Information carrier with diffraction markings

摘要

An information track 10 formed by a reflection layer (3, Fig. 1) on a thermoplastic substrate (2) and with a thermoplastic lacquer cover layer (4) has diffraction markings 10, 12, 16, 17, 18 which can be altered for purposes of value cancellation by thermal energy and/or stamping or embossing. Markings are both machine readable by infra-red light and visible by the human eye and any alteration is detectable both by machine and eye. The visible alterations may provide different colours or a change between light and dark. The machine readable (5a, Fig. 7) and eye visible (5b) markings may be at different levels in the carrier (24). The carrier may be a pass, identity card, bank note or credit card.