Method and device for document security by generating multiple reflective and transmissive latent images

Abstract

The present invention relates to a production method and to a device for document security applications including various latent images on each side. The invention comprises: depositing, according to an established pattern, at least one layer of metallized material, forming a holographic element on at least one part of one of the surfaces of a confinement substrate; defining different regions on the surface of the substrate; inducing different alignment directions for orienting a liquid crystal according to the previously defined regions; doping the liquid crystal with at least one dichroic dye; placing the liquid crystal over at least one confinement substrate, covering the holographic element; adding a second confinement substrate, forming a sandwich-type structure; and polymerizing the liquid crystal, forming a sheet.

1 . A manufacturing method for producing devices for document security including various latent images, characterized in that it comprises the following steps:
 a) depositing, according to at least one established pattern, at least one layer of at least partially metallized material, forming a holographic element on at least one part of one of the sides of at least one confinement substrate;   b) defining different regions on the surface of the at least one substrate;   c) inducing different alignment directions for orienting a liquid crystal according to the previously defined regions;   d) doping the liquid crystal with at least one dichroic dye;   e) placing the doped liquid crystal on at least one confinement substrate, covering the holographic element;   f) adding a second confinement substrate, forming a sandwich-type structure;   g) polymerizing the liquid crystal, forming a sheet.   
     
     
         2 . The method according to  claim 1 , wherein step b) further comprises defining the different regions according to the holographic element deposited on the at least one part of the surface of the substrate. 
     
     
         3 . The method according to  claim 2 , wherein defining the different regions according to the holographic element comprises using micrometric or submicrometric grooves, resulting from the material deposition of step a), for aligning the liquid crystal. 
     
     
         4 . The method according to  claim 1 , wherein it further comprises removing at least one of the confinement substrates once the liquid crystal has been polymerized. 
     
     
         5 . The method according to  claim 1 , wherein defining different regions on the inner face of the confinement substrate comprises at least one of the following techniques:
 photolithography;   masks;   physical barriers;   selective deposition;   thermal evaporation;   inkjet;   micrometric or submicrometric pattern generation;   partial (semireflective) metallization which reflects part of the incident light and transmits the rest;   selective reflective or semireflective metallization which covers a specific area of the device;   or a combination thereof.   
     
     
         6 . The method according to  claim 1 , wherein generating different alignment directions is carried out in any direction parallel to the plane of the confinement substrates, wherein the alignment directions induced on one of the sides of a substrate are independent of those induced in a second substrate and comprise the use of at least one of the following techniques:
 mechanical rubbing of the alignment layer;   photoalignment of a photosensitive material;   oblique deposition of an aligner material;   alignment by means of a micrometric or submicrometric pattern;   generation of a pattern of interdigitated electrodes oriented in different directions on the surface of the confinement plates;   or a combination thereof.   
     
     
         7 . The method according to  claim 1 , wherein the alignments induced in at least two regions are not linear with respect to one another. 
     
     
         8 . The method according to  claim 7 , wherein at least two of the induced alignments are orthogonal with respect to one another. 
     
     
         9 . The method according to  claim 7 , which further comprises determining the relative angle existing between the induced alignment directions to generate different gray levels in the latent image. 
     
     
         10 . The method according to  claim 1 , which further comprises adding an RGB color matrix to generate the latent images, wherein the color matrix is arranged such that the regions defined in the sheet are made to coincide with the pixelation of the matrix on either the outer face of the already polymerized liquid crystal sheet or on the inner face of a protective polymer layer located on the sheet.