Note: Descriptions are shown in the official language in which they were submitted.
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Optically Variable Security Element
The present invention relates to an optically variable security element for
securing valuable articles. The present invention further relates to a method
for manufacturing such a security element, a security arrangement having
such a security element, a correspondingly furnished data carrier and a
verification device for such a security element.
For protection, data carriers, such as value or identification documents, but
also other valuable articles, such as branded articles, are often provided
with
security elements that permit the authenticity of the data carrier to be
verified, and that simultaneously serve as protection against unauthorized
reproduction. The security elements can be developed, for example, in the
form of a security thread embedded in a banknote, a cover foil for a
banknote having a hole, an applied security strip, a sell-supporting transfer
element, or also in the form of a feature region applied directly to a value
document.
Security elements that display viewing-angle-dependent visual effects play a
special role in safeguarding authenticity, as these cannot be reproduced even
with the most modern copiers. For this, the security elements are furnished
with optically variable elements that, from different viewing angles, convey
to the viewer a different image impression and, depending on the viewing
angle, display for example another color or brightness impression and/or
another graphic motif.
In this connection, it is known to use security elements having multilayer
thin-film elements whose color impression for the viewer changes with the
viewing angle, and when the security feature is tilted, shifts for example
from green to blue, from blue to magenta or from magenta to green. The
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occurrence of such color changes upon tilting a security element is referred
to in the following as a color-shift effect.
From publication WO 02/073250 A2 are known optically variable thin-film
elements in whose layer structure at least one magnetic layer is integrated.
The magnetic properties of these optically variable thin-film elements can
then be used as an additional authenticating mark.
In publication EP 1 780 040 A2 is described a security element in which are
present, in a sub-region, magnetically aligned pigment particles that produce
a kinematic visual effect. Here, the magnetically aligned pigment particles
can especially also exhibit optically variable properties.
Based on that, it is the object of the present invention to further improve a
security element of the kind cited above, and especially to create a security
element having an attractive visual appearance and high counterfeit security
whose appearance can additionally be interactively influenced when
checking the authenticity.
A method for manufacturing such a security element, a security arrangement
having such a security element, a correspondingly furnished data carrier and
a verification device for such a security element are described.
According to the present invention, a generic security element exhibits an
optically variable ink layer that includes first, optically variable effect
pigments for producing a viewing-angle-dependent visual impression, and
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that includes second effect pigments that are reversibly alignable by an
external magnetic field, and in which the degree of markedness of the
viewing-angle-dependent visual impression of the optically variable effect
pigments depends on the orientation of the magnetically alignable effect
pigments relative to the plane of the ink layer.
Such a security element offers a combination of attractive visual effects,
namely, on the one hand, the optically variable effects of the first effect
pigments and, on the other hand, the reversible magnetic alignability of the
second effect pigments, through which, as described in greater detail below,
three-dimensional-seeming appearances can be interactively produced that
can, if applicable together with further information, reversibly be brought to
appear and to disappear again. In one development of the present invention,
the second effect pigments can, at a later time, through an activatable
fixative, be fully or partially fixed in a desired position such that the
security
element can especially be subsequently provided with an individual
marking, as explained in greater detail below.
According to the present invention, the two effects occur here in interaction
in that the markedness of the optically variable effect depends on the
orientation of the magnetically alignable effect pigments. The interactive
influencing of the magnetic pigments thus not only reveals previously non-
visible appearances and, if applicable, further information, but also changes
the intensity and brilliance of the optically variable effect.
To ensure a reversible magnetic alignabidity of the pigments, the second
effect pigments are preferably encapsulated in a microcapsule and are
substantially freely rotatable in the microcapsule. Here, without an external
magnetic field, the second effect pigments are preferably aligned
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isotropically within the microcapsule, so exhibit, as a whole, no preferred
direction. In practice, certain deviations from the ideal isotropic alignment
can, of course, occur here, depending, for example, on the geometric shape,
the magnetizability, the viscosity of the encapsulation liquid or the
structure
of the encapsulation.
After the application of an external magnetic field, the second effect
pigments initially align quickly and, after cessation of the external magnetic
field, return to their initial state. Without a restoring force or without
other
external forces, this return can, in some cases, last very long and require
several minutes, hours or even days. Within this period, a magnetization
pattern displayed by the security element initially remains visible also after
the removal of the verification magnet, and recedes only when an active
movement with an external magnet cancels or changes the orientation of the
second effect pigments.
To accelerate the return to the initial state, the microcapsules can include,
in
expedient embodiments, a gel that provides a restoring force for the
magnetically alignable effect pigments. For this, for example, a transparent
polymerizable substance that is preferably a mixture of photocrosslinkable
mono- and oligomers and a suitable solvent, can be introduced into the
microcapsules and, through crosslinking, a gel-like structure systematically
produced in the microcapsules that, on the one hand, allows a rotation of the
effect pigments by an external field and that, on the other hand, when a
rotation has occurred, produces a restoring force that causes the effect
pigments to quickly return to their initial position after a cessation of the
external field. In another embodiment, such a restoring force can also be
produced by a premagnetization of a magnetic layer combined with the
optically variable ink layer.
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In an advantageous embodiment of the present invention, the first effect
pigments are present outside the microcapsules of the second effect
pigments. Alternatively, the first effect pigments can also be encapsulated in
the microcapsules together with the second effect pigments. In this case, the
first effect pigments are advantageously developed to be platelet-like. Since,
in this embodiment, the alignment of the first effect pigments likewise
changes when the magnetic second effect pigments are aligned, dynamic,
interactive color effects can be produced through the joint encapsulation. In
a
special variant, the first and second effect pigments are formed by the same
magnetically alignable and optically variable effect pigments.
The second effect pigments are preferably formed on the basis of high-purity
iron powder and can, for example, be manufactured from carbonyl iron
powder treated under reducing conditions. Advantageous platelet-like iron
pigments are set forth especially in publication EP 1 251 152 B1, whose
disclosure on the manufacture and properties of such pigments is
incorporated in the present description by reference.
Here, the second effect pigments can be magnetically soft or magnetically
hard. The second effect pigments are preferably developed to be non-
spherical, for example acicular. Here, effect pigments that exhibit a platelet
form are particularly preferred. In the following, the largest diameter of a
non-spherical pigment is also referred to as the length or size of the
pigment,
while the smallest diameter is referred to as the thickness of the pigment.
