Printing inks with reversible photochromic properties.

摘要

Photochromic printing inks are disclosed which are in particular used for the printing of security documents. Prints are normally nearly colorless and become colored when energy irradiated, such as by ultraviolet light. This photocoloration is reversible. The printing inks contain photochromic compounds which are protected against oxygen and other ink components. Methods are described to prepare the inks, to print security doc­uments, and to detect counterfeiting.