OPTICAL BIOMETRIC SECURITY ELEMENT

Abstract

This invention relates to an optical element for the purpose of identification and/or prevention of forgery or copying, including at least one layer with anisotropic optical properties, wherein the anisotropic optical properties are patterned, characterized in that the pattern represents biometric information. In addition, this invention relates to a method for the preparation of an optical element for the purpose of identification and/or prevention of forgery or copying.

Claims

1. Method for the preparation of an optical element containing biometric information, comprising the steps of providing an aligning surface, transferring the biometric information into the aligning surface by modifying the initial aligning properties of the aligning surface, coating polymerizable liquid crystals on top of the aligning surface, and starting polymerization of the liquid crystals by thermal or photo-initiation after the liquid crystals are aligned.

2. Method for the preparation of an optical element comprising biometric information, comprising the steps of providing an aligning surface, transferring the biometric information into the aligning surface by modifying the initial aligning properties of the aligning surface, and coating polymerized liquid crystal material on top of the alignment layer.

3. Method according to claim 1, wherein the aligning surface is that of a layer of a photo-alignment material and the properties of the aligning surface are locally modified by transferring the biometric information into the photo-alignment material by exposure to aligning light in the form of an orientation pattern.

4. Method according to claim 3, wherein in the step of transferring the biometric information into the photo-alignment material by exposure to aligning light a photo-mask is used, which has been produced by printing the pattern representing the biometric data to a transparent substrate.

5. Method according to claim 3, wherein in the step of transferring the biometric information into the photo-alignment material by exposure to aligning light an alignment master is used to generate the orientation pattern.

6. Method according to claim 3, wherein a substrate, on which a fingerprint was directly generated by pressing a finger to the substrate surface, is used as a photo-mask for the generation of the orientation pattern.

7. Method according to claim 2, wherein the initial aligning properties of the aligning surface are modified by directly putting a fingerprint on top of the aligning surface.

8. Method for the preparation of an optical element containing biometric information, which comprises the steps of local deposition of an aligning layer material to a substrate, applying alignment treatment to the aligning layer to generate a defined orientation direction in the deposited material, coating polymerizable or polymerized liquid crystal material on top of the alignment layer, and optionally starting polymerization of the liquid crystals by thermal or photo-initiation after the liquid crystals are aligned.

9. Method for the preparation of an optical element containing biometric information, which comprises printing polymerizable or polymerized liquid crystal material to a substrate in the form of a pattern desired to represent the biometric information.

10. Method according to claim 9, wherein the substrate exhibits an aligning surface.

11. Method for the preparation of a patterned liquid crystal polymer layer containing biometric information for the purpose of identification and/or prevention of forgery and copying, comprising the steps of printing or coating a layer of polymerizable liquid crystals to a substrate with an aligning surface, exposing the layer of polymerizable liquid crystals to actinic light through a photomask to locally initiate polymerization of the liquid crystals, heating the layer to an elevated temperature, and exposing at least part of the non-polymerized areas to actinic light to initiate polymerization of the liquid crystal material in those areas.

12. Method for the preparation of a patterned liquid crystal polymer layer containing biometric information for the purpose of identification and/or prevention of forgery and copying, comprising the steps of printing or coating a layer of polymerizable liquid crystals to a substrate with an aligning surface, exposing the layer of polymerizable liquid crystals to actinic light through a photomask to locally initiate polymerization of the liquid crystals, and removing areas which are not polymerized with a solvent, which can dissolve such polymerizable liquid crystals.

13. Method according to claim 1, wherein the biometric information comprises a fingerprint.

14. Method according to claim 1, wherein the biometric information comprises a fingerprint.

15. Method according to claim 1, characterized in that the liquid crystal material contains dichroic molecules.

16. Method of using an optical element, comprising incorporating the optical element as a security element in a security device, wherein the optical element is an optical element for the purpose of identification and/or prevention of forgery or copying, comprising at least one layer with anisotropic optical properties, wherein the anisotropic optical properties are patterned, characterized in that the pattern represents biometric information.

