The invention relates to a security device and a method
for making such a security device. The invention is particularly concerned with
security devices for documents of value such as banknotes, certificates and the
It is well known to provide security devices in the form
of holograms and diffraction gratings using surface relief structures. However,
an alternative class of security device is based on non-diffractive line structures,
that is structures which produce an optically variable effect when the angle of
incidence of light varies but in which this effect is not caused by interference
An example of such a structure is described in
. In this case, a variety of line structures are embossed into a transparent,
plastics substrate, the embossed lines defining regions in which the lines extend
at different angles to each other and define different shapes that are visible to
a greater or lesser extent upon transmission and reflection of light as the substrate
such as a banknote is tilted, rotated or viewed from different angles.
describes a security device in which one or more transitory images are
embossed into a reflective surface.
discloses a further security device in which groups of elemental areas
in which lines extend at different angles from each other form respective image
discloses a decorative device in which a relief structure is formed in
a surface and has an optically variable effect.
There is a need to improve upon the known devices to increase
In accordance with a first aspect of the present invention,
a security device comprises a substrate having a reflective surface portion which
is provided with a raised line structure, the line structure defining a plurality
of segments, each segment being formed by a respective set of substantially parallel
raised lines, the lines of at least three segments extending in different directions,
each line carrying an ink which does not extend fully into the spaces between the
lines or which is sufficiently translucent between the lines so as not to obscure
the reflective surface between the lines, wherein each segment causes incident light
to be reflected non-diffractively in a variable manner as the angle of incidence
In accordance with a second aspect of the present invention,
a method of manufacturing a security device comprises providing a reflective surface
portion of a substrate with a raised line structure, the line structure defining
a plurality of segments, each segment being formed by a respective set of substantially
parallel raised lines, the lines of at least five segments extending in different
directions, and providing each line with an ink which does not extend fully into
the spaces between the lines or which is sufficiently translucent between the lines
so as not to obscure the reflective surface between the lines, wherein each segment
causes incident light to be reflected non-diffractively in a variable manner as
the angle of incidence changes.
Thus, as the device is tilted relative to the incident
light and angle of view it will exhibit optically variable effects.
The invention provides a security device which presents
a moving effect viewable across a wide range of angles (in contrast to the limited
angles over which a conventional latent image is viewable). It is simple to authenticate
yet difficult to counterfeit. It is also surprisingly visible from a distance due
to the reflective background.
The use of 3 or more segments enables a movement effect
to be achieved. Ideally, many segments should be used with lines extending in different
directions to ensure that reflected light is visible at substantially all viewing
angles. To that end segments containing lines extending at say 10 , 20 , 30 etc
to some nominal direction are preferred.
The lines are preferably embossed or debossed into the
substrate. The embossing process is preferably carried out using an intaglio plate
having recesses defining the line structure which are filled with the ink so that
the lines and ink are simultaneously provided in register.
However, in an alternative approach, the lines of ink could
be printed onto the unembossed reflective surface which is subsequently embossed
in register. The former approach is preferred since registration is more simply
The invention also extends to non-embossed raised lines
produced for example by screen or thermographic printing. Here an ink film is applied
in such a thickness that it has a relief, in the case of UV printed screen inks
this could be comparable to depth of relief achievable by intaglio.
The lines within each segment can take any convenient form
including straight (rectilinear) or curved such as full or partial arcs of a circle
or sections of a sinusoidal wave.
The lines may be continuous or discontinuous and, for example,
formed of dashes, dots or other shapes. By other shapes we mean the dots or dashes
could have a graphical form. For example microtext printed at a size of 12 microns
will appear as continuous lines when viewed with the naked eye. Under closer inspection
using an eye glass the apparent continuous line can be visualised as text. The microtext
could be alphanumeric characters, logos (e.g. trademarks), geometric shapes and
The sides of the lines typically extend at an angle offset
from a normal to the surface.
The lines within a segment typically have substantially
the same width and/or height and/or pitch but one or more of these could vary.
A particularly preferred example involves providing a region
in the security device which has greater relief when printed. This is typically
achieved by using an intaglio printing plate which is deeper in this region than
the remainder of the plate.
The line widths are typically in the range 10-300 microns,
preferably 50-150 microns. The space between the lines is typically 10-300 microns.
