In this technical article published July 5th, Dr Glenn Wood of the International Hologram Manufacturers Association looks at some of the latest developments in banknote security technology.
Today, holographic technology remains very much to the fore as part of an array of overt features which make it quick and easy for people to recognise whether or not a banknote is bonafide. But new substrate technology, particularly the introduction of transparent ‘windows’ is being incorporated on banknotes to provide new levels of anti-counterfeiting complexity.
The commemorative 1,000 Tenge note produced by Papierfabrik Louisenthal for Kazakhstan and launched earlier this year takes optical sophistication to a new level. Not only does it feature a hologram showing typical rainbow colours but a small microlenticular patch viewed by transmission. The system is called Varifeye® and combines the best features of paper and polymer.
Previously, a deckle-edge window was created in the paper substrate during the process of cylinder-mould web formation as the stock fibers collect against the deckle, leading to the characteristic feather look. Latterly, the window has been cut into the paper after laminating to a polymeric layer. Then a clear stripe of film is laminated over it running from top to bottom of the note. The clear stripe contains the microlenticular image of a camel interchanging with the letter ‘K’ when tilted.
This feature can be viewed by transmission through the window. There is also a demetallised holographic image of the Astana Baiterek monument above the text ‘Organisation for Security & Co-operation in Europe’, interchanging with the date 2010 which are viewed by reflection where it falls over the paper. (This technology was first used on the Bulgarian lev banknotes in 2005, becoming the world’s first paper notes with see through window).
For polymeric substrates, the Bank of Australia has developed its Non-diffractive Switching Image (NSI). This appears like a dynamic watermark in the clear window of a polymer-based note. Being non-diffractive, the images are seen in varying shades of grey rather than rainbow colours and switching of the image elements occurs by rotation rather than tilting.
One way or another, it seems that the window technology now becoming available to printers of banknotes is here to stay. Formerly, the opaque nature of security printing paper only allowed a watermark to be seen by transmission but most holograms are, by nature, transmissive and are rendered reflective by applying a metal coating. Once the opportunity is presented to allow them to be seen by transmission, as in a window, the opportunities for an optical tour de force are increased. This renders the note more visually attractive to inspectors and consumers and more difficult to simulate by counterfeiters.
To read the complete article, see:
New holographic technology has designs on banknote security
Wayne Homren, Editor
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