The ratio of the largest diameter to the smallest diameter of the non-
spherical
second effect pigments is preferably more than 5:1, preferably more than
10:1. This ratio is particularly preferably between 40:1 and 400:1. The
largest
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diameter of the non-spherical second effect pigments is advantageously
more than 2 gm, preferably more than 5 gm, particularly preferably more
than 10 gm and very particularly preferably more than 15 gm. The use of
magnetically alignable effect pigments in the micrometer range and
especially in the cited size range has especially the advantage that the
particle concentration compared with nanoparticles can be kept lower.
Platelet-like effect pigments, especially in the preferred size range and in
the
preferred diameter-to-thickness range, can be oriented as desired relative to
the layer plane by an external magnetic field. Depending on the orientation,
they then either largely reveal, like the slats in a window blind, the view of
underlying layers (nearly vertical orientation relative to the layer plane) or
block it partially (oblique orientation relative to the layer plane) or
completely (substantially horizontal orientation relative to the layer plane).
In this way, high contrasts between translucent and opaque layer regions can
be set for high diameter-to-thickness ratios.
In the context of the present description, "translucent" here means sheer in
the sense of a certain or complete transmittance and thus also includes
transparency. A translucent layer permits the perception of the objects
located behind or below it, even if the brightness of the objects can be
reduced and/or the color of the objects altered by the translucent layer. If,
in
contrast, the transmittance of a layer is so low that the objects located
behind
or below it are no longer perceptible, then it is no longer referred to as
translucent, but rather as opaque or opacifying.
Instead of using non-spherical, especially platelet-like second effect
pigments, it can also be provided that the second effect pigments are formed
by isotropic particles that are present in microcapsules and that align
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cooperatively, that is, e.g., chain-like, in the microcapsules through an
external magnetic field. In this way, dynamic optical effects can likewise be
produced. Here, the isotropic particles can be developed as nanoscale
particles having a particle size of 1 nm up to 1 gm, or can alternatively
exhibit particle sizes of more than 1 gm, the particle size especially being
between 1 gm and 20 gm, preferably between 2 gm and 10 gm. The diameter
of the microcapsules is advantageously between 1 gm and 200 gm, especially
between 5 gm and 80 gm, and is preferably coordinated with the particle size
of the isotropic particles in such a way that, upon magnetic alignment, in
each case, multiple isotropic particles can lie against one another
cooperatively, especially chain-like, in the microcapsules.
In an advantageous development of the present invention, the second effect
pigments are formed by coated iron pigments. Here, the iron pigments
exhibit especially the composition FeO, where x is between 1.3 and 1.5. Due
to the coating, in addition to their magnetic alignability, the second effect
pigments are provided with a further desired property. In the simplest case,
the coating is a coloring coating that includes, for example, yellow, green
and/or blue organic and/or inorganic colorants and preferably, in addition,
a white pigment having a high scattering power. Also other coatings, such as
laser-markable, fluorescent or phosphorescent coatings may be considered in
order to lend the effect pigments the appropriate properties.
The encapsulation of the second effect pigments can occur, for example, in
that iron pigments of a suitable size are selected, such as in the size range
of
10 gm to 20 gm, are dispersed in a water-insoluble solvent, suitable micellar
precursors having a controlled particle size are prepared in water, and these
are encapsulated, for example, with acrylated gelatine through coacervation.
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General information on rnicroencapsulation and on coacervation is set forth
e.g. in EP 1 479 432 B1.
Also other methods for the encapsulation are, of course, possible, such as
emulsion polymerization with acrylates, methacrylates or styrene.
The microcapsules described in this application can consist of a number of
different organic or inorganic materials. To ensure the required optical and
mechanical properties, especially the capsule material, and if polymers are
used, also their degree of crosslinking and the wall thickness of the
microcapsules can be adjusted. Advantageous capsule materials include, for
example, gelatin, modified gelatin, especially with chemical
postcrosslinking, PMMA and other polyacrylates that are well suited,
primarily due to their high transparency, polyurethanes, polyamides,
melanin! formaldehyde, silicones, but also inorganic oxide materials, such as
silicates, titanium, hafnium or iron oxides.
According to the present invention, the diameter of the microcapsules is
advantageously between about 1 gm and about 200 gm, especially between
about 1 gm and about 80 gm. The wall thickness of the microcapsules is
typically between 5% and 30%, preferably between 10% and 20% of the
diameter of the microcapsules.
The first effect pigments are advantageously pigments manufactured on the
basis of liquid crystal polymers, or so-called pearlescent pigments, such as
the silvery-white, gold luster or metallic luster pigments sold under the
name Iriodin(R) or Colorcrypt by Merck KGaA. Both pigments on the basis
of liquid crystal material and pearlescent pigments are per se translucent. In
another, likewise advantageous embodiment of the present invention, the
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first effect pigments are formed by interference layer pigments. Such
interference layer pigments typically exhibit a thin-film structure that
expediently includes at least one reflection layer, one absorber layer and one
dielectric spacing layer arranged between the reflection layer and the
absorber layer. Interference layer pigments can, per se, be translucent, even
if
opaque interference layer pigments are also known.
In one development of the present invention, the second effect pigments are
encapsulated in microcapsules, the microcapsules including an activatable
fixative through whose activation the second effect pigments are fixable in a
desired position. Such a design makes it possible to partially or completely
fix in a desired position, at a later time, the second effect pigments in
order to
introduce, for example, an individual marking into the security element. In
this way, a printed layer having the second effect pigments can still be
magnetically aligned also after the drying of the layer, and for example
through local UV irradiation or through local laser irradiation, be fixed in
the
form of patterns, characters or a code in a desired position in sub-regions.
If the second effect pigments are subsequently fixed only in sub-regions,
then a combination effect is created in which the non-fixed regions react
reversibly to external magnetic fields, while the magnetic alignment in the
regions impinged on with, for example, UV or laser radiation, is
permanently fixed.
Here, in an advantageous embodiment, the microcapsules include, as the
activatable fixative, a transparent polymerizable mixture or substance, and to
activate the fixative, an initiator, preferably a photoinitiator. For this,
upon
microencapsulation, which preferably occurs through colloidal coacervation
or microemulsion polymerization, the second effect pigments can be
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suspended, for example, in a 100% system composed of mono- and
oligomers and photoinitiator. Here, the polymerization conditions, such as
micelle or drop size, are chosen such that microcapsules of the desired size
(1 1.tm to 200 tam, preferably 5 gm to 80 m) are created. The viscosity of
the
mixture can be adjusted both through the choice of the type of mono- or
oligomer and through the variation of its ratio.
