madrid2i

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The invention relates to a novel document security and authentication system based on a transparent element on which more than one image appears depending on the manner in which said element is viewed. The system is based on cells or sheets of liquid crystal doped with one or more dichroic dyes. The images obtained with the aid of a polarizer can be printed onto a very thin (µm or 10 tens of a µm) sheet of polymer material; said images may also be in greyscale or in colour. There is no need to apply electrical signals during the production or use thereof.

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1. A procedure for manufacturing sheets having several latent images, fabricated from a polymerizable liquid crystal characterized by the following steps: - to define different areas on the inner face of at least one of the confinement plates; - to condition a number of alignment directions in the areas defined in the previous step; - to dope the liquid crystal with at least one dichroic dye; - to place the doped liquid crystal between two confinement plates; - to polymerize the liquid crystal and to extract the sheet. 2. A method according to claim 1 wherein the step for definition of areas in the confinement plates is carried out selectively on one or both inner sides of the confinement plates by means of one of the following procedures: - photolithography; - masks; - physical barriers; - selective deposition; - thermal evaporation; - ink-jet; or a combination of the above procedures. 3. A method according to claims 1 or 2 wherein the step-of alignment conditioning is done in any direction parallel to the plane of the said confinement plates, following an independent pattern for each plate. The alignment is achieved by at least one of the following procedures: - mechanical buffing of a layer of alignment material; - oblique deposition of alignment material; - photoalignment of a photosensitive material; - use of interdigitated electrodes on the confinement plates; or a combination of the above procedures. 4. A method according to any one of the preceding claims wherein the established alignments of at least two areas of the sheet are non-linear. 5. A method according to claim 4 wherein at least two conditioned alignments are orthogonal to each other. 6. A method according to any one of the claims 1 to 3 wherein the relative angle between conditioned alignments is determined in order to generate different gray levels in the latent image. 7. A method according to any one of the preceding claims wherein a step is introduced in order to add an RGB color matrix to the latent images. 8. A method according to claim 7 wherein the color matrix is set by matching the areas defined in the sheet with the matrix pixelation on the external side of the already polymerized liquid crystal sheet, or the internal side of one of the protection polymer layers of the device. 9. A method according to any one of the preceding claims wherein the doping step is accomplished by depositing a number of different dichroic dyes on the determined areas of the confinement plates thus generating areas with different colors. 10. A device for documental security that includes at least: - a liquid crystal sheet doped with at least one dichroic dye distributed within the predefined areas through some extractable confinement plates, in a way that these predefined areas maintain their orientation according to an alignment pattern that differ in an angle less or equal to 90° in at least one of the faces that form grayscale latent images that become visible when shined with polarized light, - a protection layer on both sides of the liquid crystal sheet protecting the device. 11. A device according to claims 10 wherein a number of dichroic dyes are distributed among the areas defined in the liquid crystal sheets generating different colors. 12. A device according to any one of the claims 10 or 11 wherein the device includes an RGB color matrix located between the liquid crystal sheet and the protection polymer layer. 13. A device according to any one of the claims 10 to 12 wherein the alignments have relative orientations at 0º, 45º, 90º, and 135º to generate two nonoverlapping monochrome images on each side bf the sheet. 14. A device according to any one of the claims 10 to 12 wherein mirror alignments referred to the polarizer axis are employed to generate overlapped images having grayscale. 15. A device according to any one of the claims 10 to 12 wherein the device includes in addition two confinement plates that can be extracted and reused, conditioned to generate a pattern with different areas and orientations on the liquid crystal sheet.

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