17. Method according to claim 16, wherein the security device is applied to or incorporated into a security document selected from the group consisting of an identity card, passport, driver license, certificate, birth certificate, credit card, badge, and ticket.

18. Optical element produced according to the method of claim 1.

Description

[0109] The invention will now be described by way of example with reference to the accompanying drawings, in which:

[0110] FIG. 1a shows the photo of a photo-mask of a fingerprint, generated by a direct contact method;

[0111] FIG. 1b shows a photo of an optical element according to the invention comprising a fingerprint pattern by a method of direct transfer of the fingerprint pattern into the liquid crystal layer, as observed between crossed polarizers.

[0112] FIGS. 2a and 2b show an optical element according to the invention as observed between crossed polarizers, comprising a fingerprint pattern in a liquid crystal layer by a method of indirect transfer of the fingerprint pattern, which was first transferred into a photo-alignment layer. The photo-mask of FIG. 1a was used for LPP exposure.

[0113] FIG. 2a shows a photo of the positive image.

[0114] FIG. 2b shows a photo of the negative image which appears when the optical element is rotated by 45 compared to the arrangement in FIG. 2a.

[0115] FIG. 3 shows a photo of an optical element according to the invention comprising a birefringent signature between crossed polarizers. The signature was handwritten with a liquid crystal material to a substrate comprising an alignment layer.

[0116] FIG. 4 shows a photo of an optical element according to the invention comprising a birefringent, patterned signature between crossed polarizers. The signature was written with a liquid crystal material to a substrate comprising an alignment layer exhibiting an orientation pattern.

[0117] FIG. 4 shows a direct photo in section a);

[0118] FIG. 4 shows an observation in a polarizing microscope in section b); and

[0119] FIG. 4 shows an observation in a polarizing microscope in section c), but with polarizer and analyzer rotated by 45 compared to section b).

EXAMPLES

[0120] Photo-alignment material LPP1 used in the following examples has the following chemical structure:

##STR00001##

Example 1

[0121] Composition of the Polymerizable Liquid Crystal Material M1 Designed for Generation of Patterns of Optical Retardation

TABLE-US-00001 Weight Compound (%) 2,5-bis-[4-6-acryloyloxyhexyloxy)benzoyloxy]benzoic acid 91.4 pentyl ester prepared in analogy to Schemes 1, 2, 3, 4 of U.S. Pat. No. 5,593,617 Pentaerythritol tetrakis(3-mercaptopropionate) 5.0 [00002] Irgacure 369, photoinitiator, 2-benzyl-2-dimethylamino- 3.0 1(4-morpholinophenyl)-butanone-1 from CIBA Specialty Chemicals Inc. Tinuvin 123, bis(1-octyloxy-2,2,6-tetramethyl-4- 0.5 piperidyl)sebacate from CIBA Specialty Chemicals Inc. Hydrochinon-monomethylether, from Aldrich 0.1

[0122] The clearing temperature of this composition is T.sub.c44 C.

Example 2

[0123] Composition of the Polymerizable Liquid Crystal Material M2

TABLE-US-00002 Compound Weight (%) 2,5-bis-[4-6-acryloyloxyhexyloxy)benzoyloxy]benzoic 97.0 acid pentyl Ester, prepared in analogy to Schemes 1, 2, 3, 4 of U.S. Pat. No. 5,593,617 Irgacure 369, photoinitiator, 2-benzyl-2- 1.0 dimethylamino-1(4-morpholinophenyl)- butanone-1 from CIBA Specialty Chemicals Inc. Tinuvin 123, bis(1-octyloxy-2,2,6-tetramethyl- 1.0 4-piperidyl) sebacate from CIBA Specialty Chemicals Inc. Butyl-hydroxy-toluol, from Aldrich 1.0

[0124] The clearing temperature of this composition is T.sub.c55 C.