Through suitable choice of the polymerization conditions, both
microcapsules having completely fixed effect pigments can be produced, and
microcapsules having gel structures that preferably consist of a mixture of
photopolymerizable mono- and oligomers and a suitable solvent, in which
the effect pigments can still be rotated through an external magnetic field
and for which the gel structure exerts a restoring force on the rotated effect
pigments, as explained in greater detail above.
Alternatively, the microcapsules can also include a largely inert filling with
added, short, chain-like reactive molecules that, upon irradiation, crosslink
with themselves and with the capsule wall and fix the effect pigment
included in the microcapsule in its position.
According to a further possibility, also laser-destructible nanocapsules can
be introduced into the microcapsules with a polymerization starter such that
the fixation can be triggered by laser radiation.
In a further variant, the microcapsules include liquids or pigments that can
be decomposed by laser radiation and, for example, foam up. Here, the effect
pigments included in the microcapsules are permanently fixed in their
position by the resulting increase in volume of the fixative. One advantage of
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such a variant consists in that no subsequent crosslinking can occur, for
example through leakage of polymerization starter or through UV light.
Examples of activatable fixatives that are suitable for foaming up through the
action of laser radiation and/or through a high temperature include
polymers, such as POM (polyoxymethylene), PMMA (poly(methyl
methacrylate)) or PA (polyamide), which, due to their decomposition
properties, already tend to foam up without further additives. Furthermore,
also other plastics can be used, such as polystyrene, polyester or PET, to
which a blowing agent is added to produce the desired foamability. As the
blowing agent, sodium carbonate, diphenyloxide-4-4'-disulphohydrazide or
the blowing agents of the product series Genitron(R) or Ficel(R) from
Lanxess, for example, may be used. Alternatively, also foamable hollow
spheres can be used. To increase the laser sensitivity of the foamable
polymers, in addition, absorbers can be added for the wavelength range of
the laser used.
In an advantageous development of the present invention, the optically
variable ink layer can further include third, unencapsulated and
magnetically alignable effect pigments that are magnetically aligned in the
form of a specified motif in the form of patterns, lines, characters or a
code.
Unlike the alignment of the second effect pigments, the alignment of the
third effect pigments here is permanently fixed. For the third effect
pigments, except for the lack of encapsulation, the same materials may be
used with the same size ranges and properties as for the second effect
pigments, such that the above statements in this regard also apply to the
third effect pigments.
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The encapsulated second effect pigments and the tmencapsulated third effect
pigments can be present at least partially in the same regions of the
optically
variable ink layer and/or at least partially in separate regions of the
optically
variable ink layer. In both variants, conspicuous visual effects having a high
recognition value can be produced, as explained in greater detail below.
In a preferred embodiment of the present invention, the optically variable
ink layer includes a pigment mixture having the first effect pigments, the
encapsulated second effect pigments and, if applicable, the unencapsulated
third effect pigments. Alternatively, the optically variable ink layer can
consist of multiple stacked sub-layers that each include only one type of
effect pigment.
The optically variable ink layer is preferably formed by a screen printing
layer or flexo printing layer, in some embodiments also by an intaglio
printing layer. In all cited embodiments, it can, in addition, be blind
embossed, especially to intensify the 3D effect of the magnetically aligned
effect pigments.
To permanently fix the magnetically aligned motif of the third effect
pigments, the ink layer is preferably formed on the basis of a UV-curing
color system, with purely UV systems, UV/water-based systems or also
UV/solvent-based systems being able to be used. In addition to the first,
second and, if applicable, third effect pigments, the ink layer can also
include
further pigments, especially isotropic pigments and/ or magnetically soft
pigments. Of course the further pigments or, in general, further additives can
exhibit visually and/or machine-perceptible properties that do not affect the
described visual effects of the security element according to the present
invention, or affect them only marginally.
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In an advantageous embodiment, the optically variable ink layer is applied
on a standard banknote paper or on a colored background layer. Any type of
paper may be used as the substrate material for the banknote paper,
especially cotton vellum paper. Of course, also paper that includes a
proportion x of polymer material can be used, where x can be between 0 and
100 wt. %.
The substrate material of the banknote or, in general, of a data carrier can
also be a plastic foil, such as a polyester foil. The foil can be stretched
monoaxially or biaxially. A stretching of the foil causes it to, among other
things, obtain light-polarizing properties that can be used as a further
security feature. The substrate material can also be a multilayer composite
that includes at least one layer composed of paper or a paper-like material.
Such a composite, which can also be used as a substrate material for
banknotes, is characterized by an extraordinarily high stability, which is
highly advantageous for the durability of the note or data carrier.
Further, as the substrate material, a multilayer, paper-free composite
material can be used that, especially in some climate regions of the earth,
can
be used advantageously.
All substrate materials can include additives that can serve as authenticity
features. Here, especially luminescent substances may be used that are
preferably transparent in the visible wavelength range and, in a non-visible
wavelength range, can be excited through suitable auxiliary means, such as a
UV- or IR-radiation-emitting source, to produce a luminescent radiation that
is directly visible or detectable with auxiliary means.
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Background layers having dark colors normally lead to a particularly high
brilliance of the optically variable effects. However, also a transparent or
translucent foil can be used as the substrate. In this case, the security
element
can advantageously be used in or over a window region or a through
opening of a value document as a see-through security element. The foil can
be developed as a patch that covers a sub-area of the substrate, or as a strip
that extends across the entire length or width of the data carrier. As
materials
for the foil, primarily the plastics PET (polyethylene terephthalate), PBT
(polybutylene terephthalate), PEN (polyethylene naphthalate), PP
(polyproyplene), PA (polyamide) and PE (polyethylene), may be used.
Further, the foil can be stretched monoaxially or biaxially, as already
explained above.
An opening in a banknote can already be produced at manufacture of the
security paper used for the banknote, and then exhibits a fibrous, irregular
edge. Such an edge is characteristic for openings already manufactured at
sheet formation and cannot be produced subsequently. Details on the
manufacture of such irregular edges are set forth in publication WO
03/054297 A2, the disclosure of which is incorporated herein by reference. In
other embodiments, the opening is produced only after paper manufacture
by punching or cutting, for example by laser cutting.
In one development of the present invention, the optically variable ink layer
can be applied on an information-bearing background layer, especially a
screen printing, flexo printing or an intaglio printing layer. Since the
information is perceptible in the translucent regions of the ink layer, but is
covered in the opaque regions, the ink layer and background layer can coact
to produce a further authenticity feature, as explained in greater detail
below.
