The joint project combined the developments of KRYPTEN’s Holographic Laboratory in the field of polarised hidden images – HITTM (Hidden Image Technology) and SMART-HITTM – and studies from ITMO University connected with the invention of ink based on cellulose nanoparticles. As a result, commercial inkjet printing technology for hidden images was obtained.
During their work, the researchers explored methods for the chemical synthesis of the ink and found new ways to apply the ink to a surface. The group developed programmes to apply the ink through inkjet printing to control the orientation of cellulose nanoparticles suspended in the ink to create an optical effect of coloured images visible only in polarised light.
Explaining the motivation behind the research, Andrey Smirnov, Head of KRYPTEN’s Holographic Laboratory said: ‘in Russia, there is mandatory labelling for a whole group of goods to trace their circulation from manufacturing to sale. However, this system does not guarantee package integrity and does not protect it against replacement of its contents. We actively cooperate with the leading Russian universities, study new methods of optical protection of goods against counterfeiting and develop security features ensuring the authenticity of goods’.
He also noted that ‘the project with our colleagues from ITMO’s Chembio Cluster (a network of leading research laboratories) offers new prospects for applying polarised latent images in protecting goods. NANOPRINT is a robust and cost-efficient technology manufacturers can use to protect their goods against counterfeiting’.
The new ink consists of special particles about 10 nanometres wide and around 200 nanometres long. In the initial solution they are organised chaotically. NANOPRINT technology modifies the properties of nanoparticles in the solution (applying an electric field to exert an ionic force) so that the particle dynamics arranges them parallel to each other.
As a result, cellulose nanoparticles are arranged on the surface, not in a random order, but along an axis and form a specific ordered structure. After drying, the ink creates an optically active coating. A certain thickness of image is set to create the polarised effect. The interference effect is obtained when the coating thickness is at least 10 microns.
The technology allows printing of high-resolution image elements, including digits, letters, logos and patterns that offer new opportunities for protecting goods against counterfeiting. Hidden images are visualised in polarised light from a smartphone, LCD screen or ordinary polariser. Product identification does not require any complex devices or equipment. The effect of the invisible image might capture the buyer’s attention, as well as proving the authenticity of the product.
Nanocrystalline cellulose ink offers the prospect of reducing the cost of hidden image printing compared to more expensive liquid crystals featuring similar optical effects. Inkjet printing is a fast and relatively inexpensive method of commercial printing which would make it feasible to use NANOPRINT technology in the serial production of security features to protect documents, packaging or applied to security labels.