U.S. patent application number 14/439526 was filed with the patent office on 2015-10-22 for multilayer body and method for producing a security element.
The applicant listed for this patent is OVD KINEGRAM AG. Invention is credited to Wayne Robert Tompkin, Harald Walter.
Application Number | 20150298482 14/439526 |
Document ID | / |
Family ID | 49553693 |
Filed Date | 2015-10-22 |
United States Patent
Application |
20150298482 |
Kind Code |
A1 |
Walter; Harald ; et
al. |
October 22, 2015 |
Multilayer Body and Method for Producing a Security Element
Abstract
A multilayer body (1, 2, 3) and a method for producing a
security element are described. The multilayer body has a metal
layer (21). An optically active surface relief is molded at least
in areas in a first surface of the metal layer (21) facing the
upper side of the multilayer body or forming the upper side of the
multilayer body and/or in a second surface of the metal layer (21)
facing the underside of the multilayer body or forming the
underside of the multilayer body. In at least one first area (31 to
39) of the multilayer body the surface relief is formed by a first
relief structure (61). In at least one direction (617) determined
by an allocated azimuth angle, the first relief structure (61) has
a sequence of elevations (612) and depressions (614), the
elevations (612) of which follow on from each other with a period P
which is smaller than a wavelength of visible light, wherein the
minima of the depressions (614) lie on a base surface and the first
relief structure (61) has a relief depth t which is determined by
the spacing of the maxima of the elevations (612) of the first
relief structure (61) from the base surface in a direction
perpendicular to the base surface. The profile shape and/or the
relief depth t of the first relief structure (61) is chosen such
that the colored appearance of the light (52, 53) incident on the
first area (31 to 39) at least at a first angle of incidence and
directly reflected by the metal layer (21) in the first area or
directly transmitted through the metal layer is modified, in
particular is modified by plasmon resonance of the metal layer with
the incident light.
Inventors: |
Walter; Harald; (Horgen,
CH) ; Tompkin; Wayne Robert; (Baden, CH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OVD KINEGRAM AG |
Zug |
|
CH |
|
|
Family ID: |
49553693 |
Appl. No.: |
14/439526 |
Filed: |
November 6, 2013 |
PCT Filed: |
November 6, 2013 |
PCT NO: |
PCT/EP2013/073193 |
371 Date: |
April 29, 2015 |
Current U.S.
Class: |
359/572 ;
101/32 |
Current CPC
Class: |
B41F 19/02 20130101;
B42D 25/324 20141001; G02B 5/1852 20130101; B42D 2035/24 20130101;
B42D 25/328 20141001; B42D 25/29 20141001; B42D 25/342 20141001;
G02B 5/1842 20130101; G03H 1/0244 20130101; B42D 25/378 20141001;
B42D 25/373 20141001; G03H 1/0011 20130101; G02B 5/008 20130101;
B42D 25/36 20141001; G02B 5/1861 20130101; G02B 5/1819
20130101 |
International
Class: |
B42D 25/29 20060101
B42D025/29; G02B 5/18 20060101 G02B005/18; G03H 1/00 20060101
G03H001/00; B42D 25/328 20060101 B42D025/328; G03H 1/02 20060101
G03H001/02; B41F 19/02 20060101 B41F019/02; G02B 5/00 20060101
G02B005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 6, 2012 |
DE |
10 2012 110 630.4 |
Claims
1. A multilayer body, in particular security element for security
documents, with an upper side and an underside, wherein the
multilayer body has a metal layer, wherein in a first surface of
the metal layer facing the upper side of the multilayer body or
forming the upper side of the multilayer body and/or in a second
surface of the metal layer facing the underside of the multilayer
body or forming the underside of the multilayer body an optically
active surface relief is molded at least in areas, wherein in at
least one first area of the multilayer body the surface relief is
formed by a first relief structure which, in at least one direction
determined by an allocated azimuth angle, has a sequence of
elevations and depressions, the elevations of which follow on from
each other with a period P which is smaller than a wavelength of
visible light, wherein the minima of the depressions lie on a base
surface and the first relief structure has a relief depth t which
is determined by the spacing of the maxima of the elevations of the
first relief structure from the base surface in a direction
perpendicular to the base surface, and wherein the profile shape
and/or the relief depth t of the first relief structure is chosen
such that the colored appearance of the light incident on the first
area at least at one first angle of incidence and reflected
directly by the metal layer in the first area or transmitted
directly through the metal layer is modified, by plasmon resonance
of the metal layer with the incident light.
2. A multilayer body according to claim 1, wherein the profile
shape and/or the relief depth t of the first relief structure is
chosen such that the metal layer, in the case of direct reflection
for the light incident at the first angle of incidence, in the
first area, in a first spectral range visible to the human eye with
a width of at least 50 nm, has a reflectance of less than 10%, and
in a second spectral range visible to the human eye with a width of
20 nm to 150 nm, has a reflectance that is at least 4 times higher,
relative to the average value of the reflectance in the first
spectral range.
3. A multilayer body according to claim 1, wherein the profile
shape and/or the relief depth t of the first relief structure is
chosen such that at a second angle of incidence different from the
first angle of incidence the colored appearance of the light
reflected directly by the metal layer in the first partial area or
transmitted directly through the metal layer is modified
differently wherein different colors appear at these angles of
incidence in the case of reflected light observation and in the
case of transmitted light observation.
4. A multilayer body according to claim 1, wherein the first relief
structure has a profile shape that is asymmetrical in relation to a
specular reflection at the base surface.
5. A multilayer body according to claim 1, wherein the width of the
elevations or depressions of the first relief structure, relative
to a distance of t/2 from the base surface, is at least
0.6.times.P, or at most 0.3.times.P.
6. A multilayer body according to claim 1, wherein the edge
steepness of the first relief structure, relative to a distance t/2
from the base surface, is between 70.degree. and 85.degree..
7. A multilayer body according to claim 1, wherein the edge
steepness of the first relief structure, relative to each distance
between t/4 and 3/4 t from the base surface, is between 50.degree.
and 85.degree..
8. A multilayer body according to claim 1, wherein the edge
steepness of the first relief structure, relative to each distance
between 0 and t/4 and/or between t.times.3/4 from the base surface,
is between 0.degree. and 40.degree..
9. A multilayer body according to claim 1, wherein the layer
thickness d of the metal layer in the area of the edges of the
first relief structure, relative to a distance of t/2 from the base
surface, is reduced by at least 30%, compared with the thickness of
the metal layer in the area of the maxima of the elevations and/or
the minima of the depressions.
10. A multilayer body according to claim 1, wherein the period P of
the first relief structure is between 250 nm and 450 nm.
11. A multilayer body according to claim 1, wherein the relief
depth t of the first relief structure is between 100 nm and 400
nm.
12. A multilayer body according to claim 1, wherein in the first
area, the metal layer has a layer thickness of between 10 nm and
100 nm.
13. A multilayer body according to claim 1, wherein in the first
area, the metal layer has a layer thickness d which corresponds to
an optical depth of between 0.7 and 2.3.
14. A multilayer body according to claim 1, wherein the first
relief structure is a cross grating which has a sequence of
elevations and depressions in two directions.
15. A multilayer body according to claim 1, wherein the surface
relief in one or more second areas and/or further areas is formed
by a second and/or further relief structure(s) which is or are
selected from the group: diffractive relief structure, holographic
relief structure, mirror surface, mat structure, macrostructure,
lens, grid of microlenses.
16. A multilayer body according to claim 15, wherein the at least
one first area and the at least one second area are formed by a
plurality of partial areas, wherein the partial areas of the first
area and the partial areas of the second area are interleaved.
17. A multilayer body according to claim 15, wherein the at least
one second area is formed by a plurality of partial areas separated
from each other, and the first area surrounds these partial areas
of the background area.
18. A multilayer body according to claim 1, wherein the first area
or at least one of the first areas has a patterned shaping and has
a shaping which contains an item of information which can only be
made visible using an aid, and is molded in the form of a nanotext
or a moire pattern.
19. A multilayer body according to claim 1, wherein the first area
or at least one of the first areas comprises one or more first
zones in which one or more of the parameters of the first relief
structure selected from the group: period P, azimuth angle, relief
depth t, base surface area and profile shape, differ from the
corresponding parameters of the first relief structure in one or
more second zones and/or one or more further zones of the first
area.
20. A multilayer body according to claim 19, wherein the one or
more first and second zones are molded to form a motif, wherein the
first zones form a foreground area of the motif and the second
zones form a background area of the motif, or wherein the one or
more first zones are molded to form a first motif and the one or
more second zones are molded to form a second motif.
21. A multilayer Multilayer body according to claim 19, wherein the
first, second and/or further zones in each case have at least one
lateral dimension of less than 150 .mu.m, and wherein the first,
second and/or third zones are interleaved.
22. A multilayer body according to claim 19, wherein the first
zones are arranged to represent a first motif and the second zones
are arranged to represent a second motif, or wherein the first and
the second zones are arranged to generate a multicolored
representation or to generate mixed colors by means of additive
color mixing.
23. A multilayer body according to claim 1, wherein in the first
area or in at least one of the first areas the base surface of the
first relief structure is formed by a mat structure.
24. A multilayer body according to claim 1, wherein in the first
area or in at least one of the first areas, the period P of the
first relief structure is varied in areas, by up to 10%.
25. A multilayer body according to claim 1, wherein in the first
area or in at least one of the first areas the azimuth angle of the
first relief structure is varied in areas.
26. A multilayer body according to claim 1, wherein the first area
or at least one of the first areas has a plurality of partial
areas, wherein each of the partial areas has a minimum dimension of
more than 3 .mu.m and a maximum dimension of less than 300 .mu.m,
wherein one or more of the parameters selected from the group:
shape of the partial area, area size of the partial area, position
of the center of area of the partial area, inclination angle of the
base surface of the first relief structure relative to a base
plane, angle of rotation of the base surface of the first relief
structure about an axis perpendicular to the base plane, azimuth
angle of the first relief structure, period P of the relief
structure, is varied pseudorandomly, for each of the partial areas,
within a variation range predefined in each case for the first
area.
27. A multilayer body according to claim 1, wherein the first area
or at least one of the first areas has a plurality of partial
areas, and wherein the parameters of the first relief structure in
each of the partial areas is chosen according to a relief structure
selected from a set of predefined relief structures pseudorandomly
for the respective partial area.
28. A multilayer body according to claim 1, wherein in the first
area or in at least one of the first areas the multilayer body has
dyes and/or luminescent substances which are arranged less than 1
.mu.m, away from the first surface and/or the second surface of the
metal layer.
29. A multilayer body according to claim 1, wherein the multilayer
body has at least one first layer bordering the first surface of
the metal layer and/or one second layer bordering the second
surface of the metal layer, which second layer has dyes and/or
luminescent substances, wherein the first and/or second layer
covers the first surface or the second surface of the metal layer
in areas or over the whole surface in the first area or in at least
one of the first areas in which the first relief structure is
molded into the first or second surface.
30. A multilayer body according to claim 29, wherein the first
layer and/or the second layer is applied to the first surface or
second surface of the metal layer only in the first area, or the
first layer and/or the second layer is applied to the first or
second surface of the metal layer only in areas of the first
surface or second surface in which the first relief structure is
molded into the first surface or second surface.
31. A multilayer body according to claim 29, wherein the first
layer and/or the second layer has a layer thickness of between 50
nm and 1 .mu.m.
32. A multilayer body according to claim 29, wherein the
concentration of the dyes or luminescent substances in the area of
the first and/or second layer less than 500 nm, away from the first
or second surface of the metal layer is higher than in the
remaining area of the first or second layer.
33. A multilayer body according to claim 29, wherein the first
layer and/or the second layer is a replication varnish layer, a
layer arranged between a replication varnish layer and the metal
layer, or a protective varnish layer.
34. A multilayer body according to claim 28, wherein the dye and/or
luminescent substance is a soluble dye or luminescent substance
which is dissolved in the binder of the first layer or of the
second layer.
35. A multilayer body according to claim 29, wherein the first
layer and/or the second layer has a transmittance of at least 70%,
preferably of at least 90%, in the wavelength range visible to the
human eye.
36. A multilayer body according to claim 29, wherein the
concentration of the dye and/or luminescent substances in the first
layer and/or in the second layer is chosen such that the optical
action thereof in a second area in which the surface relief is
formed by a mirror surface, a diffractive structure, a
macrostructure or a mat structure is not visible to the human
observer at an observation distance of more than 30 cm and under an
illumination with an illuminance of less than 10,000 LUX.
37. A multilayer body according to claim 29, wherein the percentage
by weight of the dye and/or of the luminescent substance in the dry
weight of the first and/or second layer is between 0.5% and
10%.
38. A multilayer body according to claim 29, wherein the color of
the dye and/or luminescent substance of the first and/or second
layer is chosen such that its color, or its color when excited,
corresponds to the color generated by the first relief structure
for a particular angle of incidence of the incident light in direct
reflection or transmission or differs from these colors.
39. A multilayer body according to claim 29, wherein two or more
first layers and/or two or more second layers are provided, the
dyes or luminescent substances of which are chosen such that the
color of the dyes or luminescent substances of the first layer
and/or of the second layer mutually differ, and wherein the first
area or at least one of the first areas has a first partial area
which is covered with one of the first and/or second layers and has
a second partial area which is covered with another of the first
and/or second layers.
40. A multilayer body according to claim 1, wherein the multilayer
body is a transfer film, a laminating film or a security
thread.
41. A multilayer body according to claim 1, wherein the multilayer
body is a security element of a banknote or an ID document.
42. A multilayer body according to claim 1, wherein the multilayer
body is a banknote, a card or an ID document.
43. A method for producing a security element comprising:
manufacturing a multilayer body comprising a metal layer with an
optically active surface relief molded into a first surface and/or
a second surface opposite the first surface, wherein in at least
one first area of the multilayer body the surface relief is formed
by a first relief structure which, in at least one direction
determined by an allocated azimuth angle, has a sequence of
elevations and depressions, the elevations of which follow on from
each other with a period P which is smaller than a wavelength of
visible light, wherein the minima of the depressions define a base
surface and the first relief structure has a relief depth t which
is determined by the spacing of the maxima of the elevations of the
relief structure from the base surface in a direction perpendicular
to the base surface, and wherein the profile shape and/or the
relief depth t of the first relief structure is chosen such that
the colored appearance of the light incident on the first area at
least at one first angle of incidence and reflected directly by the
metal layer in the first area or transmitted directly through the
metal layer is modified by plasmon resonance of the metal layer
with the incident light.
44. A method according to claim 43, wherein the multilayer body is
formed as a transfer film, and wherein, by means of an embossing
stamp formed patterned, a partial area of the multilayer body
molded correspondingly patterned is stamped onto a substrate.
45. A method according to claim 44, wherein the surface of the
substrate onto which the multilayer body is stamped has a coarse
structure or a mat structure, and wherein the stamping pressure is
chosen such that the base surface of the first relief structure is
deformed according to the coarse structure or mat structure during
the stamping.
