Field of Technology
[0001] The present invention relates to counterfeit-proof documents having multilayered
security markings. Counterfeit-proof documents may be documents of value, such as
cheques, stock certificates, banknotes, excise stamps, special federal stamps and
identification documents such as passports, ID cards, etc.
Background Art
[0002] To make fraud and counterfeiting more complicated, protected documents are normally
provided with a security marking, such as watermarks, holograms, diffractive/refractive
nanograms, fluorescent signs, security threads, etc.
[0003] However, a problem with many conventional markings is that they can be produced or
easily forged, and/or they can hardly be verified by an unskilled person without technical
equipment. The object of the present invention is to provide security markings capable
to create unusual optical effects that become apparent without any special equipment.
[0004] Conventional security elements are based on microlens raster structures. In such
security elements optical images are formed by superposition of two or more micro-raster
structures, one or more of which comprises microlens grids, while the others are raster
structures having the same spatial periods as the microlens grids; nodes of the grids
comprise repeating micro-images produced by printing methods or precision stamping
methods. In these cases moiré effects are used. There are several types of such effects,
e.g. effects of "moiré magnification" with orthogonal or collinear (parallel) shift
of parallax of observed magnifies optical images. This type of moiré effects is typical
to micro-raster structures with spherical or pseudo-spherical lenses in nodes of raster
grids.
[0005] US 2005/0180020 A1, 18.08.2005, discloses a micro-optic system in the form of a polymer film that when viewed by
unaided eye(s) in reflective or transmitted light projects one or more images which
show various visual effects such as: orthoparallactic movement; appear to lie on a
spatial plane deeper than the thickness of the polymer film; appear to lie on a spatial
plane above a surface of the polymer film; oscillate between a spatial plane deeper
than the thickness of the polymer film and a spatial plane above a surface of the
film as the film is azimuthally rotated; transform from one form, shape, size, color
(or some combination of these properties) into a different form, shape, size, or color;
appear to have realistic three-dimensionality. The films in the security element are
highly counterfeit resistant because of their complex multi-layer structure and their
high aspect-ratio elements.
[0006] Another option of using microlens structures allows stereo-vario effects to be created.
Such effects are attained using linear (lenticular) cylinder micro-raster lens structures.
In this case, printed or embossed images are formed at a distance of about three focal
distances from the plane of the lenticular raster and don't represent a grid of micro-images,
as in the previous case, but are formed by several uniquely aligned printed or embossed
images (normal, non micro-raster grid images). Each image is divided into strips having
a width of about a period of the lenticular raster, and the images are aligned (with
every other strip in accordance with a predetermined rule of symmetry variation in
the strips) to form an integral image. When such a complex printed image is viewed
through a lenticular lens raster at different angles different images will be seen;
vario or stereo effects can be thereby created, including effects of movement of the
viewed images. The systems will show no optical moiré magnification.
[0007] One of the major drawbacks of the microlens structures is that they are disposed
on the external surface of the security element (they cannot be covered with a protective
layer otherwise the required optical effects will be lost). This fact causes, first,
rapid and uncontrolled wear (abrasion) of the raster, and, second, possible appearance
of transparent layers of liquid, grease, etc. on the raster surface. Therefore, quality
of the viewed changing images may be dramatically impaired, or images may disappear
at all.
[0008] There are methods for creating floating images by forming a system of diffractive/refractive
relief structures on the surface or in the bulk of security elements (
RU 2111550 C1, 20.05.1998). A relief structure in the form of a system of incisions (grooves) with the configuration
and shape calculated through a special program is formed in a transparent layer on
the surface or in the bulk of a security element. These systems form a complex combination
of flat Fresnel lenses which form variable images "floating" above or below the surface
of the security element. The images can be viewed both in transmitted and reflected
light. These structures however suffer from low brightness and contrast of the viewed
images at small sizes of the security elements.
[0009] There are security elements using holographic methods to create changing images that
are seen as the viewing direction and lighting of the security element are varied
(
RU 2345900 C2, 10.02.2009). In these elements several holographic images are formed on the surface or within
the bulk of the security element using various optical reference frequencies (grids).
However, with the small size of security elements (which is typical for special printing
products, such as securities, security threads in banknotes, excise stamps and special
stamps, etc.) the contrast and brightness of the viewed images worsen, movement of
images becomes fuzzy and indistinct. Viewing the images becomes complicated due to
their "rainbow" nature resulting from the high spatial frequencies of the grids and
diffraction of falling non-monochromatic light on them. Special measures are required
to increase the contrast, brightness and sharpness of the viewed images and to enable
more reliable perception of their changes (movements).
