Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SECURITY DEVICES FOR SECURITY DOCUMENTS
The invention relates to improvements in security
devices for security documents.
Security documents, including documents of value and
means of identification, including banknotes, passports,
identification cards, certificates and the like, are
vulnerable to copying or counterfeiting. The increasing
availability of colour photocopiers, electronic scanning and
other imaging systems, and the improving technical quality
of colour photocopiers, has led to an increase in the
counterfeiting of such documentation. There is, therefore,
a need to continually improve the security features of such
documentation to add additional security features or to
enhance the perceptions and resistance of simulation to
existing features.
Steps have already been taken to introduce optically
variable features into such documentation which cannot be
reproduced by a photocopier or an electronic scanner. Since
the photocopying process typically involves reflecting high
energy light onto an original document containing the image
to be copied, one solution is to incorporate one or more
features into the document which have a different perception
in reflected and transmitted light. Examples of such
security features include watermarks, embedded security
threads, fluorescent pigments and the like.
One such security feature which can be applied directly
to documents of value is described in GB-A-2268906. This
security feature comprises a liquid crystal material applied
to a paper or polymer region to produce optical effects
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which differ when viewed in transmitted and reflected light,
in particular where the paper or polymer region includes a
watermark.
Another such security feature, which can be applied to
security paper, is described in EP-A-0490825. This security
paper has a superficial colour code made up of at least two
adjoining surface areas in the form of stripes. The stripes
contain different iridescent pigments and exhibit different
colours when viewed from different oblique viewing angles.
In GB-A-2283026 a security feature is described in
which a portion of the paper is transparentised with a
transparentising resin to which an iridescent substance has
been added. Different colour shifts can be seen in the
resulting paper as the paper is moved and examined in
reflected light. A colour shift can also be seen when the
light, under which it is examined, changes from transmitted
to reflected light, although no colour change can be seen
when the viewing angle is altered under just reflected
light.
One class of security features used in banknotes and
the like are those commonly referred to as "teller assist"
features. These are features that require a simple hand
held device to view them. A common teller assist security
feature is one based on luminescent materials. Luminescent
materials are well known to those skilled in the art, and
include materials having fluorescent or phosphorescent
properties. The use of luminescent features on security
threads has been described in EP-A-303725, EP-A-319157 and
WO-A-2006051231, as well as in numerous other patent
publications. It is also well known to use other materials
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that respond visibly to some form of invisible radiation,
such as IR responsive, photochromic and thermochromic
materials.
In the security feature described in EP-A-319157, there
is present on either or both sides of an elongate security
thread a fluorescent material. The security thread comprises
a plastics substrate with demetallised indicia on one side
thereof, and the fluorescent material present in the
plastics substrate or on the surface of said substrate. When
viewed under ultraviolet (UV) reflected light from the side
of the demetallised indicia, the demetallised indicia are
highlighted in the colour of the fluorescent material. In a
further example a demetallised security thread is uniformly
coated on one side with a layer containing one fluorescent
material and uniformly coated on the other side with another
fluorescent material of a different colour. When viewed
under UV light, each side reflects UV light exhibiting its
own particular colour more or less uniformly, although there
may be some colour mix in the demetallised areas. In
transmitted light, however, the demetallised areas will be
perceived as a third colour which will be a mix of the other
two colours and markedly distinguishable from them.
A similar type of security thread is disclosed in WO-A-
2006051231. The security thread described in this document
comprises an opaque layer with gaps forming indicia
supported by a transparent polymeric carrier film. Different
fluorescent materials are applied to either side of the
security thread such that, in reflection, the two surfaces
emit a different colour when exposed to UV light. When
viewed in transmission in UV light a third colour (and
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potentially a fourth colour, depending on which side of the
security thread is being viewed), is observed in the gaps
in the opaque layer resulting from the combination of the
two surface colours.
The latter two related art examples describe a security
feature in which an image is created by gaps in an opaque
layer which is visible in transmitted light or on exposure
to UV light, with zones fluorescing in two or more colours.
A problem with this type of structure is that, in order to
achieve multiple coloured fluorescent zones, the fluorescent
material must be applied to the opaque materials. In most
cases the opaque material is metallic and has a
characteristic sheen which, when exposed in a secure
document, attracts the attention of the authenticator which
is not necessarily desirable. Furthermore, if a fluorescent
material is applied to the metallic layer there may be an
undesirable reduction in the metallic sheen. This is of
particular concern if the fluorescent material is a
pigmented lacquer. The superior lightfastness of pigmented
fluorescent lacquers compared to organic dyes means that
they are the preferred materials in security devices
employed in documents, such as banknotes, where the feature
must withstand a long lifetime in circulation.
However, there is a continual need to find alternative
security features which are difficult to counterfeit and in
particular teller assist features which are easy to
recognise under the requisite predetermined conditions for
authentication purposes.