46. A method according to claim 43, wherein a blind embossing die
with a coarse structure molded in the embossing surface is pressed
onto the multilayer body, and wherein the stamping pressure is
chosen such that the base surface of the first relief structure is
deformed according to the coarse structure of the blind embossing
die.
Description
[0001] The invention relates to a multilayer body, in particular a
security element for security documents, as well as a method for
producing a security element.
[0002] It is known to apply to banknotes security elements which
have a hologram or a computer-generated diffraction grating. Such
security elements usually generate an optically variable effect by
targeted diffraction of the incident light in the first or in
higher diffraction orders and thus usually display only the
impression of a mirror surface in direct reflection.
[0003] Further, it is known to generate color effects in direct
reflection by using interference filters which can be added to a
printing ink for example in the form of interference layer
pigments. These interference filters are based on multilayer
systems made of conductive and/or nonconductive (dielectric)
layers, e.g. metal/nonconductive/metal or
nonconductive/nonconductive/nonconductive, wherein the
nonconductive layers have different refractive indices.
[0004] Further, in WO 03/059643 A1 the structure of a specific
security element is described which has an integrated optical
waveguide made of a transparent dielectric. The waveguide is
embedded between layers of plastic into which a zero-order
diffraction grating is molded. Color effects can also be generated
in direct reflection here by the coupling of the incident light
into and out of the waveguide.
[0005] The object of the invention is to specify a multilayer body
and a method for producing a security element which is
characterized by a high level of protection against forgery.
[0006] This object is achieved by a multilayer body with a metal
layer in which an optically active surface relief is molded at
least in areas in a first surface of the metal layer facing the
upper side of the multilayer body or forming the upper side of the
multilayer body and/or in a second surface of the metal layer
facing the underside of the multilayer body or forming the
underside of the multilayer body, wherein in at least one first
area of the multilayer body the surface relief is formed by a first
relief structure which, in at least one direction determined by an
allocated azimuth angle, has a sequence of elevations and
depressions, the elevations of which follow on from each other with
a period P which is smaller than a wavelength of visible light, and
wherein the minima of the depressions define a base surface and the
first relief structure has a relief depth t which is determined by
the spacing of the maxima of the elevation of the first relief
structure from the base surface in a direction perpendicular to the
base surface. This object is further achieved by a method for
producing a security element in which a multilayer body comprising
a metal layer with an optically active surface relief molded in a
first surface or a second surface opposite the first surfaces is
manufactured, wherein in at least one first area of the multilayer
body the surface relief is formed by a first relief structure
which, in at least one direction determined by an allocated azimuth
angle, has a sequence of elevations and depressions, the elevations
of which follow on from each other with a period P which is smaller
than a wavelength of visible light, and wherein the minima of the
depressions define a base surface and the first relief structure
has a relief depth t which is determined by the spacing of the
maxima of the elevations of the relief structure from the base
surface in a direction perpendicular to the base surface. The
profile shape and/or the relief depth t of the first relief
structure here is chosen in particular such that the colored
appearance of the light incident on the first area at least at a
first angle of incidence and directly reflected by the metal layer
or directly transmitted through the metal layer is modified, in
particular is modified by plasmon resonance of the metal layer with
the incident light.
[0007] The quantized oscillations of the charge carrier density in
semiconductors, metals and insulators are called plasmons; quantum
mechanically they are treated as quasiparticles. The term plasmon
is a common abbreviation for quantum of plasma oscillation. What
the photon is to electromagnetic waves, the plasmon is to
oscillations in the Fermi gas of metals. A distinction is drawn
between particle plasmons, surface plasmons and bulk plasmons. The
first two belong to the plasmon polaritons, as here oscillations of
the electron density couple with electromagnetic fields outside the
metal. Strictly speaking, surface and particle plasmons should thus
be given the adjunct polariton. The plasmon resonance in the
security elements described in this document comes under the
category of plasmon polaritons. Classically, plasmons can be
visualized as electrons which oscillate relative to the positive
ions. For better clarification, imagine a cubic metal block in a
field oriented to the right. The free electrons now move to the
left, until the field inside is balanced out. Positive ions are
uncovered at the right-hand edge. If the external field is now
switched off, the electrons migrate back to the right because they
repel each other and are attracted to the positive ions. Thus the
electrons now oscillate back and forth at the plasma frequency
until the energy is used up by friction or other kinds of damping.
Plasmons are the quantization of this natural oscillation.
[0008] The invention offers the advantage of providing security
elements with an optical appearance which clearly sets itself apart
from the previously known hologram effects with a silvery gloss
and/or in rainbow colors, and of providing novel color effects
which further increase the level of protection against forgery of
security documents. Further, these effects also cannot be imitated
by means of usual holographic techniques, and also cannot be copied
by means of dot matrix and KineMax devices, with the result that a
significant increase in the level of protection against forgery is
also effected hereby. Furthermore, this multilayer body can be
produced more cost-effectively than the known interference filters
(e.g. Fabry-Perot filters), which are usually constructed from
three or more layers, sometimes with very low thickness
tolerances.
[0009] The optical appearance of the multilayer body is
characterized in particular by a defined (i.e. largely
monochromatic) color impression (e.g. red) which is to be seen in
direct reflection and or transmission (thus under "normal"
observation conditions). The color impression is stable over a
relatively wide range of tilt angles (typically at least 10.degree.
to 20.degree.). This color impression changes, in the case of a
severe tilt (e.g. by 30.degree., to a second defined and stable
color impression (e.g. green), similar to the case of so-called
Fabry-Perot thin-film filters. Through this stability against
slight tilting, it clearly differs from so-called rainbow color
effects of first- or higher-order diffraction gratings, which often
pass through the whole color palette of the rainbow when tilted by
only 10.degree.. Furthermore, the rainbow color effects of
diffraction gratings appear, not in direct reflection, but at other
angles, which can be calculated using the diffraction equation.
[0010] According to a preferred embodiment example of the invention
the first relief structure has a profile shape that is asymmetrical
in relation to a specular reflection at the base surface. It has
surprisingly been shown, after lengthy investigations, that such
profile shapes generate a much more visible and clearer color
impression for the human observer than symmetrical profile shapes,
for example symmetrical sinusoidal or rectangular profile shapes.
Profile shapes that are symmetrical in this sense are characterized
by a mirror symmetry in respect of the base surfaces. These profile
shapes remain the same during this specular reflection, the relief
structure is only shifted by half a period P. The optical effects
in the case of observation from the two sides (at the same angle
and under the same illumination conditions) are the same in the
case of these mirror-symmetrical profile shapes, if the first
relief structure is molded in both surfaces of the metal layer and
the metal layer is embedded on both sides in a material with the
same refractive index. Asymmetrical profile shapes in this sense do
not have this mirror symmetry in the plane spanned by the base
surface. These profile shapes are different when observed from the
two sides. For example, a first relief structure with such an
asymmetrical profile shape can consist of an arrangement of narrow
peaks with wide valleys when observed from one side and can consist
of wide hills with deep, narrow valleys when observed from the
other side. Thus, investigations have also surprisingly shown that
in the case of such a formation of the profile shapes, in respect
of the plasmon resonance, the depressions act like subwavelength
holes in a metal layer and promote the generation of plasmons.
[0011] The exciting electric field is more strongly localized by
the asymmetrical profile shape (e.g. at the narrow peaks of the
relief structure), which can lead to a more pronounced resonance,
e.g. absorption. The excitation of the plasmons furthermore differs
on the two sides in the case of asymmetrical profile shapes.
[0012] Further, the profile shape of the first relief structure is
preferably chosen such that the width of the elevations and
depressions of the first relief structure (with period P and relief
depth t), relative to a distance of t/2 from the base surface (i.e.
the "full width at half maximum" or FWHM), is at least 0.6.times.P,
preferably at least 0.7.times.P, or at most 0.4.times.P, in
particular at most 0.3.times.P ("x" stands for the mathematical
operation "times"). Thus the width of the elevations or the width
of the depressions is determined at a distance of half the relief
depth t from the base surface parallel to the base surface, i.e.
the distance between neighboring edges of the first relief
structure is determined relative to a distance of t/2, and this is
chosen such that the above-mentioned conditions are satisfied. It
has been shown that, if these conditions for the profile shapes of
the first relief structure are complied with, particularly strong
and aesthetic, i.e. well-defined, color impressions can be achieved
for the human observer.
[0013] According to a preferred embodiment example of the invention
the edge steepness of the first relief structure, relative to a
distance of t/2 from the base surface, is between 60.degree. and
90.degree., further preferably between 70.degree. and
85.degree..
[0014] By edge steepness of the first relief structure is meant
here the angle enclosed with the base surface by the edges of the
relief structure in relation to a distance of t/2, i.e. the angle
enclosed with the base surface by the tangents adjoining the edges
at a distance of t/2 from the base surface. The distance from the
base surface here is determined in a direction perpendicular to the
base surface.
[0015] Investigations have shown that the strength of the color
impression generated by the first relief structure, in particular
in direct reflection or direct transmission, can also be further
improved by compliance with these conditions.
[0016] The edge steepness of the first relief structure relative to
each distance of between 1/4.times.t and 3/4.times.t from the base
surface is preferably chosen such that it is between 40.degree. and
90.degree., further preferably between 50.degree. and 85.degree..
The strength of the color impression which is generated by the
first relief structure can also be further improved hereby.
[0017] Further, it is advantageous to choose the edge steepness of
the first relief structure, relative to each distance of between 0
and 1/4.times.t and/or between 3/4.times.t and t from the base
surface, to be between 0.degree. and 50.degree., preferably between
0.degree. and 40.degree.. The strength of the color impression
which is generated by the first relief structure can also be
further improved hereby.
[0018] According to a preferred embodiment example of the invention
the layer thickness d of the metal layer in the area of the edges
of the first relief structure, relative to a distance of t/2 from
the base surface, is chosen such that it is reduced by at least
30%, further preferably by at least 50%, further preferably by
between 50% and 100%, compared with the thickness of the metal
layer in the area of the maxima of the elevations and/or minima of
the depressions. It has been shown that the color impression
generated in the first area can also be further strengthened by
these measures, and thus the optical appearance of the multilayer
body is improved.
[0019] According to a preferred embodiment example of the invention
the relief depth t of the first relief structure is between 80 nm
and 500 nm, in particular between 100 nm and 400 nm and preferably
between 120 nm and 300 nm. It has been shown that, in particular,
if the relief depth t is chosen to be in the range between 150 nm
and 300 nm, the strength of the color impression generated in the
first area can be improved.
[0020] The period P of the first relief structure is preferably
chosen to be smaller than a wavelength of visible light (=spectral
range of between 400 nm and 700 nm), preferably chosen to be
between 200 nm and 500 nm, in particular between 220 nm and 400 nm,
further preferably between 220 nm and 350 nm. It has been shown
that the color appearing to the human observer in the first area in
direct reflection/transmission is modified by adjustment of the
period P of the first relief structure, and thus the hue of the
color impression or the color effect appearing in direct reflection
or transmission at different angles of incidence and emergence can
be modified by modification of the period P of the relief structure
in the areas specified above.
[0021] The first relief structure can be formed as a linear grating
which has a sequence of elevations and depressions in one
direction. The line gratings can be constructed from straight or
also curved, in particular snake-shaped (for so-called "snake
gratings"), lines. However, it is also possible for the first
relief structure to be formed as a cross grating or hexagonal
grating or circular grating which has a sequence of elevations and
depressions in two directions. In the case of a cross grating, the
period P of the sequence of elevations and depressions in respect
of the two directions is preferably chosen to be in the range
specified above. Here, the period can be the same in both
directions in the case of a cross grating. However, the period can
also be different. This applies analogously to hexagonal gratings
and circular gratings. Investigations have further shown that the
formation of the first relief structure as a cross grating or as a
hexagonal grating is to be preferred, as stronger color impressions
appear in the case of these gratings.
[0022] In the first area the metal layer is preferably to be formed
in a layer thickness d of between 10 nm and 100 nm, preferably
between 15 nm and 80 nm and further preferably between 20 nm and 50
nm, if the multilayer body is designed for observation in reflected
light.
[0023] The described effects can already be achieved with only one
metal layer, as the core effect is not based on thin-film
interference.
[0024] In the at least one first area the multilayer body
preferably has only one metal layer, namely the metal layer in the
first and/or second surface of which the first relief structure is
molded.
[0025] In the first area, in addition to the metal layer and the
layer or layers bordering the surface or surfaces with molded first
relief structure of the metal layer, the multilayer body preferably
has no further layers into which the first relief structure is
molded. The effect generated by the metal layer with the first
relief structure can hereby be prevented from being superimposed
with interference effects and from being impaired in terms of its
brilliance.
[0026] Further, it is also possible, by combination with additional
thin layers, to achieve still further effects based on another
functional principle, in particular interference effects.
Optionally, therefore, another HRI layer, or also a layer sequence
of HRI and LRI layers, e.g. an LRI and then an HRI layer, can be
applied to the metal layer (HRI=High Refractive Index; LRI=Low
Refractive Index). The HRI layer is preferably formed of ZnS or
TiO.sub.2. The layer thickness of the HRI layer is preferably in
the range of from 20 nm to 500 nm and further preferably in the
range of from 50 nm to 200 nm. The LRI layer can be e.g. polymer or
SiO.sub.2 or MgF.sub.2. The thickness of the LRI layer is
preferably between 20 nm and 1000 nm and further preferably in the
range of from 50 nm to 500 nm.
[0027] The plasmon resonance depends, among other things, on the
refractive index of the material surrounding the metal layer.
Therefore, e.g., an HRI layer with a high refractive index modifies
the resonance and thus the color impression.
[0028] Further, it has been shown that a multilayer body according
to the invention, in the case of a corresponding design of the
layer thickness of the metal layer, generates color effects not
only in reflected light, but also in transmitted light. It has been
shown here that the optical depth (OD) of the metal layer for this
is preferably to be chosen to be between 0.5 and 2.5, in particular
between 0.7 and 2.3, further preferably between 1.0 and 2.0. The
unit of optical depth (OD) here is based on the transmittance of
the metal layer relative to an unstructured and thus smooth surface
and has the following relationship to the transmittance T:
T=10.sup.-(OD)
[0029] There is thus an algorithmic relationship between
transmittance T and optical depth OD. An optical depth of 1.0
corresponds to a transmittance of 10% and an optical depth of 2.0
corresponds to a transmittance of 1%. An optical depth of from 0.5
to 2.5 thus corresponds to an aluminum layer with a thickness of
from 6 nm to 34 nm, an optical depth of from 0.7 to 2.3 corresponds
to a layer thickness of an aluminum layer of from 8 nm to 31 nm and
an optical depth of from 1.0 to 2.0 corresponds to a layer
thickness of an aluminum layer of from 13 nm to 27 nm.
