Note: Descriptions are shown in the official language in which they were submitted.
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SUBSTRATE FOR SECURITY DOCUMENT
The invention relates to a security document and a substrate for a security
document.
A variety of security devices have been proposed in the past to prevent
security documents from being counterfeited or fraudulently produced. A
particularly
useful security device is one which is readily verifiable by a user but which
is diff icult
to produce. One example of such a security device is an enclosed clear
transparent
region in an otherwise opaque substrate.
For example W08300659 describes a polymer banknote formed from a
transparent substrate comprising an opacifying coating on both sides of the
substrate. The opacifying coating is omitted in localised regions on both
sides of the
substrate to form a transparent window region. Other examples of a security
documents with a transparent window are described in WO-A-2008/003949 and
WO-A-2006/133512.
W00039391 describes a method of making a transparent aperture in a paper
substrate. This is achieved by blinding one or more selected areas of a porous
support surface, depositing a first layer of paper fibres onto the porous
support
surface around the blinded areas, bringing an impermeable elongate security
thread
to lie in contact with the blinded areas of the support surface such that at
least the
edges of the elongate security thread overlie the deposited layer, and
depositing a
further layer of paper fibres over the first layer and the impermeable strip
to securely
embed the edges of the elongate security thread within the paper. The blinded
areas
are impermeable, which substantially prevents the deposition of fibres thereon
before the elongate security thread is laid thereover. Thus, substantially no
paper
fibres are deposited on one side of the elongate security thread in a central
region
between edges of the elongate security thread to thereby expose a continuous
area
of the elongate security thread at a first surface of the paper. Additionally
a plurality
of discrete translucent or transparent windows is formed in a second surface
of the
paper in which the elongate security thread is exposed.
An alternative method for forming a transparent region in a paper document
is to apply a transparent film in the form of a patch or a strip over a hole
formed in
the document either during or post manufacture of the substrate. Such
approaches
have been described within the prior art for example EP723501, EP724519 and
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W003054297.
The use of an enclosed transparent region prevents the generation of a
"simple" counterfeit arising from the increasing popularity of colour
photocopiers and
other imaging systems and the improving technical quality of colour
photocopies. In
addition the clear transparent region provides a feature that is easily
verifiable by the
general public.
The presence of an enclosed transparent region in an opaque document
should be identifiable by the use of transmitted light detectors in secure
document
handling machines. However the fact that the position of the enclosed window
varies, for example in different denominations of banknotes, increases the
cost and
expense of modifying the detector such that it is compatible with all design
variants.
US-A-5,783,275 describes the incorporation of security threads into security
documents such as banknotes. These security threads are provided with
holographic or other optically variable effects or alternatively with
structures having a
metallic lustre or with a security print. These are relatively complex
structures.
An example of a transparent security thread is described in US-A-
2003/0082348. This is formed by taking an opaque, paper document and
transparentising a thin line extending across the document so as to form a
thin,
thread like feature. This simulated security thread has a width typically in
the range
of 0.38-1.58mm and a transparency such that when the document is held to the
light,
the thread can be seen.
EP-A-0930174 describes a security document incorporating a plastic thread
or strip which is translucent, the translucent part possessing visually and/or
mechanically readable signs or patterns.
EP-A-0536855 describes a security paper incorporating a plastic strip which
is embedded within the paper and which is not readily visible under reflective
illumination to the unaided eye.
GB-A-1357489 describes a banknote or other paper sheet including an
opaque thread or strip.
These security documents have the advantage of providing actual or
simulated threads which enable them to be authenticated upon manual
inspection.
However, they are not ideally suited for machine authentication.
In accordance with the present invention, a polymer substrate for a security
document has at least one elongate transparent region extending through a more
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opaque area of the substrate and completely or almost completely between
spaced
locations on the boundary of the substrate, , wherein the width of the
transparent
region is at least 2mm and the transparent region has an optical density not
exceeding 0.3.
