Colour laser marking of articles and security documents

摘要

A method for preparing a colour laser marked article comprising the steps of:
a) infrared laser marking a security element including a polymeric support and a colour forming layer comprising a colour forming compound, an infrared dye and a polymeric binder comprising vinyl acetate and at least 85 wt% of vinyl chloride based on the total weight of the binder; and b) exposing the laser marked security element with light having a wavelength higher than 440 nm. The light exposure of step b) hinders the falsification of an issued security document without significant increase of background density.