Note: Descriptions are shown in the official language in which they were submitted.
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Improvement s in and relating to security documents.
Field of the Invention
The present invention concerns improvements in and
relating to security documents. More particularly, this
invention concerns a fluorescent security feature for
incorporation in a security document.
Background of the Invention
Security documents, for example banknotes, passports,
lottery tickets, some certificates and other items of
potentially high value are targets for counterfeiters, who
seek to produce counterfeit copies of the security documents
and thus illegally benefit from the high value of the
genuine items. Security documents typically include various
security devices or features that are difficult for a
counterfeiter to simulate. Such features include holograms,
security threads (typically ribbons of metallised polymer
running across the length or width of the document),
security fibres (typically small dyed fibres of twine or
small printed paper sheets, embedded in and scattered
throughout the substance of the security document), and
security planchettes (typically circular pieces of paper or
polymer embedded in and scattered throughout the substance
of the security document). Many such security devices
exhibit a fluorescent response, reproduction of which is an
additional burden for the counterfeiter.
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GB2300596 discloses a fluorescent material for use in a
security document, the material comprising a transparent or
translucent substrate and two fluorescent components, one on
each side of the substrate, which fluoresce UV light at
different visible colours, and a UV light absorber. Thus,
when the composite material is viewed alternately in
transmitted and reflected ultraviolet light the fluorescent
colour perceived by the viewer will change. Furthermore,
when the material is viewed in either transmitted or
reflected ultraviolet light, the fluorescent colour
perceived by the viewer changes when the composite material
is turned over.
GB2490603A discloses a planar security device such as a
security thread or a security fibre, for use in a security
document. The security device has a first and second side
and comprises: a substrate; a first fluorescent layer on the
first side of the substrate; a layer of UV absorbent
material on the first fluorescent layer; and a second
fluorescent layer on the layer of UV absorbent material.
Again, when the security device is viewed alternately in
transmitted and reflected ultraviolet light the fluorescent
colour perceived by the viewer will change, and, when the
material is viewed in either transmitted or reflected
ultraviolet light, the fluorescent colour perceived by the
viewer changes when the composite material is turned over.
In the example of security fibres described in GB2490603A,
the security devices are mixed into the paper pulp from
which the security document is made, so that the security
devices are randomly distributed within the security
document. In the example of a security thread, the security
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device is inserted into the security document during
manufacture of the paper, for example by threading the
device into the document using a roller. In other
embodiments, the security device is applied to the formed
security document, for example by printing or coating.
Both of the above disclosures describe examples of
security features which exhibit an effect described herein
as a "colour switch" effect. When a first side of the
device is viewed in reflected UV light, one fluorescent
layer fluoresces strongly, but the other fluorescent layer
fluoresces only weakly, if at all, because the UV absorbent
material prevents the UV light from passing through to that
other fluorescent layer. On the other hand, when the first
side of the device is viewed in transmitted UV light, the
fluorescent layer that previously fluoresced strongly, now
fluoresces only weakly, if at all, because the UV absorbent
material prevents the UV light from passing through to it.
The other fluorescent layer, however, now fluoresces
strongly because the UV light falls directly on and excites
that fluorescent layer. Because the fluorescence is in the
visible spectrum, the fluorescence passes through the UV
absorbent material and is visible to the viewer. If one
fluorescent layer fluoresces in a first colour and the other
fluorescent layer fluoresces in a second colour, then when
the illumination of the device changes from reflected to
transmitted UV light, the effect perceived by the viewer is
that the visible fluorescence changes colour.
The colour-switch materials of GB2300596 and GB2490603A
provide a striking and readily recognisable effect,
providing good protection from counterfeiters. However, it
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would be advantageous to provide an improved security device
that is still harder for counterfeiters to simulate.