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The invention therefore comprises a security device
comprising at least one at least partially light
transmitting spacer layer, on one side of which are formed
first indicia, said first indicia comprising a plurality of
repeating elements and being formed from a material which
emits a coloured visible light when excited by a form of
radiation, and on an opposing side of the spacer layer is an
absorbing material, which absorbs the said radiation but not
visible light, the absorbing material being applied in a
pattern comprising a plurality of repeating elements similar
to the elements of the first indicia and having gaps between
the elements.
Embodiments of invention will now be described, by way
of example only, with reference to the following drawings in
which:-
Figure la is a cross-sectional side elevation of a
security device according to the present invention;
Figure lb is an underneath plan view of the security
device of Figure la;
Figure 2 is a cross-sectional side elevation of a
security substrate incorporating the security device;
Figure 3 is an alternative version of the security
device of Figure 1;
Figure 4a and 4b are top and underneath plan views of
the security device of Figure 3 respectively showing the
absorbing regions and the indicia; and
Figure 5 is a cross sectional side elevation of a
security substrate to which a further alternative embodiment
of the security device has been applied.
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The security device 10 of the present invention
provides a directional teller assist security feature which
can be checked easily under ultra violet light. The
security device 10 is extremely versatile as the nature of
its construction means that it can be applied to security
documents in a number of ways.
Referring to Figure 1, the security device 10 comprises
a spacer layer 11 to one surface of which are applied
indicia 12,13 and to the other surface are applied regions
14 of an absorbing material.
The spacer layer 11 is preferably a carrier layer of a
substantially transparent polymeric substrate, such as
polyethylene terephthalate (PET) or biaxially oriented
polypropylene (BOPP). Where the spacer layer 11 is a
carrier layer, the device 10 may be formed into an elongate
security element, such as a thread or stripe, or a patch for
incorporation in or application to a paper or polymer
substrate to form a security substrate from which a security
document can be formed. When used in this form, the
thickness of the spacer layer 11 is typically in the region
of 10-40 microns, and more preferably 15-20 microns.
Alternatively, the spacer layer 11 may comprise a varnish or
the substrate of a security document itself, e.g. a layer of
BOPP film forming a polymer banknote. When used in this
form the thickness of the carrier layer 11 is typically in
the region of 40-120 microns and more preferably 70-90
microns.
This means that the security device 10 of the present
invention can thus be incorporated into or arranged on a
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security document in any of the conventional formats known
in the related art.
If the spacer layer 11 is a transparent polymeric film
it can be incorporated in a paper substrate using the method
described in WO-A-0039391 in which one side of a transparent
elongate impermeable strip is wholly exposed at one surface
of the paper substrate in which it is partially embedded,
and partially exposed in apertures at the other surface of
the substrate. The apertures formed in the paper can be used
as the spacer layer 11 in the present invention.
In the method described in W0-A-0039391 the indicia
12,13 and the absorbing layer 14 can be applied to the
spacer layer 11 during the production of the transparent
elongate impermeable strip or after it has been incorporated
into the paper substrate.
Other methods for forming transparent regions in paper
substrates are described in EP-A-723501, EP-A-724519, WO-A-
03054297 and EP-A-1398174.
The indicia 12,13 are applied to one side or surface of
the spacer layer 11, preferably by a suitable printing
process. Typically, the indicia 12, 13 are printed onto the
document, preferably by means of a process such as
lithography, UV cured lithography, intaglio, letterpress,
flexographic printing, gravure printing or screen printing.
In a preferred embodiment the indicia 12,13 are simply
printed in one process ensuring perfect registration between
elements of the indicia 12,13.
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,
The indicia 12,13 and the absorbing material regions 14
comprise a plurality of substantially similar repeating
elements, such as stripes, curves, pixels and the like. Each
set of indicia may form an image, for example in the case of
the structure shown in Figure 1 each image is divided into
strips (indicia)12 and 13 respectively and then the strips
are interlaced. The image preferably provides identifying
information and could be any one of symbols, pictorial
representations and characters including alphanumerics and
those from non-Roman scripts of which examples include but
are not limited to, Chinese, Japanese, Sanskrit and Arabic.
In the embodiment illustrated in Figures la and lb
first indicia 12 comprises a set of stripes which extend
transversely from one edge of the spacer layer 11 to an
opposing edge and repeat at intervals along the length of
the layer 11. Similarly second indicia 13 comprises a set of
stripes which also extend transversely from one edge of the
spacer layer 11 to an opposing edge and repeat at intervals
along the length of the layer 11. A stripe from the first
indicia 12 is printed adjacent a stripe from the second
indicia 13 with gaps 17 between each pair of stripes. The
indicia 12,13 are formed from two different materials,
preferably inks, which are colourless in normal daylight but
which each emit a different coloured light, e.g. red and
green, when excited by a form of radiation, such as UV
light.
