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Proceedings Paper

New color-shifting security devices
Author(s): Franco Moia
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Paper Abstract

The unbroken global increase of forgery and counterfeiting of valuable documents and products steadily requires improved types of optical security devices. Hence, the "security world" is actively seeking for new features which meet high security standards, look attractively and allow easy recognition. One special smart security device created by ROLIC's technology represents a cholesteric device combined with a phase image. On tilting, such devices reveal strong color shifts which are clearly visible to the naked eye. The additional latent image is invisible under normal lighting conditions but can be revealed to human eyes by means of a simple, commercially available linear sheet polarizer. Based on our earlier work, first published in 1981, we now have developed phase change guest-host devices combined with dye-doped cholesteric material for application in new security features. ROLIC has developed sophisticated material systems of cross-linkable cholesteric liquid crystals and suitable cross-linkable dyes which allow to create outstanding cholesteric color-shifting effects not only on light absorbing dark backgrounds but also on bright or even white backgrounds preserving the circularly polarizing state. The new security devices combine unambiguously 1st and 2nd level inspection features and show brilliant colors on black as well as on white substrates. On tilting, the security devices exhibit remarkable color shifts while the integrated hidden images can be revealed by use of a sheet polarizer. Furthermore, due to its very thin material layers, even demanding applications, such as on banknotes can be considered.

Paper Details

Date Published: 3 June 2004
PDF: 9 pages
Proc. SPIE 5310, Optical Security and Counterfeit Deterrence Techniques V, (3 June 2004); doi: 10.1117/12.530544
Show Author Affiliations
Franco Moia, Rolic Research Ltd. (Switzerland)

Published in SPIE Proceedings Vol. 5310:
Optical Security and Counterfeit Deterrence Techniques V
Rudolf L. van Renesse, Editor(s)

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