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The background layer can advantageously also exhibit thermochromic
properties to create a security element that is interactively influenceable in
a
further way. Such a thermochromic background layer can especially be
designed such that, when it is activated through a temperature increase, the
optically variable effect of the first effect pigments disappears for the
viewer.
According to one development of the present invention, the optically
variable ink layer is combined with a magnetic background layer that can be
present contiguously or in the form of patterns, characters or a code.
Through such a magnetic background layer, it can be achieved that the
optically variable ink layer already displays a desired motif without an
external magnetic field, or that an initially hidden motif is exposed by an
external magnetic field.
In a first variant, the magnetic background layer includes a magnetically soft
substance of low to negligible remanence that is arranged in the form of a
motif, for example in the form of patterns, characters or a code. Due to its
low remanence, the magnetically soft substance itself is not permanently
magnetizable, so retains no magnetization after cessation of an external
magnetic field.
If the security element is exposed to an external magnetic field, then the
magnetic background layer largely shields the magnetic field in the regions
in which the magnetically soft substance is present, such that the second
effect pigments there are influenced only a little or not at all. Through the
emerging, locally different alignment of the second effect pigments, the
external magnetic field exposes the motif that is present in the magnetic
background layer and makes it perceptible for the viewer. Thus, through the
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magnetic background layer, a reversibly displayable, magnetic motif is
produced without the external magnetic field having to exhibit the motif
shape. Rather, the verification can occur with common, widespread magnets,
such as with the permanent magnets of a mobile phone, of a portable audio
playback device or of a product security system.
Pigments having the desired magnetically soft properties include, for
example, soft ferrites, such as Zn-Mn ferrite, or various amorphous,
crystalline or nanocrystalline metals or metal alloys that are known to the
person of skill in the art for shielding static or low-frequency magnetic
fields.
Here, the pigments are preferably imprinted in the form of a magnetic
printing ink. The markedness of the effect can be adjusted especially via the
pigmentation of the printing ink and the thickness of the imprinted layer.
In a second variant, the magnetic background layer includes a magnetic
substance, having a medium to high coercive field strength, that can be
present contiguously or in the form of a motif. Here, the coercive field
strength is typically between 50 kA/m and 300 kA/m. Such a magnetic
substance can still be magnetized or remagn.etized relatively easily by an
external magnetic field. The initial magnetization in the form of a desired
motif can be produced, for example, with a strong permanent magnet. Due
to the remanence of the magnetic material, also after cessation of the
external
magnetic field, a magnetization is retained that is strong enough to keep the
reversibly alignable second effect pigments in their position.
Suitable materials for this variant include, for example, mixtures of hard and
soft ferrites or sintering materials and alloys, such as AlNiCo, CuNiFe or
chrome-cobalt steels.
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According to a third variant of this aspect of the present invention, the
coercive field strength of the magnetic substance is chosen to be so large
that
it no longer permits remagnetization through standard permanent magnets,
but rather that very strong fields are required for this, such as can be
produced, for example, with strong electromagnets or through flash
magnetization. Here, the coercive field strength of the magnetic substance is
above 300 kA/m.
In this variant, at manufacture of the security element or in a subsequent
individualization step, there can, for example, be magnetized into the
magnetic background layer a motif that cannot be removed by the means
usually available to a user. Through the alignment of the second effect
pigments, a visible, permanent magnetic pattern is created that can be
intensified or weakened by an external magnetic field.
Suitable materials for this variant include, for example, anisotropic and
especially isotropic magnetic powders based on hard ferrite, such as barium
or strontium ferrite, or magnetic powder based on sintering materials and
alloys, such as NdFeB or SmCo. Also HiCo (high coercivity) materials from
the field of magnetic cards may be considered, since these exhibit a coercive
field strength up to 4000 Oe (about 320 kA/m).
The application of a magnetic background layer to a paper substrate can
occur directly through printing an ink that includes the magnetic substances
cited in the first to third variant in the highest possible pigmentation in
the
range of about 15% to 50%. To achieve the highest possible layer thicknesses
and thus an intense effect, the ink is preferably applied in screen or
intaglio
printing.
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The application of the magnetic background layer to a foil substrate opens
up further possibilities. In this way, with known methods, one or more
layers composed of magnetic materials can be applied to a foil. For example,
the foil can be evaporated with a magnetic metal layer, for instance
composed of iron or nickel, demetalized in the form of a desired motif, and
over- or underprinted with an optically variable ink layer of the kind
described. Through vacuum methods, to a foil can also be applied various
non-metallic layers or metallic alloys that exhibit the desired magnetic
properties with respect to coercive field strength, remanence and the like.
The present invention also comprises a method for manufacturing an
optically variable security element for securing valuable articles, in which,
to
a substrate, an optically variable ink layer is applied that includes first,
optically variable effect pigments for producing a viewing-angle-dependent
visual impression, and that includes second effect pigments that are
reversibly alignable by an external magnetic field, the degree of markedness
of the viewing-angle-dependent visual impression of the optically variable
effect pigments depending on the orientation of the magnetically alignable
effect pigments relative to the plane of the ink layer. Here, the second
effect
pigments are preferably encapsulated, such that they are substantially freely
rotatable in their encapsulation.
In an advantageous development of the method, an optically variable ink
layer is applied that further includes, in addition to the first and second
effect pigments, third, unencapsulated and magnetically alignable effect
pigments, the third effect pigments being permanently aligned by an
external magnetic field to form a motif in the form of patterns, lines,
characters or a code.
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Advantageously, the first, second and, if applicable, third effect pigments
are
mixed to form a pigment mixture and printed together, preferably in the
screen printing, flexo printing or intaglio printing technique. Alternatively,
first a purely magnetic layer having the second effect pigments can be
imprinted on the substrate, and over the purely magnetic layer, a purely ink
layer printed with the first effect pigments. If appropriate, a further layer
having the third effect pigments can be provided.
The motif of the third effect pigments, which is produced by the magnetic
alignment, is advantageously permanently fixed by UV curing.
The present invention further includes a security arrangement for securing
security papers, value documents and the like, having a security element of
the kind described and having a verification element having a magnetic
motif region in which magnetic material is present in the form of patterns,
lines, characters or a code. Here, the magnetic motif region is particularly
advantageously magnetized substantially vertically to the plane of the
verification element. The motif depicted by the magnetic motif region can be
openly visible or also not be perceptible without auxiliary means, for
example by covering with a dark printing layer.
