OPTICAL INTERFERENCE AUTHENTICATING MEANS

摘要

1394021 Credit cards and the like CANADIAN PATENTS & DEVELOPMENT Ltd 1 Jan 1973 [18 Jan 1972] 26/73 Heading B6A [Also in Division G2] An optical interference authenticating arrangement comprises a filter composed of at least one optical interference layer having a known characteristic of spectral reflectance and a different known characteristic of spectral transmittance, both characteristics varying with the angle of incidence. Materials mentioned are cryolite, MgF 2 , SiO, SiO 2 , ThF 4 , ZnS, TiO 2 , ZrO 2 , Ag, Al, Au, Cu, Cr, Ge, Ni, NiCr, Si, and the filter overlies and is attached to a substrate having at least a portion of it surface, adjacent the filter, coloured to absorb some at least of the transmitted light. The substrate may be a bank note, credit card or valuable document, and the filter may be overlain by a transparent polyester film. In one embodiment the filter comprises an anti-reflection layer for the visible spectrum, having high reflectance for the infra-red, on a substrate comprising a black layer or coating which may be applied, e.g. printed, on the bank note &c. Alternatively, the filter may have high reflectance in the visible spectrum and high transmittance in the infra red, the substrate comprising a layer of patterns or inscriptions which may be printed on the bank note &c. In the first embodiment tilting the note increases the amount of light reflected; in the second, tilting causes the patterns &c. to become visible, see Figs. 6 and 7 (not shown).