabling unique designs and instant recognizability. Our patches can be applied with different application systems.