In addition to the use of motif magnets for verification of the security
elements according to the present invention, also the use of other magnets
for verification may be considered. For example, nearly all modern mobile
phones include strong permanent magnets in the loudspeakers. Also
portable audio playback devices or their head- or earphones, as well as
product security systems at the point of sale, often include permanent
magnets of sufficient strength. Due to their wide prevalence, these magnets
are available to the user almost everywhere and can, especially with security
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elements that include an above-described magnetic background layer,
advantageously likewise be drawn on for the verification of security
elements according to the present invention.
The present invention also comprises a data carrier, especially a value
document, such as a banknote, a passport, a certificate, an identification
card
or the like, that is furnished with a security element of the kind described
or
with a security arrangement of the kind described. The security element can,
especially if it is present on a transparent or translucent substrate, also be
arranged in or over a window region or a through opening of the data
carrier.
If the data carrier includes both a security element according to the present
invention and an associated verification element, then these are
advantageously arranged geometrically on the data carrier in such a way
that the security element is bringable over the verification element by
bending or folding the data carrier.
A further object of the present invention is a verification device for
checking
the authenticity of a security element of the kind described, having a
magnetic motif region in which magnetic material is present in the form of
patterns, lines, characters or a code, and that is magnetized substantially
vertically to the plane of the motif region in order to magnetically align the
second effect pigments of the optically variable ink layer of the security
element.
Further exemplary embodiments and advantages of the present invention
are explained below by reference to the drawings, in which a depiction to
scale and proportion was omitted in order to improve their clarity.
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Shown are:
Fig. 1 a schematic diagram of a banknote having a security element
according to the present invention,
Fig. 2 the security element in fig. 1 together with a verification
device,
where, in (a), the security element and verification device are
spatially separated, and in (b), the security element rests on the
verification device,
Fig. 3 a cross section through a security element according to an
exemplary embodiment of the present invention, in the left half
of the image without verification device and in the right half of
the image with,
Fig. 4 a security element according to another exemplary
embodiment of the present invention in a cross-sectional
diagram as in fig. 3,
Fig. 5 a security element according to a further exemplary
embodiment of the present invention, in cross section,
Fig. 6 top views of a section of the security element in fig. 5, in
(a)
without verification device and in (b) with verification device,
Fig. 7 a security element according to yet a further exemplary
embodiment of the present invention, in cross section,
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Fig. 8 a banknote having a security arrangement according to the
present invention, composed of a security element and a
verification element arranged mirror-symmetrically relative to
the centerline,
Fig. 9 a security element according to a further exemplary
embodiment of the present invention in a cross-sectional
diagram as in fig. 3,
Fig. 10 a security element according to the present invention, having a
magnetically soft background layer upon verification with an
external magnet, and
Fig. 11 a security element according to the present invention, having a
magnetic background layer having a magnetic substance
having a medium to high coercive field strength.
The invention will now be explained using a banknote as an example. For
this, fig. 1 shows a schematic diagram of a banknote 10 having an optically
variable security element 12 that is imprinted directly on the banknote paper.
It is understood that the present invention is not limited to imprinted
security elements and banknotes, but can be used in all types of security
elements, for example in labels on goods and packaging or in securing
documents, identity cards, passports, credit cards, health cards and the like.
In banknotes and similar documents, besides, for example, imprinted
elements, also transfer elements, security threads or security strips may be
used, and besides top view elements, also see-through elements may be
used.
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In fig. 2, the optically variable security element 12 is depicted together
with
an external verification device 20, the security element 12 and the
verification
device 20 being clearly spatially separated from each other in fig. 2(a),
while
the security element 12 in the diagram in fig. 2(b) rests on the verification
device 20.
As depicted in fig. 2(a), without the verification device 20 or with a
sufficient
spatial separation from the verification device 20, the optically variable
security element 12 displays a metallic gloss that is combined with a weakly
pronounced, consistent color-shift effect. With the color-shift effect, the
color
impression of the security element changes for the viewer upon tilting the
security element, for example from green when viewed vertically from above
to blue when viewed obliquely. However, also other color shifts are
conceivable, such as from copper-colored to green or from gold-colored to
green.
The verification device 20 for the security element 12 exhibits a motif magnet
22 whose magnetization is indicated by the magnetic field lines 24 drawn in.
The magnetic material of the motif magnet 22 is arranged in the form of
patterns, lines, characters or a code and forms, in the exemplary
embodiment, the letter "H". Here, the magnetic north pole constitutes the top
of the magnet and the magnetic south pole the bottom of the magnet, such
that the magnetization of the motif magnet stands substantially vertical to
the plane of the magnetic material. It is understood that, in the general
case,
the motif magnet of the verification device 20 can depict arbitrary patterns,
characters or codes and that its magnetization can also be reversed or formed
by a more complex sequence of magnetic north and south poles. For a high
magnetization, besides conventional magnet materials, especially also
magnetic rare earth alloys, such as samarium-cobalt or neodymium-iron-
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boron alloys, may be used for the magnetic material of the motif magnet. The
present invention also includes embodiments that can be verified without
special motif magnets, as described in greater detail below.
If the user brings the security element 12 immediately over the verification
device 20, as shown in fig. 2(b), then in this way, he interactively changes
the
visual appearance of the security element 12 in the region 26 over the motif
magnet 22. The metallic gloss of the region 26 is significantly reduced and a
dark background layer becomes visible. At the same time, the color-shift
effect in the region 26 gains considerably in brilliance and intensity.
Instead of a consistently dark background, a piece of information, for
example lettering, a serial number, a denomination specification or the like,
can also be visible in the region 26. In the region 28 away from the motif
magnet 22, the visual impression of the security element 12 remains
unchanged. The motif depicted by the motif magnet 22 is thus
characteristically reflected in the region 26 as an image-like, brilliant
color-
shift region against a metallic background.
If the security element 12 and the verification device 20 are distanced from
each other again, the state shown in fig. 2(a) returns, such that the viewer
then again sees a consistently metallically gleaming surface having a weakly
pronounced color-shift effect. The security element 12 thus exhibits a
reversible and interactively triggerable authenticating mark.
The structure of the security element 12 and the occurrence of the reversible
change in the visual appearance will now be explained in greater detail with
reference to the cross-sectional diagram in fig. 3. Here, the left half of the
image in the figure shows the security element 12 without the verification
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device 20, or a region 28 away from the motif magnet 22. The right half of the
image shows a section of the security element region 26 that is arranged
immediately over the motif magnet 22.
