Thermoplastic Acrylic Lacquer as a Base for Hot Embossing
- PDF / 3,073,875 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 104 Downloads / 167 Views
0921-T05-01
Thermoplastic Acrylic Lacquer as a Base for Hot Embossing Patrick W. Leech1, and Robert A. Lee2 1 CMIT, CSIRO, Private Bag 33, Clayton South MDC, Clayton, Victoria, 3169, Australia 2 CMIT, CSIRO, Clayton South, Victoria, 3169, Australia ABSTRACT 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 µm were configured to produce diffractive images over an area of ~25 x 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 reflow range for the lacquer, T = 120-150º C, was required in order to achieve a uniform impression across the embossed area of ~80 x 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.
INTRODUCTION Hot embossing has become a key technique in the replication of nanoscale features in polymers [1]. The molding of parallel arrays of nanostructures over large areas has been reported using a range of thermoplastic polymers including PMMA [2,3] polycarbonate [4] and cellulose acetate [5]. A prominent example of the successful application of hot embossing of sub-micron structures has been the fabrication of holograms and complex diffraction gratings known as optically variable devices (OVDs) [6]. In this process, a metal die on the surface of a rotating drum is used in the continuous embossing of a hologram into a lacquer layer in metallised or unmetallised foil. For the master image, the hologram or OVD has traditionally been fabricated by laser interference lithography. However, in recent years, the alternative method of electron beam lithography has provided master images with a sharper definition of shapes and a superior brightness [7,8]. Electron beam lithography has also allowed specification of the diffractive color within each pixel in the device together with the ability to provide a range of optically variable effects not able to be originated by traditional holographic techniques [7,8]. But the standard application of metallised foil as a base for these optically variable devices (OVDs) has imposed a significant additional cost in the fabrication process. The diffractive foil images have required a two stage fabrication process comprising the initial hot embossing of the relief structure followed by a separate stamping of the foil patch onto the security document or component [6]. In this paper, we have examined an alternative process of hot embossing into a thermoplastic acrylic lacquer, eliminating the need for metallised foil. Advantages of acrylic lacquer as a substrate include low cost, thermoplastic properties and the potential for integrati
Data Loading...