Summary of the Invention
[0010] The obj ect of the invention is to enhance the security of products through providing
a novel optical effect which renders the counterfeit-proof (protected) product more
readily identifiable and is based observation of relative movement of images as the
viewing angle varies.
[0011] The object is accomplished in a group of inventions, particularly in a multilayered
security element comprising a flexible carrier layer with optically variable structures
containing two or more groups of repeated images that move and/or change as a viewing
angle varies, wherein the optically variable structures are formed so that when the
viewing angle varies different groups of images move relative to each other.
[0012] Furthermore, in the multilayered security element images belonging to different groups
move in parallel to the plane of the viewing angle variation so that the images come
nearer or farther relative to the viewer; images belonging to different groups move
perpendicular to the plane of the viewing angle variation so that the images move
to the right or left of the viewer; images belonging to different groups move in different
axial directions with respect to the plane of the viewing angle variation, or the
movement of images belonging to different groups is combined with a smooth change
in geometric parameters of the images, such as inclination angles to the longitudinal
axis of the security element or their linear dimensions.
[0013] The multilayered security element can be made in the form of a stripe, or a local
thin-film element, or a security thread, or a thin-layer coating structure.
[0014] The optical variability is provided through embedding into the security elements
of microlens raster structures, or diffractive/refractive structures, or holographic
structures.
[0015] The object is further accomplished in a counterfeit-proof document, such as a cheque,
stock certificate, banknote, excise stamp, special federal stamp, passport, ID card
and another similar product, comprising at least one security element defined above.
[0016] In an embodiment of the counterfeit-proof document the security element is made in
the form of a stripe or a local thin-film element placed on the surface of the counterfeit-proof
document, or a thin-layer structure covering the counterfeit-proof document, or a
security thread embedded into the counterfeit-proof document.
[0017] The invention substantially resides in the fact that in a security element comprising
a flexible carrier layer with optically variable structures containing two or more
groups of repeating images that move and/or change as the viewing angle varies, the
optically variable structures are formed so that when the viewing angle varies different
groups of images, that are located closely to each other at a distance of about the
size of visible images, move relative to each other.
[0018] In embodiments, as already mentioned, images belonging to different groups move in
parallel to the plane of the viewing angle variation so that the images come nearer
or farther relative to the viewer; images belonging to different groups move perpendicular
to the plane of the viewing angle variation so that the images move to the right or
left of the viewer; images belonging to different groups move in different axial directions
with respect to the plane of the viewing angle variation, or the movement of images
belonging to different groups is combined with a smooth change in geometric parameters
of the images, such as inclination angles to the longitudinal axis of the security
element or their linear dimensions.
[0019] The optically variable structures comprise microlens raster structures, diffractive/refractive
structures or holographic structures.
[0020] A counterfeit-proof document, such as a cheque, stock certificate, banknote, excise
stamp, special federal stamp, passport, ID card and another similar product, comprises
at least one security element defined above.
[0021] The security element can be made in the form of a stripe, or a local thin-film element
disposed on the surface of the counterfeit-proof document (protected) document, or
a thin-layer structure covering the protected document, or a security thread embedded
into the protected document.
Brief Description of the Drawings
[0022]
FIG. 1 shows variants of changes in images formed by holographic threads at different
viewing angles, that is, the process of the aforementioned changing (moving) of symbols
S1 and S2.
FIG. 2 shows photographs of holographic images viewed at different angles, the images
being formed on an actual security element such as a holographic thread. Here, symbols
S1 and S2 are represented as digits "100" spaced apart at some distance (1-2 mm) along the
thread and changing their visible location and orientation depending on the viewing
angle.