[0030] It has surprisingly been shown here that in the area in
which the first relief structure is molded into the metal layer the
transmission spectrum, and thus the color seen in transmission,
changes and here the transmittance for particular wavelengths of
light is higher than would be the case with a mirror surface. The
reason for the increased transmittance in the area of the first
relief structure probably lies in the excitation of plasmons by the
incident light. The plasmons at the upper "boundary surface" of the
metal layer excite plasmons at the lower "boundary surface" and,
through this coupling, increase the intensity of the transmitted
light for this wavelength range. In the immediate vicinity of the
metal layer here, electric fields form with a superelevated field
strength, which makes it possible for the plasmons to "channel"
light through the metal layer.
[0031] It is thus possible, by means of a layered body according to
the invention, to provide a metalized security feature which
displays a first optically variable effect in reflected light
observation on the upper side, displays a second optical effect,
different from this, when observed from the underside--with a
corresponding design of the relief shape, as stated above--and
likewise displays an optical effect in transmitted light
observation (depending on the adjusted optical density OD of the
metal) with a corresponding design--as described above. In
addition, in the case of transmitted light observation, the great
advantage also results that--unlike when first- or higher-order
transmissive diffraction structures are used--a corresponding
optical effect also becomes visible in the case of direct
transmission, i.e. also in the case of observation at a
perpendicular angle, and thus a security feature is provided which
can only be imitated with great difficulty using existing
technology.
[0032] The multilayer body is preferably designed such that one or
more layers of the multilayer body possibly provided above the
metal layer and/or one or more layers of the multilayer body
possibly provided underneath the metal layer are formed transparent
or semitransparent, in particular have a transmittance of more than
15%, in particular of more than 50%, further preferably of more
than 90%, in at least a partial area of the first area. It is
hereby ensured that the optical effect generated by the metal layer
and the first relief structure is visible in reflected light
observation from the upper side, in reflected light observation
from the underside and/or in transmitted light observation. It is
hereby also possible for this partial area to be formed patterned
and for the partial area of the first area surrounding this partial
area to have at least one layer which is formed opaque, with the
result that the optical effect generated by the metal layer and the
first relief structure is visible only in the area determined by
the shaping of the first partial area. It is also possible here for
a mask layer to be provided in the multilayer body, above the metal
layer and/or underneath the metal layer, which mask layer has a
recess corresponding to the first partial area, wherein the recess
of the mask layer provided above the metal layer and that of the
mask layer provided underneath the metal layer can also be shaped
differently, with the result that different items of information
become visible in the case of reflected light observation from the
upper side and from the underside.
[0033] Further, it is advantageous if the first surface of the
metal layer is coated with a first dielectric layer and the
underside of the metal layer is coated with a second dielectric
layer, wherein the refractive indices of the first dielectric layer
and of the second dielectric layer differ by at least 0.1, further
preferably by at least 0.2. It can hereby be achieved that the
optical appearance of the first area in the case of reflected light
observation and/or transmitted light observation from the upper
side differs from the corresponding appearance in the case of
reflected light observation and/or transmitted light observation
from the underside.
[0034] Further, it is advantageous if the first surface of the
metal layer and/or the second surface of the metal layer is covered
in areas with transparent dielectric layers with different
refractive indices and the optical appearance of the multilayer
body in different partial areas of the first area is hereby
different because of the different refractive indices of this
dielectric layer.
[0035] The profile shape and/or relief depth t of the first relief
structure is preferably chosen such that in the case of direct
reflection the metal layer has a reflectance of less than 15%, in
particular of less than 10%, for the light incident at the first
angle of incidence in the first area in a first spectral range
visible to the human eye with a width of at least 50 nm, and in a
second spectral range visible to the human eye with a width of
between 10 nm and at most 200 nm, in particular 20 nm to 150 nm has
a direct reflectance that is at least twice as high, furthermore at
least 2.5 times, preferably at least 3 times and in particular at
least 4 times, higher relative to the average value of the
reflectance in the first spectral range.
[0036] This results in a color impression or colored appearance
that is defined for the human observer and relatively stable. For a
defined and relatively stable color impression in transmission, the
transmittance values can be much lower than in reflection, and can
even lie in the range of a few percent. It is important here that
in a second spectral range visible to the human eye with a width of
between 10 nm and at most 200 nm, in particular 20 nm to 150 nm,
there is a direct transmittance that is at least twice as high,
furthermore at least 2.5 times, preferably at least 3 times and in
particular at least 4 times, higher relative to the average value
of the transmittance in a first spectral range with a width of at
least 50 nm. The width of the first spectral range is further
preferably at least 100 nm.
[0037] The profile shape and/or the relief depth of the first
relief structure is preferably further chosen such that in the case
of a second angle of incidence different from the first angle of
incidence the colored appearance of the light directly reflected in
the first partial area or directly transmitted through the metal
layer is modified differently and, in particular, different,
relatively stable colors appear to the human observer at these
angles of incidence in the case of reflected light observation or
transmitted light observation (e.g. red in the case of almost
perpendicular observation and green in the case of tilting by e.g.
30.degree.). This corresponds to a defined color change during the
tilt. The first angle of incidence preferably differs from the
second angle of incidence by a value of between 10.degree. and
45.degree..
[0038] For a simple recognition of the color change, it is
advantageous if the lateral extent of the first area is at least 10
mm.sup.2, further preferably is at least 20 mm.sup.2, and thereby
is clearly recognizable as an area of surface to the naked human
eye.
[0039] According to a preferred embodiment example of the
invention, in the first area or in at least one of the first areas
the multilayer body has at least one dye and/or luminescent
substance which is arranged less than 2 .mu.m, in particular less
than 1 .mu.m, preferably less than 500 nm, further preferably less
than 300 nm away from the first surface and/or the second surface
of the metal layer. It has surprisingly been shown that dyes and/or
luminescent substances in the case of such an arrangement close to
the surfaces of the metal layer provided with the first relief
structure have a massively strengthened absorption or fluorescence,
compared with what is usually the case with these substances, for
example in the case of an arrangement close to a mirror surface or
"normal" diffractive structures. This effect is probably to be
attributed to the fact that the plasmon excitation caused by the
first relief structure generates an increased field strength. This
increased field strength is present in the near field, i.e. above
all up to a distance of approx. one wavelength of the exciting
light. This increased field strength is responsible for the
increase in the absorption or fluorescence of the dyes or
luminescent substances.
[0040] Analogous effects are used e.g. in the analysis in so-called
Surface Enhanced Raman Scattering (SERS). If the molecule is
located close to a metallic surface (above all silver and gold),
the Raman signal can be extremely enhanced. The electromagnetic
enhancement is based on excitation of surface plasmons in the
metal, which can generate locally very high fields at peaks on the
surface or in particles. This field together with the incident
light excites the molecule and thus leads to an enhanced Raman
scattering. This effect falls off rapidly over the surface, but the
molecule does not have to be bonded to the surface.
[0041] The enhancement mechanisms behind this are called surface
plasmon polariton (or SPP) enhanced absorption and surface plasmon
coupled emission (SPCE).
[0042] This discovered effect of a dye layer and/or luminescent
substance layer can, as described below, be used in various ways in
order to provide security features that are striking and can be
imitated only with difficulty:
[0043] The first and/or second layer here is preferably applied to
the first or second surface of the first metal layer in areas or
over the whole surface in the first area and thus covers the first
surface or the second surface in areas or over the whole surface in
the first area. The first and/or second layer thus directly
borders, in areas, the surface or areas of surface of the metal
layer in which the first relief structure is molded into the metal
layer. The first relief structure is thus preferably covered in
areas or completely by the first or second layer. Further, it is
also advantageous if the first or second layer is only applied to
the metal layer in the first area and thus is only provided where
the metal layer borders the first relief structure, and thus the
above-described effects are generated.
[0044] The multilayer body preferably has at least one first layer
bordering the first surface of the metal layer and/or at least one
second layer bordering the second surface of the metal layer, which
second layer has at least one dye and/or at least one luminescent
substance. The term luminescent substances here includes, in
particular, fluorescent or phosphorescent substances.
[0045] The layer thickness of the at least one first layer and/or
of the at least one second layer is preferably between 20 nm and 2
.mu.m, in particular between 50 nm and 1 .mu.m, in particular
between 100 nm and 500 nm. Through a corresponding choice of the
layer thickness of the first layer and/or of the second layer it
can be ensured here that the previously described effect
predominates in the area in which the at least one first layer
and/or second layer covers the first area, with the result that
clearly different optical impressions result in the area in which
the at least one first layer and/or at least one second layer
covers the first area and in the area in which the at least one
first layer and/or second layer does not cover the first area.
[0046] The concentration of the dyes or luminescent substances in
the area of the first and/or second layer less than 1 .mu.m,
further preferably less than 500 nm, further preferably less than
300 nm away from the first or second surfaces of the metal layer is
preferably higher than in the remaining area of the first or the
second layer. The above-described action can hereby be further
strengthened.
[0047] The at least one first layer and/or second layer can be
applied to the metal layer directly, for example by means of a
printing process, and in particular can consist of a varnish layer
or of a protective varnish layer to which the at least one dye or
luminescent substance has been added. Further, it is also possible
for the at least one first layer and/or second layer to be formed
by a replication varnish layer or by a layer applied to a
replication varnish layer and for the metal layer to be deposited
on this replication varnish layer or on the layer applied to the
replication varnish layer, for example by vacuum vapor
deposition.
[0048] The at least one dye and/or luminescent substance is
preferably a soluble dye or luminescent substance. Alternatively,
nanoparticles, such as e.g. quantum dot (QD), or also hybrid
materials, such as e.g. dye-loaded zeolite crystals (as described
for example in EP 1873202 A1), also come into consideration. Dyes
from the following substance groups are preferably used as dye:
metal-complex dyes, in particular with Cr.sup.3+ or Co.sup.2+ as
the central atom. Examples are the Neozapon dyes from BASF and
Orasol dyes from BASF (formerly Ciba). Luminescent substances from
the following substance groups are preferably used: coumarins,
rhodamines and cyanines.
[0049] The at least one first layer and/or the at least one second
layer preferably have a transmissivity of at least 70%, preferably
of at least 90%, in the wavelength range visible to the human eye.
In particular if the dye is applied over the whole surface, it is
advantageous if the transmittance of the colored layer is only
minimally modified by the dye, with the result that no coloring is
recognizable outside the first areas. According to a preferred
embodiment example of the invention the concentration of the at
least one dye and/or luminescent substance in the at least one
first layer and/or the at least one second layer is chosen such
that the optical action thereof in a second area in which the
surface relief is formed by a mirror surface, a diffractive
structure, a macrostructure or a mat structure is not visible to
the human observer at an observation distance of more than 30 cm
and under an illumination with white light (D65) with an
illuminance of at least 100 lux, preferably at least 500 lux and at
the same time less than 10,000 lux, but an optically recognizable
action develops in the first area because of the previously
described strengthening of the absorption or luminescence.
[0050] Alternatively, however, the dye is applied, in particular in
a higher concentration, only where the structures of the first area
have been replicated, or these structures of the first area are
replicated (with the usual register tolerances) where the dye is
present. A stronger influence on the color effect is thereby
possible without at the same time dyeing areas outside the first
area recognizably to the human eye.
[0051] In addition to the partial application of the dye in the
first area, it is also possible to apply the dye in different
concentrations inside and outside the first area or to apply two
different dyes inside and outside the first area.
[0052] The percentage by weight of the at least one dye or
luminescent substance in the dry weight of the first and/or second
layer is preferably between 0.1% and 20%, in particular between
0.5% and 10%.
[0053] The proportion by weight of the dye or luminescent substance
in the dry weight of the first and/or second layer is preferably
between 1 mg/m.sup.2 and 200 mg/m.sup.2, further between 2
mg/m.sup.2 and 50 mg/m.sup.2 and preferably between 3 mg/m.sup.2
and 30 mg/m.sup.2 and in particular preferably 3 mg/m.sup.2 and 15
mg/m.sup.2. This has proved to be advantageous for achieving the
above-specified effect.
[0054] The color of the at least one dye or luminescent substance
of the at least one first and/or at least one second layer is
preferably chosen such that its color, or its color when excited,
corresponds to the color generated by the first relief structure
for a particular angle of incidence of the incident light in direct
reflection or transmission, or differs from this color. Depending
on the color, different color effects, which thus at the least can
only be imitated with great difficulty by other technologies and
thus further increase the level of protection against forgery, can
thus be generated at different observation angles in direct
reflection and in direct transmission by corresponding color
mixtures.
[0055] Two or more first layers and/or second layers are preferably
provided, the dyes or luminescent substances of which are chosen
such that the colors of the dyes of these layers, or the colors of
the luminescent substances of these layers when excited, mutually
differ. Thus it is possible for example for a first layer with a
first dye to be applied to the first surface of the metal layer in
a first region which partially overlaps the first area, for a first
layer with a second dye to be applied to the first surface of the
metal layer in a second region which overlaps the first area in
areas, and for a second layer with a third dye to be applied to the
second surface of the metal layer in a third region which overlaps
the first area at least in areas and overlaps the first and second
region in areas, wherein the colors of the first, second and third
dyes differ. For one thing, with a corresponding choice of the
layer thickness of the first layers and of the second layers, the
effect already described above hereby results, that the action of
the first, second and third dyes is much stronger in the area in
which these layers overlap the first area than outside. In
addition, corresponding color mixing effects with the optical
effects generated by the first relief structure of the metal layer
in the first area results, with the result that in the case of
reflected light observation from the front and from the back side
as well as in the case of transmitted light observation
correspondingly different optical effects are also brought about in
each case.
[0056] Further, it is also possible for one or more first layers or
one or more second layers to overlap in areas. Interesting optical
effects can also be achieved hereby: as already stated above, the
filter action of the dyes and the luminescence of the luminescent
substances depend on the distance of these substances from the
first or second surface of the metal layer, with the result that,
depending the sequence in which these layers lie on top of each
other, these different color actions develop, in contrast to a
usual color mixing of color layers lying one on top of another, in
which case the sequence thereof has no influence on the resultant
mixed color.
[0057] According to a preferred embodiment example of the invention
the surface relief is formed by a second and/or further relief
structure in one or more second areas and/or further areas. The
second and/or further relief structure is a relief structure which
is preferably formed by a diffractive relief structure, a
holographic relief structure, a mat structure, a mirror surface, a
refractive, almost achromatic macrostructure (i.e. a structure with
a period of more than 5 .mu.m), a lens, a grid of microlenses or a
combination of such relief structures.
[0058] By diffractive relief structure is meant in particular a
relief structure which has a spatial frequency of between 200 and
2000 lines/mm and in particular generates an optically variable
effect by diffraction of the incident light in the first or a
higher diffraction order. Examples of this are linear or cross
gratings. Further, diffractive relief structures can also be formed
by computer-generated holograms, for example by kinoforms.