To the banknote paper 30 of the banknote 10 is applied, in the region of the
security element 12, a printing layer 32 that can depict an arbitrary piece of
information, such as a line pattern 33, an alphanumeric character string, a
logo or the like. The printing layer 32 can also, as in the exemplary
embodiment in fig. 2, form a contiguously dark, for example black,
background layer. The printing layer 32 can especially be applied to the
banknote paper 30 by means of screen printing, flexo printing or intaglio
printing.
In the present case, over this generally information-bearing printing layer 32
is imprinted, in the screen printing method using a pigment mixture
composed of first effect pigments 34 and second effect pigments 36, an
optically variable ink layer 40 having a color-shift effect.
The first effect pigments 34 are optically variable pigments, for example
interference layer pigments having a thin film structure composed of a
reflection layer, an absorber layer and a dielectric spacing layer arranged
between the reflection layer and the absorber layer. Also pigments
manufactured on the basis of liquid crystal polymers or iridescent
pearlescent pigments, as sold by, for example, Merck KGaA under the name
Iriodin(R) or Colorcrypt, may be used as the first effect pigments 34.
Besides these optically variable first effect pigments 34, the pigment mixture
includes as second effect pigments magnetically alignable, platelet-like iron
pigments 36 that, in the exemplary embodiment, are manufactured from
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carbonyl iron powder treated under reducing conditions. Such platelet-like
iron pigments can be produced having a high ratio of platelet diameter to
platelet thickness, the (largest) platelet diameter being preferably between 6
p.m and 60 [tin, especially between 101.1m and 20 rim, and the platelet
thickness especially between 40 nm and 250 nm. Details of the manufacture
and properties of such platelet-like iron pigments are set forth in
publication
EP 1 251 152 B1, the disclosure of which is incorporated in the present
description by reference.
As a distinctive feature, the second effect pigments 36 are encapsulated and
substantially freely rotatable in their encapsulation 38. Without an external
magnetic field, the second effect pigments 36 ideally exhibit no preferred
orientation within their encapsulation 38, such that the whole of the second
effect pigments displays a substantially isotropic orientation. It is
understood
that, in practice, certain deviations from an ideal isotropic alignment can
occur, depending, for example on the geometric shape, the magnetizability,
the viscosity of the encapsulation liquid or the structure of the
encapsulation.
This substantially isotropic alignment of the second effect pigments 36
corresponds to the situation shown in the left half of the image in fig. 3,
with
only four different general alignments of the pigments 36 being depicted
there for illustration.
If the security element 12 is now brought over the motif magnet 22 of the
verification device 20, then the magnetically alignable second effect pigments
36 are aligned by its magnetic field. Here, the iron pigments 36 align with
their platelet expanse along the magnetic field lines 42. Due to the shape and
magnetization of the motif magnet 22 indicated in fig. 2, the magnetic field
lines 42 in the region 26 pass substantially vertically through the ink layer
40
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and align the iron pigments 36, which are freely rotatable in their
encapsulation, likewise substantially vertically to the plane of the ink layer
40, as shown in the right image portion in fig. 3.
Due to their platelet-like form, the iron pigments 36 act for the viewer like
the slats in a window blind that can reveal the view of the underlying layers
or fully or partially block it. In the regions 28 in which the iron pigments
36
are arranged substantially isotropically (left half of the image in fig. 3),
they
restrict the view of the underlying printing layer 32 so severely that the ink
layer 40 appears opaque in this region and the metallic gloss of the iron
pigments 36 dominates the visual impression of the security element.
Through the superimposition with the metallic gloss of the second effect
pigments 36, the color-shift effect of the first effect pigments 34 visually
recedes into the background and thus appears only weakly pronounced. It is
understood that, in practice, the opaque effect of the isotropically oriented
iron pigments 36 is produced by the multitude of pigments present, which
exceeds the few pigments 36 in the schematic diagram in fig. 3 by many
times.
In the region 26, in which the iron pigments 36 are aligned substantially
vertically to the plane of the ink layer 40 by the motif magnet 22, they
reveal,
like the parallel-set slats of a window blind, the view of the underlying
printing layer 32 and a piece of information 33 present there, if applicable.
The color-shift effect of the first effect pigments 34, which are not
influenced
by the external magnetic field, is, in principle, present in both sub-regions
26
and 28. However, due to the superimposition with the metallic gloss of the
isotropically oriented second effect pigments 36, it is normally significantly
more weakly pronounced in the sub-region 28 than in the sub-region 26. The
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brilliance of the color-shift effect in the sub-region 26 also depends on the
design of the background layer 32, a particularly high brilliance being
achieved when dark inks are used.
Due to the relatively high ratio of platelet diameter to platelet thickness,
it is
possible to produce a high contrast between opaque sub-regions 28 and
translucent sub-regions 26. Furthermore, the motif produced by the platelet
orientation in the sub-regions 26, 28 appears for the human eye having an
impactful, three-dimensional-seeming appearance that is also referred to, in
the context of this description, as a 3D effect or 3D impression of the motif.
If the verification device 20 is removed from the security element 12 again,
then, after some time, the magnetically aligned iron pigments 36 relax again,
due to their free movability within the encapsulation 38, into the
substantially isotropic initial state of the left half of the image in fig. 3.
In this
way, the change in the visual appearance of the security element 12 can be
interactively triggered and reversibly withdrawn again. However, without a
restoring force, the return to the isotropic initial state can take several
minutes, hours or even days. In the event that a quicker return is desired,
there can, as described above, be provided within the encapsulation 38 a gel,
for example, that provides a restoring force for the magnetically alignable
iron pigments 36.
For the production of the ink layer 40, the second effect pigments 36 were
first encapsulated 38, the encapsulated effect pigments 36, 38 then mixed
with the first effect pigments 34 and printed together in screen printing. The
encapsulation of the second effect pigments can occur, for example, in that
iron pigments of suitable size are selected, are dispersed in a water-
insoluble
solvent, suitable micellar precursors having a controlled particle size are
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prepared in water, and these are encapsulated with acrylated gelatin
through coacervation. Also other capsule materials, as described above, are
conceivable.
The further exemplary embodiment in fig. 4 shows a security element 50 that
permits an additional interactive influencing of the visual appearance, for
example through touch. For this, a substrate 52 is provided with an imprint
54, especially an offset imprint in the form of patterns, lines, characters or
a
code 56. On the imprint 54 is applied, in screen printing, flexo printing or
intaglio printing, a thermochromic background layer 58, and on the
thermochromic layer 58 is imprinted an optically variable ink layer 40
having first 34 and second effect pigments 36, as described in connection
with fig. 3.
