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,...http://www.google.es/patents/US5830609?utm_source=gb-gplus-sharePatente US5830609 - Security printed document to prevent unauthorized copying
Security printed document to prevent unauthorized copying