A transparent region or strip of this type enables the transparent region to
be
easily detected by transmitted light detectors on cash handling equipment. The
fact
that the transparent strip traverses completely or almost completely across
the
substrate, for example the full document height, or alternatively the full
document
width, means that the position of the detector is not critical. Also, the
transmitted
light detector can be set up such that the document is only deemed authentic
when
the width of the transmitted light area corresponds to either the full width
or full
height of the transparent region.
Furthermore, setting the width of the elongate region to be at least 2mm
while requiring that it extends through a more opaque area of the substrate
means
that an authentication machine will detect a distinct flash of light when the
substrate
passes across a light source. This is further enhanced by the high degree of
transparency required.
This should be contrasted with conventional threads which will have too
narrow a width and typically too low a transparency for the required "flash"
to be
observed and detected reliably and on high speed sorting machines.
By "almost completely" we mean that the transparent region may be spaced
from the boundaries by up to 10mm.
Another problem with the known use of transparent regions is that an
enclosed clear transparent region in an opaque substrate is susceptible to
counterfeiting, for example by punching a hole in an opaque substrate and then
placing a clear transparent polymeric film over the hole.
Preferably, therefore, the at least one transparent region extends completely
between the spaced locations on the boundary of the substrate.
This minimises the counterfeiting risk since this is not possible with a
continuous transparent strip as the document must be split into two sections
and
then reassembled such that there is a transparent strip between the two
sections. It
is very difficult to achieve this without damaging the document to an extent
that
would be recognised by the authenticator.
A particularly preferred form of transparent region is rectilinear, such a
region
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extending between opposite edges of the document. However, other forms of
transparent region are envisaged including stepped, curved, spiral and the
like.
By "polymer" we mean a synthetic plastics material including a co-extrusion
or lamination of such materials.
For the purpose of the current invention a transparent region of the document
is defined as one whose optical density when measured on a transmission
densitometer, with an aperture area equivalent to that of a circle with a 1 mm
diameter, is preferably less than 0.3, more preferably less than 0.2 and even
more
preferably less than 0.1 as measured for example on a MacBeth TD932.
By a "more opaque area" we mean that the area of the substrate on either
side of the transparent region has an optical density which is at least 0.15
units
greater than the optical density of the transparent region and preferably 0.3
units
greater than the transparent region and even more preferably 0.5 units greater
than
the transparent region. Thus, for example, if the transparent region has an
optical
density of 0.1 units then the more opaque area may have an optical density of
0.25,
preferably 0.4 and more preferably 0.6.
In many cases, a single transparent region is provided. However, more than
one transparent region could be provided and this allows additional
information to be
defined by the transparent regions. For example, spacing between regions
and/or
their widths could be used to form a code. Where there is more than one
transparent region present the transparency of the individual regions may be
different. Alternatively the transparency across an individual region may be
varied.
Some examples of substrates, security documents and methods according
to the invention will now be described with reference to the accompanying
drawings,
in which:-
Figure 1 is a plan view of a first example;
Figure 2 is a schematic cross-section of the example shown in Figure 1;
Figures 3-9 and 11 are plan views similar to Figure 1 but of further examples;
and,
Figure 10 is a schematic diagram of an example of apparatus for carrying out
the method.
Figures 1 and 2 show an example of a security document of the current
invention in plan-view and cross-section respectively. In this example the
security
document comprises a transparent polymeric substrate 1 onto which is applied a
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pigmented coating 2 which may be opaque. The pigmented coating 2 can be
applied by any conventional printing process, but typically this is a gravure
printing
process. The pigmented coating may comprise a single layer applied to one side
of
the transparent substrate or, as shown, one or more layers 2 applied to both
sides of
5 the transparent substrate. The pigmented coating is omitted in one region of
the
document, on both sides, to provide a continuous transparent strip 3 which
traverses
the full height of the secure document orthogonal to the opposite, parallel
edges.
