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- 2014 (3)
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- Difficult-to-copy (3) (entfernen)
Solvent-cast films from shape memory poly(ester urethane) (PEU) containing different weight contents of microencapsulated thermochromic pigments (T-PIGs) were prepared by drying in air. Spectrophotometric investigations unveiled that gradual loading with T-PIG black resulted in continuous darkening of the films up to filler contents of 20 wt%, accompanied by a steady enhancement of thermochromic properties. Taking this composition as standard, PEU films equipped with T-PIG black, blue and red were deposited atop PEU plaques to obtain laminate structures. Herein, the cover layer thickness (100 ± 5 µm) and the good dispersion of T-PIGs inside the polymer matrix were verified by scanning electron microscopy. Machine-readable information carriers were prepared by laser engraving quick response (QR) codes into the cover layer of the laminates and subsequently cutting cuboidal samples therefrom. Finally, thermo-mechanical programming of the QR code carriers was applied to randomly distort the code patterns, thus rendering them unreadable. Upon heating, surface decolorization and shape recovering occurred; during the ensuing cooling, the surface color and contrast reappeared whereupon the QR codes could be read out. Spectrophotometric, calorimetric and thermo-mechanical investigations gave evidence that the color switching temperature of the T-PIGs roughly coincided with the melting temperature of the ester-based switching segment and thus with the activation temperature of the shape memory effect. Apart from that unique functionality, manifold design concepts may render information carriers difficult-to-copy. Therefore, we anticipate tremendous potential as anti-counterfeiting technology.
Two design approaches for multifunctional information carriers are introduced. In the first one, quick response (QR) code carriers, which were composed of poly(ester urethane) (PEU) and microencapsulated thermochromic pigments (T-PIGs), differing in color and color switching temperature (CST), were prepared. The obtained material systems exhibited machine-readable QR codes at 23 °C and a two-stage decolorization when heated, culminating in unreadable QR codes at temperatures above the highest CST of the employed T-PIGs. In the second scenario, information carriers were sealed with a dark, thermochromic PEU layer. As a result, the QR codes were hidden at 23 °C and became readable upon heating due to color fading. Beyond the characterization of the employed components, preparation methods, functionality analyses and durability investigations are reported. When heated after thermo-mechanical programming, pronounced shape memory properties could be verified. The thermo-responsiveness of such multifunctional material systems may qualify them for usage in anti-counterfeiting applications.
The selective compression of quick response (QR) and Data Matrix code carriers based on shape memory polymer (SMP) with a freely configurable steel ball type indenter and adjacent thermo-mechanical shape fixing gave notched, room temperature (23 °C) stable, temporary shapes with non-decipherable codes. The microscopic investigation of cryomicrotome sections unveiled indentation-related shape fixities of about 90 %. Independent of the selected two-dimensional code, the triggering of the SM effect resulted in sufficient shape recoveries to restore the code readability so that a maximum number of characters including 122 for a QR code (version 7) and 112 in case of a Data Matrix code (version 12) could be read with a scanning and decoding device. Due to the large number of difficult to copy shapes with on demand releasable information, SMPs may serve as viable information carriers for product and brand protection applications.