The line width to space ratio is typically 3:1 to 1:2 but preferably 2:1; i.e. for
a line width of 70 microns, the space would be between 23 and 140 microns, preferably
The line segments may or may not be individually discernable
to the unaided naked eye. Preferably, the individual lines are barely visible to
the naked eye, the main visual impression being given by the segments and the combined
Each segment can take any shape or form, for example square,
triangle, hexagon, star, flower or indicia such as a letter or number. The segments
may tessellate or nest.
In some cases, the segments may be outlined with a continuous
printed or non-printed perimeter line or the outline may simply be defined by the
extent of the raised lines, preferably carrying ink. The continuous printed or non-printed
line may define information such as indicia.
The segments will typically abut although in some cases
they may be spaced apart. The space between adjacent segments is typically in the
range of 20 microns to 2mm. Alternatively, the segments could overlap and in a particularly
preferred approach the segments are nested one within another. This latter arrangement
is particularly preferred where each segment defines a similar shape. In the most
preferred example, the nested segments are rotated relative to one another.
In another example, the segments within the security device
define a range of different shapes and, for example, might comprise a combination
of triangles and rhombi.
Additionally, the unprinted areas within one or more segments
could define additional information such as alphanumerics. The alphanumerics could
relate to information elsewhere on the document.
Where the segments are spaced apart, the plain areas between
them may be of a similar shape to that of the segments.
The segments may also be arranged into largershapes including,
for example, geometric shapes, flowers, numbers or letters.
The specularly reflective portion of the substrate may
be formed by a foil, metallic ink, metallic coating, iridescent coating, glossy
varnish, hologram, high refractive index or optical effect film. By optical effect
film we mean for example multilayer iridescent film. The reflective surface portion
can be solid or discontinuous and, for example, may contain spaces with or without
a coloured print underneath. It may be of any shape or size.
Typically, the specularly reflecting portion can be any
colour, for example metallic blue, metallic red, silver or gold, and where specularly
reflecting inks are used, these will generally give a general appearance, which
is not as highly reflecting as a foil or other specular mirror surface but a distinctive
The raised line structure may extend beyond the reflective
portion and/or the reflective portion may extend beyond the raised line structure.
The substrate is typically paper although other known substrates
such as plastics could also be used. It is known that an improved reflective effect
(whether this be via printing or foil transfer) can be achieved on a smooth substrate.
With this in mind plastic substrates are likely to show a strong reflective effect
but are less likely to emboss as well as paper. As an alternative a paper substrate
could be primed to improve its surface finish. By priming we mean the paper could
be coated, varnished or calendared prior to application of a reflective ink/foil
layer. As a further alternative the foil/reflective ink could be calendered after
application to the paper surface. This has a polishing effect again improving the
reflectivity of the metallic surface. This polishing will occur to some extent anyway
as part of the intaglio process. Where the flat smooth, uninked areas of the intaglio
plate come into contact with the reflective foil/ink they polish the foil/inks surface.
In an important aspect, where the lines are formed using
an intaglio plate, further intaglio printing or blind embossing may be carried out
using the same intaglio plate so as to achieve precise registration between the
different components. Indeed, in some cases, some of the recesses defining the security
device may be filled with ink and others left unfilled.
The colour of the ink or pigment used on the raised lines
may match the colour of the specularly reflective surface. Preferably, however,
the colour of the ink or pigment contrasts with that of the specularly reflective
surface. The advantage of this is that as the viewing angle and/or illumination
angle changes, different segments become more strongly visible. This leads to the
appearance of having two or more different colours simultaneously and is a very
cost effective way of achieving an optically variable effect.
It is possible to achieve additional effects by combining
accurately, one or more colours in the form of an ink with the raised lines in such
a way that the reflective portions of the lines which are not covered by the coloured
ink provide an optically variable effect in conjunction with the absorptive/reflective
effect of the coloured ink. Thus, the colour of the ink can be used to change the
overall appearance of the (specularly) reflective background. For example, a green
ink could be printed over a silver background to create the effect of having a green
specularly reflective surface.
In preferred examples using embossed or debossed line structures,
the ink is provided on the lines and does not extend into the spaces between the
lines. However, it is possible for the ink to extend between the lines if it is
sufficiently thin so as to be translucent.
