Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02577522 2007-02-14
Optically Variable Security Element
The present invention relates to an optically variable security element for
protecting valuable articles, exhibiting at least one piece of information and
a
light-transmitting, optically variable layer disposed over the piece of
information.
For protection, valuable articles such as branded articles and value
documents are often equipped with security elements that permit the
authenticity of the valuable articles to be verified, and that simultaneously
serve as protection against unauthorized reproduction. Valuable articles
within the meaning of the present invention are especially banknotes, stocks,
bonds, certificates, vouchers, checks and valuable admission tickets and
other papers that are at risk of counterfeiting, such as passports and other
identity documents, as well as product protection elements, such as labels,
seals, packaging and the like. In the following, the term "valuable article"
encompasses all such articles, documents and product protection means.
To prevent reproduction even with top-quality copiers, the security elements
frequently exhibit optically variable elements that, from differing viewing
angles, convey to the observer a different image impression, such as a
different color impression. For example, from publication EP 0 435 029 A2 is
known a security element having a plastic-like layer comprising a liquid
crystal polymer, which layer shows a marked play of changing colors at
room temperature.
Publication WO 97/19818 shows and describes a data carrier having an
optically variable element in which a piece of information is applied in a
color that contrasts with the data carrier and is at least partially covered
by a
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light-transmitting, optically variable layer. By laying the comparatively
large
optically variable pigments over high-resolution dark structures, also high-
resolution pieces of information can be provided with an optically variable
effect. However, users often say the security elements produced in this way
are not very ornamental, since the background printing can be printed only
with very dark printing inks, and the fine structure of the high-resolution
structures always shows paperwhite.
Based on that, the object of the present invention is to specify a generic
security element having high counterfeit security and high visual
attractiveness.
This object is solved by the security element having the features of the main
claim. A manufacturing method for the security element and a valuable
article having such a security element are specified in the coordinated
claims.
Developments of the present invention are the subject of the dependent
claims.
According to the present invention, the piece of information in an optically
variable security element of the kind cited above is formed by a series of
layers that exhibits a colored background layer and an intaglio printing layer
printed over the background layer. In this way is created a visually
appealing humanistic feature that, as explained in detail below, combines
high flexibility of optical design with high counterfeit security.
The intaglio printing layer is preferably printed with a dark printing ink,
especially with black, violet, brown, dark blue or dark green ink. Dark
portrait colors can thus be employed advantageously.
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The printing plate required for the intaglio printing is preferably cut with a
graver, but it can likewise be produced through laser, etching or
photopolymer techniques. If reference is made to "cutting" in the following,
the other techniques are, of course, to be understood as well.
In a particularly preferred embodiment, the surface area covered by the
intaglio printing layer encompasses the surface area covered by the colored
background layer. In this way, the preferably dark intaglio printing ink
covers any register variations to the background layer, so that the impression
of perfect register is created for the observer.
In a preferred embodiment, the intaglio printing layer includes at least one
gap whose shape forms a piece of information. Alternatively or additionally,
the intaglio printing layer can exhibit a fine structure of differently
oriented,
parallel lines, whose shape forms a piece of information.
The lines of the fine structure expediently exhibit a line width b of 50 m to
500 m, preferably of 100 m to 200 m auf, and are preferably disposed in a
spacing a of between 0.8 * b and 1.6 * b. Here, line spacing a designates the
spacing between same, for example left, edges of adjacent lines. If the line
spacing a corresponds precisely to the line width b, then the parallel lines
lie
next to one another with no space.
The preferred range for the line spacing a thus varies from a 20% overlap of
adjacent lines to line patterns having a space whose width is 60% of the line
width. If the adjacent lines of the fine structure overlap in an area, then a
very high and even surface coverage is achieved there, which can be
desirable especially in a border area in which the underlying border of the
background printing is to be hidden. The cutting depth of the lines is
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preferably between 5 m and 250 m, particularly preferably between 70 m
and 120 m. The cited line parameters: line width, line spacing and cutting
depth can be uniform for the entire intaglio printing layer. However, it is
often appropriate to design different areas of the intaglio printing layer to
have different line parameters, depending on the desired appearance.