[0059] Isotropic or anisotropic mat structures can be used as mat
structures. By mat structure is meant a structure with
light-scattering properties which preferably has a stochastic mat
surface profile. Mat structures preferably have a relief depth
(Peak-to-Valley=P-V) of between 100 nm and 5000 nm, further
preferably between 200 and 2000. Mat structures preferably have a
surface roughness (R.sub.a) of between 50 nm and 2000 nm, further
preferably between 100 nm and 1000 nm. The mat effect can be either
isotropic, i.e. the same at all azimuth angles, or anisotropic,
i.e. varying at different azimuth angles. By macrostructure is
meant a structure the spatial frequency of which is smaller than
100 lines/mm and which generates an optical effect substantially by
refraction. The effect is thus almost achromatic. Lenses can be
molded as refractively acting lenses or also as diffractive lenses.
A grid of microlenses is preferably formed by a one-dimensional or
two-dimensional arrangement of microlenses, for example cylindrical
lenses or spherical lenses. The grid width of a grid of microlenses
is preferably between 300 .mu.m and 50 .mu.m.
[0060] The second and the further relief structures are preferably
formed by relief structures which differ at least in one structure
parameter and thus generate different optical effects.
[0061] The at least one first area or one of the first areas and
the at least one second area in each case are preferably formed by
a plurality of partial areas. These partial areas here preferably
have at least one lateral dimension which is smaller than 300
.mu.m.
[0062] The partial areas of the first area and the partial areas of
the second area are further preferably arranged gridded in each
other (interleaved). The interleaving preferably takes place with a
size of the partial areas below the resolution limit of the human
eye, i.e. in particular smaller than 300 .mu.m.
[0063] Thus, it is possible for example for partial areas of the
first area and in partial areas of the second area to follow on
from each other alternating in one direction or in two directions.
It is hereby possible for the effect to be achieved for the human
observer that the optical effect generated by the first relief
structure in the first area and the optical effect generated by the
second relief structure in the second area are superimposed. Thus,
for example, for the human observer at one and the same position of
the multilayer body, the optical effect generated by the first
relief structure is visible at a first angle of view and the
optical effect generated by the second relief structure is visible
at a second observation angle. Preferably, at least in the area in
which the partial areas of the first area and of the second area
are interleaved, the area ratio of the total surface area of the
partial areas of the first area to the total surface area of the
partial areas of the second area is chosen to be greater than 5:1,
further preferably greater than 10:1. This high proportion of the
first area is helpful in order to guarantee a very visible color
effect.
[0064] Further, it is advantageous if the at least one second area
is formed by a plurality of partial areas separated from each other
and if the first area surrounds these partial areas as background
area. Thus, it is possible for example to arrange the partial areas
of the second area pseudorandomly or to choose their surface
orientation, for example the orientation of their longitudinal
axes, to be pseudorandom, and to surround these partial areas, thus
arranged and/or oriented pseudorandomly, with the first area as
background area. The first relief structure can here be formed for
example by a mirror surface or by an achromatic structure, in order
thus to achieve the superimposition of the optical appearance of
the first area with a glitter effect or glimmer effect. The partial
areas of the second area here preferably have lateral surface
dimensions of between 50 .mu.m and 300 .mu.m.
[0065] According to a further embodiment example of the invention,
the first area or at least one of the first areas has a patterned
shaping and is thus molded for example in the form of letters,
numbers, a symbol or a motif. This first area can be framed
contour-like by a second area, wherein this second area has a
second structure, e.g. a mat structure. This also accentuates the
contour of the first area.
[0066] It is further advantageous here if the shaping of the first
area or at least one of the first areas here is chosen such that
this shaping contains an item of information that can only be made
visible using an aid. Thus, it is possible for example for the
first area or at least one of the first areas to be formed in the
form of a nanotext which can be made visible by the human observer
only with the aid of a magnifying device. Further, it is also
possible for the first area or at least one of the first areas to
be molded in the form of a moire pattern in which a concealed item
of information is encoded which can be made visible for example by
means of a grid of microlenses or a correspondingly molded mask
layer, e.g. a line grid, which grid or layer can likewise be part
of the multilayer body.
[0067] According to a preferred embodiment example of the
invention, the first area or at least one of the first areas has
one or more first zones and one or more second zones in which one
or more parameters of the first relief structure differ. The first
relief structure in the first zones preferably differs from that in
the second zones in terms of one or more of the parameters: period
P, azimuth angle, relief depth t, base surface area and profile
shape. Thus, for example, the first relief structure in the one or
more first zones differs from the first relief structure in the one
or more second zones in terms of the azimuth orientation, in order
for example to encode information that is only recognizable by
means of a polarizer, or also in terms of the period, relief depth
or in terms of the incline of the base surface relative to a base
plane, in order for example to generate movement effects or 3D
effects.
[0068] Further, it is also possible for the first area or at least
one of the first areas to comprise another one or more third or
further zones which differ from the first zones and second zones in
that one or more of the above-named parameters of the first relief
structure in these are chosen to be different from those in the
first and second zones.
[0069] Neighboring first and second and/or first, second, third and
further zones are preferably spaced apart from each other by less
than 10 .mu.m, preferably less than 1000 nm.
[0070] The parameters of the first relief structure are preferably
chosen to be identical in the first zones, identical in the second
zones, identical in the third zones and/or identical in the further
zones.
[0071] According to a preferred embodiment example, the first and
second zones in each case have lateral dimensions of more than 300
.mu.m, in particular a width and a length of in each case more than
500 .mu.m and further preferably more than 2 mm. The one or more
first and second zones are further preferably molded to form one
motif, wherein the first zones form a foreground area of the motif
and the second zones form a background area of the motif. Further,
it is also possible for one or more first zones to be molded to
form a first motif and one or more second zones to form a second
motif.
[0072] According to a preferred embodiment example, the first,
second and/or third zones have at least one lateral dimension of
less than 300 .mu.m, in particular of less than 150 .mu.m,
preferably of less than 80 .mu.m. Further, the first, second and/or
third zones are arranged interleaved at least in areas. Thus, it is
possible for example for first, second and third zones to be
arranged following on from each other alternating in one or in two
directions.
[0073] Such a formation and arrangement of first, second and third
zones makes it possible for example to generate movement effects,
morphing effects (metamorphosis effects), multi-color
representations or colored representations which are generated by
means of additive color mixing. Thus, it is possible for example to
arrange, interleaved, first zones to represent a first motif,
second zones to represent a second motif and optionally third zones
to represent a third motif, wherein the first, second and third
motifs are visible to the observer in each case at an allocated
angle of view. Further, the parameters of the first relief
structure in the first, second and third zones can be chosen for
example such that at a particular observation angle different
colors, for example red, green and blue, are generated in the
first, second and third zones. Through the corresponding choice of
the arrangement of first, second and third zones in an area
allocated to an image point, the color of the image point generated
at this angle of view can then be generated by additive color
mixing.
[0074] According to a preferred embodiment example of the
invention, in the first area or in at least one of the first areas
the base surface of the first relief structure is formed by a
coarse structure or a mat structure. The base surface is thus not
formed in the form of a flat surface, but modeled according to the
coarse structure or mat structure. By coarse structure is meant
here a structure the period of which is larger than the period P of
the first relief structure by at least a factor of 5, further by a
factor of 10, and in particular is between 1 .mu.m and 10 .mu.m.
The relief depth of the coarse structures is by preference between
50 nm and 5000 nm, preferably between 100 nm and 2000 nm. The
coarse structure can thus have surfaces inclined differently in
areas, with the result that the effect generated by first relief
structures in direct reflection/transmission shifts correspondingly
in its angular range and thus is visible in different partial areas
of the first area at different observation angles or, with a
correspondingly random arrangement if a mat structure is used, is
visible over a wider range of observation angles.
[0075] According to a preferred embodiment example of the
invention, in the first area or in at least one of the first areas
the period P of the first relief structure is varied in areas. The
variation of the period P of the first relief structure here is
preferably up to 10%, further preferably up to 5%. The period P of
the first relief structure is preferably increased/reduced in one
or more of the edge areas of the first area or increased or
decreased depending on the distance from the center of area of the
first area. It has been shown that interesting optically variable
effects can be generated hereby and for example a "rolling bar"
effect can be generated. Alternatively or in addition to this, the
azimuth angle of the first relief structure can further also be
varied (slightly) in areas.
[0076] By a "rolling bar" effect is usually meant an optical effect
similar to a reflective cylindrical lens. In the process the areas
of the cylindrical lens which reflect the light in the direction of
an observer appear brighter than the areas which reflect the light
in other directions. Thus, this function produces a kind of "light
band" which appears to move over the cylindrical lens when the
multilayer body is tilted in the direction of the angle of view. In
the case of the structures claimed in this document, a somewhat
different "rolling bar" effect results in which, instead of the
"light band", now a "color band" appears to move over the
cylindrical lens. For example a reddish core of a cylindrical lens
(with a yellowish or greenish external area of the cylindrical
lens) can move when the multilayer body is tilted in the direction
of the angle of view.
[0077] According to a further preferred embodiment example of the
invention, the first area or at least one of the first areas has a
plurality of partial areas. Each of the partial areas has a minimum
dimension of more than 3 .mu.m and a maximum dimension of less than
300 .mu.m. One or more of the parameters selected from the group:
shape of the partial area, area size of the partial area, position
of the center of area of the partial area, inclination angle of the
base surface of the first relief structure relative to a base
plane, angle of rotation of the base surface of the first relief
structure about an axis perpendicular to the base plane, azimuth
angle of the first relief structure, period P of the relief
structure, is varied pseudorandomly, for the respective partial
area, within a variation range predefined in each case for the
first area.
[0078] For the above-named parameters, the following variation
ranges are preferably chosen:
[0079] 1) Shape of the partial area: rectangle, square, circle,
oval, hexagon, octagon, rhombus.
[0080] 2) Area size of the partial area: between 5 .mu.m.sup.2 and
6000 .mu.m.sup.2, further preferably between 5 .mu.m.sup.2 and 300
.mu.m.sup.2. If the area size of the partial areas is varied
pseudorandomly, then the variation range is preferably 10% to 50%
of the average area size of the partial areas.
[0081] 3) Position of the center of area of the partial area: here,
it has proved particularly worthwhile to choose the variation range
of the random shift between +D/2 and -D/2, wherein D is the
dimension of the partial areas in the direction of the x axis or of
the y axis, and to fix the grid width of the grid in the direction
of the x axis and/or of the y axis at 3/2 times the dimension D of
the partial areas in the direction of the x axis or y axis.
[0082] 4) Inclination angle of the base surface of the first relief
structure relative to a base plane: preferably, the inclination
angle, in particular the inclination angle A.sub.x and/or A.sub.y,
of the partial areas is varied pseudorandomly in a variation range
of from -45.degree. to +45.degree., further preferably from
-30.degree. to +30.degree., particularly preferably -15.degree. to
+15.degree., in particular to achieve a glitter effect. The base
plane here is spanned by the x axis and the y axis and the
inclination angle A.sub.x represents the inclination angle in the
case of a rotation about the x axis and the inclination angle
A.sub.y represents the inclination angle in the case of a rotation
about the y axis.
[0083] 5) Angle of rotation of the base surface of the first relief
structure about an axis perpendicular to the base plane: it is
advantageous to vary this angle of rotation of the partial areas
pseudorandomly in a variation range of from -90.degree. to
+90.degree., further preferably from -45.degree. to +45.degree. and
particularly preferably -15.degree. to +15.degree..
[0084] 6) Azimuth angle of the first relief structure: variation
range of from -90.degree. to +90.degree., further preferably from
-45.degree. to +45.degree. and particularly preferably -15.degree.
to +15.degree..
[0085] 7) Period P of the relief structure: the variation of the
period P is preferably up to 10%, further preferably up to 5%
around an average value.
[0086] Further, it is also advantageous if the first area or at
least one of the first areas has a plurality of partial areas and
the parameters of the first relief structure in each of the partial
areas are chosen according to a relief structure which is selected
from a set of predefined relief structures pseudorandomly for the
respective partial area.
[0087] Through this procedure, interesting optically variable
effects can be generated, for example colored movements, glitter,
glimmer and 3D effects.
[0088] The multilayer body is preferably formed as a transfer film,
laminating film or security thread. In addition to the metallic
layer, the multilayer body preferably also has one or more further
layers selected from the group: replication layer, varnish layer,
adhesion-promoting layer, adhesive layer, protective varnish layer,
carrier layer and decoration layer. The multilayer body thus has
for example a carrier film, preferably a transparent plastic film,
e.g. made of PET, PC, PE, BOPP with a thickness of between 10 .mu.m
and 500 .mu.m, a transparent replication layer, for example made of
a thermoplastic or UV-curable replication varnish, and an adhesive
layer, for example a cold-adhesive layer, a hot-melt adhesive layer
or a UV-curable adhesive layer.
[0089] Preferably, the multilayer body is further formed as a
security element of a security document, in particular a banknote
or an ID document, and thus molded for example in the form of a
patch or a strip. Further, it is also possible for the multilayer
body to form a security document, for example a banknote, a card
(e.g. credit card, ID card) or an ID document. The security
document can moreover be a label, packaging for a commercial
product, a ticket, a certificate or a revenue or tax stamp.
[0090] If the multilayer body is formed as a transfer film, then a
partial area of the multilayer body is preferably stamped onto a
substrate by means of an embossing stamp formed patterned. If the
multilayer body has for example a homogeneous first relief
structure which generates one of the above-described color effects,
for example a color shift from red to green in the case of a
rotation, then by an embossing stamp with a corresponding shaping,
for example the shaping of a diamond, an element with this shaping,
for example a diamond, with this color effect can be produced on
the target substrate. Further, it is also possible for the
multilayer body in this case to be applied to a substrate over the
whole surface by means of a nonspecific laminating roller. Further,
it is particularly advantageous here if the surface of the
substrate onto which the multilayer body is stamped has a surface
structure, in particular has a coarse structure or a mat structure,
and if the stamping pressure is chosen such that the base surface
of the first relief structure is deformed according to the coarse
structure or mat structure during the stamping.
[0091] Further, it is also possible and also advantageous to
process the multilayer body in one operation with a blind embossing
die, in the stamping surface of which a coarse structure is molded.
The stamping pressure here is chosen such that the base surface of
the first relief structure is deformed according to the coarse
structure of the blind embossing die while the blind embossing die
is being pressed on. This method also makes it possible to
customize the multilayer body subsequently in a subsequent work
step by corresponding deformation of the base surface of the first
relief structure and thus to introduce the additional optical
effects already described above into a security element or a
security document.
[0092] The invention is explained by way of example below with
reference to several embodiment examples with the aid of the
attached drawings.
[0093] FIG. 1a shows a schematic top view of a security document
with a security element.
[0094] FIG. 1b shows a schematic sectional representation of the
security document according to FIG. 1a.
[0095] FIG. 2 shows a schematic sectional representation of a cut
section of a security element.
[0096] FIG. 3 shows a schematic sectional representation of a cut
section of a security element.
[0097] FIG. 4a shows a schematic representation of a relief
structure.
[0098] FIG. 4b shows a schematic top view of the relief structure
according to FIG. 4a.
[0099] FIG. 4c shows a schematic sectional representation of a
relief structure.
[0100] FIG. 4d shows a schematic sectional representation of a
relief structure.