The security device may be embodied as a label such as
a transfer label which can then be adhered to a document of value. Alternatively,
the substrate of the security device could also constitute the substrate of a document
Some examples of security devices according to the invention
will now be described with reference to the accompanying drawings, in which: -
- Figure 1 is a schematic representation of a banknote bearing a security device
according to the invention;
- Figure 2 illustrates schematically and in enlarged form part of the security
device shown in Figure 1;
- Figure 3 illustrates schematically and in enlarged form part of a further security
- Figures 4A-'4C illustrate the appearance of the security device of Figure 3
when illuminated from three different directions;
- Figure 5F is a schematic cross-section through part of a segment of the device
shown in Figure 2;
- Figures 5A-5E illustrate different stages in the production of such a segment;
- Figures 6A-6C illustrate further examples of a device according to the invention;
- Figure 7A-7H illustrate examples of segments of lines;
- Figures 8 and 9A-9C illustrate nested arrangements of segments of lines;
- Figure 10 shows a further device; and,
- Figures 11A-11C illustrate three further devices.
Figure 1 illustrates a banknote formed on a paper substrate
1 and carrying printing of a conventional type and in addition carrying an example
of a security device 2 according to the invention. In this case, the security device
2 has been intaglio printed directly onto a reflective portion of the banknote substrate
and another part of the same intaglio printing plate has been used to print, at
the same time, images (the portrait and indicia "De La Rue", "2000") indicated schematically
at 3, so that these images are automatically and accurately registered with the
Figure 1 shows the feature in the context of a banknote
design with the feature numbered 2 and other printed intaglio regions numbered 3.
Further to these printed intaglio regions other regions could be provided as uninked
embossed areas, such as described in
. Figure 2 illustrates the device 2 in enlarged form. It will be noted
that the number 2000 is not printed and it is also not embossed. This is a non-printing
area on the intaglio plate within the area of the design. In addition, the device
includes a first border made up of several indicia "2000" and an outer decorative
border. All these regions are in register and printed from the same intaglio plate.
As explained above, the security device 2 can take a variety
of forms and Figure 3 illustrates one example. In this example, the security device
is made up of a variety of triangular 4 and square 5 shaped segments which are tessellated
together. In this case, although a perimeter line is shown around each shape, this
is, in fact, simply defined by the ends of the parallel lines making up the segments.
The segments are each defined by a set of substantially parallel lines with the
lines of different segments being angularly offset from one another.
Part of this security device is shown in enlarged form
under different lighting conditions in Figures 4A to 4C. Thus, in Figure 4A, the
light is incident in a direction 9 and this will be reflected by the segments 5a
and 4a-4d. This is because the lines in these segments extend at or near 90°
to the incident light direction.
When the device is rotated so that the incident light direction
is in a direction 10 (Figure 4B), a different set of segments appears bright. In
this case, the segments include segments 5b and 4e. Some of the segments appear
less bright while the remaining segments appear dark. Again, this brightness depends
upon how close the lines defining the segment extend at 90° to the incident
light direction 10.
Figure 4c illustrates a further angle of incidence 11 in
which segments 4f-4m appear bright with the remaining segments appearing dark.
The top portion of each embossed line is covered with an
ink as shown in Figure 5F. Thus in this Figure, each embossed line of a substrate
1 is indicated at 6 with the ink at 7. As can be seen, the sides of each line are
at an acute angle to a normal to the substrate and the valleys 8 between the summits
of the lines 6 are free of ink but are reflective.
If the ink 7 is chosen to have a colour which contrasts
with the reflective surface of the substrate 1 into which the lines have been embossed
then the dark segments will exhibit the colour of the ink 7 in each case. Thus,
as the security device shown in Figure 3 is rotated relative to the incident light
direction, the triangular shaped areas will switch on and off giving rise to an
appearance of movement across the device as described in Figure 4. This is a novel
effect which is relatively easily detected by a user thus making it particularly
suitable as a security device. Nevertheless, it is difficult to reproduce fraudulently.
Thus this feature is much easier to authenticate than the latent type structure.
It can also be easily located. As a secondary benefit, more with respect to OVDs,
it is relatively cheap. As the feature can be produced using the existing litho
and intaglio processes, the use of costly optically variable foils is avoided.
Figures 5A-5E illustrate different stages in the intaglio
printing of the portion shown in Figure 5F. Initially, an intaglio plate 12 having
recesses 13 is coated with ink 7, the ink filling the recesses 13 and providing
a surplus on the surface of the plate 12. This surplus is then wiped away in a conventional
manner (Figure 5B) and the substrate 1 placed onto the inked plate (Figure 5C).