Example 3

[0125] Composition of the Polymerizable Liquid Crystal Material M3 Containing Dichroic Dyes

TABLE-US-00003 Weight Compound (%) 2,5-bis-[4-6-acryloyloxyhexyloxy)benzoyloxy]benzoic acid pentyl Ester, prepared in analogy to Schemes 1, 2, 3, 4 of U.S. Pat. No. 88.0 5,593,617 Dichroic dye, prepared in analogy to WO2004/085547 10.0 [00003] Irgacure 369, photoinitiator, 2-benzyl-2-dimethylamino-1(4-morpholinophenyl)-butanone-1 from CIBA Specialty Chemicals Inc. 1.0 Butyl-hydroxy-toluol, from Aldrich 1.0

Example 4: Preparation of a Fingerprint Optical Element Using Photo-Patternable LCP Materials and a Development Process

[0126] A photomask was prepared by direct contact printing a fingerprint to a plate of fused silica. For this purpose the right index finger was inked using a fingerprint pad from I.D. Technologies. The finger was pressed to the pad and rolled from right to left during pressing. After the finger was inked it was pressed to the fused silica substrate and rolled from the right side to the left side during pressing. This process has transferred the fingerprint to the fused silica plate, which was now ready to be used as a photomask for generating an optical element according to the present invention.

[0127] Then a solution of the photo-alignment material LPP1 with a solid content of 2 weight percent in cyclopentanone was spin-coated at 2000 rpm for 60 s to a D263 glass plate to form a photo-alignment layer with a dry thickness of approximately 60 nm. The alignment layer was subsequently thermally treated on a hot-plate for 10 minutes at a temperature of 180 C. After that, the photo-alignment layer was exposed to linearly polarized UV light (LP-UV) (wavelengths between 280 and 320 nm) from normal direction. A dose of 150 mJ/cm.sup.2 was applied at an intensity of 3 mW/cm.sup.2. This process is known to induce alignment for liquid crystals in the LPP1 layer, which is parallel to the polarisation direction of the LP-UV light. In a next step, a 25 weight percent solution in cyclopentanone of the formulation M1 (Example 1) was spin-coated on top of the functionalized photo-alignment layer at 800 rpm during 60 s. A dry film thickness of approximately 800 nm was achieved this way. A thermal treatment at a temperature of 40 C. on a hot-plate was then carried out for 10 minutes. After that, a patterned UV-radiation using the mask of the fingerprint was done. For this, the film was exposed to collimated light through the black and white mask carrying the fingerprint pattern. The mask was kept at a distance of approximately 15 micron from the surface of the liquid crystalline layer using plastic spacers. Local polymerization of the liquid crystal layer was photo-Initiated by illuminating it through the mask with UV-A light of a dose of 500 mJ/cm.sup.2 under air atmosphere. After that, a development process was conducted by dipping the substrate with the prepared layers in ethyl-acetate for 10 seconds to remove the unpolymerized material.

[0128] The optical element which resulted was transparent and the fingerprint could not be seen. After arranging the optical element between crossed polarizers with the orientation direction of the LPP layer at 45 to the polarisation axis of the polarizers, the fingerprint texture could be seen with high contrast, as is demonstrated by the photo in FIG. 1b.

Example 5: Preparation of a Fingerprint Optical Element Using Photo-Patternable LCP Materials and a Curing Process at Higher Temperature

[0129] The same process for the preparation of the LPP layer and the liquid crystal layer including the exposure steps was used as in example 4 except that instead of carrying out a development process a second polymerization of the unexposed LCP zones was applied at a temperature above the clearing temperature of mixture M1. After the first UV exposure of the LCP layer, the sample was heated to 60 C. by means of a hot-plate, and a second radiation with non-collimated light of 500 mJ/cm2 (UVA and UVB) at 50 mW/cm2 was carried out without a mask in air atmosphere at 60 C.