Here, the thermochromic layer 58 is designed such that the color-shift effect
of the ink layer 40 disappears for the viewer upon activation of the
thermochromic layer 58, and only the basic structure of the iron pigments 36
is visible. If the thermochromic layer 58 changes its color, for example upon
activation through temperature increase, from black (or generally a dark
appearance) to white (or generally a light appearance), then the brilliance of
the color-shift effect upon activation is significantly reduced, up to a
degree
at which the optically variable effect of the first effect pigments 34
completely disappears for the viewer. At the same time, the imprint 54, 56 is
perceptible for the viewer through the then very light layer 58.
Upon cooling, the color of the thermochromic layer 58 changes back to black
or to the original dark appearance again, the color-shift effect of the ink
layer
40 then appears again clearly and the dark layer 58 covers anew the imprint
54, 56 arranged under it.
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In this way, a 3D piece of information made visible with the aid of the
verification device 20 can be interactively removed through a temperature
increase, or reduced to a two-dimensional piece of information. Here, the
thermochromic layer 58 acts as an interactive switch with which the view of
the imprint 54 or the piece of information 56 can be revealed for the viewer.
The thermochromic layer 58 can be developed to be contiguous, or be
provided with a piece of information, for example in the form of patterns,
lines, characters or a code. It can also exhibit a mixture of different
thermochromic inks having different activation temperatures such that,
upon a temperature increase, a cascade of changing optically variable effects
is created.
While, in the exemplary embodiments in figures 3 and 4, the first effect
pigments 34 are present outside the encapsulation 38 of the second effect
pigments 36, the first effect pigments can also be encapsulated in
microcapsules together with the second effect pigments, as shown in fig. 9.
Here, the structure of the security element 100 in fig. 9 largely corresponds
to
the structure already described for fig. 3. However, in contrast to this, the
platelet-like first effect pigments 102 manufactured on the basis of liquid
crystal polymers are encapsulated in microcapsules 106 together with the
platelet-like iron pigments 104. In this embodiment, upon alignment, the
orientation of the first effect pigments 102 changes together with the
orientation of the second effect pigments 104, such that dynamic optical
variable effects result. Through the joint rotation, also here, particularly
the
degree of markedness of the viewing-angle-dependent visual impression of
the first effect pigments 102 changes with the orientation of the second
effect
pigments 104 relative to the plane of the ink layer 40.
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In the further exemplary embodiment in fig. 5, the security element 60
includes an optically variable ink layer 40 that, in addition to the first
effect
pigments 34 already described in connection with figures 2 to 4 and the
encapsulated second effect pigments 36, 38, further includes third,
unencapsulated, magnetically alignable effect pigments 62, 64. The third
effect pigments are magnetically aligned in the form of a specified motif, a
simple strip motif composed of alternating strips 66, 68 being shown for
illustration in the exemplary embodiment shown in fig. 5.
Unlike the alignment of the second effect pigments, which can be
interactively and reversibly changed by the user with the aid of a suitable
verification device, the alignment of the third effect pigments 62, 64 is
unchanging and permanently fixed. As materials for the third effect
pigments, as for the second effect pigments, especially magnetically
alignable, platelet-like iron pigments 62, 64 may be used that can be
manufactured from carbonyl iron powder treated under reducing conditions
and that preferably exhibit the sizes and properties already specified in the
description of the second effect pigments. The second and third effect
pigments introduced into the ink layer can also be identical except for the
missing encapsulation of the third effect pigments.
For the manufacture of the ink layer 40, the first effect pigments 34, the
encapsulated second effect pigments 36, 38 and the unencapsulated third
effect pigments 62, 64 were mixed and printed together in screen printing.
Then a suitable external magnetic field having the form of the desired motif
was applied to magnetically align the third effect pigments. As already
described above, the magnetically alignable iron pigments 36, 62, 64 align
themselves in the external field with their platelet expanse along the
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magnetic field lines such that, in those regions 68 in which, in the alignment
step, the magnetic field lines stand vertical to the substrate plane, the iron
pigments 64 are aligned substantially vertical to the plane of the ink layer
and, accordingly, in the regions 66 in which the magnetic field lines run
parallel to the substrate plane, an orientation of the iron pigments 62 lying
substantially in the plane of the ink layer results, as depicted in fig. 5.
The ink layer 40 is then dried with the still magnetically aligned iron
pigments 36, 62, 64. Here, to permanently fix the magnetically produced
motif of the third effect pigments 62, 64, especially UV-curing color systems
are used, with purely UV systems, UV/water-based systems or also
UV/solvent-based systems being able to be used. Through the drying step,
the aligned, unencapsulated third effect pigments 62, 64 are permanently
fixed in their orientation, while the encapsulated second effect pigments 36,
due to their free rotatability within the encapsulation, return again to a
substantially isotropic alignment distribution after the removal of the
external magnetic field.
Upon viewing the security element 60 without the verification device 20, its
visual impression is dominated by the isotropically distributed and thus
opaque-appearing second effect pigments 36. As depicted in the top view in
fig. 6(a), the security element 60 without verification device thus displays a
metallic gloss that is combined with a weakly pronounced, consistent color-
shift effect.
If the security element 60 is brought over the verification device 20 having
the motif magnet 22, then the movable and magnetically alignable second
effect pigments 36 are aligned in some regions, by the magnetic field of the
verification device, vertically to the plane of the ink layer 40, as already
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described in connection with fig. 3. The permanently fixed third effect
pigments 62, 64 and the non-magnetic first effect pigments 34 are not
influenced by the magnetic field of the verification device 20.
In the strip regions 68, both the second effect pigments 36 and the third
effect
pigments 64 are then oriented vertically to the plane of the ink layer 40 such
that the view of the printing layer 32 is revealed there. In contrast, in the
strip regions 66, the third effect pigments 62 oriented parallel to the plane
of
the ink layer block the view through, the ink layer 40 remains opaque there
also in the presence of the verification device 20.
In this way, as depicted in the top view in fig. 6(b), for one, the
verification
device 20 reveals, within the region of the motif magnet 22, the permanently
fixed magnetic motif 66, 68 that, due to its occurrence through the different
alignments of platelet-like pigments 62, 64, exhibits a pronounced 3D effect
for the viewer. In fig. 5, for the sake of simplicity, only two orientations
of
the third effect pigments 62, 64 are shown, but it is understood that, through
appropriate orientation of the magnetic field lines in the alignment step, it
is
possible to set arbitrary angles between the iron pigment platelets and the
plane of the ink layer, and thus also to produce complex, magnetic motifs.
