This is an example of an inkjet printed rainbow hologram. Credit: ITMO University
This new method is expected to significantly reduce the cost and time needed to create the so-called rainbow holograms, commonly used for security purposes – to protect valuable items, such as credit cards and paper currency, from piracy and falsification.
The team, led by Alexander Vinogradov, SCAMT in ITMO University, developed colorless ink made of nanocrystalline titania, which can be loaded into an inkjet printer and then deposited on special microembossed paper, resulting in unique patterned images. The ink makes it possible to print custom holographic images on transparent film in a matter of minutes, instead of days as with the use of conventional methods.
“The conventional way of preparing a rainbow hologram is incredibly time-consuming and consists of several stages. First, one needs to create a master hologram, which is usually laser recorded on a thin layer of photosensitive polymer. The polymer is then dried and wash-out to get rid of unexposed parts,” explains Aleksandr Yakovlev. “The resulting stencil is then transferred to a metallic matrix, which eventually serves to emboss holographic microrelief on the surface of a transparent polymer film.”
The new nanocrystalline ink makes it possible to cut the expenditures related to the production of rainbow holograms by several times. The ink is applied with a simple inkjet printer on a microembossed surface, which is afterwards covered by varnish. As a result, the holographic image is exclusively seen in those areas, where the protective ink was deposited.
“The peculiarity of our ink lies in its high refractive index in all visible range of light,” says project supervisor Alexander Vinogradov, “The use of nanocrystalline ink forms a layer with high refractive index that helps preserve the rainbow holographic effect after the varnish or a polymer layer is applied on top.”
The new technique opens the possibility of obtaining holograms of practically any size, makes the process easier and cheaper and, for the first time, leads to the creation of unique custom holograms in a matter of minutes. http://en.ifmo.ru/en/viewnews/5268/Inkjet_Hologram_Printing_is_Possible_Now.htm
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