[0130] After completing the above process observation of the optical element between crossed polarizers showed that the LCP areas that were crosslinked during the first curing process were birefringent whereas the areas crosslinked during the second process were isotropic. The optical appearance of the optical element was the same as that of example 4.

Example 6: Preparation of a Fingerprint Optical Element Using Retardation Patterning Obtained with Two LCP Layers

[0131] A photo-aligned layer was prepared on a substrate as described in example 4. On top of the LPP layer a polymerizable liquid crystalline composition M1 was coated and homogeneously UV-irradiated without a mask to polymerize the layer.

[0132] Then a second layer of the polymerizable liquid crystalline formulation M1 was spin-coated on top of the first polymerized liquid crystalline layer with the spin parameters of 800 rpm during 60 s. For this, a 25 weight percent solution in cyclopentanone was used. A dry film thickness of approximately 800 nm was achieved this way. A thermal treatment at a temperature of 40 C. on a hot-plate was then carried out for duration of 10 minutes. After that, a patterned radiation curing of the LCP-layer with collimated light through a photo-mask exhibiting a fingerprint pattern was done. The UV dose was 1000 mJ/cm.sup.2 (UVA and UVB) at 8 mW/cm.sup.2. The mask was kept at a distance of approximately 15 micron from the surface of the liquid crystalline layer.

[0133] Then the film was processed as described in example 5, whereby the unexposed zones were polymerized above the clearing temperature of composition M1.

[0134] In this case, no additional photo-alignment layer was used in between the two liquid crystal polymer films. Thus, the second, patterned liquid crystal polymer film is aligned parallel to the first one.

[0135] The resulting optical element was transparent and no Image could be observed in non-polarized light. When the element was arranged between crossed polarizers the fingerprint texture could be seen consisting of two different gray levels. The two gray levels were caused by areas with higher retardation corresponding to the sum of the retardations of the two liquid crystal polymer films and areas with lower retardation corresponding to the retardation of only the lower, un-patterned liquid crystal polymer film.

[0136] The same optical performance could have been achieved when a birefringent film were used instead of the first LCP film. In this case the birefringent film could have been used as the substrate as well.

Example 7: Preparation of a Fingerprint Optical Element Using Retardation Patterning with Two LCP Layers Whereby the Alignment of the Second LCP Layer is Perpendicular to the First Layer

[0137] A first LPP layer and a first LCP layer were prepared on a substrate like in example 6. Then, by means of spin-coating a solution of LPP1 with a solid content of 2 weight percent in cyclopentanone, a second alignment layer with a dry thickness of approximately 60 nm was prepared on top of the first LCP layer with the spin parameters of 2000 rpm during 60 s. The alignment layer was subsequently thermally treated on a hot-plate for 10 minutes at a temperature of 180 C. After that, the photo-alignment layer was exposed to LP-UV light (wavelengths between 280 and 320 nm) with the polarisation axis chosen to be perpendicular to the orientation direction of the first alignment layer. A dose of 150 mJ/cm.sup.2 was applied at an intensity of 3 mW/cm.sup.2.

[0138] Then a second layer of polymerizable liquid crystal material was prepared using a 25 weight percent solution of M1 in cyclopentanone. The solution was spin-coated on top of the second alignment layer at 800 rpm for 60 s. A dry film thickness of approximately 800 nm was achieved this way. A thermal treatment at a temperature of 40 C. on a hot-plate was then carried out for duration of 10 minutes.

[0139] After that, a patterned radiation curing of the LCP-layer with collimated light through a photo-mask exhibiting a fingerprint pattern was performed. The UV dose was 1000 mJ/cm.sup.2 (UVA and UVB) at 8 mW/cm.sup.2. The mask was kept at a distance of approximately 15 micron from the surface of the liquid crystalline layer. Then the film was processed as described in the example 5.

[0140] The resulting optical element was transparent and no image could be observed in non-polarized light. When the element was arranged between crossed polarizers the fingerprint texture could be seen consisting of two different gray levels.