Pressure is then applied between the plate 12 and substrate 1 (Figure 5D) causing
the substrate to enter the recesses 13. The substrate is then removed and draws
with it most of the ink 7 contained within the respective recesses 13 but leaving
a small remainder as can be seen in Figure 5E. The resultant, printed substrate
has the form shown in Figure 5F.
A typical segment size is 2mm by 2mm or an equivalent area.
By equivalent area we include the fact that the segment could be long and thin and
could be a line bordering an area. For example in Figure 6A each "segment", such
as 14, is essentially a line around a square. In the figure drawn real size one
can see that the width of this line is not that great but the line is quite long.
Essentially the segments should be of a size and shape such that they can be visualised
with the unaided eye. That is one should be able to discern the changing visual
impression of each segment as viewing angle changes.
Figures 6B-6c illustrate further examples of arrangements
of segments, such as 15 and 16.
Figures 7A to 7H illustrate a variety of other shapes which
the segments can take. Figures 7A-7F show segments with a printed perimeter line
in register with the embossed lines while Figures 7G and 7H show segments bounded
only by the extent of the parallel lines. Multiple versions of segments shown in
Figures 7G and 7H could be located adjacent one another but leaving a narrow unprinted
line between them.
Figure 8 illustrates an example of the security device
in which a set of hexagonal shaped segments 20-23 are nested one within the other,
each hexagon being rotated relative to the immediately adjacent inner and outer
hexagons. Each hexagon 20-23 is defined by a set of lines with the angles of the
lines being different and also their line widths and pitches. The segments could
vary from 70µm thick lines with 30µm spacing progressively up to 150µm
thick lines with 75µm spacing. As this security device is rotated, it will
appear as a rotating hexagon which diminishes or expands in size. This is a particularly
attractive but secure feature.
Figures 9A-9C illustrate further examples of nested segments.
Figure 9A shows a device with nested and rotated segments, the segments provided
with a printed perimeter line. Figure 9B shows a device with nested and rotated
segments, the segments not provided with a perimeter line. Figure 9C shows a device
with nested and rotated segments, the segments provided with an unprinted perimeter
In the next example, a region is provided in the feature
design on the intaglio plate which is deeper compared to the remainder of the feature
design. This will in turn equate to a region that has a greater relief when printed.
To explain this, consider the design of security device shown in Figure 10. The
design shown in Figure 10 comprises two elements: a background 31 of nested segments
all rotated with respect to each other, and a central numeral 1 indicated by reference
30. In this simple example the central numeral 1 can be originated such that the
intaglio plate was deeper in this area compared to the surrounding nested segments.
In a different example, using a structure such as that
shown in Figure 6A, a latent effect may be created. Here the feature comprises only
a series of nested segments rotated with respect to each other with no apparent
secondary element. Indeed if originated as per normal practice one would still only
have the one feature as already described: But it is possible to selectively produce
deeper regions on the plate and thus produce an area in a defined shape (say a numeral
1) that is deeper than the surrounding area. This would not be readily recognisable
under normal viewing but should be viewable when the device is viewed at an acute
angle. One example of how this might be achieved using the polymer process is given
- 1. Exposure through the line structure film work onto photopolymer as usual.
- 2. Carry out a first wash out of say 10 seconds to give a depth of, for example,
50 microns to produce a photopolymer with the line structure having a nominally
consistent depth of 50 microns.
- 3. Carry out a second exposure using a solid design; say a numeral 1 or a pattern.
The photopolymer will be hardened everywhere except where masked by the numeral
1 or pattern.
- 4. Carry out a second wash out. Where the plate has been hardened further no
further washing out of the photopolymer occurs however in the numeral/pattern region
which was subject to the further exposure additional photopolymer is washed out
resulting in a deeper engraving say 70 microns.
Other known techniques could be used to produce the intaglio
plate such as mechanical or laser origination techniques. For example as disclosed
As explained throughout, where intaglio printing is used
to produce the security device, it is possible to provide uninked embossed areas
as well as printed ink areas using the same plate.
Figure 11 illustrates some further examples of banknotes
(shown schematically) carrying security devices. In Figure 11A, the device comprises
a line of star shapes each fabricated in the manner shown in Figure 7D but with
different line orientations.
Figures 11B and 11C illustrate vertical and circular arrangements
of star shapes.