Regions 14 of the absorbing material are also
preferably applied by a suitable printing process, in
register with the indicia 12,13. In this embodiment the
absorbing regions 14 comprise transverse stripes (each
stripe having a width equal to the width of an adjacent pair
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of stripes from indicia 12,13) repeating along the length of
the spacer layer 11 with gaps 18 between each stripe which
match the gaps 17 between the stripes of the indicia 12,13.
If the inks/materials used for the indicia 12,13 are
excitable by UV light, then the absorbing material must be a
UV absorbing material. If the inks/materials used for the
indicia 12,13 respond to another form of radiation, the
absorbing material must be one which absorbs that form of
radiation.
When the example shown in Figure 1 is viewed under a UV
lamp from the direction of arrow X (i.e. from the same side
as the absorbing material 14) with the lamp 15 held at A,
towards one end of the security device 10, a set of stripes
in one colour (e.g. red) can be seen. If the stripes are
arranged to form an image then a red image would be
observed. This occurs as the UV light can only pass through
the gaps 18 between the absorbing regions 14 and excite the
ink/material used to form the stripes of the first indicia
12, which is closest to the lamp 15. The absorbing regions
14 prevent any radiation from getting to the stripes of the
second indicia 13. Since the absorbing regions 14 only
absorb UV light, the fluorescent light resulting from
excitation of the ink material of indicia 12 is visible
through the overlying absorbing regions 14 to provide a red
image 20.
When the lamp 15 is held at position B, at the other
end of the device 10, the UV light is now only able to reach
the stripes of the second indicia 13, whilst the absorbing
regions 14 prevents the UV light from reaching the stripes
of the first indicia 12. Thus the fluorescent light
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resulting from excitation of the ink/material of second
indicia 13 now becomes visible through the absorbing regions
14 and a set of green stripes 21 is observed. If the
stripes 21 are arranged to form an image then a green image
will be observed in this viewing condition.
The security device 10 thus provides a security feature
which fluoresces differently depending on where the lamp 15
is held along the length of the device 10.
The effect of the security feature is derived from the
fact that the UV (or other radiated) light is only able to
pass into, and through, the spacer layer 11 at an angle
which allows it to reach the elements making up either the
first indicia 12 or the second indicia 13, but not both.
This limitation is effected by the gaps 18 between the
absorbing regions 14. In this embodiment the registration
of the indicia 12,13 relative.to the absorbing regions 14 is
important to create clean fluorescent images. The combined
width of the pairs of stripes of the indicia 12,13 is
therefore preferably substantially equal to the width of the
stripes of the absorbing regions 14. The width of each of
the gaps 17,18 between the stripes is preferably
substantially the same and the width of the gaps 17,18 is
preferably substantially the same as the width of each of
the stripes of the indicia 12, 13.
In one preferred embodiment the indicia 12,13 and
absorbing regions 14 are litho printed in stripes of 20 to
40 micron widths, which gives a good resolution to the
radiating indicia. The use of litho printing enables
perfect back to back registration of the absorbing regions
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14 and indicia 12,13, which is very difficult for a
counterfeiter to achieve.
In another embodiment of the invention (not
illustrated), first and second indicia 12,13 are applied
along the length of the security device 10 and third and
fourth indicia are applied in a transverse direction across
the width of the device 10 to give four different viewing
positions. The inks/materials used to form the third and
fourth indicia are preferably different from those used in
the first and second indicia 12,13 or they may be the same.
In yet another embodiment of the present invention (see
Figure 2), the security device 10 is formed directly on a
security substrate from which a security document is to be
formed, such as a polymer banknote; the spacer layer 11
being provided by a layer of transparent BOPP film which
forms the base substrate of the banknote. Each surface of
the BOPP film is coated with a layer of white ink 16 with
registered gaps which form windows 19. The absorbing
regions 14 and indicia 12,13 are applied to the film which
provides the spacer layer 11 within the windows 19. The
security feature gives the same two views as described in
relation to Figures la and lb.
To further improve the effect of the security feature,
a UV scattering layer, such as a titanium dioxide loaded
varnish, is coated on the spacer layer 11 before the
absorbing regions 14 are applied.
In yet another embodiment of the invention as shown in
Figure 3, no gaps are provided between the elements of
indicia 12, 13. The elements of the absorbing regions 14
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are applied to the reverse side of the spacer layer 11, but
at a slightly offset angle to the indicia 12, 13.