Example 8: Preparation of a Fingerprint Optical Element Using Photo-Patterning of the Photo-Alignment Layer

[0141] A solution of the photo-alignment material LPP1 with a solid content of 2 weight percent in cyclopentanone was spin-coated at 2000 rpm for 60 s to a D263 glass plate to form a photo-alignment layer with a dry thickness of approximately 60 nm. The alignment layer was subsequently thermally treated on a hot-plate for 10 minutes at a temperature of 180 C. After that, the photo-alignment layer was twice exposed to LP-UV light (wavelengths between 280 and 320 nm). The first dose of 200 mJ/cm.sup.2 was locally applied on the photo-alignment material at an intensity of 3 mW/cm.sup.2 using the mask of a fingerprint. In a second step, the mask was removed and the UV-polarisation plane was adjusted at 45 relative to that of the first exposure and a second LP-UV exposure was performed with an energy of 40 mJ/cm.sup.2 and an intensity of 3 mW/cm.sup.2.

[0142] In a next step, a layer of the polymerizable liquid crystal material M2 was prepared on top of the patterned photo-alignment layer. For this, a 40 weight percent solution of M2 in anisole was used spin-coated at 800 rpm for 60 s. A dry film thickness of approximately 1200 nm was achieved this way. A thermal treatment at a temperature of 50 C. on a hot-plate was then carried out for a duration of 10 minutes. After that, a radiation curing was done. For this, the film was exposed to UV light of 500 mJ/cm2 (UVA and UVB) at 50 mW/cm.sup.2 under nitrogen.

[0143] The resulting optical element was transparent and no image could be observed in non-polarized light. When the element was arranged between crossed polarizers with the edges parallel one of the polarisation axis, the fingerprint texture could be seen with a high contrast as demonstrated by FIG. 2a. Upon rotation of the optical element by 45 the fingerprint pattern appeared with a negative contrast as demonstrated in FIG. 2b.

[0144] When rotating the device between the crossed polarizers, the contrast of the fingerprint image varies between the positive image and the negative image.

Example 9: Preparation of a Fingerprint Optical Element by Inkjet Printing

[0145] The scanned picture of a fingerprint was used as the biometric information to be directly printed as a birefringent pattern by inkjet printing. The digitized biometric information was stored on the hard disk drive of a computer.

[0146] A triacetate cellulose (TAC) foil was washed with isopropanol solvent. By means of Kbar coating (wire coating), a hard-coat solution of CrystalCoat MP-1175UV from SDC Technologies Inc. with a solid content of 40 weight percent in a solvent blend methylethylketone-toluol (60/40) was coated on the TAC foil, leading to a protective layer with a dry thickness of approximately 2000 nm (wire diameter of 0.08 mm by a speed of 10 m/sec). The protective layer was subsequently thermally treated in an oven for 1 minute at a temperature of 80 C. After that, the protective layer was exposed to UVA and UVB light (wavelengths between 280 and 400 nm). A dose of 200 mJ/cm.sup.2 was applied at an intensity of 20 mW/cm.sup.2.

[0147] On top of the hard coat an alignment layer with a dry thickness of approximately 60 nm was prepared from a solution of LPP1 with a solid content of 2 weight percent in a solvent blend methylethylketone-cyclohexanone (80/20) by Kbar coating (coating bar with wire diameter of 0.05 mm, speed of 10 m/sec).

[0148] The alignment layer was subsequently thermally treated in an oven for 2 minutes at a temperature of 80 C. After that, the photo-alignment layer was exposed from the normal direction to LP-UV light (wavelengths between 280 and 320 nm). A dose of 100 mJ/cm.sup.2 was applied at an intensity of 3 mW/cm.sup.2.

[0149] On top of the alignment layer the pattern of the stored biometric information was printed with the polymerizable liquid crystal mixture M2 in a 20 wt % (weight %) concentrated in MIBK. A modified desktop printer, DCP-115C from Brother Company based on drop-on-demand piezo technology was used for that purpose.

