TABLE OF CONTENTS All of the optically variable device technologies described in sections 1 to 3 above have one thing in common. They all use embossed hot stamping foil as the transfer medium for attaching the optical microstructure to the security document requiring protection from counterfeiting. However foil based OVD technology, while in standard use throughout the world today on more than 70 different types of banknotes, is not regarded by security printers as the most preferred protection measure for security documents.
Firstly the foil basis of the technology requires a separate foil production facility and this reduces security, due to the risks associated with the transporting of the security foil to the security printing plant, and adds to production costs because of the need for specialised equipment for hot stamping the foils onto the security document. Secondly, and more recently, a new problem has arisen due to the inherently uncontrolled nature of holographic and diffractive OVD technology and some of its optical effects. Counterfeiters can now buy sophisticated dot matrix (Lee CK et al. 2000) master plate origination technology off-the-shelf so to speak and can also buy the necessary foil embossing and hot stamping technology from other sources. Thirdly the diffraction grating basis of OVD foils has an inherent problem due to the periodic nature of the grating groove structures in most of these devices. The more periodic the grating structure the greater the possibility of holographic copying (McGrew 1990) of the microstructure using holographic contact copying techniques. Counterfeit banknotes...
