Separating Information on Transparent Polypropylene Labels on Packaging with Dual Properties for the Visible Spectrum and Instrumental Infrared Observation

Transparent linear NIR digital graphics with the intention of security information were printed on a polypropylene material. A label for expensive juices in transparent glass or plastic packaging is demonstrated. Obligatory information about the contents of the liquid was made to be read with the naked eye. The "Z" (near-infrared) information is expanded with data integrated for joint digital printing. This data does not disrupt the original, planned visual appearance of the label, "V" (visible). Although the two graphics are in the same place, the IR graphics on the label cannot be discerned with the naked eye. This brings elements of secrecy and protection against attempts to counterfeit the contents of the transparent packaging. The separation and recognition of the two pieces of information, V and Z, are achieved with a security camera in the near-infrared mode or with one of the many NIR detectors that surround us. In the article, the "VZ" algorithm for the integration of two independent graphics and the limitations set by digital printing are published. Toner properties and the method for developing the recipes for the composition of twin colorants for two spectral ranges are presented using spectroscopy.

Anti-Counterfeiting White Light Printed Image Multiplexing by Fast Nanosecond Laser Processing

Passive plasmonic metasurfaces enable image multiplexing by displaying different images when altering the conditions of observation. Under white light, three-image multiplexing with polarization-selective switching has been recently demonstrated using femtosecond-laser-processed random plasmonic metasurfaces. Here, the implementation of image multiplexing is extended, thanks to a color-search algorithm, to various observation modes compatible with naked-eye observation under incoherent white light and to four-image multiplexing under polarized light. The laser-processed random plasmonic metasurfaces enabling image multiplexing exhibit self-organized patterns that can diffract light or induce dichroism through hybridization between the localized surface plasmon resonance of metallic nanoparticles and a lattice resonance. Improved spatial resolution makes the image quality compatible with commercial use in secured documents as well as the processing time and cost thanks to the use of a nanosecond laser. This high-speed and flexible laser process, based on energy-efficient nanoparticle reshaping and self-organization, produces centimeter-scale customized tamper-proof images at low cost, which can serve as overt security features.

Lanthanide Polyoxometalate Based Water-Jet Film with Reversible Luminescent Switching for Rewritable Security Printing

Luminescent security printing is of particular importance in the information era. However, the use of conventional paper still carries a lot of economic and environmental issues. Therefore, developing new environmentally friendly security printing material with a low cost is imperative. To achieve the aforementioned goals, novel lanthanide polyoxometalate doped gelatin/glycerol films with high transparency, high strength, and good flexibility have been developed via a solution-casting method. The electrostatic interaction between zwitterionic gelatin and polyoxometalate was confirmed by attenuated total reflection Fourier transform infrared spectroscopy. Luminescent spectra and digital images indicated that the films exhibited reversible luminescent switching properties through association and dissociation of hydrogen bonds between glycerol and water molecules, allowing its potential application as water-jet rewritable paper for luminescent security printing. Furthermore, the printed information can be conveniently "erased" by heating, and the film can be reused for printing. The film exhibited excellent ability to be both rewritten and re-erased. A QR code pattern and hybrid printing were employed to improve the security of information. In addition, the rewritable films possessed excellent regeneration ability and low toxicity, as well as good stability against UV irradiation and organic solvents. The water-jet rewritable film based on lanthanide polyoxometalate for luminescent security printing, to the best of our knowledge, has not yet been reported up to date. This work provides an attractive alternative strategy on fabricating rewritable films for luminescent security printing in terms of cutting down the cost, simplifying the preparation process, and protecting the environment.

Hyperspectral Imaging of Photonic Cellulose Nanocrystal Films: Structure of Local Defects and Implications for Self-Assembly Pathways

Cellulose nanocrystals (CNCs) can spontaneously assemble into chiral nematic films capable of reflecting circularly polarized light in the visible range. As many other photonic materials obtained by bottom-up approaches, CNC films often display defects that greatly impact their visual appearance. Here, we study the optical response of defects in photonic CNC films, coupling optical microscopy with hyperspectral imaging, and we compare it to optical simulations of discontinuous cholesteric structures of increasing complexity. Cross-sectional SEM observations of the film structure guided the choice of simulation parameters and showed excellent agreement with experimental optical patterns. More importantly, it strongly suggests that the last fraction of CNCs to self-assemble, upon solvent evaporation, does not undergo the typical nucleation and growth pathway, but a spinodal decomposition, an alternative self-assembly pathway so far overlooked in cast films and that can have far-reaching consequences on choices of CNC sources and assembly conditions.

Multifunctional Random-Laser Smart Inks

With the superiority of laser-level intensity, narrow spectral line width, and broad-angular emission, random lasers (RLs) have drawn considerable research interests for their potential to carry out a variety of applications. In this work, the applications associated with optical-encoded technologies, including security printing, military friend or foe identification (FFI), and anticounterfeiting of documents are highlighted, and the concept of a transient RL "smart ink" has been proposed. The proof-of-concept was demonstrated as invisible signatures, which encoded the messages through the spectral difference of spontaneous emission and RL under specified conditions. Next, the possibility of encoding the data with multibit signals was further confirmed by exploiting the threshold tunability of RLs. Moreover, the transient characteristic of this smart ink and its capability to be attached on freeform surfaces of different materials were also shown. With the advantages of a facile manufacturing process and multiple purposes, it is expected that this ink can soon be carried out in a variety of practical utilities.

Inkjet-Printable Hydrochromic Paper for Encrypting Information and Anticounterfeiting

Developing rewritable papers has gathered immense interest in recent times in view of developing sustainability in print media without exhausting environmental resources. We herein present a rapid and facile procedure for the fabrication of a communication medium by treating the surface of a paper with synthetic organic molecules, after which plain water could be used as an ink to print and reprint numerous times on the treated paper before disposal. Interestingly, as the paper comes in contact with water, the molecules are driven to reorganize in a slip-stacked arrangement. This alters their ground and excited state properties by hydrogen-bond-assisted nonradiative decay, in which the associated changes are visible to the naked eye. The changes evolved are sensitive to the solubility parameter of the solvent and thermally reversible, thus linking the hydrochromic property to the paper. Against a background of concerns over a rise in counterfeiting and leaks of confidential information, prospects for encrypted communications and anticounterfeiting is herein demonstrated.

Conjugated polymer dots for ultra-stable full-color fluorescence patterning

Stable full-color fluorescence patterning are achieved by multicolor polymer-dot inks. The fluorescent patterns show extraordinary stability upon various treatments, offering a superior combination of bright fluorescence, excellent photostability, chemical resistance, and eco-friendship.