[0150] The distance between the print head and substrate during the printing was maximally 1 mm. A resolution of 600 dpi was chosen. Other printer parameters were:

Paper type: Normal paper
Quality of printing: optimal
Printing mode: both directions (from right to left and from left to right)
Colour: colour level

[0151] After printing, a thermal treatment at a temperature of 50 C. in an oven was carried out for a duration of 10 minutes. After that, a radiation curing was done. For this, the film was exposed to UV light with 500 mJ/cm2 (UVA and UVB) at 3 mW/cm.sup.2 under nitrogen.

[0152] After above processes the foil comprising the coatings was still transparent and the printed pattern could not be seen in non-polarized light. After arranging the optical element between crossed polarizers with the orientation direction of the LPP layer at 45 to the polarisation axis of the polarizers, the fingerprint texture could be seen with high contrast,

Example 10: Preparation of a Signature Optical Element Using Photo-Patterning of the Photo-Alignment Layer

[0153] A signature was directly written to a fused silica glass plate with a black ink (black marker Artline854 from Shachihata).

[0154] As in example 4 an alignment layer and a layer of polymerizable liquid crystals was prepared using the same parameters as in example 4. The above plate comprising the signature was then used as a photomask to transfer the signature into the liquid crystal layer. Every other step and the related parameters were the same as in example 4.

[0155] The resulting optical element was transparent and the signature could not be seen In non-polarized light. After arranging the optical element between crossed polarizers with the orientation direction of the LPP layer at 45 to, the polarisation axis of the polarizers, the signature could be seen with high contrast.

Example 11: Preparation of a Signature Optical Element Writing with a Pen Filled with Polymerizable Liquid Crystal Material on Top of an Alignment Layer

[0156] An alignment layer was prepared on a TAC film in the same way as in example 9.

[0157] A pen was filled with 30% solution of M2 in cyclopentanone instead of the normal ink. A signature was directly written on the alignment layer on the triacetate film using this pen.

[0158] After writing the signature the sample was annealed at a temperature of 50 C. in an oven during 10 minutes. After that, a radiation curing was done: the film was exposed to UV light of 500 mJ/cm2 (UVA and UVB) at 3 mW/cm.sup.2 under nitrogen. The thickness of the layer, which had the form of the signature, was determined to about 1.5 m.

[0159] The substrate comprising the liquid crystal signature was still transparent and the signature could not be seen in non-polarized light. However, the signature could be seen bright on a dark background when the substrate was arranged between crossed polarizers, as is demonstrated in FIG. 3. When one of the polarizers was rotated by 90, the contrast of the image was inversed, leading to a dark appearance of the signature on bright background.

[0160] When the substrate was placed on a metallic reflector, the signature could be observed with a single polarizer arranged between the observer and the substrate.

Example 12: Preparation of a Signature Optical Element Writing with a Pen Filled with LCP on an Alignment Layer Comprising an Orientation Pattern

[0161] An alignment layer was coated on a triacetate foil comprising a hard coat layer following the related processes of example 9. Instead of inducing a uniaxial alignment an orientation pattern in the LPP layer was generated by the double exposure process described in example 8 using a chromium photomask comprising a line pattern with 100 m line width and 100 m gap between the lines instead of the fingerprint photomask.

[0162] Like in example 11, handwriting using a pen filled with the liquid crystal solution was performed on the substrate comprising the patterned alignment layer.

[0163] After writing, the sample was annealed and cured like in example 11.