If the printing layer 32 includes a piece of information 33, in the shown
exemplary embodiment for instance the repeating numeric string "10," then,
for another, this piece of information 33 becomes visible in the sub-regions
of
the strips 68 that lie over the motif magnet 22, while it always remains
covered in the opaque-appearing strips 66. Through a movement of the motif
magnet 22 over or under the security element 60, the user can interactively
and reversibly make visible the initially hidden 3D motif 66, 68 and the piece
of information 33 of the printing layer 32 across the entire region of the
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security element 60. Such an interactive embodiment has a high recognition
value for the viewer and thus generally exhibits a very high counterfeit
security.
The second and third effect pigments can also be present in separate regions
of a security element 70, as shown in the exemplary embodiment in fig. 7.
The security element 70 includes in a sub-region 72 a permanently fixed
magnetic motif 74, 76 having a 3D effect that, as already explained for fig.
5,
is produced by the different magnetic alignments and subsequent fixation of
unencapsulated iron pigments 78.
In a further sub-region 80, the iron pigments 82 are present in encapsulated
form and thus reversibly alignable. In the sub-region 80, the visual
appearance of the security element 70 can then be interactively changed with
the aid of a verification device 20. In particular, for this purpose, a
verification device 20 having a motif magnet can be used whose motif
corresponds to the permanently fixed magnetic motif 74, 76. When checking
the authenticity, then, in addition to the 3D motif 74, 76, the same motif is
depicted again interactively in the region 80, such that a self-explanatory
security element having a high attention value is created.
It is understood that also the embodiments in figures 5 and 7 can, if needed,
be combined with a thermochromic background layer to create a further
interaction possibility.
In the embodiments described so far, the authenticity check of the security
element applied to the banknote 10 occurs in each case with a separate
verification device 20. However, for the authenticity check, it is also
possible
to provide a verification element on the banknote itself such that the
security
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element and the verification element form a cohesive security arrangement,
as now explained with reference to the exemplary embodiment in fig. 8.
The banknote 90 shown in fig. 8(a) includes a security element 92 of the kind
described above, and a verification element 94 that, with respect to the
centerline 96 of the banknote 90, is applied mirror-symmetrically to the
security element 92. The verification element 94 exhibits a magnet region 98
in which magnetic material is present having a magnetization vertical to the
paper plane and in the form of a desired motif, such as the crest depicted by
way of example in fig. 8(a). The motif form of the magnet region 98 can be
openly visible or also be covered, for example by a dark overprint.
By folding the banknote 90 about the centerline 96, the verification element
94 having the magnet region 98 comes to lie on the security element 92, as
shown in fig. 8(b). The magnetization of the magnet region 98 then
interactively and reversibly changes the visual impression of the security
element 92 in the manner described above. For example, the visual
appearance of the security element 92 can change from a uniform metallic
gloss having a weakly pronounced, consistent color-shift effect (fig. 8(a)) to
a
motif depiction of a crest in which the inside of the crest stands out dark
and
having a brilliant, clearly pronounced color-shift effect. In the inside of
the
crest, also further information can be visible, such as the denomination of
the
banknote. The banknote 90 can thus be checked for authenticity by simple
folding, without external verification means being required.
If the security element and the verification element will be arranged on the
same data carrier, it is particularly appropriate to coordinate the motif that
appears when checking the authenticity with a motif that is openly visible on
the data carrier, such as the denomination of a banknote, an imprinted logo
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or the like, since the authenticity check is then self-explanatory for the
user
and a particularly easy distinguishability and verifiability is ensured.
It is possible to produce further interesting effects with embodiments in
which the optically variable ink layer 40 is combined with a magnetic
background layer that can be present contiguously or in the form of patterns,
characters or a code. For the security element 110 in fig. 10, on a substrate
112
composed of paper or foil is applied a magnetic background layer 114 that
exhibits, in the form of a desired motif, regions 116 having a magnetically
soft substance 120 of low or negligible remanence. Over the magnetic
background layer 114 is arranged an optically variable ink layer 40 having
encapsulated, magnetically alignable effect pigments 122 of the kind
described above. The likewise present first effect pigments are not shown in
fig. 10, to improve diagram clarity.
With an isotropic alignment of the effect pigments 122, the motif formed by
the magnetic background layer 114 is not perceptible without an external
magnetic field. If the security element 110 is now exposed to the magnetic
field of an external magnet 124, then the magnetic background layer 114
largely shields the external magnetic field in the regions 116. The
magnetically alignable effect pigments 122 are thus not influenced in these
regions 116, or are influenced only a little, and remain substantially in
their
isotropic initial orientation. In contrast, the effect pigments 122 in the
unshielded regions 118 align, as described above, along the magnetic field
lines.
As a result, in interplay with the optically variable first effect pigments
and/
or further background layers, in effect, a different visual appearance of the
regions 116 and 118 results such that the motif formed by the magnetic
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background layer 114 becomes visible for the viewer. After removal of the
external magnet 124, no magnetization remains in the magnetic background
layer 114 due to the low remanence of the magnetic material 120, such that
the effect pigments 122 return to their initial position again and the
displayed motif disappears again.
Here, the verification can occur with an arbitrary magnet 124, since the
displayed motif is stored in the magnetic background layer 114 of the
security element 110 itself. Especially permanent magnets that are easily
available everywhere are suitable, such as are built into mobile phones,
portable audio playback devices or product security systems.
Fig. 11 shows a security element 130 according to a modification of the
embodiment in fig. 10, in which the magnetic background layer 132 includes
a contiguous magnetic substance having a medium to high coercive field
strength (50 kA/m to 300 kA/m).
The magnetic background layer 132 was initially magnetized by a strong
permanent magnet in the form of a desired motif having regions of high field
strength or very low field strength. Due to the remanence of the magnetic
material 132, an appropriate magnetization having regions of high
magnetization 134 or of very low magnetization 136 remains in the
background layer 132 also after cessation of the external magnetic field.
Here, the field strength of the regions of high magnetization 134 is large
enough to hold the reversibly aligmable second effect pigments 122 in their
position, while the orientation of the second effect pigments 122 in the
regions of very low magnetization 136 remains substantially isotropic. The
initially embossed magnetic pattern 134, 136 is thus preserved.
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In a further variant, the magnetic background layer 132 can also include a
magnetic substance having a very high coercive field strength of more than
300 kA/m. Such a hard magnetic material can be remagnetized only with
very strong magnetic fields, such that, with normal usage, an initially
introduced pattern is permanently preserved.