The pigmented coating(s) 2 of the secure document, such as a banknote,
then undergoes further standard security printing processes including one or
more of
the following; wet or dry lithographic printing, intaglio printing,
letterpress printing,
flexographic printing, screen-printing, and/or gravure printing as well as
being
provided with identifying indicia etc as is conventional. The resulting print
is not
shown in Figure 1.
As mentioned above, the transparent strip 3 enables the transparent region
to be easily detected by transmitted light detectors on cash handling
equipment. An
example in schematic form of suitable cash handling equipment is show in
Figure
10. In this apparatus, a radiation source 30, such as an optical source, is
located
above a document feed path indicated by an arrow 32 in Figure 10. Below the
feed
path 32 is located a radiation sensor 34 such as a CCD array and both the
source
30 and sensor 34 are connected to a processor 36. As a document 38 similar to
the document shown in Figures 1 and 2 is fed in a conventional manner between
the
source 30 and sensor 34, initially the pigmented coating 2 will substantially
attenuate
the intensity of the light passing through the document. However, when the
transparent strip 3 is located between the source and the sensor, the
intensity of
received radiation will suddenly increase and this increase will be detected
by the
processor 36. Typically, the length of the sensor 34 in a direction
perpendicular to
the direction of movement along the transport path 32 will be at least equal
to the
length of the transparent region 3. Thus, when the document 38 passes along
the
path 32 short edge first, a "flash" of transmitted light will be detected by
the sensor
34 equivalent to the width of the transparent strip 3. The length of time the
"flash" of
transmitted light is detected for will correspond to the width of the
continuous
transparent region 3. The width of the transparent strip 3 can be varied
between
families of secure documents to provide a method of coding. A more complex
coding
system can be introduced into the document by providing multiple continuous
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transparent strips which can either be of the same width or different widths
(as
described below).
Figures 3 and 4 show alternative configurations for the continuous
transparent region. In Figure 3 a continuous transparent strip 5 traverses the
full
width of the secure document 6 orthogonally to the opposite, short parallel
edges.
The continuous transparent strip does not have to be linear and a stepped
transparent region 7 which traverses the full height of the secure document is
illustrated in Figure 4. Alternatively the continuous strip can be curved.
Figure 5a shows a further alternative configuration for the continuous
transparent region in which the transparent region extends between adjacent
edges
rather than parallel edges. In Figure 5a the document comprises one continuous
transparent strip 20 extending between adjacent edges. In Figure 5b the
document
comprises two continuous transparent strips 20,21 between adjacent edges
positioned in opposite corners of the note. The advantage of the configuration
in
Figure 5b is that there will always be at least one "flash" of transmitted
light
irrespective of the position of the detectors in relation to the height of the
note.
Figure 5c shows a further design alternative where a continuous transparent
strip runs diagonally between opposed corners. The advantage of this design is
that
a flash will be seen by a detector mounted in any position on either/both
short edge
and long edge feed machines.
Figure 6 shows a further design alternative where a continuous transparent
strip
8 is integrated into the design of the secure document 10. Figure 6
illustrates an
example where the transparent strip 8 comprises a first continuous transparent
region 9
formed by omitting the pigmented coating on a transparent polymeric substrate
as
referred with reference to Figures 1 and 2. The strip extends completely
between the
opposite long edges of the document 10. The optical density in this region
will be less
than CO. Immediately adjacent to this region is a region 11 of increased
transparency
compared to the rest of the pigmented substrate and this is achieved by
removing one
of the pigmented coatings or reducing the thickness of the pigmented coatings.
This
region will typically have an optical density of between 0.1 and 0.3. In this
example the
optical density of region 11 is 0.25.