Summary of the Invention
The present invention, in a first aspect, provides a
method of producing a security document, the method
comprising:
(i) providing a security document substrate having
a face;
(ii) providing a first fluorescent layer, the first
fluorescent layer being fluorescent in a first
visible colour when it is exposed to
ultraviolet light;
(iii) providing a UV blocking layer, the UV blocking
layer being opaque to ultraviolet light but
transmitting visible light;
(iv) providing a security transfer, the security
transfer being mounted on a transfer substrate,
and comprising a second fluorescent layer, the
second fluorescent layer being fluorescent in a
second, different, visible colour when it is
exposed to ultraviolet light;
(v) affixing the security transfer to the face of
the security document such that the transfer
substrate is furthest from the face of the
security document substrate and the second
fluorescent layer is closer to the transfer
substrate than are any of: the first
fluorescent layer and the UV blocking layer;
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(vi) removing the transfer substrate from the
security transfer, leaving the second
fluorescent layer affixed to the face of the
security document.
The method thus provides a method of providing a
"colour switch" security feature in a security document.
The incorporation of one or more of the layers required to
produce a colour switch effect in a security transfer
enables the colour switch layers to be applied easily and in
a much greater range of patterns (which may be intricate)
than in the prior-art methods, and in combinations not
possible using the prior-art methods. In contrast to the
prior-art methods, the present method enables a colour-
switch image (for example fine text, or a larger area of
multi-tone print) to be provided in a specific place on a
security document. Moreover, a complex pattern can be
produced from a single transfer process without the need to
print multiple layers in register in multiple passes. By
transferring only part of a large sheet in a single transfer
process, for example, precise register of the edges of the
transferred pattern can be achieved.
It may be that the security transfer further comprises
an adhesive layer. It may be that the adhesive layer is the
layer of the security transfer furthest from the transfer
substrate.
Optionally, there is a release layer between the
transfer substrate and the security transfer.
It may be that the first fluorescent layer is provided
as a separate layer on the security document substrate. It
may be that the first fluorescent layer is provided as a
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separate layer by affixing the first fluorescent layer to
the security document substrate using a transfer.
Alternatively, it may be that the security document
substrate is the first fluorescent layer.
It may be that the UV blocking layer is provided as a
separate layer on the security document substrate. It may be
that the UV blocking layer is provided as a separate layer
on the first layer. It may be that the UV blocking layer is
provided as a separate layer by affixing the UV blocking
layer to the security document substrate using a transfer.
Alternatively, it may be that the security document
substrate is the UV blocking layer. Thus, it may be that
the security document substrate is the first fluorescent
layer and the UV blocking layer. It may be that the UV
blocking layer is transparent to visible light.
It may be that the first fluorescent layer is on the
same side of the security document substrate as the security
transfer. It may be that the first fluorescent layer is on
the opposite side of the security document substrate to the
security transfer. It may be that the UV blocking layer is
on the same side of the security document substrate as the
security transfer. It may be that the UV blocking layer is
on the opposite side of the security document substrate to
the security transfer.
It may that the first fluorescent layer is on the same
side of the security document as the UV blocking layer. It
may be that the first fluorescent layer is on the opposite
side of the security document substrate to the UV blocking
layer.
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It may be that the first fluorescent layer is on the
same side of the security document substrate as the second
fluorescent layer. It may be that the first fluorescent
layer is on the opposite side of the security document
substrate to the second fluorescent layer. It may be that
the UV blocking layer is on the same side of the security
document substrate as the second fluorescent layer. It may
be that the UV blocking layer is on the opposite side of the
security document substrate as the second fluorescent layer.
It may be that the first fluorescent layer, the UV
blocking layer and the second fluorescent layer are on the
same side of the security document substrate.
It may be that the security document substrate is the
UV blocking layer and the first fluorescent layer is on a
first side of the security document substrate and the second
fluorescent layer is on the other side of the security
document substrate.
It may be that the layers are formed by different
coloured fluorescent images that are laid down separately.