[0164] The substrate comprising the liquid crystal signature was still transparent and the signature could not be seen in non-polarized light. However, the signature could be seen bright on a dark background, as demonstrated in section a) of FIG. 4, when the substrate was arranged between crossed polarizers. The orientation pattern induced in the alignment layer could be recognized by naked eyes, although it was very small. When observed in a polarizing microscope, it could easily be seen, that the micropattern was adapted in the corresponding areas of the signature. For best observation, the substrate was adjusted by rotation for maximum contrast of the pattern. The lines of the handwriting appeared interrupted by the line originating from the photomask used for exposure of the alignment layer, as demonstrated in section b) of FIG. 4. When either substrate or both, polarizer and analyzer, were rotated by 45, the contrast of the black and white pattern inside the lines of the handwriting was inverted, as demonstrated in section c) of FIG. 4. The inversion of the contrast in section c) of FIG. 4 can easily be observed at a position of a defect, one of which is inside the rectangles in sections b) and c) of FIG. 4, which were drawn for easier recognition.

Example 13: Preparation of a Signature Optical Element Writing with a Pen Filled with LCP on an Alignment Layer Comprising a Tilt Orientation Pattern

[0165] The example follows the description of parameters of example 12, except that a tilt pattern was generated instead of an azimuthal orientation pattern. A tilt angle can be induced in the LPP material by oblique LP-UV exposure, which is a known method in the art. The LPP layer was irradiated through the mask from an oblique angle of +45 with regard to the normal of the substrate. The polarization plane of the LP-UV light was parallel to the incidence plane of the light. After exposure, the mask was removed and the substrate with the LPP layer was turned in the opposite direction so that the normal to the plate and the UV incidence direction formed an angle of 45. The subsequent second exposure was made without a mask. Handwriting with the liquid crystal and the other process steps were the same as in example 12.

[0166] When the resulting optical element was observed between crossed polarizers, the signature was observed as in example 12. As long as the substrate was viewed from a normal direction the line pattern applied to the alignment layer in form of a tilt pattern could not be seen. However, when the substrate was tilted around an axis perpendicular to the azimuthal orientation direction, a line pattern with bright and dark zones inside the handwriting was clearly visible. When the sample was tilted in the opposite direction the complementary pattern was obtained.

Example 14: Preparation of a Signature Optical Element Writing with a Pen Filled with a Dichroic LCP Formulation on a Patterned Alignment Layer Based on Azimuthal Variation

[0167] Mainly all the process steps of example 12 were applied, except that dichroic formulation M3 was used in the pen instead of M2 and that the polarisation direction of the LP-UV was rotated by 90 for the second LP-UV exposure step instead of 45.

[0168] After finishing all the process steps, the signature could already be seen in non-polarized light, since the dichroic liquid crystal material absorbs visible light. However, the line pattern induced in the alignment layer could not be seen as long as viewed from a normal direction to the substrate. When the signature was observed with a polarizer on top of the substrate, the line pattern could be recognized inside the handwriting.

[0169] When the substrate was observed again without a polarizer in front and the substrate was tilted around an axis parallel to one of the two orientation directions of the orientation pattern, the line pattern inside the handwriting could again be recognized. When the substrate was tilted around an axis parallel to the other orientation direction, the contrast of the line pattern was inverted.

[0170] Since the line pattern can be made visible with and without a polarizer, the optical element of this example has both first and second level security feature.

Example 15: Preparation of a Signature Optical Element Writing with a Pen Filled with a Dichroic LCP Formulation on a Patterned Alignment Layer Based on Tilt Variation

[0171] The process steps of example 13 were applied, except that dichroic formulation M3 was used in the pen instead of M2. After finishing all the process steps, the signature could already be seen In non-polarized light, since the dichroic liquid crystal material absorbs visible light. However, the line pattern induced in the alignment layer could not be seen as long as viewed from a normal direction to the substrate.

[0172] When the substrate was tilted around an axis perpendicular to the azimuthal orientation directions induced in the LPP layer, the line pattern inside the handwriting could be recognized. When the substrate was tilted in the opposite direction the contrast of the line pattern was inverted.

[0173] When the signature was observed through a polarizer and the polarizer was rotated around an axis normal to the substrate, the intensity of the signature color varied periodically.

[0174] Since the line pattern can be made visible without a polarizer, the optical element of this example exhibits a first level security feature. The second level security feature is available be observation through the polarizer.