Figure 4a shows the absorbing regions 14 slightly
offset to the vertical boundary of the spacer layer 11 and
Figure 4b shows the equivalent view for the indicia 12, 13
which are parallel to the vertical boundary of the spacer
11. This example could of course be reversed with the
indicia 12, 13 offset to the vertical boundary of the spacer
11 and absorbing regions 14 parallel to the vertical
boundary of the spacer 11. Alternatively both the absorbing
regions 14 and the indicia 12,13 could be offset to the
vertical boundary of the spacer layer 11, but in this case
they would be offset by a different degree.
As the lamp 15 is moved along the length of the
security device 10, the alternating fluorescent stripes (red
and green) of the indicia 12,13 appear to move along the
length of the device 10 are also similar to a barber's pole.
In this embodiment, the indicia 12, 13 are not registered
with respect to the bands of the absorbing layer 14 and the
width of the stripes of the indicia 12, 13 do not correlate
to either the gaps 18 or the width of the stripes of the
absorbing regions 14. In a preferred construction the width
of the bands are 10 m to 1000 m and more preferably 10 m to
100 m, and the preferred range of offset angle is 0-15 and
more preferably 0-5 .
A preferred method for forming the example in Figure 3
is illustrated in Figure 3b. In this case indicia 12 in the
form of stripes are applied onto one side of the spacer
layer 11 and then a continuous block of the ink ultimately
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forming the second indicia 13 is applied so as to cover the
indicia 12 and the exposed regions of the spacer 11. The
security device 10 will have the same optical effect as the
security device viewed of Figure 1 when viewed in the
direction of the arrow X as long as first indicia 12 is
sufficiently opaque under UV illumination to block out the
effect of indicia 13.
It should be noted that, whilst some embodiments of the
invention utilise two sets of indicia 12,13, in others only
one set of indicia 12 may be present. This is illustrated in
Figure 3c, where the security device 10 comprises just one
set of indicia 12. However, when viewed a second set of
stripes is formed by the omission of any material in this
region. In this case as the UV lamp 15 is moved along the
length of the security device 10, a set of fluorescent
stripes with a single colour alternate with a set of
colourless strips both of which appear to move along the
length of the device 10, again similar to a barber's pole.
Although it is preferred that the spacer layer 11 is
transparent, it may be translucent and it may be coloured.
If it is translucent, however, it must not interfere with
the fluorescing indicia 20, 21.
In yet another embodiment of the invention, inks are
selected for the indicia 12, 13 which are visible in normal
light. In a further embodiment the inks used to form indicia
12 and 13 may appear the same colour in normal light but
emit different colours when excited by a form of radiation.
Suitable inks include those cited in EP-A-1567358 and WO-A-
9840223.
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Suitable UV absorbing inks include a UV barrier coating
supplied by Sun Chemical with the product code NMHR-70-
20669. A suitable UV absorbing compound which could be
applied to conventional inks is a hydroxyphenyl triazine
class of UV absorber sold under the name Tinuvin 400 by
Ciba .
The security feature may also be combined with a
machine readable feature, such as a magnetic ink, and in
particular a transparent magnetic ink such as those
described in GB-A-2387812 and GB-A-2387813. Alternatively a
machine readable aspect may be provided by the introduction
of separate machine-readable layers. In addition to magnetic
materials detectable materials that react to an external
stimulus include but are not limited to fluorescent,
phosphorescent, infrared absorbing, thermochromic,
photochromic, electrochromic, conductive and piezochromic
materials.
It will be further understood by those skilled in the
art that the substrate of the present invention may be used
in combination with existing approaches for the manufacture
of security elements. Examples of suitable constructions
that can be used include, but are not limited to, those
described in WO-A-03061980, EP-A-0516790, WO-A-9825236, and
WO-A-9928852.
=
Figure 5 shows a different embodiment of the security
device 10 applied to a base substrate 25 to provide a secure
substrate for the use in making security documents such as
documents of value and means of identification, including
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bank notes, passports, identification cards, certificates
and the like. An aperture 26 is created in a secure
substrate 25, for example as described in EP-A-723501, EP-A-
724519, WO-A-03054297 and EP-A-1398174. A first polymeric
substrate ha bearing indicia 12,13 (positioned on either
surface of first substrate 11a) is applied to the secure
substrate 25 such that it over covers the aperture. A second
polymeric substrate llb bearing absorbing layer 14
(positioned on either surface of the second substrate 11b)
is than applied to cover the opposite side of the aperture
26. If an adhesive is used to adhere the first and second
polymeric substrates 11a,11b to the secure substrate 25 it
is preferred that the adhesive is omitted in the aperture
region. The advantage of this embodiment is that the
aperture 26 increases the distance between the indicia 12,13
and the absorber 14 and therefore demands on the
registrational tolerances and size of the indicia is
reduced. In this case illustrated, if the indicia 12,13 and
absorber 14 are on the respective inner surfaces, the spacer
layer 11 is air.
