Process for producing dichroic security features for securing value documents

A process for producing a security feature for securing a value document, wherein said security feature exhibits a blue color upon viewing in transmitted light and a metallic yellow color upon viewing in incident light, said process comprising the following steps:

• a) printing a UV-Vis radiation curable ink on a transparent or partially transparent region of a substrate of a value document to provide an ink layer;
• b) heating the ink layer obtained at step a) at a temperature of 55° C. to 100° C. for at least one second so that the ink layer exhibits a metallic yellow color upon viewing in incident light;
• and
• c) UV-Vis curing the ink layer obtained at step b) to form the security feature;
• wherein the UV-Vis radiation curable ink comprises:
• i) silver nanoplatelets having a mean diameter in a range of 50 to 150 nm with a standard deviation of less than 60%, a mean thickness in a range of 5 to 30 nm with a standard deviation of less than 50%, and a mean aspect ratio higher than 2.0, wherein the mean diameter is determined by transmission electron microscopy and the mean thickness is determined by transmission electron microscopy;
• ii) from 40 wt-% to 75 wt-% of either a cycloaliphatic epoxide, or a mixture of a cycloaliphatic epoxide and one or more UV-Vis radiation curable compounds other than the cycloaliphatic epoxide;
• iii) one or more cationic photoinitiators;
• iv) a polyvinyl chloride copolymer containing at least 69 wt-% of vinyl chloride;
• v) a perfluoropolyether surfactant functionalized with one or more functional groups selected from the group consisting of:
• hydroxyl, acrylate, and methacrylate;
• and
• vi) 0-25 wt-% of an organic solvent;
• a weight percent of ii), and vi) being based on a total weight of the UV-Vis radiation curable ink.