It may be that different coloured fluorescent images are
laid down in a series of different strata. It may be that a
stratum of fluorescent images contains one or more
discontinuities. Thus, it may be that when a subsequent
fluorescent image is laid down there are areas in which the
subsequent image is on top of a previous ink and it may be
that there are other areas (where the previous image stratum
was discontinuous) where the subsequent image is adjacent to
the previous image, and therefore forms part of the same
physical layer. Thus, it may be that the first fluorescent
layer also contains areas which fluoresce in one or more
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a ddi t i on a 1 visible colours when exposed to ultra violet
light. It may be that the second fluorescent layer also
contains areas which fluoresce in one or more additional
visible colours when exposed to ultra violet light. It may
be that the first layer only fluoresces in the first visible
colour and the second layer fluoresces in the second visible
colour and one or more additional visible colours. It may
be that the second layer only fluoresces in the second
visible colour and the first visible layer fluoresces in one
or more additional visible colours.
It may be that the security transfer is affixed to the
face of the security document such that the first
fluorescent layer is between the security document substrate
and the second fluorescent layer. It may be that the
security transfer is affixed to the face of the security
document such that the UV blocking layer is between the
security document substrate and the second fluorescent
layer. It may be that the security transfer is affixed to
the face of the security document such that the UV blocking
layer is between the first fluorescent layer and the second
fluorescent layer.
It may be that the UV blocking layer is provided as
part of the security transfer. It may be that the security
transfer comprises a release layer, the second fluorescent
layer and the UV blocking layer. It may be that the second
fluorescent layer is sandwiched between the UV blocking
layer and the release layer on the transfer substrate.
It may be that the first fluorescent layer is provided
as part of the security transfer. It may be that the
security transfer comprises a release layer, the second
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fluorescent layer and the first fluorescent layer. It may
be that the security transfer further comprises the UV
blocking layer. It may be that the second fluorescent layer
is sandwiched between the first fluorescent layer and the
release layer on the transfer substrate. It may be that the
UV blocking layer is sandwiched between the first
fluorescent layer and the second fluorescent layer on the
transfer substrate. Thus, it may be that the structure of
the security transfer is, in order: first fluorescent layer,
UV blocking layer, second fluorescent layer, release layer,
transfer substrate.
It may be that the removing of the transfer substrate
from the security transfer takes place during the affixing
of the security transfer to the face of the security
document. Alternatively, it may be that the removing of the
transfer substrate from the security transfer takes place
after the affixing of the security transfer to the face of
the security document.
It may be that the security transfer, prior to the
affixing, is in the form of a sheet or ribbon. It may be
that only a (transverse) portion of the second fluorescent
layer on the sheet or ribbon is affixed to the face of the
security document. It may be that only a (transverse)
portion of the UV blocking layer on the sheet or ribbon is
affixed to the face of the security document. It may be
that only a (transverse) portion of the first fluorescent
layer on the sheet or ribbon is affixed to the face of the
security document. It may be that the portion of the sheet
or ribbon that is affixed to the face of security document
is a device, a pattern, a complex shape, an irregular shape
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or an image; for example, it may be a character (e.g. a
letter or a number).
It may be that the security transfer is affixed to the
face of the security document by stamping a die against the
transfer substrate. It may be that the die has a shape
corresponding to a portion of the security transfer, so that
only that portion of the security transfer is affixed to the
face of the security document by the stamping of the die.
It may be that the portion of the sheet or ribbon that is
affixed to the face of security document is a device, a
pattern, a complex shape, an irregular shape or an image;
for example, it may be a character (e.g. a letter or a
number).
It may be that the stamping head is hot during the
stamping process. Alternatively, it may be that the
stamping head is cold (for example at room temperature)
during the stamping process.
It may be that the security transfer is affixed to the
face of the security document by applying an adhesive to the
face of the security document and/or to the security
transfer.