The use of variable transparent regions of different optical densities
increases the complexity of the device and provides an advantage in machine
readability. For example if the document in Figure 6 is passed through a
transmitted
light detector short edge first then a first "flash" of transmitted light will
be detected of
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a particular intensity associated with region 11 with an optical density of
0.25. The
length of time for which this first "flash" of transmitted light is detected
will
correspond to the width of the transparent region 11. If the note continues to
pass
through the detector a second flash of transmitted light is detected
corresponding to
the width of the transparent region 9 with a optical density of 0.1. The
intensity of
the transmitted light will be greater for region 9 compared to region 11 due
to region
9 having a lower optical density. If the note continues to pass through the
detector a
third "flash" of transmitted light is detected associated with a further part
of region
11. In more complex examples more than two regions of varying optical density
may
be present within the strip 8. In Figure 6 the secure document also comprises
a fully
enclosed transparent region 12, as well as continuous transparent region 8
which
extends across the full height of the document.
In a further example, illustrated in cross-section in Figure 7, a single
transparent
region 25 is formed by reducing the number of pigmented coatings in that
region rather
than fully exposing the transparent polymeric substrate 1. In the example in
Figure 7
the transparent region 25 only has one layer of pigmented coating 2A while the
remainder of the document has four layers 2A-2D. The coating in the
transparent
regions must be sufficiently light transmitting that the optical density of
the region does
not exceed 0.3.
Figure 8 illustrates an example where the security document comprises multiple
transparent strips 40-42 which can be used to form a code. The strips 40-42
are shown
as dark lines for ease of understanding the drawing. In this case, the code is
formed
firstly by the fact that there are three strips 40-42 and secondly because the
distance
between adjacent strips 40;41 and 41;42 is different. Figure 9 illustrates a
further
example where multiple strips 43-45 are provided of different widths (as well
as with
different spacings) and again illustrated as dark lines. A series of banknotes
can
comprise different numbers of strips to indicate denomination. As the document
in
Figure 8 is passed by the transmitted light detector 34 the number of
"flashes" of
transmitted light which are of full note width will determine its
denomination. In the
example in Figure 9 both the number of "flashes" and the duration of each
"flash" will
determine the denomination. Of course, other variations are possible such as
varying
widths and same spacing.
In some detector systems it may be difficult to differentiate between the edge
of
the document and the continuous transparent strip and the detector may
inaccurately
interpret the continuous strip as the edge of a document having an incorrect
length. This
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problem may simply be overcome by programming the detector to recognise the
duration of the "flash" of light associated with the continuous strip which
may be shorter
or longer than that associated with the edge of the note. Alternatively,
unlike a void, the
polymeric substrate forming the transparent strip will reflect a fraction of
the incident
light and this reflected light could be detected by a second detector to
confirm that this is
part of the document and not an edge. This method for determining the presence
of
enclosed transparent regions in polymer banknotes is described in
US20030043365.
In a further embodiment, to avoid confusion with the edge of the note, the
transparent continuous strip, can be provided with an optical structure which
provides a
scattering or diffusing screen. This will reduce the level of transmitted
light below that
observed for a fully transparent substrate or a void, but the level of
transmitted light will
still be such that a significant portion of light can pass through the screen
and activate
the detectors.
The continuous transparent strip can be of any width but preferably the width
of
the strip is in the range 2mm to 30mm and even more preferably in the range
2mm to
20mm.
As mentioned above, the invention is applicable to substrates for security
documents prior to applying the security printing processes.
It will also be understood that in all the examples described with reference
to
the drawings, the transparent regions extend fully between the sides or
boundaries
of the substrate. This has two particular advantages as explained in the
introduction, namely ensuring that the document can be detected optically and
increasing the difficulty of fraudulently reproducing the document. However,
in some
examples of the invention, the transparent region need not extend fully
between
edges of the document and could terminate a short distance before reaching the
boundary, for example up to about 10mm. An example of such a document is
illustrated in Figure 11 where a transparent region or strip 50 terminates
short of the
edges or boundary of the document by a distance D.
The current invention is most applicable to banknotes but can also be used in
other secure documents such as a fiscal stamp, cheque, postal stamp,
certificate of
authenticity, brand protection article, bond or payment voucher.