[0101] FIG. 4e shows a diagram to illustrate the reflection
behavior of a metal layer with a relief structure molded in a
surface.
[0102] FIGS. 4f and 4g in each case show a schematic sectional
representation of a relief structure.
[0103] FIG. 5a and FIG. 5g show diagrams to illustrate the
reflection behavior or transmission behavior of a metal layer with
a relief structure molded into a surface.
[0104] FIG. 6a shows a schematic sectional representation of a cut
section of a security element.
[0105] FIG. 6b shows a schematic sectional representation of a cut
section of a security element.
[0106] FIG. 6c shows a diagram to illustrate the reflection
behavior of the security element according to FIG. 6a.
[0107] FIG. 6d shows a schematic sectional representation of a cut
section of a security element.
[0108] FIG. 6e and FIG. 6f show diagrams to illustrate the
reflection behavior of a security element.
[0109] FIG. 7a shows a schematic top view of a security
element.
[0110] FIG. 7b shows a schematic top view of the security element
according to FIG. 7a after application of two layers containing a
dye or luminescent substance.
[0111] FIG. 8a and FIG. 8b show schematic top views of an area of a
security element.
[0112] FIG. 9a and FIG. 9b show schematic top views of an area of a
security element.
[0113] FIG. 9c shows a diagram to illustrate the reflection
behavior of the security element according to FIGS. 9a and b.
[0114] FIG. 10a and FIG. 10b show schematic top views of an area of
a security element.
[0115] FIG. 11 shows a schematic top view of a cut section of a
security element comprising a second area, formed of several
partial areas, and a first area.
[0116] FIG. 12a shows a schematic sectional representation of a
transfer film.
[0117] FIG. 12b shows a schematic sectional representation of an
arrangement for stamping the transfer film according to FIG. 12a
onto a substrate.
[0118] FIG. 12c shows a schematic top view of a cut section of the
transfer layer of the transfer film according to FIG. 12a.
[0119] FIG. 12d shows a schematic top view of a cut section of the
substrate according to FIG. 12b after the stamping.
[0120] FIG. 13 shows a schematic sectional representation of a cut
section of a security element.
[0121] FIG. 14a shows a schematic representation of a cut section
of a security element in which an area covered with a relief
structure is formed by several partial areas.
[0122] FIG. 14b shows a schematic representation to illustrate the
orientation of the base surface of a relief structure provided in
the partial areas according to FIG. 14a.
[0123] FIG. 1a and FIG. 1b show a security document 1. The security
document 1 is preferably a banknote. However, it is also possible
for the security document 1 to be for example an ID document, a
label for product assurance, an ID card or credit card, prepaid
card, a hang tag for a commercial product or a certificate, in
particular a software certificate.
[0124] The security document 1 has a carrier substrate 10 and a
security element 2 applied to the carrier substrate 10.
[0125] The carrier substrate 10 is preferably a paper substrate,
for example with a layer thickness of between 50 or 500 .mu.m.
However, it is also possible for the substrate 10 to be a plastic
substrate or a substrate made of one or more plastic and/or paper
layers. Further, it is also possible for one or more further
security elements, in addition to the security element 2, also to
be applied to the substrate 10 or to be integrated into the layer
structure or the layers of the substrate 10. The substrate 10 thus
has for example one or more of the following elements as further
security elements: a watermark, a security print, a security
thread, a patch with one or more security features which are
effected for example by a holographic or diffraction-optical
structure.
[0126] The security element 2, in the embodiment example according
to FIG. 1a and FIG. 1b, has a strip-like shaping and extends over
the whole width or length of the security document 1. Further, the
security element 2 covers a window area 12 of the substrate 10, in
which the substrate 10 has a recess or through hole or is formed
transparent. Thus, in this area, the security element 2 is visible
both in the case of observation from the front side and in the case
of observation from the back side of the security document 1.
However, it is also possible for the security element 2 to have
another shaping, for example to be formed as a patch, or not to be
arranged in a window area of the security document 1, but to be
applied completely on an opaque area of the substrate 10.
[0127] The security element 2 is preferably a laminating film which
has a carrier substrate, a metal layer, one or more optional
decoration layers and an adhesive layer, with which the laminating
film is fixed to the substrate 10. The carrier substrate is
preferably a transparent plastic film with a layer thickness of
between 10 .mu.m and 500 .mu.m, in particular between 15 .mu.m and
150 .mu.m, for example made of BOPP or PET or PC (polycarbonate).
The adhesive layer is preferably a hot-melt adhesive layer, a
cold-adhesive layer or a UV-curable adhesive layer, or a
heat-curable or heat-crosslinking adhesive layer, or a hybrid
adhesive layer with thermoplastic and heat- and/or radiation-curing
components.
[0128] Further, it is also possible for the security element 2 to
be formed as a transfer film or transfer layer of a transfer film.
In this case, a release layer is also provided between the carrier
layer and the metal layer, or the carrier film is not provided.
Further, it is also possible for the security element 2 to be
formed as a security thread and not, as shown in FIG. 1b, to be
applied to the surface of the substrate 10, but rather to be
embedded at least in areas in the substrate 10 or to be arranged
alternating on the upper side and the underside of the substrate
10. In this case, the security element 2 preferably consists of a
carrier film, the metal layer, one or more optional decoration
layers and optionally an adhesion-promoting layer which is provided
on the upper side and/or the underside of the security element
2.
[0129] Further, it is also possible for the security element 2 to
be provided by layers of the substrate 10, in particular if the
security document 1 is a security document in the form of a card.
In this case, the security element consists of a metal layer and
one or more optional decoration layers which effect the functions
described below.
[0130] The security element 2 preferably has one or more areas 31,
32, 41 and 42 in which a metal layer is provided at least in areas.
An optically active surface relief is molded at least in areas into
the surface of the metal layer facing the upper side of the
security document and/or into the surface of the metal layer facing
the underside of the security document 1. In the one or more areas
31 and 32, this surface relief is formed here by a first relief
structure which, in at least one direction determined by an
allocated azimuth angle, has a sequence of elevations and
depressions, the elevations of which follow on from each other with
a period P which is smaller than a wavelength of visible light. The
more precise structure of this first relief structure is explained
below again with reference to numerous embodiment examples. In the
one or more areas 41 and 42, the surface relief is formed by a
second and/or further relief structure which is or are selected
from the group: diffractive relief structure, holographic relief
structure, mirror surface, mat structure, macrostructure, lens or
grid of microlenses. Further, it is also possible for the second
and/or further relief structure not to be molded in a surface of a
metal layer in one or more of the areas 41 and 42, but rather to be
molded between two transparent layers of the security element 2
which differ in terms of their refractive index by more than 0.2,
or to be molded in the surface of a high or low refractive index
dielectric layer, for example a ZnS layer.
[0131] The areas 32 and 42 here overlap the window area 12 at least
in areas, with the result that the security element 2 in the areas
32 and 42 is visible at least in areas from the upper side and
underside of the security document 1. In the areas 32 and 42, the
optical effect generated by the first or second relief structure is
thus visible in the case of observation from the upper side of the
security document 1, in the case of observation from the underside
of the security document 1 and/or in the case of observation in
transmitted light. The areas 31 and 41 are preferably not arranged
in the window area 12. The optical effect formed by the first
relief structure or second relief structure in the areas 31 or 41
is thus preferably only visible in the case of reflected light
observation from the front side of the security document 1.
[0132] Further, it is also possible for the security element 2 to
have still further security features, for example to have a
security print, one or more layers containing optically variable
pigments, one or more layers containing fluorescent or
phosphorescent substances or one or more layers which provide a
machine-readable security feature, e.g. a barcode, a magnetic
strip, machine-readable pigments, feature substances or
taggants.
[0133] As also represented in FIG. 1a and FIG. 1b, the areas 31,
32, 41 and 42 represent areas of the security document 1 or
security element 2 which result in the case of a top view
observation of the security element 2, i.e. form areas in respect
of an observation perpendicular to a plane defined by the upper
side or underside of the security document 1 or security element 2.
This also applies to the other areas, zones and partial areas
described here.
[0134] Further, the number of the areas 31, 32, 41 and 42 and their
types of molding are represented by way of example in FIG. 1a, with
the result that the areas 31, 32, 41 and 42 can have another
shaping, can be provided in another number, and furthermore it is
also sufficient if only one area 31 or one area 32 is provided in
the security element 2.
[0135] The structure of the security element 2 in a partial area 31
is explained below by way of example with reference to FIG. 2.
[0136] FIG. 2 shows a cut section of the security element 1 which
has an upper side 201 and an underside 202. Further, the security
element 2 has a metal layer 21--optionally also only partially
provided--in the surface of which facing the upper side 201 a
relief structure 61 is molded and/or in the surface of which facing
the underside 202 a relief structure 61 is molded. As shown in FIG.
2, the relief structure 61 here is preferably molded in both
surfaces the metal layer 21.
[0137] In addition to the metal layer 21, the security element 2
preferably also has one or more layers not shown in FIG. 2, for
example a replication varnish layer, one or more varnish layers,
one or more adhesion-promoting layers and one or more further
decoration layers.
[0138] The upper surface of the metal layer 21 preferably forms the
upper side 201 of the security element 2, or the one or more layers
of the security element 2 which are provided between the upper side
201 and the metal layer 21 are formed--at least in the areas
31--transparent or translucent and, at least in the areas 31,
preferably have a transmittance in the wavelength range visible to
the human eye of more than 30%, in particular more than 50%,
preferably of more than 80%.
[0139] During the production of the security element 2, a
preferably transparent replication varnish layer is applied for
example to a preferably transparent carrier film, optionally with a
preferably transparent adhesion-promoting layer interposed. A
surface relief is then molded at least in areas into the
replication varnish layer by means of UV replication or by means of
heat/pressure. The relief structure 61 here is molded as first
relief structure in the areas 31 and 32, and optionally the
above-described second relief structures are molded in the areas 41
and 42. The metal layer 21 is then applied for example by means of
vacuum vapor deposition and optionally structured patterned by
means of a demetallization method. Then, a preferably transparent
protective varnish layer and/or adhesive layer is optionally
applied. Further, it is also possible for another one or more
further layers to be introduced into the security element 2 during
the manufacture of the security element 2, as already stated
above.
[0140] The relief structure 61, in at least one direction
determined by an allocated azimuth angle, has a sequence of
elevations 612 and depressions 614, the elevations of which follow
on from each other with a period P which is smaller than a
wavelength of visible light. The relief structure 61 has a relief
depth t which is determined by the spacing of the maxima 613 of the
elevations 612 of the relief structures 61 from a base surface,
which is defined by minima 615 of the depression 614 of the relief
structure 61, relative to a direction perpendicular to this base
surface.
[0141] The following relationship results from the diffraction
equation, wherein m stands for diffraction order (m=0, +1, +2, . .
. ), .theta..sub.m for the angle of the diffraction and
.theta..sub.inc for the angle of the incident light:
m .lamda. P = sin .theta. m + sin .theta. inc ##EQU00001##
[0142] If P<.lamda. (and m does not equal 0), the following
results from this in the case of perpendicular light incidence:
sin .theta. m = m .lamda. P > 1 ##EQU00002##
[0143] It can be seen from this that in the case of a period P
which lies between .lamda. and .lamda./2, in almost all observation
situations, a diffraction of the light in higher diffraction orders
no longer takes place and if P<.lamda./2 a diffraction in higher
diffraction orders takes place for no more angles, with the result
that "classical" diffraction phenomena are only of secondary
importance.
[0144] The relief structure 61 is now chosen such that the period P
is chosen to be in the range between 200 nm and 500 nm, in
particular between 220 nm and 400 nm and preferably in the range
between 220 nm and 350 nm. The depth t of the relief structure 61
is preferably chosen to be between 80 nm and 500 nm, in particular
between 100 nm and 400 nm and particularly preferably between 150
nm and 300 nm.
[0145] The metal layer 21 preferably consists of aluminum, copper,
gold, silver, chromium or an alloy with these metals.
[0146] The thickness of the metal layer d is preferably chosen to
be between 10 nm and 100 nm, in particular between 15 nm and 80 nm
and particularly preferably between 20 nm and 50 nm.
[0147] The relief structure 61 is preferably formed by a linear
grating, a cross grating, a hexagonal grating, a circular grating
or still more complex grating shapes.
[0148] The color impression or color effect of the relief structure
61 is visible in direct reflection, i.e. in mirror reflection or on
the condition that .alpha..sub.in=.alpha..sub.ex, .alpha..sub.in is
the angle of the incident light 51 and .alpha..sub.ex is the angle
of the direct light 52, relative to the surface normals of the base
surface 616, as shown in FIG. 2. Preferably, through a
corresponding choice of the relief depth t and the profile shape of
the relief structure 61, a clearly recognizable color change is
further also generated if the angle of incidence and that of
emergence are changed at the same time from for example 10.degree.
to 30.degree.. Such color changes are also easily verifiable by
laypeople and in particular are also easily recognizable in diffuse
light. Sometimes a change from one color (e.g. red) to another
(e.g. green) occurs, sometimes a change from an intense color in
particular with a high color saturation (e.g. dark yellow) to a
weak color in particular with a low color saturation (e.g. light
yellow) occurs and sometimes a color changes to a silver, in
particular achromatic, color impression.
[0149] The profile shape of the relief structure 61 is preferably
chosen such that the edges in the reflection spectrum are
relatively strong, in particular have a change in the reflectance
of more than 10%, preferably of more than 15%, over a wavelength
range of 50 nm. The average pitch of at least one edge or flank in
the reflection spectrum is therefore preferably greater than 2%/10
nm over a wavelength range of at least 50 nm. Furthermore, the
reflection spectrum preferably has a first area with a width of at
least 50 nm, with a reflectance below 15%, preferably below 10%,
and a second area with a width of at least 10 nm and a width of at
most 200 nm (reflection edge), with a reflectance which is at least
twice as high, preferably 2.5 times higher, than in the first area.
Further, the second area is at least 20 nm wide, preferably at most
150 nm wide.
[0150] 100% reflection here is preferably defined as the measured
reflectance of the metal layer at a smooth, i.e. unstructured,
boundary surface, with otherwise the same framework conditions
(such as e.g. metal layer embedded or at surface etc.).
[0151] It has now surprisingly been revealed that the profile shape
of the relief structure 61 is of decisive importance to achieve
clearly visible color impressions in direct reflection. This is now
explained in more detail below with reference to FIG. 4a to FIG.
4g:
[0152] FIG. 4a shows a schematic 3D view of a relief structure 61
in the form of a cross grating with a period P in an x direction
and a y direction perpendicular to the x direction of for example
in each case 350 nm as well as a relief depth of for example 200
nm. The relief structure 61 shown in FIG. 4a thus has a sequence of
elevations 612 and depressions 614 in the x direction and in the y
direction. The distance between the maxima 613 of the elevations
612 and the minima 615 of the depressions 614 defines the relief
depth here. The maxima 613 of the elevations 612 here represent in
each case the highest point or, if the elevations have a flat
surface at their highest point, represent the highest points of the
elevations 613. The minima 615 of the depressions in each case
represent the lowest point of the depressions or the lowest points
of the depressions.
