Optical security articles and methods of making same are described comprising a first layer substantially transparent to visible light and having a first refractive index, the first layer having a relief pattern on a first surface thereof and a substantially smooth second surface, and an adhesive layer...http://www.google.fr/patents/US5591527?utm_source=gb-gplus-shareBrevet US5591527 - Optical security articles and methods for making same
Optical security articles and methods for making same