It may be that an adhesive layer is provided as part of
the security transfer. It may be that the security transfer
comprises a release layer, the second fluorescent layer and
the adhesive layer. It may be that the security transfer
further includes the UV blocking layer. It may be that the
security transfer further includes the first fluorescent
layer. It may be that the adhesive layer is the layer of
the security transfer furthest from the security transfer
substrate. Thus, it may be that the structure of the
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security transfer is, in order: adhesive layer, first
fluorescent layer, UV blocking layer, second fluorescent
layer, release layer, transfer substrate.
It may be that a layer of adhesive is applied to the
face of the security document substrate.
It may be that the adhesive is applied selectively to
one or more portions of the security document and/or of the
security transfer, so that only a portion of the security
transfer is affixed to the face of the security document by
the adhesive. It may be that the portion of the sheet or
ribbon that is affixed to the face of security document is a
device, a pattern, a complex shape, an irregular shape or an
image; for example, it may be a character (e.g. a letter or
a number).
It may be that the adhesive is a curable adhesive. It
may be that the adhesive is an adhesive cured by ultraviolet
light. It may be that the adhesive is a varnish, for
example a UV-curable varnish.
It may be that the transfer substrate is a film. It may
be that the transfer substrate is a foil.
It may be that the transfer substrate is opaque to
visible light. It may be that the transfer substrate is
opaque to UV light. It may be that the transfer substrate
is opaque to both visible and UV light.
It may be that a plurality of the security transfers is
applied, simultaneously or in sequence. It may be that each
further security transfer includes a release layer. It may
be that each further security transfer includes an adhesive
layer. It may be that a further security transfer includes
one more layer, which may be any of a fluorescent layer or a
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UV blocking layer. It may be that an additional security
transfer includes two fluorescent layers. It may be that an
additional security transfer includes a UV blocking layer.
Thus, it may be that the structure of any additional
security transfers is substantially identical to the
structure of the first security transfer. Alternatively, it
may be that any additional security transfer includes only a
single layer.
That enables, for example, a multi-colour image to be
produced; it may be that at least one, preferably two or
more, of the colours are visible only as fluorescent
colours. To achieve that using prior-art printing methods
would require multiple printing passes and exact
registration of each layer one on top of the other (which is
difficult or impossible to achieve on fine printed text or
multi-tone graduations, or for complex patterns and
colours).
Thus, it may be that the method further comprises the
step of:
providing a second security transfer, mounted on a
transfer substrate, and comprising a fourth fluorescent
layer, a UV blocking layer and a third fluorescent layer,
the third fluorescent layer being fluorescent in a third
visible colour when it is exposed to ultraviolet light, the
fourth fluorescent layer being fluorescent in a fourth,
different, visible colour when it is exposed to ultraviolet
light, and the UV blocking layer being opaque to ultraviolet
light but transmitting visible light;
affixing the security transfer to the face of the
security document having the affixed layers of the (first)
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security transfer, so that the third fluorescent layer of
the second security transfer is adjacent to the face of the
security document substrate and the fourth fluorescent layer
of the second security transfer is furthest from the face of
the security document substrate; and
removing the transfer substrate from the second
security transfer, leaving the fourth fluorescent layer, UV
blocking layer and third fluorescent layer of the second
security transfer affixed to the face of the security
document.
It may be that the first, second, third and fourth
visible colours are all different from each other. It may
be that the first and fourth visible colours or the first
and third visible colours are the same. It may be that the
second and third visible colours or the second and fourth
visible colours are the same.
It may be that the layers of the second security
transfer at least partially overlap with the layers of the
first security transfer on the security document.
The method may further comprise the steps of
providing at least one further security transfer
mounted on a transfer substrate, and comprising a further
distal fluorescent layer, a UV blocking layer and a proximal
fluorescent layer, the further fluorescent layers being
fluorescent in two further, different, visible colours when
exposed to ultraviolet light, and the UV blocking layer
being opaque to ultraviolet light but transmitting visible
light;
affixing the security transfer to the face of the
security document having the affixed layers of the (first)
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security transfer and the second security transfer, so that
the proximal fluorescent layer of the further security
transfer is adjacent to the face of the security document
substrate and the distal layer of the further security
transfer is furthest from the face of the security document
substrate; and
removing the transfer substrate from the
further security transfer, leaving the distal layer,
intermediate layer and proximal layer of the further
security transfer affixed to the face of the security
document.
