Field activated security articles including polymer dispersed liquid crystals, and including micro-encapsulated field affected materials

Abstract

In a first aspect this invention provides a security article comprising an electrically actuated optical switch comprised of a liquid crystal material. In one embodiment the liquid crystal material is disposed in a layer of polymer dispersed liquid crystal material. In a second embodiment the liquid crystal material is microencapsulated with an orientable dye. In a second aspect this invention provides a document or currency that comprises a paper matrix that includes at least one security article, i.e. a security thread. In a third aspect this invention provides a device for verifying an authenticity of a document or currency of a type that includes at least one security article, i.e. at least one security thread. The at least one security thread includes the liquid crystal material having a visual characteristic that is switched between two states as a function of a presence or absence of an electric field between first and second electrodes. In one embodiment the device for verifying the authenticity of the document or the currency includes an external pump source for generating a stimulated emission the at least one security article disposed within the document or currency. In one embodiment the external pump source includes a pulsed Nd:YLF laser, a frequency doubling KTP crystal and a device to provide stimulated Raman scattering.

What is claimed is:  
     
         1 . A security thread, comprising an electrically actuated optical switch comprised of a layer of polymer dispersed liquid crystal (PDLC) material, wherein said polymer is comprised of an ink.  
     
     
         2 . A security thread as set forth in    claim 1   , wherein said electrically actuated optical switch is responsive to an applied electric field for varying a visual characteristic of said security thread.  
     
     
         3 . A security thread as set forth in    claim 1   , wherein said electrically actuated optical switch is responsive to an applied electric field for varying a visual characteristic of an indicia formed with said ink.  
     
     
         4 . A document or currency, comprising a paper matrix that includes at least one security thread, said at least one security thread being comprised of at least one layer of electrically actuated polymer dispersed liquid crystal material, wherein said polymer is comprised of an ink.  
     
     
         5 . A device for verifying an authenticity of a document or currency of a type that includes at least one security thread, comprising first and second electrodes and an excitation source coupled to said electrodes, said first and second electrodes being spaced apart for accommodating therebetween said document or currency, at least one of said electrodes being transparent, said at least one security thread being comprised of at least one layer of polymer dispersed liquid crystal material having a visual characteristic that is switched between two states as a function of a presence or absence of an electric field between said first and second electrodes, wherein said polymer is comprised of an ink.  
     
     
         6 . A security thread, comprising an electrically actuated optical switch comprised of a patterned layer of polymer dispersed liquid crystal material, wherein said polymer is comprised of an ink.  
     
     
         7 . A security article, comprising a plurality of micro-capsules which include liquid crystal material and an orientable dye.  
     
     
         8 . A security article as set forth in    claim 7   , wherein each of said plurality of micro-capsules is comprised of a capsule of diameter in a range of about two to hundreds of micrometers.  
     
     
         9 . A document or currency, comprising a matrix that includes at least one security article, said at least one security article being comprised of a plurality of micro-capsules that contain electrically actuated, liquid crystal material.  
     
     
         10 . A document or currency as set forth in    claim 9   , wherein said at least one security article is comprised of a security thread that includes said plurality of micro-capsules.  
     
     
         11 . A document or currency as set forth in    claim 9   , wherein said at least one security article is comprised of a security ink disposed on or within said matrix, said security ink comprising said plurality of micro-capsules.  
     
     
         12 . A security object, comprising a plurality of micro-capsules each containing liquid crystal material and at least one orientable dye for enhancing a contrast between on and off states of said liquid crystal material.  
     
     
         13 . A security article, comprising at least one layer that contains an optical gain medium and a plurality of micro-capsules that contain an electrically actuated optical switch comprised of liquid crystal material.  
     
     
         14 . A security article as set forth in    claim 13   , wherein when excited said optical gain medium emits a laser-like emission of one of a desired color or a desired wavelength.  
     
     
         15 . A security article, comprising at least one layer comprised of a plurality of micro-capsules that contain liquid crystal material and a material for generating a stimulated emission, in response to an optical pump, and electrically activated scattering sites for scattering said stimulated emission.  
     
     
         16 . A method of forming a security article comprising the steps of: 
 combining a liquid crystal material and an orientable dye; and    micro-encapsulating the liquid crystal material and the orientable dye to form the security article.    
     
     
         17 . A method of forming a security article as set forth in    claim 16   , further comprising the step of drying the micro-capsules to obtain a powder.  
     
     
         18 . A method of forming a security article as set forth in    claim 17   , wherein the powder is intermixed with a security ink disposed on or within a matrix.  
     
     
         19 . A method of forming a document or currency comprising the steps of: 
 combining a liquid crystal material and an orientable dye;    micro-encapsulating the liquid crystal material and the orientable dye;    drying the micro-capsules to obtain a powder; and    intermixing the powder with a security object disposed on or within a matrix of the document or currency.    
     
     
         20 . An optical source for exciting a security article that contains an optical gain medium, said optical source comprising: 
 a laser having an output providing light having a first wavelength;    a frequency doubler that is optically coupled to said laser output for converting a portion of said light to frequency doubled light, said frequency doubler having an output providing frequency doubled light having a second wavelength;    coupled to said output of said frequency doubler, means for shifting said frequency doubled light to light having a longer wavelength than said second wavelength; and    means for conveying said light having said longer wavelength to a region of interest which contains at least one security article disposed therein.    
     
     
         21 . An optical source as set forth in    claim 20   , wherein said laser is comprised of one of a Nd:YLF laser and a Nd:YAG laser.  
     
     
         22 . An optical source as set forth in    claim 20   , wherein said light having said first wavelength is comprised of light having one of a 1.053 micrometer wavelength and a 1.06 micrometer wavelength.  
     
     
         23 . An optical source as set forth in    claim 20   , wherein said frequency doubled light having said second wavelength is comprised of light having one of a 526.5 nm wavelength and a 532 nm wavelength.  
     
     
         24 . An optical source as set forth in    claim 20   , wherein said shifting means is comprised of means for performing stimulated Raman scattering.  
     
     
         25 . A security article, comprising one of thin micron scale fibers, planchets and particles which include a substrate and containing gain media, wherein said security article produces a laser-like emission when excited by an external source.  
     
     
         26 . A security article as set forth in    claim 25   , wherein when said laser-like emission is comprised of specific narrow band wavelengths used to authenticate a document which contains said security article disposed therein.