Thermal paper with security features and security ink therefor

摘要

A thermal paper with a latent image (10) derived from a water-based security ink has more than one means of security. A variable light absorbing and/or transmitting pigment or dye in the ink is a first security means, and a water repelling agent in the ink is a second security means. A pseudo-watermark from the coloration of the ink under ambient conditions may be a third security means. Visible images can be generated from the printed ink upon exposure to UV or infrared light. The security ink includes a carrier for said pigment or dye, and the water repelling agent is dispersed in this carrier in an amount sufficient to render the ink waterproof once dried. By virtue of the waterproof nature of the latent image (10), visible images can also be generated by overwriting the latent image (10) with a water soluble ink.