POLYMER-BASED OPTICALLY VARIABLE DEVICES

摘要

A polymer-based optically- variable device for security applications has a high degree of color uniformity over the device area. The uniformity of thickness of the structure used in such devices is optimized by controlling previously neglected process parameters such as the temperature distribution of the deposition nozzle (32), the substrate (10) and the deposition drum (38), their emissivities, the micro-roughness of the substrate, and the rate of monomer re-evaporation. Re-evaporation is minimized by initiating radiation-curing within two seconds of monomer deposition. The equipment is carefully monitored to eliminate all sources of emissivity non-homogeneities, such as surface blemishes in the surface areas exposed to the substrate (10). Substrates with haziness less than 5% and gloss greater than 90% are preferred. As a result, a maximum thickness variation of less than 5% over the transmissive layer (14) of the optically variable device is found to ensure that no appreciable color- shift variation is visible to the naked eye.