It may be that none of the layers applied to the
security document fluoresce in the same visible colour as
any of the other layers. It may be that at least two of the
layers fluoresce in the same visible colour. It may be that
no two layers from the same security transfer fluoresce in
the same visible colours.
It may be that the method further comprises the step
of:
providing a further security transfer, mounted on a
transfer substrate, and comprising at least one of: a
fluorescent layer or a UV blocking layer, the fluorescent
layer being fluorescent in a visible colour when exposed to
ultraviolet light, and the UV blocking layer being opaque to
ultraviolet light but transmitting visible light.
affixing the security transfer to the face of the
security document having the affixed layers of any previous
security transfer, so that the at least one of the
fluorescent layer or the UV blocking layer is adjacent to
the face of the security document substrate and,
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removing the transfer substrate from the further
security transfer, leaving the at least one of the
fluorescent layer or UV blocking layer of the further
security transfer affixed to the face of the security
document.
It may be that the security document is a bank note.
It may be that the security document is a passport. It may
be that the security document is a paper document. Thus, it
may be that the security document substrate is a paper.
It may be that the affixed layers form at least one
device, image or character on the face of the security
document, for example a letter or a number.
It will be understood that the layers of the security
transfer are in the order from furthest to closest to the
face of the security substrate when the security transfer is
affixed: a transfer substrate (when present), a release
layer (if present), a second fluorescent layer, a UV
blocking layer (if present), a first fluorescent layer (if
present) and an adhesive layer (if present). It may be that
there is no further intermediate layer between any of the
transfer substrate, the release layer (if present), the
second fluorescent layer, the UV blocking layer, the first
fluorescent layer, the adhesive layer and the face of the
security document substrate. Alternatively, it may be that
there is one or more further intermediate layers between any
of the transfer substrate, the release layer (if present)
the second fluorescent layer, the UV blocking layer (if
present), the first fluorescent layer (if present), the
adhesive layer (if present) and the face of the security
document substrate.
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It will be understood that the layers of the security
document are in the order: a security document substrate, an
adhesive layer (if present), a first fluorescent layer (if
present), a UV blocking layer (if present) and a second
fluorescent layer. It may be that there is no further
intermediate layer between any of the security document
substrate, the adhesive layer (if present), the first
fluorescent layer (if present), the UV blocking layer (if
present) and the second fluorescent layer. Alternatively, it
may be that there is one or more further intermediate layers
between any of the security document substrate, the adhesive
layer, the first fluorescent layer (if present), the UV
blocking layer (if present) and the second fluorescent
layer.
The further intermediate layer may be substantially
transparent to UV light, to visible light or to both UV and
visible light. It will be understood that the visual effect
may be most striking if there are no intermediate layers, or
if the intermediate layers are substantially transparent as
intermediate layers may cause loss of light intensity, which
may weaken the visual effect.
It may be that the first fluorescent layer (if present)
and the second fluorescent layers each cover only part of
the transfer substrate and are non-coextensive, for example
non-overlapping. Therefore, when the illumination of the
device changes from reflected to transmitted UV light, the
effect perceived by the viewer is that the visible
fluorescence 'jumps' from one layer to the other. Such an
effect may be even more striking, and easier to detect in an
automated fashion, than a colour change. In particular,
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such an effect is apparent regardless of the ability to
detect colour.
The colour switch or the 'jumping' effect will also be
observed if the security document is turned over, while
remaining viewed in reflected light, or if the security
document is turned over while remaining viewed in
transmitted light.
It may be that the first fluorescent layer and second
fluorescent layer overlap. It may be that the first
fluorescent layer and the second fluorescent layer are co-
extensive. It may be that the first fluorescent layer is
covered by the second fluorescent layer.