[0153] Here, low and high are relative to a top view observation of
the surface of the metal layer 21 into which the relief structure
61 is molded, i.e. here are relative to an observation from the
upper side of the security element 2. In this sense, FIG. 4a shows
a top view of the upper side of the metal layer 21 of the security
element 2.
[0154] A base surface 616, which is a flat surface in the case
shown in FIG. 4a, is further defined, as shown in FIG. 4a, by the
minima 615 of the depressions. However, it is also possible for the
base surface 616 not to be formed by a flat surface, but rather to
be formed, for example, by a coarse structure or a mat structure or
a bent or curved surface, as also explained thoroughly later.
[0155] FIG. 4b shows a schematic top view of the relief structure
61 according to FIG. 4a with the elevations 612, the depressions
614, the maxima 613 of the elevations 612 and the minima 615 of the
depressions 614. Further, in FIG. 4b, on the coordinate axes x and
y are drawn in, which describe the directions in which the
elevations 612 and depressions 614 follow on from each other.
[0156] FIGS. 4c and 4d, as well as FIG. 4f and FIG. 4g now
illustrate a cut through the relief structure 61 according to FIG.
4a and FIG. 4b along the cut line S-S' illustrated in FIG. 4b.
[0157] In FIG. 4c and FIG. 4d, as well as FIG. 4f and FIG. 4g, in
each case a cut section from the relief structure 61 according to
FIG. 4a and FIG. 4b with several elevations 612 and depressions 614
is shown, in a cut plane perpendicular to the base surface 616 and
running along the line S-S'.
[0158] As shown in FIG. 4c and FIG. 4d, the elevations 612 have
maxima 613 and the depressions 614 have minima 615. Further, in
FIG. 4c, the width 618 of the elevations 612 is drawn relative to a
distance t/2 from the base surface 616 and, in FIG. 4d, the width
618 of the depressions 614 is likewise drawn relative to a distance
t/2. Both correspond to the "full width half maximum" (FWHM).
[0159] Surprisingly, it has now been shown that profile shapes
which are asymmetrical in relation to a specular reflection at the
base surface 616, and thus, in particular, as already explained
above, with their profile shape reflected at the base surface,
differ by more than only one phase offset, produce much stronger,
and aesthetic, color impressions for the human eye than symmetrical
profile shapes. Symmetrical profile shapes in this sense are
characterized by a mirror symmetry in the base surface 616, i.e. in
the embodiment example according to FIG. 4a to FIG. 4d by a mirror
symmetry in the x/y plane. The profile shape remains the same in
the case of such a relief structure with such a specular
reflection, the relief structure is only shifted by half a period
(see sinusoidal profile A in FIGS. 4c and 4d). The optical effects
in the case of observation from the two sides (under the same angle
and illumination conditions) are thus the same in the case of these
symmetrical profile shapes, if the metal layer 21 is embedded on
both sides in a material with the same refractive index.
Asymmetrical profile shapes in this sense do not have this mirror
symmetry in the base surface 616 or x/y plane. The profile shapes
clearly differ in the case of observation from the two sides (see
e.g. profile E in FIGS. 4c and 4d). For example, such a relief
structure consists of an arrangement of narrow peaks with wide
valleys when observed from one side and of wide hills with narrow,
deep valleys when observed from the other side. It has surprisingly
been shown that the thus-formed "plateaus", in respect of the
generation of plasmons, have a similar action to holes in a metal
layer, which is probably how the advantages over symmetrical
profile shapes are achieved. To determine the symmetry of a relief
structure, the relief structure is thus reflected at the base
surface 616 or at the x/y plane and then it is checked whether the
profile shape is still identical, i.e. corresponds to the
unreflected profile shape, and thus the relief structure remains
identical except for a shift by half a period. Experiments and
theories (calculations on the basis of so-called rigorous
diffraction) have shown that the optical behavior of such
asymmetrical gratings differs when the grating is observed from the
two sides.
[0160] Further, it is advantageous if the width of the elevations
612 or depressions 614 of the relief structure, relative to a
distance of t/2 from the base surface, is at least 0.6.times.P,
preferably at least 0.7.times.P, or at most 0.4.times.P, in
particular at most 0.3.times.P. This is explained in FIG. 4c and
FIG. 4d in respect of relief structures 61 with several profile
shapes A to E.
[0161] FIG. 4c now illustrates the width 618 of the elevations 612
relative to a distance t/2 from the base surface 616. As shown
there, the width 618 of the elevations 612 here is ascertained in
the direction of the sequence of the elevations 612 and depressions
614, at a distance t/2 from the base surface 616. The profile shape
A has a width 618 of 0.5P, the profile shape B a width of
0.57.times.P, the profile shape C a width of 0.63.times.P, the
profile shape D a width of 0.69.times.P and the profile shape E a
width of 0.75.times.P. The profile shape A represents a profile
shape which is mirror-symmetrical in respect of a specular
reflection at the base surface 616 or x/y plane and which, as set
out above, is preferably not to be chosen here. The profile shapes
B to E represent profile shapes which are asymmetrical in the above
sense and which are preferably chosen.
[0162] FIG. 4d shows a corresponding formation of relief structures
61 with profile shapes A to E, wherein here the profile shapes A to
E are determined by a corresponding width 618 of the depressions
614 relative to a distance of t/2 from the base surface 616.
[0163] It has now been shown that the width 618 is preferably to be
chosen to be 0.6.times.P or 0.4.times.P, in particular 0.7.times.P
or .ltoreq.0.3.times.P, in order to generate color impressions
and/or color effects that are particularly aesthetically clear to
the human eye. Further, the width 618 is preferably to be chosen to
be in the range of from 0.9.times.P to 0.6.times.P or 0.1.times.P
to 0.4.times.P, further preferably from 0.85.times.P to
0.7.times.P, or 0.15.times.P to 0.3.times.P.
[0164] Calculations based on so-called rigorous diffraction with
the profile shapes A to E from FIG. 4c yielded the reflection
spectra represented in FIG. 4e for an example of a cross grating
with the following parameters and illumination conditions: P=300
nm, t=150 nm, .alpha.=30.degree., .phi.=45.degree..
[0165] As can be seen, the reflectance of the symmetrical profile
shape A lies clearly above 10% almost in the entire visible
spectral range. This results in a light, low-contrast color
impression. Furthermore, the reflection peak at approx. 550 nm is
formed very narrow. The color impression is a relatively light
yellow.
[0166] As the width 618 of the profile shape increases--and thus as
the asymmetry increases--the reflection spectrum changes
significantly. The reflection peak becomes wider and the reflection
minima become lower (reflectance <10%), which is necessary for a
high-contrast color. The profile shape C shows low reflection
minima with up to only 3% reflection for example on both sides of
the peak at approx. 550 nm, which leads to a clear and strong green
color impression. The asymmetrical profile shapes are therefore
preferred.
[0167] FIG. 4f and FIG. 4g also each show two further examples of
asymmetrical profile shape variants (dashed and continuous lines),
the profile shapes F, G, H and I. The dashed profile shapes F and H
have been shifted in the z direction for better clarity. FIG. 4f
shows examples of profile shapes F and G with pronounced peaks at
the elevations 612. FIG. 4g shows asymmetrical profile shapes with
a narrow plateau at the elevations 612.
[0168] Further, it has surprisingly also been shown that a clearly
recognizable color impression and/or color effect can also be
achieved in transmission by means of the molding of the relief
structure 61 into a metal layer. This is illustrated below with
reference to FIG. 3.
[0169] FIG. 3 shows a cut section of the security element 2 in the
area 32. The security element 2 is constructed like the security
element 2 according to FIG. 2 and thus has the metal layer 21 and
the relief structure 61 which is molded into the upper surface
and/or under surface of the metal layer 21 and which, as already
explained above with reference to FIG. 2 and FIG. 4a to FIG. 4d,
consists of a sequence of elevations 612 and depressions 614.
[0170] In contrast to the embodiment example according to FIG. 2,
here the metal layer 21 is chosen such that the metal layer has an
optical depth OD in the range of from 0.5 to 2.5, in particular
from 0.7 to 2.3 and particularly preferably from 1.0 to 2.0.
[0171] The unit of optical depth (OD) here is ascertained relative
to an unstructured and thus smooth surface (corresponds to a mirror
surface). The following relationship exists here between the
optical depth OD and the transmittance T:
T=10.sup.-(OD)
[0172] An algorithmic relationship thus exists between optical
depth and transmittance T. An optical depth of 1.0 corresponds to a
transmittance of 10% and an optical depth of 2.0 corresponds to a
transmittance of 1%.
[0173] It has surprisingly been shown that the color impression or
the color effect of the relief structure 61 is visible in direct
transmission, i.e. is visible on the condition that
.alpha..sub.in=.alpha..sub.ex or the incident light and the
emergent light lie on one line (disregarding the light refraction
inside the security element 2), wherein .alpha..sub.in is the angle
of the incident light 51 and .alpha..sub.ex is the angle of the
transmitted light 53 relative to the surface normal of the base
surface 616.
[0174] Here too, the relief depth t and the profile shape are
preferably chosen such that a clearly recognizable color change is
recognizable when the angles of incidence and of emergence are
changed at the same time, for example are changed from 0.degree. to
20.degree.. Such color changes are also easily verifiable for a
layperson.
[0175] It is surprising that such an effect occurs in transmission
in the case of a metal layer and furthermore also that much more
light in a spectral range of the incident light is transmitted
through areas of the metal layer 21 which are covered with the
relief structure 61 than through an area with mirror surfaces or
also with "normal" holographic gratings. This difference in the
transmittance results even though the mass density of metals is the
same in all areas. The relief structure 61 has the effect that a
spectral area of the visible light is preferably, i.e. with a
higher intensity, transmitted through the metal layer 21, whereby
the transmitted light appears colored. The transmission spectrum
here is dependent, among other things, on the period P and the
relief depth t, the profile shape, as well as on the angle of
illumination and the observation angle. The transmission spectrum,
and thus also the color impression, can change both in the case of
tilting (i.e. in the case of rotation about an axis lying in the
plane spanned by the multilayer body) and in the case of turning of
the security element 2, whereby the easily verifiable effects
already described above result.
[0176] The reason for the selectively increased transmittance in
the area 32 of the relief structures 61 probably lies in the
excitation of plasmons by the incident light. An electric field
with increased field strength hereby forms in the immediate
vicinity of the metal layer. The plasmons at the "upper boundary
surface" of the metal layer 21 excite plasmons at the "lower
boundary surface" and, through this coupling, increase the
transmission of the transmitted light. Through a corresponding
choice of the layer thickness of the metal layer, it is brought
about that such a coupling results and thus light can be
"channeled" through the metal layer 21.
[0177] Both in transmission and in reflection, it has been shown
here that the following effects can be achieved by the modification
of the parameters of the relief structure 61:
[0178] It has transpired that the colors and color effects
generated in direct reflection or transmission strongly depend on
the period P of the relief structure 61. As the period P increases,
the reflection peak or the reflection edge or the transmission peak
and the transmission edge shift to larger wavelengths in the
reflection or transmission spectra.
[0179] FIG. 5a and FIG. 5b show simulation data calculated on the
basis of so-called rigorous diffraction, for the reflected
(R.sup.0) and, respectively, transmitted (T.sup.0) intensity as a
function of the wavelength .lamda. and the period P. The simulation
data are averaged over the TE and TM polarization and thus
correspond to the case of unpolarized illumination and observation.
The symmetrical profile shape A was used. The (relatively slowly
increasing) high-pass edge of the reflection correlates to peaks in
the transmission. In FIG. 5a and FIG. 5b high intensity is
represented light and low intensity is represented dark. The
lightness scale is represented from 0 to 70% for reflection and
from 0 to 10% for transmission.
[0180] FIG. 5c now shows a corresponding diagram for three
simulated reflection spectra for the periods P=250 nm, P=300 nm and
P=350 nm. As is revealed in the three reflection spectra outlined
in FIG. 5c, the reflection edge in the three periods represented
moves over the visible spectral range and shifts by approximately
80 nm from the period 250 nm to period 350 nm. However, the shape
of the spectra also changes as the period increases.
[0181] The period P can thus be used to set a particular color
impression. For an optimization of the color contrast, however, for
each period the profile shape and the grating depth are to be
adapted. This was not carried out in FIG. 5c, in order to vary only
one parameter and to show the peak shift.
[0182] In FIGS. 5d to 5f, the influence of the choice of the
parameters of the relief structure 61 on the optical effects
appearing in reflection is further illustrated with reference to
several examples. FIG. 5g shows the optical effect in transmission.
The data in FIGS. 5d to 5g as well as 6c are measured reflection
spectra of film models. The spectrometer used, AvaSpec-2048, is
from Avantes. The illumination took place using the white-light
source LS-1 with a color temperature of 3100.degree. K from Ocean
Optics via optical fibers and a measuring head which can be used
for different angles of incidence and emergence (i.a.
.alpha.=8.degree. and .alpha.=30.degree.). The dark reference was
measured against a mat black surface. The light reference (100%
defined) for reflection was measured against an aluminum mirror.
For transmission, the light incident directly from the illumination
fiber into the measuring fiber was used as light reference.
[0183] An asymmetrical cross grating with a period P of 300 nm, a
grating depth of 150 nm and a width 618 of the depressions 614 of
0.7.times.P is chosen here as relief structure 61, regarding this
see also the statements re FIG. 4a to FIG. 4d. A layer of aluminum
with a thickness d=24 nm is used as metal layer 21.
[0184] The illumination and measurement of the reflection spectra
take place in the x/z plane, i.e. at an azimuth angle
.phi.=45.degree.. In respect of the definition of the axes,
reference is made to FIG. 4a to FIG. 4d. The continuous line shows
the measured reflection spectrum in direct reflection at an angle
.alpha.=8.degree., the dashed line at .alpha.=30.degree..
[0185] As is recognizable from FIG. 5d, at .alpha.=8.degree. the
light at a wavelength of approx. 530 nm is reflected ever more
strongly as the wavelength increases, while the reflectance below
530 nm largely lies below 10%. This results in a good reddish color
impression even under usual observation conditions. The reflection
spectrum measured at an angle of incidence of 30.degree. (dashed
line), in contrast, shows a reflection peak at a wavelength of
approx. 535 nm as well as a reflection edge above 600 nm. This
spectrum results in a metallic green color impression.
[0186] Further, a security element with such a relief structure 61
also shows a color effect in the case of rotation in the x/y plane,
i.e. when the azimuth angle .phi. is changed. This is shown in FIG.
5e. FIG. 5e shows the measured reflection spectra at an
illumination and observation angle .alpha. of 30.degree., wherein
the dashed line shows the spectrum at a grating oriented by the
azimuth angle .phi.=45.degree., i.e. according to the x/z plane,
and the continuous line shows the spectrum after rotation through
45.degree., i.e. at .phi.=0.degree..