To make the piece of information on the intaglio printing layer more easily
perceptible for the observer, it can be surrounded by a positive or negative
border contour. A positive border contour is a circumferential dark border
line that is visible in the printing image, and a negative border contour is a
corresponding circumferential gap.
The counterfeit security of the security element can be further increased by
providing the intaglio printing layer with machine-readable feature
substances, especially magnetic feature substances, infrared-absorbing or
infrared-transparent feature substances, or phosphorescent, fluorescent or
other luminescent substances.
The background layer can be a liquid crystal layer having a color shift
effect,
an interference layer, a metal layer or a printing layer.
The background layer is preferably a background printing layer that is
imprinted in a uniform tone with a chromatic ink or a metallic ink, for
example a gold or silver ink. Especially offset printing, indirect printing,
screen printing or other printing methods known to the person skilled in the
art may be used as the printing method.
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The background layer, too, can include machine-readable feature substances,
especially infrared-transparent feature substances, or phosphorescent,
fluorescent or other luminescent substances.
In an advantageous embodiment of the security element according to the
present invention, the background printing layer includes at least one gap,
whose shape forms a piece of information. Alternatively or additionally, the
background printing layer can be imprinted in a pattern, the shape of the
pattern forming a piece of information. The colored background layer can be
executed in monochrome or in polychrome.
The piece of information on the intaglio printing layer and/or the
background layer can constitute an image motif, a portrait, a logo or a code,
such as a bar code or an alphanumeric character string.
In some embodiments, both the intaglio printing layer and the background
layer include a piece of information. In this case, advantageously, the pieces
of information in both layers are related to or complement one another. A
replication constitutes the simplest case of pieces of information that are
related to one another. For example the denomination of a banknote can be
introduced into both the background layer and the intaglio printing layer in
a gap or a pattern. In the case of complementary pieces of information, the
complete piece of information is yielded only by the combination of both
sub-pieces of information. For example, complementary sub-groups of a
serial number or complementary parts of a portrait can be introduced into
the two layers.
The optically variable layer advantageously includes optically variable
pigments, interference layer pigments or pigments produced on the basis of
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liquid crystal polymers. Preferably, it exhibits a color shift effect as the
optically variable effect. The application of the optically variable layer to
the
security element expediently occurs through imprinting, for example in
screen printing, through coating or spraying.
In a development of the present invention, the optically variable layer
includes at least one gap, whose shape forms a further piece of information.
Here, advantageously, the further piece of information on the optically
variable layer is related to or complements the piece of information on the
intaglio printing layer and/or the background printing layer. For example,
the color shift effect in the optically variable layer and the color
impression of
the background can be so color coordinated with one another that, from
certain viewing directions, the optically variable layer exhibits the same
color
as the background printing. From these viewing directions, the further piece
of information encoded in the gap is then not perceptible, while it stands out
clearly from other viewing directions from which the color impression of the
optically variable layer differs from the color impression of the background
layer.
Advantageously, the surface area covered by the optically variable layer
encompasses the surface area covered by the intaglio printing layer. Here, in
the surface area covered by the optically variable layer and not covered by
the intaglio printing layer, the security element preferably exhibits a light
coloration, such as paperwhite. The light-transmitting, optically variable
layer is then almost invisible outside the intaglio printing layer over the
light
background, while its optically variable effect appears clearly over the dark
intaglio printing layer.
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Through the combination of background printing layer and intaglio printing
layer, also a very dark background can be achieved, which is advantageous
for clearly emphasizing the color shift effect at least in sub-areas of the
security element.
The present invention also includes a method for manufacturing a security
element of the kind described above, in which
- a colored background layer is applied to, preferably is imprinted on, a
substrate,
- an intaglio printing layer is printed over the background layer, the series
of layers comprised of the background layer and the intaglio printing
layer exhibiting a piece of information, and
- a light-transmitting, optically variable layer is applied, especially is
imprinted over the piece of information.
The present invention further includes a valuable article, such as a branded
article, a value document or the like, having a security element of the kind
described above. Here, particularly advantageously, the piece of information
in the security element is related to or complements a piece of information
applied to another location on the valuable article. For example, the piece of
information in the security element can repeat the denomination imprinted
in another location on a banknote, or a graphic motif, such as a portrait,
imprinted on a value document. The valuable article can especially be a
security paper, a value document or a product packaging.