Best Embodiment of the Invention
Example 1
[0023] On the surface of a holographic foil a rainbow holographic relief is produced using
digital "dot matrix" methods or analog holography methods; when viewed at a certain
viewing angle α
0 the rainbow holographic relief forms an image of two symbols S
1 and S
2 spaced apart at a distance l
0. As the viewing angle α
0 varies at an angle Δα, the viewed image changes so that the distance between the
symbols increases by a value Δl When the viewing angle is further increased by Δα
the distance between the symbols increases to l
0+2Δl With further increase in the viewing angle by nΔα the distance between the viewed
symbols will increase accordingly by nΔl Starting from a value of n=M the sign of
Δl can be changed and the distance between the symbols will begin decreasing. At sufficiently
small values of Δα and Δ1 and a smooth change in the viewing angle symbols S
1 and S
2 will appear to move first away of each other and then towards each other. Therewith
movement of the symbols will be easier recognized owing to physiological peculiarities
of vision. In course of the movement the symbols may further change their shape, size
and orientation (as shown in the second and third lines of symbolic images in FIG.
1), which further improves the perception of movement of the symbols.
Example 2
[0024] Similarly to the above embodiment of an optical variable structure based on a rainbow
holographic element in Example 1, floating images with differently directed movement
of their fragments can be formed in diffractive/refractive structures such as a combination
of Fresnel lenses aligned with each other or a thin-film nano-prismatic system of
diffractive optical elements. In the first case, floating images are formed by structures
produced by embossing with master dies that are manufactured by precision engraving
of concentric annular grooves (incisions) having a predetermined profile, which form
a system of intersecting Fresnel lenses. The engraving has a resolution (typical size
of groove profile) of about 1 - 10 µm. In the second case, the structure which forms
floating images is manufactured using electronic, ionic, or laser nano- lithographic
printers with a resolution of about 10-100 nm. The structure comprises nano-sized
hills and pits distributed according to a predetermined law.
Example 3
[0025] Floating images with differently directed movement of groups of individual fragments
can be also formed in optical elements based on microlens raster structures and micro-image
grid systems. In this case, the observed movement character of the magnified moiré
images is defined by properties and orientation of micro-image and microlens grids.
In a simplest embodiment, certain local areas of a micro-image raster having dimensions
of about 10 - 100 spatial periods (typical size of a spatial period of grids is generally
10-100 µm) are left free of micro-images. When viewed, these areas will appear to
float above the plane with moving magnified patterns of micro-images, i.e. an apparent
differently directed movement of the local areas relative to remote moving background
images will be formed.
Industrial Applicability
[0026] The present invention makes it possible to simplify the process of detection of counterfeited
and forged documents since the security of products can be enhanced owing to the provision
of a novel optical effect which renders the protected product more readily identifiable
and is based on observation of relative movement of images as the viewing angle varies.
1. A multilayered security element comprising a flexible carrier layer with optically
variable structures containing two or more groups of repeating images that move and/or
changing as a viewing angle varies, characterized in that the optically variable structures are formed so that when the viewing angle varies
different groups of images move relative to each other.
2. A multilayered security element according to claim 1, characterized in that images belonging to different groups move in parallel to the plane of the viewing
angle variation so that the images come nearer or farther relative to the viewer.
3. A multilayered security element according to claim 1, characterized in that images belonging to different groups move perpendicular to the plane of the viewing
angle variation so that the images move to the right or to the left of the viewer.
4. A multilayered security element according to claim 1, wherein images belonging to
different groups move in different axial directions with respect to the plane of the
viewing angle variation.
5. A multilayered security element according to claim 1, characterized in that the movement of images belonging to different groups is combined with a smooth change
in geometric parameters of the images, such as inclination angles to the longitudinal
axis of the security element or their linear dimensions.
6. A multilayered security element according to any one of claims 1 to 5, characterized in that the element is made in the form of a stripe, or a local thin-film element, or a security
thread, or a thin-layer coating structure.
7. A multilayered security element according to any one of claims 1 to 5, characterized in that the optically variable structures comprise microlens raster structures.
8. A multilayered security element according to any one of claims 1 to 5, characterized in that the optically variable structures comprise diffractive/refractive structures.
9. A multilayered security element according to any one of claims 1 to 5, wherein the
optically variable structures comprise holographic structures.
10. A counterfeit-proof document, such as a cheque, stock certificate, banknote, excise
stamp, special federal stamp, passport, ID card and other similar item, comprising
at least one security element as defined in any one of claims 1 to 9.
11. A counterfeit-proof document according to claim 10, characterized in that the security element is made in the form of a stripe or a local thin-film element
disposed on the surface of a protected document.
12. A counterfeit-proof document according to claim 10, characterized in that the security element is made in the form of a thin-layer structure covering a protected
document.
13. A counterfeit-proof document according to claim 10, characterized in that the security element is made in the form of a security thread embedded into a protected
document.