Optical structure having a relief effect
The invention relates to an optical structure ( 5 ) having a relief effect, comprising: —a support ( 7 ) adapted for aligning liquid crystals, —a deposit ( 9 ) in contact with the support of a substance in the form of at least one pattern ( 11 ), which partially covers the support, and—a liquid crystal layer ( 13 ) which at least partially covers the support and said pattern and is in contact with the support.
1 . An optical structure with relief effect, comprising:
a support suitable for aligning liquid crystals;
a pattern comprising an ink or a varnish that is deposited on the support in a liquid state and then dried, wherein the pattern is free of liquid crystals and has a dry weight of 1.5 g/m 2 or less; and
a layer of liquid crystals disposed on the support and at least partially covering the pattern, the layer of liquid crystals comprising:
a first zone directly covering the pattern;
a transition zone delimited by the contour of the pattern and extending around the pattern; and
a second zone in which the liquid crystals are in contact with the support, the second zone being distinct from the first zone and the transition zone,
wherein the transition zone has a lower number of liquid crystal domains per unit of surface area than the first zone and the second zone, with a domain being defined as a region in which the liquid crystals have substantially a same alignment, with the alignment being different from an alignment of liquid crystals of adjacent regions.
2 . The structure of claim 1 , wherein the pattern is transparent and colorless in the visible range.
3 . The structure of claim 1 , wherein the pattern comprises the ink.
4 . The structure of claim 1 , wherein the pattern is a solid color.
5 . The structure of claim 1 , wherein the support is transparent or translucent.
6 . The structure of claim 1 , wherein the support comprises an axially stretched plastic film.
7 . The structure of claim 6 further comprising an adhesion primer layer disposed between the film and the layer of liquid crystals.
8 . The structure of claim 1 , wherein a portion of the liquid crystals directly contact the pattern.
9 . A security element comprising the optical structure of claim 1 .
10 . A secure document comprising the optical structure of claim 1 .
11 . The document of claim 10 , wherein the optical structure is visible on a front side and an opposing back side of the document.
12 . The document of claim 10 , wherein:
the document comprises a fibrous substrate having a window; and
the optical structure is comprised by a security element disposed in the window.
13 . A method for manufacturing an optical structure with a relief effect, the method comprising:
depositing an ink or varnish that is free of liquid crystals on a support in a liquid state and then drying the ink or varnish to form a pattern on the support, the pattern having a dry weight of 1.5 g/m 2 or less; and
depositing a layer of cholesteric liquid crystals on the pattern and the support, the cholesteric liquid crystals being configured to produce a goniochromatic effect, the layer of liquid crystals comprising:
a first zone directly covering the pattern;
a transition zone delimited by the contour of the pattern and extending around the pattern; and
a second zone in which the liquid crystals are in contact with the support, the second zone being distinct from the first zone and the transition zone,
wherein the transition zone has a lower number of liquid crystal domains per unit of surface area than the first zone and the second zone, with a domain being defined as a region in which the liquid crystals have substantially a same alignment, with the alignment being different from an alignment of liquid crystals of adjacent regions.
14 . The method of claim 13 , wherein:
the depositing of the ink comprises printing the ink on the support; and
the depositing of the liquid crystal layer comprises inkjet printing, flexography, screen printing, photogravure, or typography.
15 . A method for authenticating the security element of claim 12 , the method comprising observing the optical structure through the window to determine whether the pattern appears as a relief image.
16 . The method of claim 15 , wherein the observing the optical structure comprises observing the optical structure from at least two different observation directions from a same side of the support, in order to determine whether the appearance of the pattern changes.
17 . The method of claim 15 , wherein the observing the optical structure comprises observing the optical structure from opposing sides of the support, in order to determine whether the pattern appears as reversed relief images.
18 . The method of claim 15 , wherein the observing the optical structure comprises observing polarized light radiated onto the optical structure, in order to determine whether first portion of the cholesteric liquid crystals that contact the pattern and a second portion of the cholesteric liquid crystals that contact the support have different appearances.
19 . The method of claim 18 , further comprising moving the optical structure, in order to determine whether there is a change in the appearances of the first portion of the cholesteric liquid crystals and the second portion of the cholesteric liquid crystals.
20 . The method of claim 19 , wherein the polarized light is emitted by a liquid crystal display screen.