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Overall, the described design options for the background layer, the intaglio
printing layer and the optically variable layer offer high flexibility for the
design of security elements according to the present invention. Moreover, in
the manufacturing method according to the present invention, the optically
variable layer is applied only as the last layer, so that a low rejection rate
and
thus economical manufacturing can be achieved. Since the optically variable
layer does not have to be stamped, its color shift effect appears very
clearly.
Further exemplary embodiments and advantages of the present invention are
explained below by reference to the drawings, in which a depiction to scale
and proportion was omitted in order to improve their clarity.
Shown are:
Fig. 1 a schematic diagram of a banknote having an optically variable
security element according to an exemplary embodiment of the
present invention,
Fig. 2 a cross section through the banknote in fig. 1 along the line II-II,
Fig. 3 in (a) to (e), different variants for designing the background
layer of security elements according to the present invention,
Fig. 4 in (a), (c), (e), (f) and (g), different variants for designing the
intaglio printing layer of security elements according to the
present invention, and in (b) and (d), details of the designs in
(a) and (c),
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Fig. 5 in (a) to (c), sections through the intaglio printing layer of
security elements according to the present invention for
different ratios of line width b and line spacing a, and
Fig. 6 in (a) and (b), two more-complex exemplary embodiments of
the present invention in exploded view.
The invention will now be explained in greater detail using a banknote as an
example. Fig. 1 shows a schematic diagram of a banknote 10, which exhibits,
in addition to the denomination 12 and a portrait depiction 14, an optically
variable security element 16. The security element 16 includes a piece of
information 18, in the exemplary embodiment a replication of the
denomination 12 that is normally imprinted on the banknote multiple times.
The security element can also repeat other pieces of information, for example
an image motif, such as the portrait 14, or constitute a logo or a code, such
as
a bar code or an alphanumeric character string. To increase the counterfeit
security of the banknote, the piece of information 18 in the security element
16 is typically related to or complements a piece of information that is
likewise present in another location on the banknote 10, so that a simple
authenticity test is available to the user.
The structure of the security element 16 in fig. 1 will now be explained in
greater detail with reference to the schematic sectional view in fig. 2, which
shows a section through the banknote 10 along the line II-II.
First, a colored background layer 22 is imprinted with screen printing on the
entire surface of the banknote paper 20. In the exemplary embodiment, the
background layer 22 is imprinted with a uniform tone, for example red, blue
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or green. If desired, the background layer 22 can also be printed with a
metallic effect ink and be, for example, bronze, silver, copper or gold
colored.
Other printing methods known to the person skilled in the art may also be
used for the application of the background layer 22, such as offset printing
or
indirect printing.
Over the background layer 22 is then imprinted with a dark ink, for example
black, an intaglio printing layer 24. The intaglio printing layer 24 includes,
in
addition to a fine structure described below, a gap 26, whose shape forms the
piece of information 18 in fig. 1, in the exemplary embodiment the numeral
"1". As shown in fig. 2, through the intaglio printing, the security element
16
exhibits in the non-gap areas 28 of the intaglio printing layer 24 a tactilely
palpable relief structure having heavy inking.
Here, the surface area covered by the intaglio printing layer 24 is somewhat
larger than surface area covered by the background layer 22. In this way, the
dark intaglio printing ink covers any register variations to the background
printing, so that the impression of perfect register is created for the
observer.
Over the series of layers comprised of the background layer 22 and the
intaglio printing layer 24 is applied a light-transmitting, optically variable
layer 30, for example a printing layer having cholesteric liquid crystal
pigments. The liquid crystal layer 30 shows a color shift effect in which the
color impression of the layer changes for the observer, for example from blue
to green.
The surface area covered by the liquid crystal layer 30, in turn, is executed
to
be somewhat larger than the surface area covered by the intaglio printing
layer 24, so that the color shift effect of the liquid crystal layer 30 is
almost
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invisible outside the dark intaglio printing layer 24 over the light banknote
paper. In contrast, in the dark, non-gap areas 28 of the intaglio printing
layer
24, the color shift effect stands out clearly. Within the gap 26, the color
impression of the background layer 22 dominates. Overall, the security
element can thus offer the observer an attractive visual impression through
the choice of color of the background and the design of the intaglio printing,
and in addition, exhibits a high security value through the tactilely palpable
relief structure and the optically variable liquid crystal layer.