Thus, it may be that the second fluorescent layer
covers the first fluorescent layer, but does not extend
substantially beyond the area covered by first fluorescent
layer.
According to a second aspect of the invention, there is
provided a security transfer including: an optional adhesive
layer; a first fluorescent layer, the first fluorescent
layer being fluorescent in a first visible colour when it is
exposed to ultraviolet light; a UV blocking layer, the UV
blocking layer being opaque to ultraviolet light buy
transmitting visible light; a second fluorescent layer, the
second fluorescent layer being fluorescent in a second,
different, visible colour when it is exposed to ultraviolet
light; and an optional release layer, and wherein the UV
blocking layer is sandwiched between the first fluorescent
layer and the second fluorescent layer, the optional
adhesive layer if present is on the opposite side of the
first fluorescent layer to the UV blocking layer, and the
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optional release layer if present is on the opposite side of
the second fluorescent layer to the UV blocking layer.
According to a third aspect of the invention, there is
provided a mounted security transfer including: an optional
adhesive layer; an optional first fluorescent layer, the
first fluorescent layer being fluorescent in a first visible
colour when it is exposed to ultraviolet light; a second
fluorescent layer, the second fluorescent layer being
fluorescent in a second, different, visible colour when it
is exposed to ultraviolet light; and an optional release
layer, and wherein the optional release layer if present is
sandwiched between the second fluorescent layer and the
transfer substrate, and the optional first fluorescent layer
if present is sandwiched between the optional adhesive layer
if present and the second fluorescent layer on the opposite
side of the second fluorescent layer to the transfer
substrate.
According to a fourth aspect of the invention, there
is provided a security document manufactured by the method
of the first aspect of the invention.
According to a fifth aspect of the invention, there is
provided a security document including a security document
substrate having a face, a first fluorescent layer, a UV
blocking layer, and a second fluorescent layer, the first
fluorescent layer being fluorescent in a first visible
colour when it is exposed to ultraviolet light, the UV
blocking layer being opaque to ultraviolet light, but
transmitting visible light, and the second fluorescent layer
being fluorescent in a second, different, visible colour
when it is exposed to ultraviolet light, wherein the second
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fluorescent layer is part of a security transfer affixed to
the face of the security document, the security transfer
having an inner face proximal to the security substrate and
an outer face distal to the security substrate and the
second fluorescent layer is closer to the outer face of the
security transfer than either of the first fluorescent layer
or the UV blocking layer.
The security transfer, on the security document
substrate, does not include a transfer substrate (which will
have been removed during affixing of the security transfer
to the security document). It may be that the security
transfer, on the security document substrate, does not
include a release layer (in which case, the release layer if
present initially will have been removed with the transfer
substrate). Alternatively, it may be that the security
transfer, on the security document substrate, does include a
release layer (in which case, the release layer will not
have been removed with the transfer substrate).
It will of course be appreciated that features
described in relation to one aspect of the present invention
may be incorporated into other aspects of the present
invention. For example, the security document of the second
or third aspects of the invention may incorporate any of the
features described with reference to the method of the
invention and vice versa.
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Description of the Drawings
Embodiments of the present invention will now be
described by way of example only with reference to the
accompanying schematic drawings, of which:
Figure 1 is a schematic plan view of a security document
according to a first example embodiment of the
invention;
Figure 2 is a schematic close-up of a portion of the
security document of Fig. 1;
Figure 3 is a security transfer for use in manufacturing
the security document of Fig. 1;
Figure 4 is a die for use in a method of manufacturing
the security document of Fig. 1; and
Figure 5 is a schematic diagram of a step in an
alternative process of manufacturing the
security document of Fig. 1.
Detailed Description
A security document 10 according to an example
embodiment of the invention includes several complementary
security features. The security document 10 is principally
formed from a security document substrate 20, a sheet of
paper without optical brighteners. Embedded in the security
document substrate 20 are a plurality of security fibres 30,
which are small nylon fibres that were mixed into the paper
pulp from which the security document substrate 20 was
formed, and are hence distributed randomly across the face
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of the security document substrate 20. Also embedded within
the security document substrate 20 is a security thread 40,
which runs across the width of the security document
substrate 20.
