Security printed document to prevent unauthorized copying

Abstract

A paper substrate is laminated with a metalized layer forming a mirrored surface. A partially transparent black diffraction grating is applied by stochastic screening to the mirrored surface. The diffraction grating forms a frequency modulated pattern from selected geometric shapes. Information, such as alphanumeric indicia or graphics, is printed on the stochastic screen to thus form a reflective diffraction device which is printable in a conventional manner while inhibiting reproduction of the printed information by conventional techniques, including black and white and color photo-reproduction and facsimile machines. The partially transparent black stochastic screen forms a diffraction grating on the metalized layer so that when illuminated from the light source of either a specular or diffuse illumination-type photocopier, random interference patterns of light occur at the interface of the metalized surface and the stochastic screen. The diffracted light is not readable by a photocopier drum with the result that the indicia is not legibly reproduced. Thus, the indicia printed on the security document is protected from counterfeiting and unauthorized copying.

Dependencies are inferred from the claim text.