Fig. 3 shows, in (a) to (e), different variants of the design of the
background
layer 22. Here, fig. 3(a) first shows a full-surface background layer 22, as
the
security element 16 in figures 1 and 2 also exhibits. The background layer 22
in fig. 3(b) exhibits a gap 32 in the shape of a piece of information, here
the
numeral "1". It is understood that this piece of information on the
background layer 22 can be combined with a piece of information on the
intaglio printing layer 24.
In addition to simple gaps, the background layer 22 can also exhibit
patterned areas 34, whose shape forms a piece of information, as shown in
fig. 3(d). Fig. 3(e) shows a further variant, in which the background layer 22
exhibits both an information-bearing gap 32 and an information-bearing
patterned area 34. The gap 32 and the patterned area 34 can also complement
one another to form a complete piece of information, as illustrated, for
example, by the split numeral "1" in fig. 3(c).
Variants for designing the intaglio printing layer 24 are depicted in fig. 4.
Fig.
4(a) shows a full-surface intaglio printing layer 24 having a fine structure
comprised of a high-resolution line pattern 42, 44. The main surface of the
intaglio printing layer 24 is provided with a first line pattern 42, in which
the
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parallel lines enclose an angle of -45 with the horizontal reference
direction.
In sub-areas 46, whose shape forms a piece of information, here the numeral
"1" in each case, the parallel lines of the second line pattern 44 enclose an
angle of +45 with the reference direction.
The information-bearing sub-areas 46 and the oval span of the intaglio
printing layer 24 are each surrounded by a positive border contour 48, that
is,
a circumferential dark border line that is visible in the print image, which
is
depicted more precisely in the detail 50 shown in fig. 4(b). In the exemplary
embodiment, the parallel lines of line pattern 42, 44 exhibit a line width b
of
100 m and a line spacing a of 120 gm. Here, the line spacing a is defined as
the spacing between same, for example upper, edges of adjacent lines. As
explained below, line spacings a that are smaller than the line width may
also be used, so that adjacent lines overlap. In the exemplary embodiment,
the cutting depth of the lines is about 50 gm.
Fig. 4(c) shows a further variant of the intaglio printing layer 24, in which,
unlike the embodiment in fig. 4(a), the information-bearing sub-areas 46 are
provided with a negative border contour 52. As can be seen in the detailed
cutout 54 in fig. 4(d), the negative border contour 52 is a gap that encircles
the sub-areas 46 and that is visible in the print image. Both the positive
border contour 48 in fig. 4(a) and the negative border contour 52 in fig. 4(c)
result in the piece of information being easier for the observer to perceive.
The intaglio printing layer 24 in fig. 4(c) further exhibits an information-
bearing gap 56, which corresponds to the gap 26 shown in fig. 2. There is an
unobstructed view of the colored background layer 22 through the gap 56,
for example according to one of the variant of fig. 3.
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Optionally, it is possible to provide further intaglio printing elements
within
the gap 56. These are preferably executed to be so flat that the intaglio
printing ink is translucent. For example, within the gap 56, intaglio printing
elements in the shape of the number "1"can be incorporated (not shown).
In the variant of fig. 4(e), the oval of the intaglio printing layer 24 is
additionally surrounded by a circumferential border area 58, which is
printed with high colored-surface coverage. For example, the line pattern 60
of the border area 58 can exhibit the angle orientation of the sub-areas 46
and
be printed with a line width b of 100 m and a line spacing a of 90 gm.
Expediently, the background layer 22 and the intaglio printing layer 24 are so
aligned with one another that the border of the background layer 22 is
covered by the circumferential border area 58. Potential register variations
between the background layer 22 and the intaglio printing layer 24 are then
hidden for the observer by the border area.
The variant of fig. 4(f) is designed similarly to the variant of fig. 4(e),
but the
line pattern 60 of the circumferential border area 58 exhibits a different
angle
orientation than the line patterns 42 and 44 on the main surface or on the
information-bearing sub-areas 46. By way of example, in the exemplary
embodiment, the angle orientation of the lines in the border area 58 is 0 . As
in fig. 4(a), the sub-areas 46 are provided with a positive border contour.