The security document 10 of Fig. 1 includes an affixed
security transfer 50. In this example, the security
transfer 50 is in the form of characters forming the word
"Spinks". The security transfer 50 is substantially
invisible when the security document 10 is illuminated by
visible light, but it becomes visible under UV light, since
it is formed from a plurality of fluorescent layers, as
discussed further below.
The affixed security transfer 50 is shown in more
detail in Fig. 2. When the security document 10 is viewed
and illuminated towards the face of the paper on which the
transfer is affixed, the letters "S" 60a, "i" 60b and "k"
fluoresce in red, and the letters "p", 70a, "n" 70b, and "s"
fluoresce in green. The affixed security transfer 50
exhibits a colour switch effect. So when the security
document 10 is illuminated towards the other face of the
paper, whilst still being viewed towards the face of the
paper on which the security transfer 50 is affixed, the
colours of the letters 60a-c, 70a-c change. Specifically,
in this example, the colours of the two sets of letters 60a-
c and 70a-c swap, so that the letters "S" 60a, "i" 60b and
"k" fluoresce in green, and the letters "p", 70a, "n" 70b,
and "s" fluoresce in red.
If the security document 10 is viewed towards the face
of the paper opposite to that on which the security transfer
50 is affixed then the colour combinations are reverse from
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those just described, so, when the security document 10 is
illuminated in reflected light (i.e. towards the face of the
paper opposite to that on which the transfer is affixed),
the letters "S" 60a, "i" 60b and "k" fluoresce in green, and
the letters "p", 70a, "n" 70b, and "s" fluoresce in red, and
when the security document 10 is illuminated towards the
other face of the paper (i.e. in transmitted UV light), the
letters "S" 60a, "I" 60b and "k" fluoresce in red, and the
letters "p", 70a, "n" 70b, and "s" 70c fluoresce in green.
The security transfer 50, prior to being affixed to the
security document substrate 20, is in the form of a ribbon
having the cross-sectional structure shown schematically in
Fig. 3. The security transfer 50 is mounted on a transfer
substrate 90 (which in this example is opaque to light, both
visible and UV). There is a release layer 100 on the
transfer substrate 90, and a second fluorescent layer 110 on
the release layer 100, an opaque, UV blocking, layer 120 on
the second fluorescent layer 110, and a first fluorescent
layer 130 on the intermediate layer 120. In this example,
there is also an adhesive layer (not shown) on the first
fluorescent layer. In this example, the release layer 100,
second fluorescent layer 110, UV blocking layer 120 and
first fluorescent layer 130 are printed successively onto
the transfer substrate. Portions of the security transfer
50 are affixed to the security document substrate 20, by one
of the methods described in more detail below, to form the
letters "S" 60a, "i" 60b and "k" 60c of the device 50.
During the affixing, the transfer substrate 90 and the
release layer 100 are removed from the transfer 50, so that
the second fluorescent layer 110, the UV blocking layer 120
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and the first fluorescent layer 130 remain on the security
document substrate 20.
When the affixed security transfer 50 is directly
illuminated with UV light, the UV light will cause the
second fluorescent layer 130 to fluoresce, in red for the
letters "S" 60a, "i" 60b and "k" 60c. The UV light does not
penetrate the UV blocking layer 120, so the first
fluorescent layer 110 does not fluoresce. The UV blocking
layer 120 is transparent to the visible fluorescence from
the first fluorescent layer 130, and so the letters "S" 60a,
"i" 60b and "k" 60c will appear red when viewed from either
side of the security document 10.