[0187] As shown in FIG. 5e, a clear shift of the reflection peak
from 535 nm to approx. 600 nm is to be recognized. The reflection
edge also shifts to larger wavelengths. The color impression
changes from metallic green to yellowish.
[0188] As the relief structure 61 chosen as set out above is
asymmetrical, the color impressions which result in the case of
observation from the upper side 201 (pol. 1) and from the underside
202 (pol. 2) also differ as a result. This is shown in FIG. 5f.
[0189] FIG. 5f shows two measured spectra at an illumination and
observation angle .alpha.=8.degree. as well as in the case of a
direction of view in the x/z plane (.phi.=45.degree.). The
continuous line represents the spectrum in the case of reflected
light observation from the front side (corresponds to the
observation situation according to FIG. 5d) and the dashed line
represents the spectrum in the case of observation from the back
side (pol. 2). The dashed line has a clear reflection peak at
approx. 490 nm. Furthermore, the reflection edge is shifted by
approximately 25 nm to higher wavelengths and is somewhat less
steeply pronounced. Because of the reflection peak, the color
impression in the case of observation from the back side is a less
strong red color impression (thus a lighter red) than in the case
of observation from the front side. Pol. 1 is preferred in this
example.
[0190] FIG. 5g shows three measured spectra in transmission. The
illumination and measurement of the transmission spectra take place
at an azimuth angle .phi.=0.degree.. In respect of the definition
of the axes, reference is made to FIG. 4a to FIG. 4d. The
continuous line shows the measured transmission spectrum in direct
transmission at an angle .alpha.=0.degree., the dashed line shows
this at .alpha.=25.degree. and the dotted line shows this at
.alpha.=45.degree.. A clear transmission peak shift from 512 nm via
587 nm to 662 nm is to be recognized. The color impression which
these transmission peaks generate is also modified by the other
spectral features, e.g. the peaks or plateaus between 450 nm and
500 nm. Overall, these transmission spectra result in a color shift
from greenish (.alpha.=0.degree.) via grayish (.alpha.=25.degree.)
to reddish (.alpha.=45.degree.).
[0191] The color impression both in reflection and in transmission
can be significantly modified by an additional HRI layer. Thus, the
model according to FIG. 5d shows, instead of the red color
impression at .alpha.=8.degree., a dark green color impression, if
an approx. 60 nm thick HRI layer made of e.g. ZnS borders the
aluminum layer on the observation side. The thickness of this HRI
layer is preferably in the range of from 20 nm to 80 nm.
[0192] FIG. 6a shows a further formation of the security element 2,
in which dyes and/or luminescent substances are arranged in the
immediate vicinity of the metal layer 21.
[0193] FIG. 6a shows the security element 2 with the metal layer
21. In the area 31 the relief structure 61 is molded into the metal
layer 21 and a second relief structure 62 or a mirror surface (not
shown) is molded in the area 41. In respect of the design of the
metal layer 21 and of the relief structure 61 and the layer
structure of the security element 2, reference is made to the
previous statements according to FIG. 1 to FIG. 5f. The security
element 2 according to FIG. 6a furthermore has another layer 22
which contains the one or more dyes and/or luminescent
substances.
[0194] It has surprisingly been shown that the color impression
and/or color effect which is generated by the relief structure 61
as previously described can also be significantly strengthened and
also spectrally modified, if a dye and/or luminescent substance is
located in the immediate vicinity of the metal layer 21. Immediate
vicinity here means closer than 2 .mu.m, in particular closer than
1 .mu.m, further preferably closer than 500 nm, and further
preferably closer than 300 nm. The dye and/or luminescent substance
here is preferably provided in a dielectric layer of the security
element 2 which directly borders the metal layer 21, as shown in
FIG. 6a by way of example with reference to the layer 22. The
dielectric layer 22 here can be a layer applied to the metal layer
21, in particular formed patterned. However, it is also possible
for the dye or luminescent substance to be contained in a layer
which is introduced into the security element 2 before application
of the metal layer 21. Thus, the layer 22 can be for example a
replication varnish layer or a layer applied to a replication
varnish layer. It is also possible for the replication varnish
layer to consist of a stack of two or more layers, of which only
the top layer, which forms the boundary surface to the metal layer
21, is provided with the dye and/or luminescent substance. This has
the advantage that the layer 22 can be chosen to be very thin and
yet the total thickness of the replication varnish layer lies in a
usual thickness range, as has proved worthwhile in production.
Alternatively, the layer 22 can also be vacuum-applied, e.g.
vapor-deposited or deposited by means of PECVD.
[0195] Dissolved dyes and/or luminescent substances are preferably
used as dyes and/or luminescent substances. In particular, the use
of metal complex dyes has proved worthwhile. Alternatively,
nanoparticles such as e.g. quantum dot (QD) also come into
consideration, or also hybrid materials such as e.g. dye-loaded
zeolite crystals (such as are described for example in EP 1873202
A1). Further, the use of the following luminescent substances has
proved worthwhile: coumarins, rhodamines and cyanines.
[0196] The layer 22 to which the one or more dyes or luminescent
substances are added is preferably formed very permeable to light.
It preferably has a transmittance of at least 70%, in particular of
90%, in the wavelength range of from 400 to 700 nm. For many
applications it is important that the transparency of the colored
layer 22 is so high that no effect of the dye is recognizable in
areas with the structure 62.
[0197] It is advantageous here in particular if the dye or
luminescent substance is for the most part arranged in the
immediate vicinity of the surface of the metal layer 21 in which
the relief structure 61 is molded. This is shown in FIG. 6a. It has
surprisingly been shown that in an arrangement of luminescent
substances and dyes in the immediate vicinity of the surface of the
metal layer 21 in which the relief structure 61 is formed the
absorption of the dye or the luminescence of the luminescent
substance is clearly increased. This is probably to be attributed
to the fact that an increased field strength in the near field,
i.e. up to a distance of approx. one wavelength of the exciting
light, is generated by the plasmons generated by the relief
structure 61. The electric field (E field) falls off, as
illustrated in FIG. 6a, exponentially with the distance from the
surface, i.e. in the z direction. This probably leads to the clear
increase in the absorption/luminescence of the dyes or luminescent
substances, if these are arranged in the immediate vicinity, as set
out above, of the surface of the metal layer 21 in which the relief
structure 61 is molded. If the layer 22, as illustrated in FIG. 6a,
is thus designed correspondingly thin or the concentration
distribution of the dye in the layer 22 is chosen such that it is
for the most part arranged in the immediate vicinity of the metal
layer, the dyes or luminescent substances of the layer 22 for the
most part contribute to the above-named strengthening of the
effect, whereby they allow the effects explained in the following
to be implemented in a particularly striking manner. FIG. 6b shows
the security element according to FIG. 6a, with the difference that
here the layer 22 is chosen to be relatively thick. Even if the
total amount of dyes in the layer 22 is chosen to be the same in
the embodiment examples according to FIG. 6a and FIG. 6b, then in
the embodiment example according to FIG. 6b much less dye or
luminescent substance is arranged at a distance with increased E
field and the strengthened absorption or luminescence only occurs
to a small extent, as the dye which is at a distance of more than
one wavelength from the surface of the metal layer 21 mainly acts
as a "normal" color filter. In the embodiment examples according to
FIG. 6a and FIG. 6b, the reflecting light 54 or 55 is
correspondingly differently influenced by the dye or luminescent
substance.
[0198] The layer thickness of the layer 22 is preferably to be
chosen to be in the range of from 20 nm to 2 .mu.m, in particular
50 nm to 1 .mu.m and particularly preferably in the range of from
100 nm to 500 nm.
[0199] Numerous striking and surprising optical effects can be
achieved by the utilization of the above-described effect.
[0200] If a dye which has a similar color impression to the relief
structure 61 is used, the following effect can be achieved: if for
example a red dye is applied to the metal layer 21 in an area with
a relief structure 61 which (without dye) has a red color
impression in the case of almost perpendicular observation and has
a green color impression in the case of tilted observation (for
instance at 30.degree.), then the red color impression is clearly
strengthened. If the concentration of the red dye in the layer 22
is low enough, then the green color impression remains almost
unchanged. Overall, this results in a more strongly visible color
tilt effect from red to green. It has been shown that, for this,
the concentration of the red dye can be so low that a metallic
mirror which is likewise coated with the color layer appears almost
unchanged, i.e. without additional color effect or color shade.
This has the advantage that the color layer can be applied over the
whole surface and need not be applied partially and
register-accurate relative to the areas with the relief structure
61.
[0201] Alternatively, a yellow dye can also bring about a
strengthening both of the red and of the green color impression. In
addition, such a yellow dye applied over the whole surface can
produce the impression of a gold foil in areas without the relief
structure 61 if the concentration of the dye is high enough.
[0202] Depending on the selection of the dye, the color impression
can thus be modified in a targeted manner.
[0203] Optionally, the dye can also have still other additional
functions. For example, the dye can have fluorescent properties,
which can be examined using a simple laser pointer. If, for
example, Lumogen Red is used as dye and the multilayer body is
irradiated by a laser pointer with the wavelength 532 nm, then the
color of the light spot changes from green (areas without the dye)
to yellow (areas with the dye).
[0204] Alternatively, the dye is applied, in particular in a higher
concentration, only where the structures of the first area have
been replicated, or these structures of the first area are
replicated (with the usual register tolerances) where the dye is
present. A stronger influence on the color effect is thereby
possible without at the same time dyeing areas outside the first
area recognizably to the human eye.
[0205] This is shown by way of example in FIG. 6d: FIG. 6d shows
the security element 2 with the metal layer 21 and with several
optional further layers, in particular a replication varnish layer,
in particular a transparent replication varnish layer, provided
underneath the metal layer 21, one or more further layers, in
particular transparent further layers, for example a replication
varnish layer, one or more varnish layers and an adhesion-promoting
layer. In the area 31 the relief structure 61 is molded into the
metal layer 21, and a second relief structure 62 or a mirror
surface is molded in the area 41. In respect of the design of the
metal layer 21 and of the relief structure 61 and the layer
structure of the security element 2, reference is made to the
previous statements according to FIG. 1 to FIG. 5f. The security
element 2 according to FIG. 6a furthermore also has the layer 22
which contains the one or more dyes and luminescent substances. In
respect of the design of the layer 22, reference is made to the
previous statements, in particular regarding FIG. 6a to FIG. 6c. As
shown in FIG. 6d, the layer 22 is only applied to the metal layer
21 in the area 31 and thus only applied to the metal layer 21 in
the area in which the relief structure 61 is molded into the metal
layer 21.
[0206] In addition to the partial application of the dye in the
first area, it is also possible to apply the dye in different
concentrations inside and outside the first area or to apply two
different dyes inside and outside the first area.
[0207] By register accuracy or registration accuracy is meant the
positional accuracy of two areas of surface and/or layers relative
to each other. This positional accuracy is set for example via
so-called register marks or registration marks or other technical
aids, e.g. optical sensors. Depending on the processes used, the
tolerances of the positional accuracy, i.e. the register
tolerances, differ in size and can for example range within the
range of from a few micrometers to a few millimeters.
[0208] If the concentration is chosen to be much higher, then the
red color impression of the relief structure 61 is also massively
strengthened. In the case of tilted observation, however, the red
color impression can then also be present. This corresponds to a
stable red color which is only visible in the area of the relief
structure 61, thus register accurate relative to the area of the
relief structure 61. Thus, for example, the layer 22 can be applied
over the whole surface both in the area 31 and in the area 41. As
the above-described strengthening effect does not occur in the area
41, if the concentration of the dye and/or luminescent substance in
the layer 22 is chosen to be correspondingly low the red color
impression is thus not visible or barely visible to the human
observer in the area 41, but is visible in the area 31 because of
the above-described strengthening effect. Thus, for example, a red
color impression can hereby be structured with a much higher
register accuracy than is possible by means of a printing method,
and can be arranged absolutely register accurate relative to
optically variable effects which are generated for example by
second or first relief structures.
[0209] If, for example, a dye is used which has a different color
impression from the relief structure 61, the color impression of
the security element 2 is not only strengthened, but also modified.
If, for example, a blue dye is applied to a relief structure that
appears red, then a strongly purple color impression can be
generated.
[0210] Further, it is also possible for the color of the dye to be
chosen such that it matches the color of the relief structure 61
which is generated at a larger reflection angle (for example
.alpha..sub.in=.alpha..sub.ex=30.degree.). The following can hereby
be brought about: if, for example, the relief structure 61 brings
about a color change in which the two colors have a strongly
different reflectivity (wherein, for example, the color at
.alpha..sub.in=.alpha..sub.ex=0.degree. has a much stronger
reflection than the color occurring at
.alpha..sub.in=.alpha..sub.ex=30.degree.), the color of the dye can
be chosen such that it matches the weaker of the two colors. The
visibility of the weaker color impression can hereby be improved.
Further, it is possible to apply the layer 21 patterned, for
example in the form of a logo, a text or an image, and to choose
the color of the dye such that it matches the color which appears
when the security element 2 is rotated. In this way it can be
achieved that, for example, the logo or the image suddenly appears
with higher luminous intensity when the security element 2 is
rotated.
[0211] The influence of the layer 22 on the color impression of the
security element 2 is further illustrated in FIG. 6c. FIG. 6c now
shows the color impression of the security element 2 in reflection
without dye (continuous line) and with dye (dashed line) in the
case of a design of the relief structure 61 according to FIG. 5a to
FIG. 5f. The illumination angle and observation angle are
8.degree.. Here, a dyed polymer layer 150 nm thick was applied to
the metal layer 21 made of aluminum. The polymer layer has a red
dye, namely Arcotest test ink 42 mN, which is embedded in a matrix
of polyacrylic acid and is so strongly diluted that an unstructured
area of the metal layer, i.e. a mirror area, appears almost
unchanged to the human observer. Further, the transmittance of the
polymer layer is chosen such that at least 90% of the incident
visible light in the wavelength range of from 400 nm to 700 nm
passes through the polymer layer. Nevertheless, the two measured
reflection spectra with and without dyes differ markedly, as shown
in FIG. 6c. The interaction of the dye with the metal layer with
molded relief structure 61 leads, as shown in FIG. 6c, for one
thing to a shift of the high-pass edge by approx. 60 nm to higher
wavelengths. At the same time, the reflected intensity increases
above a wavelength of 600 nm. Overall, a wider reflection minimum
and a more strongly pronounced reflection edge form, which results
in a stronger red hue. At .alpha.=30.degree. (not shown) the
reflection edge likewise shifts to larger wavelengths due to the
dye. At the same time, the intensity of the reflection peak at
approx. 535 nm reduces.
[0212] FIGS. 6e and 6f show measured reflection spectra of an
example of a security element 2 which is provided with a layer 22
which has a dye in such a high concentration that the security
element 2 appears to be dyed. FIGS. 6e and 6f now show the color
impression of the security element 2 in reflection without dye
(continuous line) and with dye (dotted line) in the case of a
design of the relief structure 61 according to FIG. 5a to FIG. 5f.
The illumination angle and observation angle are 8.degree. in FIGS.
