Abstract: The present invention provides a reversible piezochromic system that gives high contrast images upon an application of pressure to the system. The system has a short color-reversal time and can be prepared inexpensively by admixing a suitable electron donating compound and a suitable electron accepting compound. The reversible piezochromic systems of the present invention are useful for preparing a printing ink that can be used to print, for example, banknotes, to prevent forgeries.

Abstract: The present invention provides a reversible thermochromic system that is a two-component system based on an electron donating compound (color former) and an electron accepting compound (developer). A temperature increase to the melting point of the developer causes the system to change from a colorless state to a colored state and a temperature drop below the recrystallization temperature of the developer causes the system to change from the colored state to the colorless state. The thermochromic system of the present invention is applicable to various types of inks, such as a flexographic printing ink, a screen printing ink, a lithographic printing ink, and an intaglio printing ink. The invention also provides a method for preparing the thermochromic system of the present invention.