When however the affixed security transfer 50 is
illuminated indirectly, through the security document
substrate 20, i.e. from the other side of the security
document 10 from the side on which the transfer 50 is
affixed, the UV light will cause the first fluorescent
fluorescent layer 110, to fluoresce, in green for the
letters "S" 60a, "i" 60b and "k" 60c. The UV light is
blocked by the opaque, UV blocking, layer 120. Thus the
second fluorescent layer 130 does not fluoresce. The UV
blocking layer 120 is transparent to the visible
fluorescence from the distal layer 110, and so the letters
"S" 60a, "i" 60b and "k" 60c will appear green when viewed
from either side of the security document 10.
In this example, the letters "p", 70a, "n" 70b, and "s"
70c are formed from a second security transfer (not shown),
identical to the described security transfer 50 save that
the second fluorescent layer 110 fluoresces in green, and
the first fluorescent layer 130 fluoresces in red.
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Thus, when a face of the security document 10 is viewed
in first transmitted and then reflected UV light, or one
face is viewed and then the security document is turned over
to view the other without changing the direction of the UV
light, the colours of the fluorescence of the two sets of
letters 60a-c, 70a-c will appear to swap over, creating a
striking and memorable effect.
In an example method of affixing to the security
document substrate 20, the security transfer 50 forming the
letters "S" 60a, "i" 60b and "k" 60c is stamped onto the
security document substrate 20 using a hot die 140 (shown
schematically in Fig. 4). The die 140 includes a base 150
and elements 160 that form the mirror image of the letters
"S" 60a, "i" 60b and "k" 60c. The die 140 is applied by
machine to the transfer substrate 90 of the security
transfer 50, to selectively stamp portions of the ribbon of
security transfer 50, shown in Fig. 3, onto the security
document substrate 20, thereby forming the affixed security
transfer 50.
The letters "p", 70a, "n" 70b, and "s" 70c are affixed
by the same method, using an appropriate die on the second
security transfer.
The stamping with die 140 may be hot- or cold-
stamping, both of which are techniques well-known to the
person skilled in the art, and are therefore not described
further here.
In a further example method, a UV-curable varnish 70 is
applied to the security document substrate 20. The varnish
70 is applied selectively, to regions where the letters "S"
60a, "i" 60b and "k" 60c are to be formed. The security
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transfer 50 is pressed, by passage through rollers, against
the security document substrate 20 and the security document
and transfer 50 are exposed to UV light, to cure the
varnish 70. The transfer 50 is then lifted from the
5 security document substrate 20. The second fluorescent
portion 130, opaque portion 120 and first fluorescent
portion 110 of the security transfer 50 are retained on the
security document substrate 20 in the areas to which the
adhesive is applied, thus forming the letters "S" 60a, "i"
10 60b and "k" 60c of the affixed transfer 50, in colour-switch
form.
The process is repeated using the second security
transfer to form the letters "p", 70a, "n" 70b, and "s" 70c.
Whilst the present invention has been described and
illustrated with reference to particular embodiments, it
will be appreciated by those of ordinary skill in the art
that the invention lends itself to many different variations
not specifically illustrated herein.
In some other embodiments the security document
substrate is the first fluorescent layer. The security
document substrate also fulfils the function of the UV
blocking layer. The security transfer is mounted on a
transfer substrate. There is a release layer on the
transfer substrate, and a second fluorescent layer on the
release layer. The security transfer is affixed to the
security document substrate and the transfer substrate and
the release layer are removed from the transfer so that the
second fluorescent layer remains affixed to the security
document.
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Where in the foregoing description, integers or
elements are mentioned which have known, obvious or
foreseeable equivalents, then such equivalents are herein
incorporated as if individually set forth. Reference should
be made to the claims for determining the true scope of the
present invention, which should be construed so as to
encompass any such equivalents. It will also be appreciated
by the reader that integers or features of the invention
that are described as preferable, advantageous, convenient
or the like are optional and do not limit the scope of the
independent claims. Moreover, it is to be understood that
such optional integers or features, whilst of possible
benefit in some embodiments of the invention, may not be
desirable, and may therefore be absent, in other
embodiments.
