Printed 3D Nanostructures Against Counterfeiting

Security features are to protect bank notes, documents, and branded products against counterfeiting. Losses caused by product forgery and counterfeiting may be enormous. According to the German Engineering Association, the damage caused in 2016 in its branch alone amounted to EUR 7.3 billion. In the Advanced Materials Technologies journal, researchers of Karlsruhe Institute of Technology (KIT) and the ZEISS company now propose to use printed 3D microstructures instead of 2D structures, such as holograms, to improve counterfeit protection.

Today, optical security features, such as holograms, are frequently based on two-dimensional microstructures,” says Professor Martin Wegener, expert for 3D printing of microstructures at the Institute of Nanotechnology of KIT. “By using 3D-printed fluorescent microstructures, counterfeit protection can be increased.” The new security features have a side length of about 100 µm and are barely visible with the eye or a conventional microscope. For their production and application, Wegener and his team have developed an innovative method that covers all processes from microstructure fabrication to the readout of information.

The microstructures consist of a 3D cross-grid scaffold and dots that fluoresce in different colors and can be arranged variably in three dimensions within this grid. To produce and print such microstructures, the experts use a rapid and precise laser lithography device developed and commercialized by the Nanoscribe company, a spinoff of KIT. It enables highly precise manufacture of voluminous structures of a few millimeters edge length or of microstructured surfaces of several cm² in dimension. The special 3D printer produces the structures layer by layer from non-fluorescent and two fluorescent photoresists. A laser beam very precisely passes certain points of the liquid photoresist. The material is exposed and hardened at the focus point of the laser beam. The resulting filigree structure is then embedded in a transparent polymer in order to protect it against damage.


How To Fight Counterfeiting using Inkjet Printing

From water marks to colored threads, governments are constantly adding new features to paper money to stay one step ahead of counterfeiters. Now a longhorn beetle has inspired yet another way to foil cash fraud, as well as to produce colorful, changing billboards and art displays. In the journal ACS Nano, researchers report a new kind of ink that mimics the beetle’s color-shifting ability in a way that would be long-lasting and difficult to copy.
longhorn beetlecolor-changing ink
Zhongze Gu, Zhuoying Xie, Chunwei Yuan and colleagues from SouthEast University (China) explain that some U.S. bills have color-changing features to help thwart attempts by counterfeiters to make fake money. But these features based on the chemical structural changes of dyes, pigments or polymers tend to fade when exposed to light and air. Researchers have been developing a new set of color-changing materials known as colloidal photonic crystals that are bleach resistant. The methods that use these crystals remain expensive, however. Inkjet printing is a fast, precise and low-cost alternative, but until now, researchers had not developed the right inks for making such color-changing and complex patterns. For inspiration, Gu’s team turned to Tmesisternus isabellae, a longhorn beetle that can shift from gold to red and back again, depending on the humidity.