6e and 30.degree. in FIG. 6f. Here, a dyed polymer layer approx.
240 nm thick was applied to the metal layer 21 made of aluminum.
The polymer layer has a yellow dye, in particular Solvent Yellow
82, which is embedded in a matrix of polymethyl methacrylate
(PMMA). The concentration of the yellow dye is so high that the
security element 2 looks like a so-called "gold foil" in areas
without the relief structure 61. For comparison, the reflection
spectrum of the dyed security element 2 measured at 8.degree. in an
area without relief structure--i.e. just dye on aluminum--is to be
seen in both figures as a thin, dashed line.
[0213] The interaction of the yellow dye with the metal layer with
molded relief structure 61 leads, as shown in FIG. 6e, on the one
hand to a massively higher reflected intensity above a wavelength
of 560 nm. The edge of the reflection spectrum is also much
steeper. On the other hand, the reflected intensity below 500 nm is
depressed to below 10% reflection. Both yield a stronger and more
contrast-rich red color impression at this observation angle of
8.degree.. At an observation angle of 30.degree. there is likewise
a stronger and more contrast-rich--in this case green--color
impression (FIG. 6f). The reflection peak relevant for the green
color impression is shifted slightly to higher wavelengths and,
above all, has steeper edges.
[0214] Through the use of one or more layers 22 which contain one
or more dyes and/or luminescent substances, for example the effects
explained with reference to FIG. 7a and FIG. 7b can thus be
implemented:
[0215] FIG. 7a and FIG. 7b in each case show a cut section of the
security element 2 which has several areas 31 and a background area
41 surrounding them. In the areas 31--as set out above--the relief
structure 61 is molded into the metal layer 21 and a relief
structure 62 different from this, for example a holographic
structure, or a mirror surface is molded in the area 41. The relief
structure 61 can be identical in the areas 31, or can differ, e.g.
differ in terms of the period P.
[0216] As shown in FIG. 7b, a first layer 22 is further arranged in
areas 81 and a second layer 22 is arranged neighboring the metal
layer 21, for example printed onto the metal layer 21, in an area
82. The layer 22 provided in the areas 81 here has a first dye and
the layer 22 provided in the area 82 has a second dye, wherein the
first dye and the second dye are different dyes, which have
different colors. Through the interaction between the relief
structure 61 in the areas 31 and the dyes of the layers 22 arranged
in the areas 81 and 82 two different color impressions result which
are, however, limited precisely to the area of the relief structure
61, i.e. to the areas 31. This occurrence of the strong color
impressions is limited in FIG. 7b to the surface areas identified
in black. The other areas of the security element 2, for example
the areas 41, are covered with relief structures which do not
govern with the dyes of the layers 22, with the result that in
these areas the color effect layers 22 are not or are barely
visible. For this, the concentration of the dyes with layers 22 is
preferably to be chosen, as set out above, such that areas which
are printed with these layers and have no relief structures formed
like the relief structure 61 are almost unchanged, i.e. appear not
to be colored. Alternatively, the areas 81 and 82 with the dyes can
prove to be smaller than the areas 31. In the case of
register-accurate replication into these areas 81 and 82 it is
hereby possible to ensure that the dyes are only present in areas
31 with the relief structure.
[0217] Further, the above-described interactions between dyes or
luminescent substances and the relief structures 61 also occur in
transmission, with the result that the above embodiment examples
according to FIGS. 6a to 7b are also transferable correspondingly
to a design of the security element according to FIG. 3.
[0218] The parameters of the relief structure 61, i.e. in
particular the period P, the azimuth angle, the relief depth t, the
base surface area and the profile shape can be chosen to be
constant in the whole region of an area 31 or 32. Thus, it is
possible for example for an area 31 molded in the form of a letter
"A" to be covered, in a rectangular area, with a relief structure
61 which appears red in the case of perpendicular observation and
green in the case of inclined, i.e. tilted, observation. Further,
an area 32 molded in the form of a letter "B" is provided which is
covered with a different relief structure 61 which appears yellow
in the case of perpendicular observation, and in which this color
disappears when tilted. Further, a background area 41 is provided
in which the relief structure is formed by a mat structure. In the
case of perpendicular observation, a red "A" and a yellow "B" thus
appear against a gray background.
[0219] It is further also possible for one or more of these
parameters to vary in the area 31 or 32. Thus, it is possible, for
example, for the period of the relief structure 61 to increase
slightly from the edge to the center of an area 31 or 32 and then
to decrease again slightly towards the opposite edge. The variation
of the period here should be less than .+-.10%, better less than
.+-.5%, in particular should be between 10 nm and 50 nm. Through
such a procedure, movement effects can be achieved. It has been
shown that the steep edge and also the peak in the reflection or
transmission spectra of the relief structure 61 moves with an
increasing grating period towards larger wavelengths. This peak
shift or edge shift is utilized for the above-named movement
effect. Further, it is also conceivable for a movement effect to be
imitated by variation of the azimuth angle .phi.. In the case of
cross gratings, however, it is to be taken into account that the
azimuth angle can only be varied between 0.degree. and 45.degree.,
in the case of hexagonal gratings only between 0.degree. and
30.degree..
[0220] Further, it is also possible for the areas 31 and 32 to
comprise one or more zones in which one or more of the parameters
of the first relief structure 61 are chosen to be different.
[0221] Thus, FIG. 8a and FIG. 8b in each case show an area 35 which
is molded in the form of an "I" and "F" respectively and which in
each case is divided into several zones 351, 352, 353 and 354. In
the zones 351, 352, 353 and 354, in each case one or more of the
parameters of the relief structures 61 are chosen to be different,
in particular the period P, the relief depth t or the azimuth angle
of the relief structure 61. Further, it is also possible for one or
more of the above-named parameters to be varied differently in the
respective zones 351, 352, 353 and 354, as has also already been
stated previously.
[0222] The zones 351, 352, 353 and 354 further preferably have at
least one lateral dimension of less than 300 .mu.m, for example a
width of less than 300 .mu.m and a length of more than 2 mm. In
this way, for example, movement effects in opposite directions can
also be realized in the areas 35.
[0223] In the case of the "I" from FIG. 8a, a "rolling bar" effect
results in which a color band appears to move over the "I". For
example, a reddish core of the "I" (with a yellowish or greenish
external area) can move when the multilayer body is tilted in the
direction of the angle of view.
[0224] In the case of the "F" from FIG. 8b, the "rolling bar"
effect can even be designed such that it moves from left to right
in the vertical bar of the "F" and from top to bottom in the
horizontal bars of the "F". These are very striking effects, even
for laypeople.
[0225] FIG. 9a and FIG. 9b further show an area 36 of the security
element 2 which consists of two zones 361 and 362. In the zones 361
and 362 the parameters of the relief structure 61 are chosen such
that these areas differ in terms of their polarization properties.
Thus, FIG. 9c shows the reflectance of a cross grating with a
period of 300 nm and a depth of 150 nm for the TE-polarized
component of the reflected light as well as for the TM-polarized
component of the reflected light (at an observation angle of
25.degree.). When the TE-polarized component is observed, a
substantially yellow color impression appears. If the polarizer is
rotated through 90.degree., the TM component which appears red is
seen. The averaged spectrum TE and TM is seen unpolarized. When
observed without polarizer, the color impression of the relief
structure 61 is typically very similar to almost identical, in the
case of rotation in the x/y plane, i.e. independently of the
azimuth angle. This applies in particular to cross gratings. When
observed resolved through a polarizer, this is not necessarily the
case, with the result that a design can also be realized which,
when observed without polarizer, has a monochromatic surface but,
when observed with polarizer on the other hand, reveals an
additional item of information.
[0226] For this, the relief structure 61 in the zones 361 and 362
is chosen such that the azimuth angle .phi. of the relief structure
61 differs in the zones 361 and 362, for example the azimuth angle
.phi. in the zone 362 is chosen to be rotated through at least
15.degree. relative to the zone 361. Preferably, when cross
gratings are used, the azimuth angles .phi. in the zones 361 and
362 are arranged rotated through approx. 45.degree. relative to
each other.
[0227] Through this procedure, a security feature can thus be
realized in which, in the case of observation without polarizer, an
area, for example the area 36, appears in a uniform color, but in
the case of observation through a polarizer an item of information
standing out due to a different coloring becomes visible, thus for
example the zone 361 appears yellow and the zone 362 appears
red.
[0228] Further, it is possible, through a corresponding design of
the relief structure 61, also to integrate glitter effects or
glimmer effects into the colored appearance. This is illustrated
below with reference to FIG. 10a to FIG. 10d.
[0229] FIG. 10a and FIG. 10b show an area 37 which is composed of a
plurality of partial areas 371. The partial areas 371 preferably
have as irregular as possible a shaping. In each of the partial
areas 371 the parameters of the relief structure 61 are chosen
according to a predetermined relief structure which is selected
from a set of predefined relief structures pseudorandomly for the
respective partial area 371. Several relief structures, for example
relief structures G1, G2, G3 and G4, are predefined, which differ,
for example, in terms of their azimuth orientation and/or their
period and their relief depth. From this set of relief structures
G1 to G4, for each of the partial areas 371, one of the relief
structures G1 to G4 is then selected pseudorandomly and a
corresponding relief structure is molded as relief structure 61 in
the respective partial area 371.
[0230] Further, such glitter effects can also be realized by means
of the arrangement of areas shown in FIG. 11.
[0231] FIG. 11 shows a cut section from a security element 2 which
has an area, consisting of a plurality of partial areas 431, in
which the relief structure 62 is molded, and consists of an area 39
in which the relief structure 61 is molded and which forms the
background area of the partial areas 431. The relief structure 62
preferably consists of a mirror surface or an achromatic structure,
for example a blaze grating, the azimuth orientation of which is
chosen randomly. Further, the partial areas 431 are preferably
arranged randomly in front of the background of the area 39 and/or
chosen pseudorandomly in terms of their orientation, for example
the orientation of their longitudinal edges. Metallic glittering is
hereby added to the color surface, which has a high-quality effect
similar to metallic paints for cars.
[0232] In respect of the formation of the relief structure 61 in
the area 39 reference is made to the previous statements.
[0233] Further, it is also possible for the relief structure 61 to
be molded in the partial areas 431 and for the relief structure 62
to be molded in the area 39.
[0234] Further, it is also possible for the security element 2 to
be provided by stamping a partial area of a transfer layer of a
transfer film. FIG. 12a thus shows, by way of example, a transfer
film 3 with a carrier film 25, a release layer 24, a protective
varnish layer 23, a replication varnish layer 27, the metal layer
21, a protective varnish layer 28 and an adhesive layer 26. The
relief structure 61 is molded into the metal layer 21. In respect
of the design of the metal layer 21 and the relief structure 61
reference is made here to the above statements and in particular to
FIG. 1 to FIG. 11.
[0235] The transfer film 3 is then, as shown in FIG. 12b, molded by
means of an embossing die 9 onto the surface of a substrate, for
example of the substrate 10 of the security document 1. After the
stamping, the carrier film 25 is then peeled off with the areas of
the transfer layer which have not been pressed against the
substrate 10 by the embossing die 9. Two different effects can be
achieved hereby: thus, firstly, the metal layer 21 provided in the
area 33 over the whole surface in the transfer film 3, with the
relief structure 61 (see FIG. 12c), is not completely transferred
onto the substrate 10, but only transferred patterned in the area
in which the embossing die presses the transfer film 3 against the
substrate 10. After the stamping, for example, the design of the
metal layer 21 shown in FIG. 12d, with the relief structure 61,
thus results, i.e. the metal layer 21 with the relief structure 61
is provided in an area 34 on the substrate 10 which is molded for
example in the form of the number "50". Further, depending on the
type of substrate, the following effect results: as indicated in
FIG. 12b, the surface of the substrate 10 preferably does not have
a smooth and flat surface, but has a surface which has a certain
degree of surface roughness, for example shows a mat appearance, or
in which a coarse structure has already been molded. The stamping
pressure with which the embossing die 9 now presses the transfer
film 3 against the substrate 10 is now preferably chosen such that
the base surface 616 of the relief structure 61 is deformed
according to the relief structure of the surface of the substrate
10, for example is deformed likewise in the form of a mat structure
or a coarse structure. It has been shown that, through such a
procedure, for example the angle of view at which the color effects
of the relief structure 61 in the area 34 are visible can be
significantly increased, or that additionally movement,
shape-change (morphing) or 3D effects can be introduced in this way
into the security element 2 by corresponding choice of a coarse
structure.
[0236] Alternatively, it is also possible to process a security
element 2 with the metal layer 21 and the relief structure 61
molded in this in a further operation by means of a blind embossing
die, in the stamping surface of which a coarse structure or mat
structure is molded. Here too, the stamping pressure with which the
blind embossing die is pressed against the security element 2 is
preferably chosen such that the base surface of the relief
structure 61 is deformed according to the coarse structure or mat
structure of the blind embossing die, whereby the above-described
advantages can also be achieved by this procedure.
[0237] Further, it is also possible to design the relief structure
61, even during the production of the security element 2, such that
the base surface of the relief structure 61 does not have the form
of a flat surface, but has the shaping of a coarse structure or mat
structure. However, the depth of such structures is usually much
smaller than can be achieved in the case of blind embossing. FIG.
13 shows, by way of example, a cut section of a security element 2
with the metal layer 21 into which such a relief structure 61 is
molded. In respect of the design of the security element 2,
reference is made to the previous statements according to FIG. 1 to
FIG. 11. In an area 38 the base surface 616 of the relief structure
61, as shown in FIG. 13, is now molded not as a plane, but in the
form of a coarse structure, whereby the above-described effects can
be realized.
[0238] Further, it is also possible to provide movement effects and
glitter effects by the following procedure: one area or several
areas of the security element 2 have a plurality of partial areas,
wherein each of the partial areas has a minimum dimension of 3
.mu.m and a maximum dimension of less than 300 .mu.m. FIG. 14a
shows, by way of example, the cut section of such an area of the
security element 2 with a plurality of partial areas 30.
[0239] In the partial areas 30 the relief structure 61 is now
molded into the metal layer 21. For each of the partial areas 30,
one or more of the parameters of the relief structure 61 and/or the
partial area 30 is further varied pseudorandomly. It is
particularly advantageous here to vary at least one of the
parameters: shape of the partial area, area size of the partial
area, position of the center of area of the partial area,
inclination angle of the base surface 616 of the relief structure
61 relative to a base plane, angle of rotation of the base surface
616 of the relief structure 61 about an axis perpendicular to the
base plane, azimuth angle of the relief structure 61, period P of
the relief structure, pseudorandomly within a respectively
predefined variation range. FIG. 14b thus illustrates, for example,
a corresponding pseudorandom variation of the inclination angle of
the base surface 616 of the relief structure 61 for the partial
areas 30.
[0240] Outside the partial areas 30 the relief structure 61 is
preferably not molded into the metal layer 21. In these areas the
relief structure 62 is preferably molded or the metal layer 21 is
not provided in these areas, with the result that in these areas no
optical action is developed by the metal layer 21.
* * * * *