Holographic security device
AssigneeDe La Rue Holographics Limited
InventorsKenneth John Drinkwater, Brian William Holmes
Life of this patent
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Abstract
A holographic effect is generated on a holographic security device by diffraction of light by a surface relief pattern on a film. When illuminated, a moire pattern is generated from a pair of overlapping, regular arrays of lines or dots. Each array has a line of symmetry. The lines of symmetry are aligned. The device exhibits an ordered variation in the form of observed moire patterns in a direction parallel with the alignment direction of the lines of symmetry and a color variation but substantially no form variation transverse to alignment direction.
Claims27
A holographic security device in which a holographic effect is generated by the diffraction of light, the security device comprising a film having a surface relief pattern produced from at least two overlapping, regular arrays of lines or dots which have been holographically recorded on the film using a Benton slit so as to generate a color variation on tilting of the device, each regular array having an axis of mirror symmetry, the axes of mirror symmetry being aligned with each other and in the same plane as the Benton slit, the surface relief pattern adapted to generate a hologram including a moire pattern having an axis of mirror symmetry in the same plane as the Benton slit and exhibiting an ordered variation in the form of the observed moire pattern in a direction parallel with the alignment direction of the axes of mirror symmetry of the at least two arrays and a color variation but substantially no form variation transverse to the alignment direction.
A holographic security device comprising a surface relief on a film, the surface relief produced from a regular array of lines or dots which has been holographically recorded on the film using a Benton slit so as to generate a color variation on tilting the device, the regular array having an axis of mirror symmetry in the same plane as the Benton slit, the security device further comprising a transparent member separate from the film and having another regular array on lines or dots on the transparent member, the another array having an axis of mirror symmetry, the surface relief and the another array on the transparent member, member adapted to generate a moire pattern having an axis of mirror symmetry when the axes of mirror symmetry of the arrays are aligned with each other and in the same plane as the Benton slit, and exhibiting an ordered variation in the form of the observed moire pattern in a direction parallel to the alignment direction, and exhibiting a color variation but substantially no form variation transverse to the alignment direction.
Dependencies are inferred from the claim text.