The further variant of fig. 4(g) differs from the variant shown in fig. 4(e)
merely through the especially wide formation of the negative border contour
52, which places a special accent on the information-bearing sub-areas 46.
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It is understood that each of the variants of the intaglio printing layer 24
in
fig. 4 can be combined with each of the variants of the background layer 22 in
fig. 3.
Fig. 5 shows in (a) to (c) sections through the intaglio printing layer 24 for
various ratios of line width b and line spacing a. Here, the intaglio printing
layer does not have to be executed with a uniform ratio across the entire
surface area, but rather, each of the embodiments in fig. 5(a) to (c) can be
present in various sub-areas of the intaglio printing layer.
In the embodiment in fig. 5(a), the line spacing a is only slightly larger
than
the line width b, for example, the line width is 100 gm and the line spacing
110 m. In this way, the intaglio printing ink is applied across the entire
surface, but with considerably varying thickness. The lines can thus be
perceived as such by the eye with no problem, but the overall surface
appears to be very dark. The color shift effect of the liquid crystal layer 30
stands out clearly in the area over such an intaglio printing layer.
In fig. 5(b) is shown an embodiment having a large line spacing a, for
example having a line spacing of 160 gm, with a line width of 130 m. In the
spaces 62 without printing ink, the background layer 22 or the banknote
substrate 20 not depicted in fig. 5(b) is visible. The individual lines thus
stand
out even more clearly for the human eye, and the overall impression of the
surface becomes lighter. In this way, the effect of the liquid crystal layer
30 is
weakened compared with the embodiment in fig. 5(a).
Finally, fig. 5(c) shows an area of an intaglio printing layer 24 in which the
individual lines overlap, that is, the line spacing a is smaller than the line
width b. For example, with a line width b of 130 m, the line spacing a can be
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only 110 m. Here, the line width is determined for a non-overlapped line 64
(drawn in as a dotted line in fig. 5(c)). Through this overlapping, a very
high
and even surface coverage is achieved. Such an embodiment of the intaglio
printing layer is particularly suitable for a circumferential border area,
such
as the border area 58 in fig. 4, in which the underlying border of the
background layer 22 is to be hidden.
Fig. 6 shows in (a) and (b) two more-complex exemplary embodiments of the
present invention, where the layers disposed on top of one another are
illustrated in exploded view for clarity. The security element 70 in fig. 6(a)
exhibits a full-surface colored background layer 72, over which an intaglio
printing layer 74 is disposed. The intaglio printing layer 74 includes a fine
structure comprised of parallel lines of differing angle orientation that form
information-bearing sub-areas 76 in the shape of the numeric string "10". The
sub-areas 76 are each surrounded by a negative border contour.
The intaglio printing layer 74 further includes an aperture 78 in the shape of
a graphic motif, here a zebra head, in which the colored background layer 72
becomes visible. In addition, the background layer 72 also shows through in
the spaces in the parallel lines of the intaglio printing layer 74.
The circumferential border area 80 of the intaglio printing layer 74 is
printed
with high surface coverage, so that the border of the background layer 72
that lies under the border area 80 cannot be perceived by the observer.
Over the background layer 72 and the intaglio printing layer 74 is applied a
liquid crystal layer 82, whose color shift effect stands out especially in the
non-gap dark area of the intaglio printing layer 74. In contrast, within the
gap 78, the color impression of the background layer 72 dominates. Outside
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the intaglio printing layer 78, the liquid crystal layer 82 lies directly over
the
light banknote paper, so that the color shift effect of the liquid crystal
pigments is practically not perceptible there.
Fig. 6(b) shows a further exemplary embodiment of a security element 90
according to the present invention, in which the colored background layer 92
is imprinted in the shape of a piece of information, here, in the shape of a
zebra head. The intaglio printing layer 94 likewise includes in its fine
structure a piece of information, namely the numeric string "10". Over both
layers is again applied a full-surface liquid crystal layer 96.
Since the intaglio printing layer 94 exhibits no gap in this exemplary
embodiment, the optical impression is darker than in the case of the intaglio
printing layer 74 of the exemplary embodiment in fig. 6(a). However, the
color and design of the zebra head 92 can be clearly perceived through the
spaces between the parallel lines of the intaglio printing layer 94.
