Hot embossing of grating-based optically variable images in thermoplastic acrylic lacquer

We report the novel use of thermoplastic acrylic lacquer (automotive paint) in the hot embossing of nanoscale structures. Replicas of grating arrays have been produced in coatings of acrylic lacquer using a standard embossing process. The master dies for the experiments comprised grating arrays fabricated by electron beam lithography. Grating patterns with a pitch of 0.7–1.3 lm were configured to produce diffractive images over an area of ~25 · 25 mm. The embossing experiments used a replicated Ni shim as a die and were performed at 100–150 C and 80 kN force. A temperature above the glass transition temperature for the lacquer, T = 120–150 C, was required in order to achieve a uniform impression across the embossed area of ~80 · 80 mm. The diffractive grating patterns which were embossed into acrylic lacquer have shown optical effects suitable as a security feature including image switching and color movement.